Дисертації з теми "Peas Diseases and pests"

Thirty-four cultivars of pea (Pisum sativum) were assayed for tumorigenesis after inoculation with Agrobacterium tumefaciens strain B6. The response of the 34 cultivars fell into 3 significantly different groups based on tumor weights: high, medium, and low susceptibility. The least susceptible cultivar, Sweet Snap, also formed the smallest tumors in comparison to 5 other cultivars when inoculated with 5 other strains of Agrobacterium. Preliminary experiments indicate that neither chemotaxis, binding, vir-gene induction, nor T-DNA expression are limiting factors in Sweet Snap's reduced susceptibility. In an inheritance study, the F1, F2, and F3 progeny from an initial cross between Sweet Snap and Wando (a more susceptible cultivar) formed tumors that were intermediate in weight between the two parents.

Copies of author's previously published articles inserted. Bibliography: leaves 128-143. This thesis describes the development of serological and nucleic acid based diagnostic methods for pea-seed borne mosaic virus (PSbMV), the isolation of specific effects on infected pea plants, the collection and biological comparison of new PSbMV isolates from Pakistan, the cloning and sequencing of specific parts of the genome of selected isolates, nucleotide and amino acid sequence comparisons between selected isolates, and the development of a ribonuclease protection assay (RPA) for identifying genomic differences among the PSbMV isolates. It is the first comparison of a range of geographically different isolates of PSbMV on the basis of both biological and molecular properties.

In this study, surveys were conducted in pea and potato fields in North Dakota and Central Minnesota to investigate the incidence and abundance of plant-parasitic nematodes in these fields. Moreover, the effect of the pin nematode, Paratylenchus nanus, on plant growth and yield of six field pea cultivars was determined under greenhouse conditions. Similarly, the influence of lesion nematode, Pratylenchus penetrans, and wilt fungi, Fusarium oxysporum alone and together on growth and yield of potato cultivar ‘Red Norland’, was evaluated in microplots under field conditions. The results indicate Paratylenchus spp. and Pratylenchus spp. are the most frequent nematodes, respectively, in pea and potato fields. Pin nematodes reproduced on field pea cultivars and caused up to 37% reduction in plant height and 40% reduction in yield. Additionally, both P. penetrans and F. oxysporum alone, and together had significant negative effect on growth and yield of potato.

Copies of author's previously published articles inserted. Bibliography :leaves 65-80 Ice nucleation active (INA) bacteria were detected in a pea field in South Australia. They were identified as strains of Pseudomonas syringae and Pseudomonas flourescens biotype 1. Some chemical agents were tested on the two ice nucleating species, as cryoprotectants.

Includes bibliographical references (leaves 82-92). Five isolates of pea seed-borne mosaic virus were compared by host range and symptomatology on 16 pisum sativum cultivars lines, 21 lines of Lathyrus and Lens spp. and several indicator species

Corrigendum inserted at the back. Includes bibliographical references (leaves 133-158). Ch. 1. General introduction -- ch. 2. General materials and methods -- ch. 3. Biological characterisation of Australian PSbMV isolates -- ch. 4. Developing nucleic acid based diagnostics for PSbMV -- ch. 5. Detection of PSbMV isolates by RT-PCR and RFLP analysis -- ch. 6. Developing an internal control for PSbMV RT-PCR -- ch. 7. Molecular analysis of the PSbMV VPG -- ch. 8. PSbMV sequence and phylogenetic analysis -- ch. 9. General discussion Sixteen pea seed borne mosaic virus (PSbMV) isolates were collected between 1995 and 1998. These isolates were biologically distinct yet serologically indistinguishable. The conclusion is that PSbMV is widespread and occurs at a low incidence in Australia. Reports sequence information on new isolates of PSbMV which has allowed genomic regions to be identified which distinguish PSbMV pathotypes and isolates; and, to the development of PSbMV nucleic acid hybridisation and RT-PCR assays.

Thesis (MSc)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The codling moth, Cydia pomonella (Lepidoptera: Tortricidae), is the key pest of apples and pears worldwide. The withdrawal of certain fundamental chemicals from codling moth management spray programmes, due to concerns about human, environmental and ecosystem health, has resulted in the search for softer, more environmentally friendly, and safer control measures. Entomopathogenic nematodes (EPNs), naturally occur in the soil, and actively search for hosts. The interest in using EPNs from the families Heterorhabditidae and Steinernematidae as a control measure was sparked in 1953, when an EPN was discovered in an insect. The aim is to incorporate EPNs in an integrated pest management (IPM) programme, to ensure minimal residue and eventually residue-free pome fruit production in South Africa. In order to ensure EPN success, both the environmental and technical factors influencing their efficacy, were investigated in this study. The biocontrol potential of three imported EPN isolates, being Steinernema feltiae and two isolates of Heterorhabditis bacteriophora (Hb1, Hb2), as well as a local isolate, Steinernema yirgalemense, were evaluated for the control of the codling moth under local conditions. All concentrations of S. yirgalemense, applied by immersion in a suspension of nematodes, gave > 98% control. The two formulated isolates of H. bacteriophora, Hb1-f and Hb2-f, gave < 30% control. When using the same nematode isolates, produced in vivo, S. yirgalemense still resulted in a higher codling moth control of > 90%, compared to 54% and 31% control of the H. bacteriophora Hb1 and Hb2 isolates, respectively. In follow up field trials, S. feltiae resulted in ≥ 80% control, and was thus more effective than both S. yirgalemense and the H. bacteriophora (Hb1) isolates, with 66% and 24%, and 24% and 9% control, for two separate trials, respectively. To validate the data obtained from the field trials, subsequent laboratory bioassays were conducted evaluating temperature regimes, following the same cycle as under natural conditions, with a constant humidity of 100%. Steinernema feltiae proved to be most effective, causing > 90% mortality, followed by S. yirgalemense, with 78% mortality. The two H. bacteriophora isolates (Hb1, Hb2) under the above-mentioned laboratory conditions, resulted in 73% and 59% control, respectively. Humidity thus seems to be the most important factor affecting EPN efficacy during above-ground applications. Steinernema feltiae proved to be a better candidate than S. yirgalemense for the control of the codling moth. The efficacy of different EPN isolates in controlling diapausing codling moth larvae at different temperatures was also evaluated, under local conditions, using spray application. Steinernema feltiae and two isolates of H. bacteriophora Hb1 and Hb2, including two local isolates, S. yirgalemense and Steinernema jeffreyense, were evaluated. The use of S. jeffreyense resulted in the most effective control, with 67% mortality, followed by H. bacteriophora (Hb1) with 42%, and then by S. yirgalemense with 41%. Laboratory bioassays simulating field conditions revealed that S. feltiae was most virulent to codling moth larvae, with 67% mortality by infection, followed by S. yirgalemense with 58%, the H. bacteriophora strain Hb1 with 48%, and the Hb2 strain with 24%. A comparison of the infection and penetration rate of two isolates of H. bacteriophora (Hb1, Hb2), S. feltiae and S. yirgalemense, which was carried out in multiwell plates at 14°C and 25°C, respectively, confirms the dramatic effect of temperature on EPN efficacy. At 14°C, all treatments with EPN species resulted in slower codling moth mortality than they did at 25°C, as after 48 h, < 15% mortality was recorded for all species, whereas at the warmer temperature, > 98% mortality was recorded for all species. After the exposure of washed, cool-treated larvae to 25°C for 24 h, the application of both S. feltiae and S. yirgalemense resulted in 100% mortality, whereas the application of the two H. bacteriophora isolates, Hb1 and Hb2, resulted in 68% and 54% control, respectively, over the same time period. At 14°C, S. feltiae had the highest average penetration rate of 20 IJs/insect, followed by S. yirgalemense with 14 IJs/insect, whereas S. yirgalemense had the highest penetration rate at 25°C, with 39 IJs/insect, followed by S. feltiae, with 9 IJs/insect. The two H. bacteriophora isolates had higher average penetration rates at the higher temperature. This study has highlighted the biocontrol potential of S. jeffreyense, as well as showing that S. feltiae is a cold-active nematode, whereas the other three EPN isolates prefer warmer temperatures. Stacked wooden fruit bins are regarded as preferred overwintering sites for codling moth diapausing larvae. Control strategies against the codling moth in South Africa have been hampered by the reinfestation of orchards by nearby stacked infested fruit bins or by the movement of bins between orchards. Worldwide, wooden fruit bins are systematically being replaced with plastic bins, which, in South Africa, will only be phased out over a few years. The objective of this study was to evaluate the potential of H. bacteriophora, S. feltiae, and S. yirgalemense, to disinfest miniature wooden fruit bins under controlled conditions in the laboratory. After dipping minibins in a suspension of 25 IJs/ml of all three EPN species, under optimum conditions of temperature and humidity, the highest percentage of control was obtained using S. feltiae (75%) followed by S. yirgalemense (57%), and then by H. bacteriophora (Hb1) (27%). The addition of adjuvants significantly increased (p < 0.001) S. feltiae infectivity to > 95%, whereas it did not result in a significant increase in H. bacteriophora or S. yirgalemense infectivity. The results indicated that H. bacteriophora would not be a suitable candidate to use for the control of the codling moth larvae in wooden fruit bins. The current preferred candidate for control would be S. feltiae, whose efficacy could be increased by means of the addition of an adjuvant. During winter, when the whole codling moth population are larvae and in diapause, no control measures are applied in orchards. This study has shown that EPNs can be sprayed in orchards to lower the codling moth cohort emerging after winter, as well as be included in an IPM programme. EPNs can act as a second line of defence, through supplementary control, and ensure effective control of the codling moth larvae which survived chemical spray applications, to safeguard against resistant codling moth populations in the next season.
AFRIKAANSE OPSOMMING: Kodlingmot, Cydia pomonella (Lepidoptera: Tortricidae), is ‘n belangrike plaag van appels en pere wêreldwyd. Die onttrekking van sekere fundamentele chemikalieë vanuit die kodlingmot beheerprogram weens die kommer oor menslike, omgewings en ekosisteemgesondheid, het gelei tot die soektog na sagter, meer omgewingsvriendelike en veiliger beheermaatreëls. Entomopatogeniese nematodes (EPNs) kom natuurlik in die grond voor en soek aktief na gashere. Die belangstelling in die gebruik van EPNs van die families Heterorhabditidae en Steinernematidae as 'n beheermaatreël is te danke aan die ontdekking van 'n EPN in ‘n insek in 1953. Die doel is om EPNs in 'n geïntegreerde plaagbeheerprogram (GPB) te inkorporeer om sodoende minimale residue te verseker en uiteindelik residu vrye produksie van kernvrugte in Suid-Afrika. Ten einde die sukses van EPNs te verseker, is beide die omgewings- en tegniese faktore wat hul doeltreffendheid beïnvloed in die studie ondersoek. Die biologiese beheer potensiaal van drie ingevoerde EPN isolate, Steinernema feltiae en twee Heterorhabditis bacteriophora (Hb1, Hb2) isolate, sowel as 'n plaaslike isolaat, Steinernema yirgalemense, is vir die beheer van kodlingmot onder plaaslike toestande geëvalueer. Alle konsentrasies van S. yirgalemense, wat deur indompeling in ‘n suspensie van nematodes toegedien is, het > 98% beheer tot gevolg gehad. Die twee geformuleerde isolate van H. bacteriophora, Hb1-f en Hb2-f, het < 30% beheer gegee. Met die gebruik van dieselfde nematode isolate, wat in vivo geproduseer is, het S. yirgalemense nog steeds 'n hoër kodlingmot beheer van > 90% opgelewer, in vergelyking met die 54% en 31% beheer van die H. bacteriophora Hb1 en Hb2 isolate, onderskeidelik. Steinernema feltiae het in opvolg veldproewe ≥ 80% beheer tot gevolg gehad en was dus meer effektief as beide S. yirgalemense en die H. bacteriophora (Hb1) isolate, met 66% en 24% en 24% en 9% beheer onderskeidelik in twee afsonderlike veldproewe. Om die resultate van die veldproewe te bevestig, is daaropvolgende laboratorium biotoetse uitgevoer en temperatuur regimes is geëvalueer deur die selfde siklus as onder natuurlike toestande te volg, met 'n konstante humiditeit van 100%. Die studie het bewys dat S. feltiae die mees doeltreffende isolate was met > 90% mortaliteit, S. yirgalemense het gevolg met 78% mortaliteit. Die twee H. bacteriophora isolate (Hb1, Hb2) het onderskeidelik onder bogenoemde laboratorium toestande 73% en 59% beheer tot gevolg gehad. Humiditeit blyk dus die belangrikste faktor te wees wat EPN se doeltreffendheid tydens bogrondse toediening affekteer. Die studie het bewys dat S. feltiae 'n beter kandidaat as S. yirgalemense vir die beheer van kodlingmot is. Die doeltreffendheid van verskillende EPN isolate vir die beheer van diapause kodlingmot larwes sowel as EPN se aktiwiteit by verskillende temperature is ook onder plaaslike toestande, deur bogrondse bespuitings, geëvalueer. Steinernema feltiae en twee isolate van H. bacteriophora (Hb1, Hb2), S. yirgalemense en ‘n ander plaaslike isolaat, Steinernema jeffreyense, is geëvalueer. Die gebruik van S. jeffreyense, het tot die mees effektiewe beheer gelei, met 67% mortaliteit, gevolg deur H. bacteriophora (Hb1) met 42%, en dan S. yirgalemense met 41%. Laboratorium biotoetse wat veldtoestande simuleer, het bewys dat S. feltiae die mees doeltreffend teen kodlingmot larwes is, met 67% mortaliteit tydens infeksie, gevolg deur S. yirgalemense met 58%, die H. bacteriophora Hb1 isolaat met 48%, en die Hb2 isolaat met 24%. 'n Vergelyking van die infeksie- en penetrasie tempo van twee isolate van H. bacteriophora (Hb1, Hb2), S. feltiae en S. yirgalemense wat in 12-put plate teen 14°C en 25°C uitgevoer is, het die dramatiese effek van temperatuur op EPN doeltreffendheid bevestig. By 14°C het alle EPN spesies behandelings stadiger kodlingmot mortaliteit as by 25°C na 48h tot gevolg gehad. ‘n Mortaliteit van < 15% is vir alle spesies aangeteken terwyl by die warmer temperature is > 98% mortaliteit vir alle spesies aangeteken. Na die blootstelling van afgespoelde, koel behandelde larwes aan 25°C vir 24 uur, het die toediening van beide S. feltiae en S. yirgalemense, 100% mortaliteit van larwes tot gevolg gehad terwyl die toediening van die twee H. bacteriophora isolate, Hb1 en Hb2, onderskeidelik 68% en 54% beheer tot gevolg gehad, oor dieselfde tydperk. By 14°C, het S. feltiae die hoogste gemiddelde penetrasie tempo van 20 ILs/ larwe, gevolg deur S. yirgalemense met 14 ILs/ larwe tot gevolg gehad, terwyl S. yirgalemense die hoogste penetrasie tempo getoon het by 25°C met 39 ILs/ insek, gevolg deur S. feltiae met 9 ILs/ insek. Die twee H. bacteriophora isolate (Hb1 en Hb2) het ook hoër gemiddelde penetrasie tempo by die hoër temperatuur getoon. Hierdie studie het die biobeheer potensiaal van S. jeffreyense beklemtoon, asook weereens bevestig dat S. feltiae ‘n koue-aktiewe nematode is, terwyl die ander drie EPN isolate warmer temperature verkies. Hout vrugtekratstapels, word beskou as ‘n ideale oorwintering skuiling vir kodlingmot diapause larwes. In Suid-Afrika word beheerstrategieë teen kodlingmot in die wiele gery deur die herbesmetting van boorde deur nabygeleë besmette hout vrugtekratte of deur die beweging van kratte tussen boorde. Hout vrugtekratte word wêreldwyd stelselmatig vervang met plastiek kratte. Dit sal egter eers oor ‘n aantal jare in Suid-Afrika uitgefaseer word. Die doel van hierdie studie was om die potensiaal van H. bacteriophora, S. feltiae, en S. yirgalemense te evalueer deur miniatuur hout vrugtekratte onder gekontroleerde toestande in die laboratorium te disinfekteer. Na die onderdompeling van die mini vrugtekratte in 'n nematode suspensie van 25 ILs/ml van al drie EPN spesies, onder optimale toestande van temperatuur en humiditeit, is die hoogste persentasie van beheer met die gebruik van S. feltiae (74,85% ± 3.64%) verkry. Die byvoeging van toevoegings middels het S. feltiae se vermoë om te infekteer betekenisvol (p <0,001) tot > 95% verhoog, maar dit het nie tot 'n betekenisvolle toename in die infektiwiteit van H. bacteriophora of S. yirgalemense gelei nie. Die resultate dui daarop dat H. bacteriophora nie 'n geskikte kandidaat is om te gebruik vir die beheer van kodlingmot larwes in besmette hout kratte nie. Die voorkeurkandidaat tans vir beheer is S. feltiae, waarvan die doeltreffendheid verhoog kan word deur middel van die byvoeging van 'n bymiddel. Gedurende die winter wanneer die hele kodlingmot populasie as larwes in diapause is, word geen beheer in boorde toegepas nie. Hierdie studie het getoon dat EPNs in boorde gespuit kan word om sodoende die opkomende kodlingmot populasie na die winter te verlaag en kan ook ingesluit word in 'n GPB program. Die EPNs kan as 'n tweede verdedigingslinie optree en doeltreffende beheer van kodlingmot larwes verseker wat chemiese bespuitings oorleef het, en sodoende beskerming teen weerstandige kodlingmot populasies in die volgende seisoen bied.

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Thesis (MScAgric)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Botrytis cinerea Pers. Fr. [teleomorph Botryotinia fuckeliana (de Bary) Whetzel] causes serious losses of over 200 crops worldwide, including rooibos seedlings and pears. This pathogen is characterized by morphological, physiological and genetic diversity. The genetic diversity and population structure have not been investigated for B. cinerea populations in South Africa. Botrytis cinerea collected from rooibos seedlings and in pear orchards in the Western Cape of South Africa were investigated in the present study. The study was done with the aid of microsatellite markers, the amplification of mating type alleles MAT1-1 and MAT1-2 and determination of resistance towards various fungicides. Population dynamics was inferred and a similar picture emerged in both production systems. Botrytis cinerea annually causes severe losses of rooibos seedlings (Aspalathus linearis) in nurseries situated in the Clanwilliam region. Sampling was done in five nurseries and the cryptic species status of the isolates obtained was determined through restriction enzyme digestion of the Bc-hch gene. All but one (206 out of 207) of the isolates belonged to Group II or B. cinerea ‘sensu stricto’. Analysis of the B. cinerea Group II population, using seven microsatellite loci, was performed to assess the genetic population structure. Total gene diversity (H) was high, with a mean of 0.67. Two of the nurseries populations’ sample sizes were severely limited after clone correction, yet 100 genotypes were discerned among the 206 isolates genotyped. The percentage of maximal genotypic diversity (G) ranged between 16 and 68 for the five populations, with a total value of 17 for the 100 genotypes. One genotype, represented by 27 clones, was isolated from four nurseries. Relatively low but significant population differentiation was observed in total between nurseries (mean FST = 0.030, P = 0.001). The distribution of mating types MAT1-1 and MAT1-2 differed significantly from the ratio of 1:1 for the total population plus two of the nurseries’ populations. Three nursery populations had an equal mating type distribution. The index of association (IA) analyses suggests that the populations are asexually reproducing. Analysis of molecular variance (AMOVA) indicated that 97% of the total genetic variation is distributed within subpopulations. Fungicide resistance frequency against iprodione for 198 of the genotyped isolates displayed highly varying levels of resistance amongst the five nurseries. The mean total incidence of resistance towards iprodione was 43%, ranging from 0% to 81% for the five nurseries. Baseline sensitivity towards pyrimethanil yielded an average EC50 value of 0.096 mg/L. Botrytis cinerea isolates were collected from pear blossoms (Pyrus communis) in four orchards. Two orchards in the Ceres area and two in the Grabouw area were sampled from. A total of 181 isolates were collected from the four orchards. Incidence of blossom infection in the orchards ranged from 3% to 17%. Overall, there was a high incidence of isolates that had only the Boty transposable element (74%) compared to those harbouring both (Boty and Flipper), simultaneously (transposa, 24%). One isolate examined had the Flipper element only. Cryptic species status according to restriction enzyme digestion of the Bc-hch gene indicated that all the isolates belonged to Group II or B. cinerea ‘sensu stricto’. Analysis of the Group II population, through the use of seven microsatellite loci, was performed to assess the genetic population structure. Total gene diversity (H) was high, with a mean of 0.69 across all populations. Although two of the subpopulations displayed a high clonal proportion, overall 91 genotypes were discerned among the 181 isolates. The percentage of maximal genotypic diversity (G) ranged between 18 and 33 for the four populations, with a total value of 14 for the 91 genotypes. One genotype, represented by 27 clones, was isolated from all orchards. Moderate, but significant population differentiation was present in total among orchards (mean FST = 0.118, P = 0.001). The distribution of the mating types, MAT1-1 and MAT1-2, did not differ significantly from a 1:1 ratio for the total population as well as the subpopulations. Index of association (IA) analyses, on the other hand, suggests that the populations reproduce asexually. Analysis of molecular variance (AMOVA) indicated that 88% of the total genetic variation is distributed within subpopulations, 9% between subpopulations and only 3% between production areas. Fungicide resistance frequency against fenhexamid, iprodione and benomyl varied, with the highest levels of resistance present against benomyl and low levels of resistance seen towards iprodione and fenhexamid. In conclusion, this study has shown that there exist within the studied populations of B. cinerea, obtained from rooibos nurseries and pear orchards, an adaptive capacity to overcome current means of control. The use of population genetics to further our understanding of how plant pathogens interact and spread throughout a given environment is of cardinal importance in aiding the development of sustainable and integrated management strategies. Knowledge of the dispersal of B. cinerea in the two studied cropping systems has shed light on the inherent risk that it poses, and this together with knowledge of the levels of resistance that occurs should serve as an early warning to help divert possible loss of control in future.
AFRIKAANSE OPSOMMING: Botrytis cinerea Pers. Fr. [teleomorf Botryotinia fuckeliana (de Bary) Whetzel] veroorsaak ernstige verliese van meer as 200 gewasse wêreldwyd, insluitende rooibossaailinge en pere. Hierdie patogeen word deur morfologiese, fisiologiese, asook genetiese diversiteit gekenmerk. Die genetiese diversiteit en populasie-struktuur van B. cinerea populasies wat in Suid-Afrika voorkom, is nog nie ondersoek nie. Botrytis cinerea verkryg vanaf rooibossaailinge en in peerboorde in die Wes-Kaap van Suid-Afrika is ondersoek. Hierdie studie is met behulp van mikrosatellietmerkers, amplifikasie van die twee paringstipe gene (MAT1-1 en MAT1-2), asook die bepaling van weerstandsvlakke teenoor verskeie swamdoders, uitgevoer. Populasie-dinamika is afgelei en ‘n soortgelyke tendens is in beide produksie-sisteme waargeneem. Botrytis cinerea veroorsaak jaarliks ernstige verliese van rooibossaailinge (Aspalathus linearis) in kwekerye in die Clanwilliam-area. Monsters is in vyf kwekerye versamel en die kriptiese spesiestatus van die verkrygde isolate is deur restriksie-ensiemvertering van die Bc-hch geen bepaal. Almal behalwe een (206 uit 207) isolaat het aan Groep II of B. cinerea ‘sensu stricto’ behoort. Analise van die B. cinerea Groep II populasie, deur middel van sewe mikrosatellietmerkers, is uitgevoer om die genetiese populasiestruktuur te bepaal. Totale geendiversiteit (H) was hoog, met ‘n gemiddelde van 0.67. Alhoewel twee van die kwekerye se monstergrootte erg ingeperk is ná kloonverwydering, is daar nogtans 100 genotipes onder die 206 isolate wat geïsoleer is, waargeneem. Die persentasie van maksimale genotipiese diversiteit (G) het tussen 16 en 68, vir die vyf populasies, gewissel, met ‘n totaal van 17 vir die 100 genotipes. Een genotipe, verteenwoordig deur 27 klone, is uit vier kwekerye geïsoleer. Relatief lae dog noemenswaardige populasie-differensiasie is in totaal tussen kwekerye waargeneem (gem. FST = 0.030, P = 0.001). Die verspreiding van die twee paringstipes (MAT1-1 en MAT1-2) het beduidend verskil van ‘n 1:1 verhouding vir die totale populasie, asook twee van die kwekerye se populasies. Die drie oorblywende kwekerye se populasies het egter ‘n gelyke verdeling van die twee paringstipes getoon. Die indeks van assosiasie (IA) analises toon dat die populasies ongeslagtelik voortplant. Analise van molekulêre variasie (AMOVA) het aangedui dat 97% van die totale genetiese variasie binne die subpopulasies versprei is. Hoogs variërende vlakke van weerstand tussen die vyf kwekerye teenoor die swamdoder iprodioon, is vir die 198 isolate wat getoets is, gevind. Die totale gemiddelde frekwensie van weerstand teenoor iprodioon was 43%, wat tussen 0% en 81% vir die vyf kwekerye gevarieer het. Fondasie-vlak-sensitiwiteit vir pyrimethanil het ‘n gemiddelde EC50 waarde van 0.096 mg/L opgelewer. Botrytis cinerea isolate is ook vanuit peerbloeisels (Pyrus communis L.) vanuit vier boorde versamel, twee uit elk van die Ceres- en Grabouw-areas. In totaal is 181 isolate vanuit die vier boorde versamel. Die frekwensie van bloeiselinfeksie het tussen 3% en 17% gewissel. Oor die algemeen was daar ‘n hoë frekwensie van isolate wat slegs die Boty transponeerbare element teenwoordig gehad het (74%) in vergelyking met dié wat tegelykertyd beide (Boty en Flipper) teenwoordig gehad het. Een isolaat het slegs die Flipper element gehad. Bepaling van die kriptiese spesiestatus met behulp van restriksie-ensiemvertering van die Bc-hch geen het aangedui dat alle versamelde isolate tot Groep II of B. cinerea ‘sensu stricto’ behoort het. Analise van die Groep II populasie, deur middel van sewe mikrosatellietmerkers, is uitgevoer om genetiese populasie-struktuur te bepaal. Totale geendiversiteit (H) was hoog, met ‘n gemiddelde van 0.69 oor alle populasies. Alhoewel twee subpopulasies ‘n hoë klonale fraksie getoon het, is 91 genotipes tussen die 181 isolate wat verkry is, onderskei. Die persentasie van maksimale genotipiese diversiteit (G) het tussen 18 en 33 vir die vier populasies gewissel, met ‘n totale waarde van 14 vir die 91 genotipes. Een genotipe, verteenwoordig deur 27 klone, was in al vier boorde teenwoordig. Gematigde dog beduidende populasie differensiasie was in totaal tussen boorde teenwoordig (gem. FST = 0.118, P = 0.001). Die verspreiding van die paringstipes (MAT1-1 en MAT1-2) het nie betekenisvol van ‘n 1:1 verhouding vir die totale populasie, insluitende die subpopulasies, verskil nie. Indeks van assosiasie (IA) analises het egter aangedui dat die populasies ongeslagtelik voortplant. Analise van molekulêre variasie (AMOVA) het aangedui dat 88% van die totale genetiese variasie in subpopulasies te vinde was, 9% tussen subpopulasies en slegs 3% tussen produksie-areas. Frekwensie van swamdoder weerstandbiedendheid vir fenhexamid, iprodioon en benomyl het gewissel, met die hoogste vlakke teenoor benomyl waargeneem, maar baie lae vlakke teenoor fenhexamid en iprodioon. Samevattend het hierdie studie getoon dat die populasies van B. cinerea wat in hierdie twee produksie-sisteme, op rooibossaailinge en in peer boorde, ondersoek is, ‘n aanpasbaarheid toon om huidige metodes van beheer te oorkom. Die gebruik van populasiegenetika as ‘n hulpmiddel om ons kennis van patogeen-interaksies en -verspreiding te verbreed, is van kardinale belang in die ontwikkeling van geïntegreerde en volhoubare beheermaatreëls. Kennis van die verspreiding van B. cinerea in die bestudeerde gewasproduksiestelsels, werp lig op die inherente risiko wat dié patogeen inhou. Dít, tesame met kennis van die weerstandsvlakke wat voorkom, kan as ‘n vroegtydige waarskuwing dien ten einde moontlike verlies van beheer in die toekoms te help teenwerk.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2009.
ENGLISH ABSTRACT: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (obscure mealybug), is a common and serious pest of apples and pears in South Africa. Consumer and regulatory pressure to produce commodities under sustainable and ecologically compatible conditions has rendered chemical control options increasingly limited. Information on the seasonal occurrence of pests is but one of the vital components of an effective and sustainable integrated pest management system needed for planning the initiation of monitoring and determining when damage can be expected. It is also important to identify which orchards are at risk of developing mealybug infestations while development of effective and early monitoring tools for mealybug populations will help growers in making decisions with regards to pest management and crop suitability for various markets. It is also essential to determine the presence and efficacy of naturally occurring biological control agents in orchards so as to ascertain the potential of biological control as a viable alternative in orchards. However, under the current integrated pest management protocol, it has been difficult to determine this, due to the sporadic and relatively low incidence of mealybug infestations in some orchards, or by simply relying on naturally occurring field populations of biocontrol agents. Knowledge of the environmental conditions under which P. viburni population levels may become destructive is also essential for timing the release of insectary reared natural enemies as well as understanding the population ecology of this pest and its natural enemies. Information was gathered regarding the seasonal phenology of P. viburni and its natural enemies in pome fruit orchards in the Western Cape Province during the 2007/08 and 2008/09 growing seasons. Seasonal population studies showed that P. viburni has multiple overlapping generations with all life stages present throughout the year. The highest orchard infestations occurred during the summer period until early winter (January to early June). This was followed by a decrease in population from late June to November, before another increase in December. Presence-absence sampling of mealybugs on the host plant revealed that woody parts of the tree, such as the trunk and old stems were the most preferred sites for mealybug habitation, due to the availability of protected refuge sites. Migration of mealybug populations to newer growth and the upper sections of the tree crown, such as the new stems, leaves and eventually the fruit, was observed from December throughout the summer period until the early winter in June. Fruit colonization in both apples and pears commenced in January, when the fruit had developed a size sufficient for P. viburni to penetrate and occupy spaces such as the fruit core, calyx and stem end. There was no evidence of P. viburni occurring beneath the soil surface or on the roots of host trees. Two natural enemies of mealybugs, namely Pseudaphycus maculipennis (Mercet) and Coccidoxenoides perminutus (Girault), were found to be active in apple and pear orchards in the Western Cape. However, the status of C. perminutus as a parasite of P. viburni still needs to be verified despite evidence of emergence from P. viburni mummies, which was not sufficient enough to suggest that it is a useful biological control agent. Seasonal abundance trends of the two natural enemies revealed that their lifecycle is synchronized with that of the host. However, there was no evidence of P. maculipennis activity in Ceres. No predators were found during the course of this study. The rate of P. viburni parasitism at harvest was 46.52%, with P. maculipennis and C. perminutus constituting 98.966% and 1.034% of the parasitoids recovered from mealybug mummies, respectively. Studies on the use of pheromone traps as early monitoring tools for P. viburni showed that there was a positive and significant relationship between the fruit infestation and number of P. viburni adult males caught in pheromone-baited traps (r2 = 0.454). The action threshold level was estimated to be 2.5 male P. viburni caught per trap per fortnight at an economic threshold of 2% fruit infestation.
AFRIKAANSE OPSOMMING: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (ligrooswitluis), is ‘n algemene en ernstige plaag van appels en pere in Suid-Afrika. Druk deur verbruikers en regulasies om kommoditeite onder volhoubare en ekologies verenigbare toestande te produseer het chemiese beheeropsies toenemend beperk. Inligting oor die seisoenale voorkoms van plae is een van die essensiële komponente van ‘n effektiewe en volhoubare geïntegreerde plaagbestuurprogram. Dit is in die aanvanklike beplanning van monitering en om te bepaal wanneer skade verwag kan word. Dit is ook belangrik om boorde vroegtydig te identifiseer wat die risiko het om witluisbesmettings te ontwikkel. Die ontwikkeling van effektiewe en vroeë moniteringstegnieke vir witluisbevolkings sal produsente help met besluitneming rakende plaagbestuur en die geskiktheid van gewasse vir verskeie markte. Dit is ook noodsaaklik om die teenwoordigheid en effektiwiteit van biologiese beheer agente wat natuurlik in boorde voorkom te bepaal ten einde die potensiaal van biologiese beheer as ‘n lewensvatbare alternatief vas te stel. Onder die huidige geïntegreerde plaagbestuurprotokol was dit egter moeilik om laasgenoemde te bepaal weens die sporadiese en relatiewe lae voorkoms van witluisbesmettings in sommige boorde of deur bloot staat te maak op die veldpopulasies van biologiese beheer agente wat natuurlik voorkom. Kennis van die omgewingstoestande waaronder P. viburni bevolkingsvlakke skadelik raak is ook noodsaaklik vir die beplanning van vrylating van biologiese beheer agente, asook om die bevolkingsekologie van hierdie plaag en sy natuurlike vyande te verstaan. Inligting oor die seisoenale fenologie van P. viburni en sy natuurlike vyande in sagtevrugte boorde in die Westelike Kaapprovinsie is gedurende die 2007/08 en 2008/09 groeiseisoene versamel. Seisoenale bevolkingstudies het getoon dat P. viburni verskeie oorvleuelende generasies het met alle stadia teenwoordig regdeur die jaar.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2009.
ENGLISH ABSTRACT: The obscure mealybug, Pseudococcus viburni (Signoret) (Pseudococcidae), is one of the common and serious pests of apples and pears in South Africa. The management of this pest in South Africa is dominated by the use of insecticides, while research into using natural enemies for biological control of mealybugs is still ongoing. Increasing concern over the environmental impact, pesticide residues in fruits, resistance, and expense associated with frequent use of insecticides make it necessary to investigate alternative biological control methods, such as the use of entomopathogenic nematodes, for the control of mealybugs. Entomopathogenic nematodes have proven comparable or even superior to chemicals in controlling certain insect pests, without residue problems or a harmful effect on the environment. An important aspect of using endemic nematodes includes the identification of species of nematodes and their symbiotic bacterial cells. A study was carried out to describe a new species of Steinernema, which was recovered during a previous survey in citrus orchards in three provinces of South Africa. Morphometrics, morphology, crossbreeding, drawings, light microscopy and Scanning Electron Microscopy (SEM) photographs were used to describe the new species. A cryopreservation method has been simplified and optimised for the long-term storage of Steinernema khoisanae (SF87) and Heterorhabditis zealandica (J34). Different cryoprotectants used included 15% glycerol, 8% ethylene glycol and 8% dimethyl sulfoxide (DMSO), in which S. khoisanae was incubated at room temperature for periods of two, three, four and five days, followed by a methanol wash. An optimum survival rate of 69% was obtained for S. khoisanae after a four-day incubation period in 15% glycerol. This technique has been used for the cryopreservation of H. zealandica, with a 78% survival rate. The thawed nematodes of both species were able to infect Galleria mellonella larvae after 42 days of cryopreservation (-196ºC) and were able to complete their life cycles.
AFRIKAANSE OPSOMMING: Die ligrooswitluis, Pseudococcus viburni (Signoret) (Pseudococcidae), is een van die algemene en ernstige peste van appels en pere in Suid-Afrika. Die bestuur van hierdie pes word tans in Suid-Afrika deur die gebruik van insekdoders gedomineer terwyl navorsing oor die gebruik van natuurlike vyande vir die beheer van P. viburni nog aan die gang is. Die verhoogde kommer oor die omgewing, residue in vrugte, weerstand, en die koste verbonde aan die gereelde gebruik van chemiese middels maak dit nodig om alternatiewe biologiese metodes van beheer, soos die gebruik van entomopatogeniese nematodes vir die beheer van witluis, te ondersoek. In ander lande is reeds aangetoon dat entomopatogeniese nematodes onder sekere omstandighede en vir sekere insekte gelykwaardige of selfs beter beheer kan gee as chemiese middels. ʼn Belangrike aspek van die gebruik van endemiese nematodes vir die beheer van insekte sluit die korrekte identifikasie van die spesies met hul geassosieerde bakteriese simbionte in. ʼn Nuwe spesie van Steinernema is uit ʼn vorige opname van entomopatogeniese nematodes in sitrusboorde in drie provinsies van Suid-Afrika geïsoleer. Morfometrie, morfologie, kruisteling, ligmikroskoop en SEM fotografie is gebruik om ʼn nuwe spesies te beskryf. ʼn Kriopreserveringsmetode is ontwikkel en ge-optimaliseer vir die langtermyn bewaring van Steinernema khoisanae (SF87) en Heterorhabditis zealandica (J34). Verskillende kriobeskermingsmiddels insluitend 15% gliserol, 8% dimetiel sulfokied (DMSO) en 8% etileen glikol, waarin S. khoisanae vir periodes van twee, drie, vier, en vyf dae geïnkubeer is, is teen kamertemperatuur, getoets, gevolg deur ʼn metanolbad. Optimum oorlewing van 69% is verkry vir S. khoisanae nadat die infektiewe larwes (IJ) vir vier dae in 15% gliserol gehou is. Hierdie tegniek is ook toegepas op H. zealandica, met 78% oorlewing van die IJ. Die ontvriesde nematodes van beide spesies was in staat om Galleria mellonella larwes suksesvol te infekteer en hulle lewensiklus te voltooi nadat hulle vir 45 dae onder kriopreservering gehou is teen -196ºC.

Sclerotinia sclerotiorum causes white mold and severe yield losses of pea. 484 accessions from the Pisum core collection were screened for resistance using a mini-agar plug technique. 49, 41, and 13 accessions were identified with partial resistance based on lesion expansion inhibition (LEI), nodal transmission inhibition (NTI), and both traits combined, respectively. A genetic linkage map based on F2 DNA from the cross, Lifter/PI240515, was developed with 78 markers on 9 linkage groups (LG) spanning 734 cM. Two quantitative trait loci (QTL) were identified based on phenotypic data from F2:3 and F3:4 families. A single QTL on LGIII explained 34.1% of the phenotypic variation for LEI, while a second QTL on LGII(b) explained 2.5% of the phenotypic variation for NTI. This is the first report of QTL for S. sclerotiorum resistance in pea which will be useful in development of resistant pea varieties.

Stony corals (Order Scleractinia) are susceptible to a variety of diseases, which can occur from abiotic or biotic factors, or a combination of both. Public aquaria provide opportunities to study coral disease. Because coral mucus is the first line of defense against disease, the Biolog EcoplateTM is a useful tool to detect differences in microbial assemblages in the surface mucopolysaccharide (mucus) layer when comparing healthy and diseased corals. Histological examination is essential to document structural changes in coral tissue in response to diseases. This study identifies and characterizes diseases in captive corals through visual recognition, characterization of carbon utilization by microbial assemblages in coral mucus samples, and histological examination. In March 2010, surveys were sent to public aquaria throughout the United States that house corals. If the survey was returned indicating that the aquarium had diseased coral specimens present, sample kits were sent to the aquarium to acquire photographs, mucus samples for microbial carbon utilization analysis, and tissue samples for histological examination. Eighteen aquaria participated in the survey and 25 sets of samples were provided. The gross lesions from diseased samples fit into six categories: discoloration associated with darkening of the tissue or with color loss (bleaching), growth anomalies, and tissue loss associated with pests, with brown jelly, or with no obvious cause. Seven categories of possible contributing factors were reported: addition of inadequately quarantined corals to the tank, damage during transport, change of location, manual stress, and variations in light, salinity, or temperature. Introduction of inadequately quarantined specimens was the most common possible contributing factor to pest introduction. Significant differences in carbon source utilization were found between tank-water samples and mucus from both healthy and diseased areas of sampled corals. Although mucus samples from healthy and diseased samples did not differ in carbon source utilization overall, D-mannitol was used by 52% of microbial assemblages from mucus from diseased areas compared with only 17% of microbial assemblages from healthy mucus samples. Histologically, the most commonly observed features across all samples were healthy zooxanthellae, endolithic organisms, and nematocysts, all of which are normal features that can be influenced by stress factors. Brown granular material and ciliates were found associated with some anomalies, primarily the three categories of tissue loss. The presence of dense aggregates of zooxanthellate-engorged ciliates in corals afflicted with brown jelly was highly similar to histological observations of brown band syndrome, previously described from natural coral reefs.

Dissertation (PhD (Agric))--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Fungi belonging to the genus Botryosphaeria are heterotrophic micromycetes that can be pathogens on woody plants. They cause serious, and in some cases devastating losses to crops through leaf necrosis, stem cankers and plant death. The Proteaceae cut-flower industry in South Africa accounts for 70% of the national cut-flower enterprise. Botryosphaeria diseases are a major impediment to production and trade of Proteaceae and there is an urgent need to investigate the etiology, epidemiology and control of these diseases. Losses of one of the most important proteas, P. magnifica, amount to 50% or more, locally. The main aims of this study were therefore to establish the etiology and aspects of epidemiology of Botryosphaeria stem cankers on P. magnifica and other Proteaceae, and to investigate methods of disease control. Although there is a vast body of information pertaining to this fungus, which was reviewed in Chapter 1, there is relatively little information available on Botryosphaeria on Proteaceae. The taxonomy of Botryosphaeria requires thorough review, and molecular techniques need to be employed to resolve species identities. In Chapter 2, it was found that Phyllachora proteae, a leaf pathogen of proteas, produced a Fusicoccum anamorph, which is described as F. proteae. A sphaeropsis-like synanamorph was associated with F. proteae and a new combination for P. proteae is proposed in Botryosphaeria, as B. proteae. The taxonomy of Botryosphaeria is in disarray at both the generic and the specific level. In Chapter 3 the taxonomic history of Botryosphaeria is reviewed, and the genus circumscribed and distinguished from other morphologically similar genera. Although several anamorph genera have been linked to Botryosphaeria, based on morphological observations and phylogenetic analysis of lTS rDNA sequence data, two anamorph genera are now recognised, those with pigmented conidia (Diplodia), and those with hyaline conidia (Fusicoccum). Botryosphaeria proteae should thus be excluded from Botryosphaeria. Several pathogenic Botryosphaeria spp. have an endophytic phase within their hosts. They are therefore imported unwittingly into other countries where they may pose a risk to agriculture and indigenous vegetation. The current global distribution of Botryosphaeria spp. associated with Proteaceae is clarified and a key to these taxa associated with Proteaceae is provided in Chapter 4. Five Botryosphaeria spp. are associated with cut-flower Proteaceae worldwide viz. B. lute a, B. obtusa, B. protearum, B. proteae and B. rib is. B. protearum is described as a new species. A thorough understanding of disease epidemiology is essential to effect a reduction of losses. In Chapter 5, I show that on P. magnifica, lesions caused by Botryosphaeria protearum, which lead to the formation of stem cankers, are initiated in the mid-rib vein or margin of leaves. Koch's postulates were satisfied and it was found that the number of lesions that developed from artificial inoculations correlated with starch levels present in leaves at the time of inoculation. In Chapter 6 it is shown that B. protearum exists as an endophyte in leaves of P. magnifica in naturally occurring as well as cultivated plants. In natural stands of proteas stem cankers are rare, but in cultivated plantations the incidence is high. Nutritional analyses indicate that higher levels of nitrogen occur in leaves of cultivated plants in spring, which could enhance disease development. High levels of sodium in the leaves of wild plants may restrict disease development. The severe economic losses caused by B. protearum make the search for improved methods of disease control essential. Fungicide applications form an important component of an integrated approach to disease management. In Chapter 7, in vitro tests demonstrate that tebuconazole, benomyl, prochloraz me, iprodione and fenarimol reduce the mycelial growth of B. protearum effectively. In the field there was a 25-85% reduction in the occurrence of stem cankers by applying fungicides or sanitation pruning. The best control was achieved by using benomyl, bitertanol, fenarimol, iprodione, prochloraz manganese chloride alternated with mancozeb and tebuconazole prophylactically. If sanitation pruning is combined with regular applications of fungicides, disease can be combated.
AFRIKAANSE OPSOMMING: Mikrofungi wat tot die genus Botryosphaeria behoort, is heterotrofiese organismes, wat patogenies op houtagtige plante kan wees. Hulle veroorsaak ernstige, en in sommige gevalle, verwoestende verliese, deur blaarnekrose, stamkankers en plantafsterwing. Die Proteaceae snyblom-industrie in Suid-Afrika maak 70% van die nasionale snyblomindustrie uit. Botryosphaeria siektes is 'n belangrike struikelblok in die produksie en handeldryf van Proteaceae, en daar is 'n ernstige behoefte om die etiologie, epidemiologie en beheer van siektes te ondersoek. Verliese van een van die belangrikste proteas, P. magnifica, beloop plaaslik 50% of meer. Die hoof doelstellings van hierdie studie was dus om die etiologie en epidemiologie van Botryosphaeria stamkankers op P. magnifica en ander Proteaceae vas te stel en metodes van siektebeheer te ondersoek. Hoewel daar 'n wye hoeveelheid inligting rakende die swam bestaan, wat in Hoofstuk I hersien is, is daar relatief min inligting oor Botryosphaeria op Proteaceae beskikbaar. Die taksonomie van Botryosphaeria benodig deeglike hersiening, en molekulêre tegnieke word benodig om spesie-identiteite op te klaar. In Hoofstuk 2 is gevind dat Phyllachora proteae, 'n blaarpatogeen van proteas, 'n Fusicoccum anamorf produseer, wat as F. proteae beskryf word. 'n Sphaeropsis-agtige synanamorf is met F. proteae geassosieer en 'n nuwe kombinasie vir P. proteae is as B. proteae in Botryosphaeria voorgestel. Die taksonomie van Botryosphaeria is, beide op die genus- as die spesievlak, in wanorde. In Hoofstuk 3 word die taksonomiese geskiedenis van Botryosphaeria hersien, en die genus word omskryf en van ander morfologies soortgelyke genera onderskei. Hoewel verskeie anamorf genera al met Botryosphaeria op grond van morfologiese waarnemings en filogenetiese analise van ITS rDNA volgorde data verbind is, word twee anamorf genera nou herken, dié met gepigmenteerde konidia (Diplodia), en dié met deurskynende konidia (Fusicoccum). Botryosphaeria proteae moet dus van Botryosphaeria uitgesluit word. Verskeie patogeniese Botryosphaeria spp. het 'n endofitiese fase in hul lewenssiklus. Hulle word dus onwetend in ander lande ingevoer waar hulle 'n gevaar vir landbou en inheemse plantegroei kan inhou. Die huidige wêreldverspreiding van Botryosphaeria spp. wat met Proteaceae geassosieer word is opgeklaar, en in Hoofstuk 4 word 'n sleutel tot die taksa wat met Proteaceae geassosieer word verskaf. Vyf Botryosphaeria spp. word met snyblom Proteaceae wêreldwyd geassosieer, naamlik B. lutea, B. protearum, B. proteae, B. ribis en B. obtusa. B. protearum word as 'n nuwe spesie beskryf. 'n Deeglike kennis van siekte-epidemiologie is noodsaaklik ten einde verliese te verminder. In Hoofstuk 5 dui ek aan dat letsels wat lei tot stamkankers, veroorsaak deur Botryosphaeria protearum op P. magnifica, in die hoofnerf of rant van blare ontstaan. Koch se postulate is uitgevoer en daar is vasgestel dat die aantal letsels wat vanuit kunsmatige inokulasies ontwikkel het korreleer met die styselvlakke teenwoordig in die blare ten tye van die inokulasie. In Hoofstuk 6 word getoon dat B. protearum as 'n endofiet in die blare van P. magnifica. In natuurlike standplase van proteas is stamkankers skaars, maar in verboude plantasies is die voorkoms hoog. Voedingsanalises dui aan dat hoër vlakke van stikstof in die blare van verboude plante in die lente voorkom, wat siekte-ontwikkeling moontlik kan bevorder. Hoë vlakke van natrium in die blare van natuurlike plante mag siekteontwikkeling beperk. Die ernstige ekonomiese verliese wat deur B. protearum veroorsaak word, maak die soektog na verbeterde metodes van siektebeheer noodsaaklik. Fungisiedtoedienings maak 'n belangrike deel uit van 'n geïntegreerde benadering tot siektebeheer. In Hoofstuk 7 dui in vitro toetse aan dat tebuconazole, benomyl, prochloraz me, iprodione en fenarimol die miseliumgroei van B. protearum effektief verminder. 'n Vermindering van 25-85% is aangetoon in die voorkoms van stamkankers in die veld, deur die toediening van fungisiedes en sanitasiesnoei. Die beste beheer is verkry deur die voorkomende toediening van benomyl, bitertanol, fenarimol, iprodione en prochloraz manganese chloride, afgewissel met mancozeb en tebuconazole, op plante in die veld. Indien sanitasiesnoei met gereelde toedienings van fungisiedes gekombineer word, kan die siekte bekamp word.

Thesis (MSc)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: This thesis consists of four chapters that present research findings on Colletotrichum diseases associated with Proteaceae worldwide. The first chapter is a review of literature regarding the taxonomy and histology of Colletotrichum species associated with Proteaceae. The literature is not restricted to Proteaceae hosts, as information regarding Colletotrichum on Proteaceae is very limited. In chapter two, Colletotrichum spp. associated with proteaceous hosts growing in various parts of the world were identified based on morphology, sequence data of the internal transcribed spacer region (ITS-I, ITS-2), the 5.8S gene, and partial sequences of the B-tubulin gene. Four species of Colletotrichum were associated with Proteaceae. Colletotrichum gloeosporioides was isolated from Protea cynaroides cultivated in South Africa and Zimbabwe and from a Leucospermum sp. in Portugal, but is known to occur worldwide on numerous hosts. A recently described species, C. boninense, was associated with Zimbabwean and Australian Proteaceae, but also occurred on a Eucalyptus sp. in South Africa. This represents a major geographical and host extension for the species, and a description of the African strains is provided. Colletotrichum crassipes was represented by a single isolate obtained from a Dryandra plant in Madeira. Colletotrichum acutatum was isolated from Protea and Leucadendron in South Africa as well as from other proteaceous hosts occurring elsewhere. Colletotrichum acutatum f. sp. hakea was isolated from Hakea in South Africa. In chapter three, pathogenicity of these Colletotrichum species to certain proteas was established, relative aggressiveness of the different species tested and host response to them were compared as well as the effect that wounding had on host response. From the results obtained it is concluded that C. acutatum and C. gloeosporioides are the primary pathogens associated with Colletotrichum leaf necrosis, and C. acutatum is the main cause of anthracnose and stem necrosis of Proteaceae in South Africa. A histological study was performed in chapter four in response to the findings from the previous chapter. The behaviour of two C. acutatum isolates (one originating from Protea and the other from Hakea, C. acuataum f.sp. hakea) was studied on inoculated Protea leaf surfaces using light and scanning electron microscopy. Colletotrichum acutatum from Protea formed melanised appressoria on the leaf surface, whereas C. acutatum from Hakea formed very low numbers of both melanised and unmelanised appressoria. Most of the appressoria formed by C. acutatum from Protea were formed on the cell junctions and on the periclinal walls of the epidermal cells. From this study it is clear that C. acutatum f. sp. hakea is not a pathogen of Protea. Consequently the current use of this isolate as a biological control agent of Hakea in South Africa poses no threat to indigenous Protea species. Colletotrichum acutatum from Protea (although closely related to C. acutatum f. sp. hakea), is a pathogen of Protea, which was confirmed by histological observations. In conclusion, the present study has shown that several species of Colletotrichum are associated with diseased Proteaceae. These species differed in their pathogenicity and aggressiveness when inoculated onto certain protea cultivars. These differences could be partially explained by examining the behaviour of C. acutatum on the leaf surface. It is clear, however, that the distribution of the different species, their aggressrveness on different Proteaceae and their modes of infection needs to be investigated further. This work provides a basis for future research on the long-term effective management of these pathogens in fynbos production.
AFRIKAANSE OPSOMMING: Hierdie tesis bestaan uit vier hoofstukke wat handeloor navorsing van Colletotrichum siektes van Proteaceae wêreldwyd. Die eerste hoofstuk is 'n oorsig van literatuur rakende die taksonomie en histologie van die Colletotrichum spesies wat met Proteaceae geassosieer word. Die literatuur oorsig is nie beperk tot die Proteaceae nie aangesien baie min inligting rakende Colletotrichum op Proteaceae bestaan. In die tweede hoofstuk word die Colletotrichum spesies wat met proteas in verskeie dele van die wêreld geassosieer word, op grond van morfologie, DNS volgorde data van die interne getranskribeerde spasieerder area ("ITS-I, ITS-2"), die 5.8S geen, en gedeeltelike DNS volgordes van die B-tubulin geen geïdentifiseer. Vier Colletotrichum spesies is met die Proteaceae geassosieer. Colletotrichum gloeosporioides is geïsoleer vanaf Protea cynaroides wat in Suid-Afrika en Zimbabwe gekweek is en vanaf 'n Leucospermum sp. in Portugal, maar is bekend op verskeie gashere wêreldwyd. 'n Spesie wat onlangs beskryf is, C. boninense, is met Zimbabwiese en Australiaanse Proteaceae geassosieer, maar kom ook op 'n Eucalyptus sp. in Suid-Afrika voor. Dit is 'n groot uitbreiding van die geografiese voorkoms en gasheerreeks van hierdie spesie en 'n beskrywing van die Afrikaanse rasse word gegee. Colletotrichum crassipes is verteenwoordig deur 'n enkele isolaat wat vanaf 'n Dryandra plant in Madeira verkry is. Colletotrichum acutatum is vanaf Protea en Leucadendron in Suid-Afrika asook vanaf ander proteas wat elders voorkom, geïsoleer. Colletotrichum acutatum f. sp. hakea is vanaf Hakea in Suid-Afrika geïsoleer. In hoofstuk drie is die patogenisiteit van hierdie Colletotrichum spesies teenoor sekere proteas getoets, die relatiewe aggressiwiteit van die verskillende spesies is vergelyk, asook die gasheer se reaksie teenoor die spesies en die effek wat verwonding op die gasheer gehad het. Daar kan afgelei word vanaf die resultate dat C. acutatum en C. gloeosporioides die primêre patogene is wat met Colletotrichum blaarnekrose geassosieer word, en dat C. acutatum die hoof oorsaak is van antraknose en lootnekrose van Proteaceae in Suid-Afrika. 'n Histologiese studie is in hoofstuk vier uitgevoer in reaksie op die bevindings van die vorige hoofstuk. Die gedrag van twee C. acutatum isolate (een vanaf Protea en die ander vanaf Hakea, C. acutatum f.sp. hakea) op die oppervlaktes van geïnokuleerde Protea blare is bestudeer deur gebruik te maak van lig- en skandeer-elektronmikroskopie. Colletotrichum acutatum vanaf Protea vorm gemelaniseerde appressoria op die blaaroppervlak, terwyl C. acutatum vanaf Hakea klein hoeveelhede van beide gemelaniseerde en ongemelaniseerde appressoria vorm. Meeste van die appressoria wat deur C. acutatum vanaf Protea gevorm word, vorm op die aanhegtingspunte tussen selle en op die periklinale wande van die epidermale selle. Vanuit hierdie studie is dit duidelik dat C. acutatum f. sp. hakea nie 'n patogeen van Protea is nie. Gevolglik hou die huidige gebruik van hierdie isolaat as biologiese beheer agent van Hakea in Suid-Afrika geen gevaar in vir inheemse Protea spesies nie. Colletotrichum acutatum vanaf Protea (alhoewel dit naverwant is aan C. acutatum f. sp. hakea) is 'n patogeen van Protea en hierdie stelling is ook bevestig deur histologiese waarnemmgs. Ter samevatting het hierdie studie getoon dat verskeie Colletotrichum spesies geassosieer word met siektes van Proteaceae. Hierdie spesies het van mekaar verskil rakende patogenisiteit en aggressiwiteit nadat hulle op sekere protea kultivars geïnokuleer is. Hierdie verskille kon gedeeltelik verklaar word deur die gedrag van C. acutatum op die blaaroppervlaktes van verskillende protea kultivars. Dit is duidelik dat die verspreiding van die verskillende spesies, hulle aggressiwiteit op verskillende Proteaceae en hul infeksie metodes verder ondersoek moet word. Hierdie studie verskaf 'n basis vir toekomstige navorsing rakende lang-termyn effektiewe bestuur van hierdie patogene in fynbos aanplantings.

The hypotheses challenged in this project were (1) people are the source for meticillin-resistant Staphylococcus aureus (MRSA) in pets, (2) risk factors for MRSA infection and carriage mirror those described in humans, (3) S. aureus continues to evolve on animals, (4) MRSA is carried by a substantial number of companion animals and (5) pets can be a reservoir for MRSA. Risk factors for MRSA pet infection were determined in a UK-wide case-control study enrolling dogs and cats with S. aureus infection (138 MRSA; 122 MSSA), their veterinary staff and owners. MRSA were typed and 12 paired human-animal isolates were compared by whole genome microarrays. MRSA carriage was examined in selected populations of dogs, cats and horses (n=1692) in the Greater London area and dog-to-dog transmission of MRSA was examined during an outbreak in a rescue kennel. Key findings were (a) an occupational risk for MRSA carriage in UK first opinion veterinary staff (9%), (b) antimicrobial therapy, surgery and admission to veterinary hospitals as major risk factors for pet MRSA infection; (c) human healthcareassociated lineages predominated amongst animals but (d) host-specific variation occurred within the same lineage, (e) MRSA carriage in the studied animal populations was low «1.5%), (f) "classical" risk factors were not involved in animal carriage but co-carriage of other staphylococci was protective against MRSA, (g) decolonisation occurred naturally and (h) dog-to-dog transmission was not observed. MRSA ST398 was identified from one horse, the first isolation from an animal in the UK. These findings support the concept that pets acquire MRSA primarily from people but are unlikely natural hosts for healthcare-associated MRSA. Therefore, rigorous personal and environmental hygiene combined with conscientious use of antimicrobial agents should be highly effective in veterinary clinics. Bacterial interference should be further investigated as a preventative measure. Vigilance is warranted as new strains may evolve on and spread between companion animals.

[Truncated abstract] Field pea (Pisum sativum) has many benefits when included in the crop rotation system in broadacre grain farming. These benefits include a disease break and improved weed control for cereals and less dependence on nitrogenous fertilisers due to the leguminous nature of pea. Currently, field pea adoption in Australia is low because the crop is susceptible to the fungal disease `black spot’ (Mycosphaerella pinodes) and has low stem strength and a lodged canopy. Black spot causes yield losses averaging 10-15% per year. Lodging results in difficult and costly harvesting, increased disease pressure and increased wind erosion from exposed soil surface when stems break at the basal nodes. This project aimed to address these problems through breeding, and through the application of quantitative genetics theory to a recurrent selection program. A quantitative measurement of relative stem strength was developed which could be used effectively in the field on single plants. Accurate laboratory measurements of stem strength were closely correlated with the field measure of compressed stem thickness in the basal node region. A diallel analysis of stem strength of the progeny of crosses among a range of pea lines with different values of compressed stem thickness concluded that the genetic control of stem strength was additive, with no maternal inheritance or dominance or epistasis effects.

The effects of intraspecific and interspecific competition, host plant, and prior host plant experience on fecundity, rate of oviposition and mortality of adults and larval survival of Delia radicum Bouche (Cabbage Maggot (CM)), D. antiqua Meigen (Onion Maggot (OM)), and D. platura Meigen (Seed Corn Maggot (SCM)), were studied on cabbage, onion and bean plants.
An optimum density for maximum fecundity per female was observed when the four experimental densities were compared. This optimum density was higher on host than on non-host plants. CM females were host specific and did not oviposit on non-host plants. Rates of oviposition and mortality over a 30-day period were calculated for each density. The rate of oviposition was slower at higher densities on host plants for CM, OM and SCM. The rate of mortality increased at the highest density for CM (cabbage), OM (bean) and SCM (cabbage), but remained unaffected for OM on onion and cabbage and for SCM on onion and bean, when densities were compared. For OM, a delay in the rate of oviposition and mortality on cabbage (non-host plant) when compared with onion (host plant), suggests that cabbage was not as readily accepted as an oviposition site. Interspecific competition experiments at six density ratio's of SCM:OM indicated increased fecundity, or an increase in the rate of oviposition for OM, at the lower densities when single and mixed species were compared. For SCM no effects on fecundity were recorded, but the rate of oviposition was slower and rate of mortality faster at the lowest density in the presence of OM. Similar studies with SCM and CM showed no such effects of competition.
Host plant exposure of SCM females during the pre-oviposition period resulted in a delay in initial acceptance of subsequent host plants as oviposition sites. This happened only when females were exposed to a secondary host during the pre-oviposition period. Once oviposition began, host discrimination ceased and a switch in oviposition sites to the preferred host did not alter the rate of oviposition. In CM, the rate of larval development increased at density 6 (optimum density). Above this density a decrease in the rate of development and a significant reduction in pupal weight was observed. Time required for fly emergence was not affected by increasing larval densities.

Thesis (PhD)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: The population density of the white wax scale, Ceroplastes destructor Newstead, has increased since 1994 in certain areas of Western and parts of Eastern Cape Provinces of South Africa where citrus is grown, particularly on Citrus reticulata (Blanco). A study was conducted to investigate its morphology, biology and ecology as contributions to the development of a sound integrated management programme. Characteristics of the immature stages and adult females were described and illustrated from field-collected and slide-mounted specimens. A key to the different stages and morphometeric characteristics useful for separating them are provided. No significant differences in female fecundity were found between orchards (P > 0.05). However, fecundity varied significantly between female size classes from the same orchard (P < 0.001). Female body-size also differed significantly between orchards (P < 0.05) and was significantly positively correlated with fecundity (P < 0.01). C. destructor has one discrete generation per year in South Africa. Oviposition commenced in November and continued through to the end of December with a few females ovipositing until mid January. Population density of the second instar peaked in February while the third instar extended from March to the end of July, followed by a peak population of adults in August. Seven primary and three secondary parasitoids, as well as four predator species attacking C. destructor were identified. Aprostocetus (= Tetrastichus) ceroplastae (Girault) was the dominant species, accounting for 78.87% of the total primary parasitoids reared. Peak numbers of parasitoids and predators were synchronized with peak emergence of susceptible scale stages, indicating that the host-parasitoid/predator system contained a density-dependent regulatory mechanism. Key mortality factors varied slightly between two of the orchards. Key stage mortality determined from a cohort life table was generally in the third instar (LIlI) and preovipositional female (POF) stage. Significant density-dependent mortality factors were demonstrated for the first instar (LI) and PDF stage. Dispersal of C. destructor is by first instar nymphs and the numbers caught on a series of yellow sticky traps varied significantly between crawler densities at the source, trap distances and trap directions from the source (P < 0.001). The numbers caught were positively correlated to the initial crawler density at the source (P < 0.01), suggesting that dispersal was density dependent. Trap distance and the numbers caught were inversely correlated (P < 0.01). Evaluation of effects of different densities of C. destructor on growth, survivorship and reproduction of scales as well as on leaf bearing ability of trees and area of leaf surface covered with sooty mould fungus was carried out on naturally infested Syzygium (= Eugenia) malaccensis (L.) plants. Scale body size and fecundity were inversely related to scale density (P < 0.01), suggesting density-dependent intraspecific competition. Scale survivorship generally declined with increasing density whereas scale parasitism and predation were positively correlated with density (P < 0.05). At high scale densities production of new leaves was significantly reduced (P < 0.01), reducing the resource base for subsequent generations of scale. Scale density and leaf area covered with sooty mould fungus were significantly positively correlated (P < 0.05). The toxicity of four synthetic insecticides against the three immature stages of C. destructor and of eight insecticides against the parasitoid A. ceroplastae was evaluated. Development of the first and second instars of C. destructor was completely arrested by the chemicals. Female fecundity, fertility and body sizes of survivors of treatments applied at the LIII stage were not significantly affected by any of the chemicals (P > 0.05). All the chemicals exhibited high toxicity to A. ceroplastae and hence are not recommended for integrated management of C. destructor in citrus orchards where A. ceroplastae plays an important role.
AFRIKAANSE OPSOMMING: Die populasiedigtheid van die witwasdopluis, Ceroplastes destructor Newstead, het sedert 1994 toegeneem in sekere gebiede van die Weskaap en Ooskaap provinsies van Suid-Afrika waar sitrus verbou word, veralop Citrus reticulata (Blanco). 'n Studie van hierdie insek se morfologie, biologie en ekologie is onderneem as bydrae tot die ontwikkeling van 'n geïntegreerde bestuursprogram. Die karaktertrekke van die onvolwasse stadia en die volwasse wyfies is beskryf en geïllustreer vanaf eksemplare wat in die veld versamel is en op g1asplaatjies gemonteer is. 'n Sleutel vir die verskillende stadia en morfometriese kenmerke wat nuttig is om hulle te onderskei, word voorsien. Geen beduidende verskille in die vrugbaarheid van wyfies van verskillende boorde is gevind nie (P < 0.05). Vrugbaarheid het egter betekenisvol verskil by die verskillende grootteklasse van wyfies uit dieselfde boord (P < 0.001). Die liggaamsgrootte van wyfies uit verskillende boorde het betekenisvol verskil (P < 0.05) en was betekenisvol positief gekorreleer met vrugbaarheid (P < 0.01). C. destructor het een generasie per jaar in Suid-Afrika. Eierlegging het in November begin en aangehou tot aan die einde van Desember, met enkele wyfies wat nog tot in middel Januarie eiers gelê het. Die populasiedigtheid van die tweede instar het 'n hoogtepunt in Februarie bereik, terwyl die derde instar van Maart tot aan die einde van Julie geduur het, gevolg deur 'n piekbevolking van volwassenes in Augustus. Sewe primêre en drie sekondêre parasitoïde asook vier predator spesies wat C destructor aanval, is geïdentifiseer. Aprostocetus (=Tetrastichus) ceroplastae (Girault) was die dominante spesies wat 78.87% van die totale aantal primêre parasitoïde wat uitgeteel is, uitgemaak het. Die pieke in die getalle van parasitoïde en predatore was gesinchroniseer met pieke in die verskyning van die gevoelige stadia, wat dui op die aanwesigheid van 'n digtheidsafhanklike regulatoriese meganisme. Die sleutel mortaliteitsfaktore het effens gevarieer tussen twee van die boorde. Die sleutelstadium van mortaliteit, soos bepaal m.b.v. 'n kohort lewenstabel, was gewoonlik die derde instar (LIlI) en die preoviposisionele wyfie (POW). Betekenisvolle digtheidsafhanklike mortaliteitsfaktore IS aangetoon vir die eerste instar (LI) en die POW. Die verspreiding van C.destructor vind plaas deur die eerste instar nimfe en die getalle wat op 'n reeks van taai geel valle gevang is, het betekenisvol gewissel volgens kruiperdigthede by die bron, asook die afstand en rigting van die valle vanaf die bron (P < 0.001). Die getalle wat gevang is, was positief gekorreleer met die aanvanklike kruiperdigtheid by die bron (P < 0.01), wat daarop dui dat verspreiding digtheidsafhanklik was. Die afstand van die valle en die aantal wat gevang is, was omgekeerd gekorreleer (P < 0.01). 'n Evaluering van die invloed van verskillende digthede van C. destructor op die groei, oorlewing en reproduksie van dopluise, asook die vermoë van bome om blare te dra en die area van die blaaroppervlak wat met roetskimmel besmet is, is uitgevoer op plante van Syzygium (= Eugenia) malaccensis (L.) met 'n natuurlike besmetting. Die liggaamsgrootte en vrugbaarheid van die dopluise was omgekeerd gekorreleer met hulle digtheid (P < 0.01), wat dui op digtheidsafhanklike intraspesifieke kompetisie. Die oorlewing van die dopluise het oor die algemeen afgeneem met toenemende digtheid, terwyl parasitisme en predasie positief gekorreleer was met digtheid (P < 0.05). By hoë dopluisdigthede het die produksie van nuwe blare betekenisvol afgeneem (P < 0.01), wat die hulpbronbasis vir daaropvolgende generasies van dopluise verswak. Die dopluisdigtheid en blaaroppervlak wat met roetskimmel bedek was, was positief gekorreleer (P < 0.05). Die toksisiteit van vier sintetiese insektemiddels teenoor die drie onvolwasse stadia van C. destructor en van agt insektemiddels teenoor die parasitoïd A. ceroplastae is geëvalueer. Die ontwikkeling van die eerste en tweede instars van C. destructor is heeltemal stopgesit deur die middels. Die fekunditeit, fertiliteit en liggaamsgrootte van wyfies wat toedienings op die LIIl stadium oorleef het, is nie betekenisvol ge-affekteer deur enige van die middels nie (P < 0.05). Al die middels was baie toksies teenoor A. ceroplastae en word dus nie aanbeveel vir die geïntegreerde bestuur van C. destructor waar A. ceroplastae 'n belangrike rol speel nie.

A new disease affecting potatoes was first detected in Mexico in 1993. Affected plants had aerial symptoms similar to those caused by potato purple top and psyllid yellows, but tubers had internal brown discoloration when sliced and dark stripes and streaks when processed to produce potato chips. The disease has been found in many potato production areas in Guatemala, Mexico, Honduras, New Zealand and the United States. The disease, termed Zebra Chip (ZC), has been associated with the presence of heavy infestations of the potato-tomato psyllid (Bactericera cockerelli). In 2009, a research group in New Zealand discovered that a new disease in tomato and pepper plants was caused by Candidatus Liberibacter solanacearum (Lso) and subsequently this same bacterium was associated with ZC in potato samples from Texas. The objectives of this study were: to assess the accumulation of Lso in various potato organs, to determine the effect of plant age on detection of Lso, symptom development and plant death, and (iii) to determine the effect of phosphorous acid on the development of ZC. Results from these studies showed significant differences in Lso populations between above and below ground tissues of the potato plant, with Lso populations in stolons and tubers being three to four times higher than those of leaf tissue and over seventy times greater than in stems. Time for detection of Lso by PCR in potato leaves of different ages at the time of inoculation ranged from 21 to 26 days after inoculation, symptoms development took 23 to 36 days. Plant death, took 24 to 47 days in plants of different age groups at the time of inoculation. In plants 15 weeks old at the time of inoculation, Lso was detected after 14 days in one plant out of 18; in plants 16 weeks old at the time of inoculation, Lso was detected after seven days in two plants out of 18. Phosphorous acid applications had no effect on the populations of Lso in potato tubers, onset of symptoms or plant death. All tubers showed ZC symptoms, making them unacceptable for the market.
North Dakota State University. Department of Plant Pathology

Soybean (Glycine max [L.] Merr.) is one of the most important crops in the world. The average annual yield losses due to soybean diseases and pests are estimated to be around 11% in the United States. Soybean yield losses due to sudden death syndrome (SDS), caused by the fungus Fusarium virguliforme O'Donnell & T. Aoki have been problematic in majority of the soybean producing states. In recent years, reniform nematode (RN, Rotylenchulus reniformis Linford and Oliveira) and frogeye leaf spot (FLS), caused by the fungus Cercospora sojina K. Hara have emerged as a major problem in the southern soybean producing states. Planting resistant cultivars is one of the most cost-efficient methods in managing SDS, RN, and FLS, therefore it would be critical to identify and map the quantitative trait loci (QTL) that underlie their resistances. Two soybean populations were evaluated in this study. The ‘Essex’ × ‘Forrest’ 77 near-isogenic lines were screened in the field to evaluate the disease index of SDS. The Essex × Forrest and ‘Flyer’ × ‘Hartwig’ recombinant inbred lines were screened in the greenhouse to assess the reproduction index of RN and the disease severity of FLS. The BARCSoySNP6k chip was used to genotype the two populations. Four QTL that underlie SDS resistances were mapped in the same region as Rfv06-01, Rfv06-02, Rfv13-01, and Rfv19-01. The Rfv06-02 interval in this study was smaller than the one previously reported. Rrr08-01, Rrr13-01, Rrr15-01, Rrr18-01, and Rrr18-02 were reported to confer resistances to RN. Rrr08-01, Rrr13-01 and Rrr15-01 were novel whereas Rrr18-01, and Rrr18-02 were mapped in previous studies. cqSCN-001 (soybean cyst nematode, Heterodera glycines Ichinohe) was identified in the same region as Rrr18-01, and Rrr18-02 whereas cqSCN-006 was identified in the same region as Rrr15-01. These findings provide further evidence that there are common sources of genetic resistances to RN and SCN. Rcs15-01 and Rcs15-02 were reported to confer resistances to FLS. Rcs15-01 was novel and Rcs15-02 was mapped at the same region as an Rcs mapped in a previous study. This indicated that Rcs15-02 has dual resistances to C. sojina races. Candidate genes were inferred in this study. The QTL mapped in this study could potentially be used in soybean breeding programs that aim to introgress genetic resources that confer resistances to SDS, RN, and FLS.

Bibliography: pages 175-184.
The occurrence of maize dwarf mosaic virus (MDMV) in field grown maize was investigated. For this purpose, maize showing mosiac symptoms was collected from different maize growing areas in South Africa by Prof. M.B. von Wechmar. These samples from Transvaal, Orange Free State and Natal were then investigated for the presence of MDMV and possible strains of this virus. Three virus isolates were purified and partially characterised. These isolates were serologically compared together with a fourth isolate SCMV 4975, obtained from the U.S., to establish strain relationships.

Research on exposure to animals and risk of type 1 diabetes (T1D) has had conflicting results with some researchers finding that animal exposure reduces the risk of T1D and others finding no association between animal exposure and T1D. Previously conducted studies on the association between animal exposure and T1D are case-control studies that have been limited by recall bias. The purpose of this study is to investigate the association between early life animal exposure and the risk of persistent, confirmed islet autoantibodies (IA) and T1D diagnosis among an eligible cohort of genetically high T1D risk participants enrolled in the international prospective cohort study, The Environmental Determinants of Diabetes in the Young (TEDDY). It is hypothesized that children who are exposed to animals in early life will have a lower risk of developing IA and T1D than children who are not exposed to animals in early life. A total of 7,432 TEDDY participants were included in the study. The associations between early life animal exposure and the outcomes of interest were explored using Cox proportional hazards models. In order to control for confounding, a propensity score analysis was applied by three different methods: adjustment for the propensity score variable in the Cox proportional hazards model, stratification on propensity score groups, and propensity score pair matching. Early life animal exposure was not associated with diabetes autoimmunity or T1D onset in this genetically high T1D risk population. These findings were consistent across all three propensity score analysis methods and when directly adjusting for HLA type. The hypothesis that children who are exposed to animals in early life will have a lower risk of developing IA and T1D than children who are not exposed to animals in early life is not supported by this study. The results of this study suggest that there is no association between early life animal exposure and development of T1D. Performing this analysis again after longer follow-up has been completed for the study population is recommended as it may elucidate the effect of animal exposure on T1D and IA risk. Further studies are also needed on animal exposure and T1D in different types of environments (e.g., high residential density) and the effect of different types of animal exposures (e.g., species, duration) on T1D and IA risk. Additionally, studies on differences in perceptions of pets across countries could also aid the interpretation of studies on animal exposure and health outcomes.

Germinating uredospores of race C17 of Puccinia graminis f.sp. tritici form characteristic infection structures (appressorium, infection peg, vesicle, infection hypha) in response to a 1.5 h heat shock at 29° C administered 2 h after germination at 19° C. The proportion of sporelings forming infection structures was augmented by nutrients, n-nonyl alcohol and, an appropriately timed heat shock. The heat shock temperature required to induce maximum differentiation had a very precise optimum which varied slightly for each spore lot. Variations one degree above or below this optimum reduced the percent differentiation by greater than 40%. The presence of an inhibitor of protein synthesis, puromycin, in the germination medium: (1) prevented uredosporeling differentiation but had no effect on germination, (2) significantly reduced the proportion of germtubes forming appressoria, and (3) in most cases prevented the division of germtube nuclei. It was concluded that essential differentiation-specific proteins are synthesized from the onset of germination, throughout the formation of appressoria and to the completion of differentiation. These results were consistent with the observed effects of heat shock on the rate of protein hydrolysis. During germination there was a net hydrolysis of protein leading to an increase in size of the endogenous pool of free amino acids and to an increased leakage of amino acids to the germination medium. Heat shock effectively reduced the amount of endogenous free amino acids and the extent to which amino acids were lost to the medium. It was concluded that in heat shocked sporelings protein synthesis was increased relative to protein hydrolysis by comparison with the relative rates of these two processes in germinating (non-shocked) uredosporelings. Moreover, there was no net protein synthesis during the formation of infection structures induced by heat shock. The loss of amino acids to the germination medium was selective, particularly in heat shocked sporelings.
Land and Food Systems, Faculty of
Graduate

Field experiments were conducted in two different growing environments to evaluate the spread and movement of Dickeya dadantii. A procedure to inoculate seed potatoes with Dickeya dadantii was developed to use during this study. Spread of Dickeya dadantii from inoculated potato seed to healthy potato seed during the handling, cutting and planting procedures was not detected at either location. Spread of Dickeya dadantii from inoculated seed to surrounding progeny tubers in the field was documented in both locations. In Florida, 33% of progeny tubers tested positive for Dickeya using PCR, and in North Dakota, 13% of the progeny tubers tested positive. Stunting was observed in plants grown from Dickeya dadantii inoculated seed tubers in North Dakota, but not in Florida. These results indicate that Dickeya dadantii may spread during the seed handling and cutting processes and can spread in the field from infected seed tubers to progeny tubers.

Studies presented in this dissertation highlight the importance of fungal pathogens in forestry nurseries in South Africa. Both Acacia meamsii seedlings and Eucalyptus hybrid cuttings are shown to be affected by important nursery pathogens. Chapter one presents an evaluation of the potential importance of pathogens to Eucalyptus hedge plants maintained in hydroponics. Hydroponics is a new technology being used in South African forest nurseries, which allows for the rapid establishment of Eucalyptus hedge plants. However, no information is available on pathogens affecting Eucalyptus in hydroponics. By applying information on pathogens of other hydroponic crops, several potentially important pathogens were identified and these reside in the genera Phytophthora, Pythium and Fusarium. Possible disease symptoms in Eucalyptus caused by these pathogens include wilting, stem cankers and root rots. Implementation of appropriate control measures that include cultural, biological and chemical practices could prevent and/or reduce disease impact in hydroponics. Chapter two presents the results of a survey of the roots of Eucalyptus hedge plants grown in an ebb and flow hydroponic system. An interesting result of the survey was the discovery of Cylindrocladium pauciramosum in the hydroponic system. This is the first report of the pathogen in a hydroponic system. Other important pathogens in the genera Phytophthora and Pythium were also isolated. Two Pythium species, namely P. dissotocum and P. helicoids, found in the roots and nutrient solution are new to Eucalyptus. Several Fusarium species were also isolated of which two, namely F. nygamai and F. lateritium, are also new to Eucalyptus. Chapter three of this dissertation presents the results of a survey of Eucalyptus cuttings conducted at four forestry nurseries in KwaZulu-Natal, South Africa. Several well-known Eucalyptus nursery pathogens were isolated. Cylindrocladium pauciramosum was identified as the dominant pathogen on Eucalyptus cuttings. This was confirmed based on morphological characteristics and DNA sequence comparisons. Pathogenicity tests conducted using a spore suspension of C. pauciramosum indicated that this pathogen is capable of infecting most commercial Eucalyptus clones used in South Africa. Chapter four considers a serious disease of Acacia mearnsii seedlings caused by an unidentified species of Cylindrocladium. Cylindrocladium pauciramosum was isolated from A. mearnsii seedlings showing girdling and stem canker symptoms. The pathogen was identified based on morphological characteristics and DNA sequence comparisons. Pathogenicity tests with Acacia seedlings confirmed the susceptibility of this tree to C. pauciramosum infection. This dissertation clearly indicates that Cylindrocladium pauciramosum is an important nursery pathogen in South African forestry nurseries. This pathogen has already been shown to be limiting during production of planting stock. I hope to have highlighted the importance of C. pauciramosum and other nursery pathogens in forestry nurseries in South Africa. This study will also hopefully provide information to forestry nursery managers and help them improve production.
Dissertation (MSc)--University of Pretoria, 2004.
Microbiology and Plant Pathology
Unrestricted

White mold caused by Sclerotinia sclerotiorum attacks a wide host range of broad-leafed plants which includes potatoes. Current control is limited to the use of chemicals, but biological control has emerged as an eco-friendly alternative. For the study, 19 bacterial strains and 18 fungal strains obtained from soil samples taken from a potato field naturally infested with the pathogen S. sclerotiorum were tested for the effects on S. sclerotiorum mycelium growth and sclerotia viability in vitro. A total of eight bacterial strains and six fungal strains proved to be effective in the inhibition of S. sclerotiorum mycelium growth on PDA plate using a dual culture technique. These antagonistic microbes were six Bacillus subtilis, Bacillus pumilis, Bacillus marisflavi, Fusarium solani, Fusarium equiseti, Fusarium chlamydosporum, Aspergillus niger, Aspergillus insuetus and Penicillium citrinum. There was a significant difference (p<0.05) in the interaction between S. sclerotiorum mycelium growth and the time after inoculation with a S. sclerotiorum mycelium plug for both bacterial and fungal soil isolates. An additional sclerotia viability test was carried out using four of the eight antagonistic bacteria, and six of the antagonistic fungi. The results showed that two Bacillus species, namely B. pumilis and B. marisflavi can effectively reduce sclerotia viability. The other two bacteria (both B. subtilis), recorded low percentage reduction in sclerotia viability. As for the six antagonistic fungi, the viability test proved to be less effective in determining sclerotia viability. However, the result of this study supports the use of bio-control agents, not only because they are environmentally friendly, but because they are also an effective way of controlling the plant pathogen, S. sclerotiorum.

Rattus sordidus (canefield rat) is a major pest in north Queensland sugarcane growing areas, causing losses of between $2 and $4 million each year. A further $0.2 to $0.4 million is expended on annual baiting campaigns. This procedure provides only short-term results, is seldom cost-effective and is hazardous to non-target species and the environment. There was a close relationship between the dynamics of R. sordidus populations and the crop cycle. During the 1987/88 crop cycle, breeding occurred over the January- July period and coincided with the period when summergrasses were abundant in crops and the predominant food source of R. sordidus. The relationship between the onset of breeding, the first appearance of summergrasses and diet of R. sordidus indicates that breeding is dependent on the availability of a non-cane food source. The level of in-crop weed biomass may therefore play an important role in the regulation of population and damage levels throughout a district. Consequently, a number of agricultural practices which affect in-crop weed levels may have a significant effect on R. sordidus populations. The practice of green cane harvest and trash-blanketing has increased in most northern sugarcane growing districts since the early 1980's. This practice differs to the conventional technique in that crops are not burnt prior to harvest and following harvest the trash, comprising the green "tops" and dry leaf material, is left as a "trash-blanket" on the ground and minimum or zero tillage techniques employed. Suppression of weed germination and growth is a major agronomic advantage associated with this technique. In-crop weed control may also be achieved through the application of herbicides. The monetary benefit associated with yield increases as a result of reduced weed competition in young crops has lead to an increase in the number of crops treated with herbicide. This study investigated the effect of green cane harvesting and trashblanketing, the conventional agricultural practice and herbicide applications on the dynamics of R. sordidus populations during the 1987/88 crop cycle.

False codling moth is a known pest of economic importance to many cultivated crops in South Africa and Africa south of the Sahara, and is particularly severe on citrus. If the fruit is infested just before harvest the chances of detecting signs of infestation are very low. As a result, the risk of packaging infested fruit and exporting them as healthy fruit is high. It is therefore a priority to develop a post-harvest technique for detection of False codling moth in citrus fruit at different levels of infestation in order to reduce phytosanitary risk. Compounds released and detected were indicative of infestation and were not insect produced but naturally produced fruit volatiles emitted at higher levels as a result of the insect within the fruit. Five major volatile compounds of interest were released by the infested oranges. These major volatile compounds include D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene, caryophyllene and naphthalene. Limonene was one of the most abundant volatile compounds released by the infested citrus fruit. Naphthalene, which is possibly produced due to larval feeding and development within the fruit maintained higher concentrations than controls throughout the infestation within the fruit. Naphthalene would be a good indicator of False codling moth infestation, however, not primarily for early infestation detection. A significantly higher concentration of D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene and naphthalene was detected using the SEP over the SPME technique. The application of an SPME procedure and the utilization of this method for detection of volatiles present in the headspace of intact infested fruit are evaluated and the possible volatile compounds diagnostic of Thaumatotibia leucotreta infestation of orange fruit and differences in volatile compound response in different orange varieties is discussed.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2005.
The occurrence of both pre- and postharvest leaf blackening in certain Protea species and cultivars is a problem that severely limits their marketability, vase life and transport options. This research focuses on : (I) The distribution of carbohydrates in inflorescence bearing stems of certain Protea cultivars from harvest, following pulsing with a 10 g.L-1 glucose solution until four weeks postharvest. Stems were held under a variety of postharvest conditions, and (II) The suppression of Protea postharvest leaf blackening with specific focus on the cultivar ‘Sylvia’ (P. eximia x P. susannae).

12 pp.
plant disease bulletins; July 2006 original publishing date, rev. 10/08
Cacti, agaves and yuccas are classified as succulents, plants that have highly specialized anatomical features such as thick waxy cuticles, fleshy or minimal leaves, modified leaves (spines), and roots with extra storage capabilities for food and water. These modifications allow them to survive and thrive in harsh desert environments. They survive long periods of drought in areas of sparse rainfall and intense heat. During stressful periods, many succulents cease to grow, drop unnecessary leaves, dehydrate and become dormant until conditions for growth return. Despite their adaptations, succulents suffer from diseases, insect pests and cultural problems. Some of the more common problems that occur in cacti, agave and yuccas in Arizona are discussed in this bulletin.

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on fungicides including quinone outside inhibitor (QOI) fungicides. We collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the QOI fungicide pyraclostrobin. To gain an understanding of the molecular basis of QOI resistance, we cloned the full-length coding region of Cbcytb. All tested QOI-resistant isolates harbored a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay was developed to discriminate QOI-sensitive and QOI-resistant isolates based on the G143A mutation. Our results indicate that QOI resistance has developed in some European C. beticola populations in Italy and monitoring the G143A mutation is an essential fungicide resistance management strategy.

Thesis (MScAgric)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Leaf blackening, a postharvest disorder which is characterized by a dark brown to black discoloration, is found in most commercially important Protea cut flower species and cultivars. As this disorder is known to increase with storage time, it is a major concern to the South African industry as the use of sea freight is increasingly preferred due to lower transport costs and a more favourable carbon footprint. The cause of leaf blackening has been strongly linked to a carbohydrate stress exerted by the large inflorescence, thus requiring the utilization of sugar bound polyphenols in the foliage, which when removed, can oxidize enzymatically or non-enzymatically. A study where harvesting was done throughout the season as well as on selected days at 08:00, 12:00, 15:00 and 17:00, concluded that leaf blackening incidences in Protea cv. Sylvia stems varies significantly throughout the season, between years and even with the harvest time of day. Leaf blackening incidences increased from October onwards and remained high until February, before decreasing to acceptably lower levels towards March to May. Carbohydrate- and phenolic content together with water status of leaves at harvest was not able to accurately predict incidence of the associated leaf blackening. However, irrespective of the season of harvesting, leaf blackening was significantly lower when stems were harvested later in the day than compared to stems harvested in the morning. Low sucrose and high water content at these harvest times was positively correlated to high incidences of leaf blackening. In a next study where uptake dynamics of glucose pulsing was investigated, Protea cv. Sylvia was harvested at different times throughout the day, dehydrated to various levels and pulsed with an increasing range of glucose concentrations. Pulsing solution uptake per stem was found to be highly influenced by these factors, as dehydration of stems and a harvest time later during the day both decreased stem water potential, which then increased pulse-solution uptake within a certain time period. The daily harvest time influenced transpiration, whilst pulse-solution uptake decreased with an increase in glucose pulse concentration. When stems were pulsed pre-storage with an increasing range of glucose concentrations, not only did pulses of between 4.7 – 13.7% glucose significantly delayed the incidence of leaf blackening, but it also maintained a positive water balance longer in stems during vase life. Ethanol or acetaldehyde vapour did not provide a viable alternative for reducing leaf blackening incidence in Protea cv. Sylvia, although a synergistic effect was found when ethanol vapour or pulsing was used in combination with glucose. A commercial verification trial disclosed that Protea magnifica and Protea ‘Pink Ice’ reacted more beneficial to ethanol vapour than was observed in ‘Sylvia’. This study confirms that carbohydrate availability within the Protea cut stem remains a key factor in the control of leaf blackening. Factors which assist in maintaining high internal carbohydrate levels, such as enhanced glucose pulse uptake or effective vase solution utilization will contribute to providing an optimum control of leaf blackening during vase life following long-term cold storage.
AFRIKAANSE OPSOMMING: Loofblaarverbruining is ‘n na-oes defek wat gekarakteriseer word deur ‘n donker bruin na swart verkleuring wat voorkom in meeste kommersieël belangrike Protea snyblom spesies en kultivars. Hierdie defek is bekend daarvoor dat dit toeneem met stoortyd, dus is dit ‘n groot kommer vir die Suid-Afrikaanse industrie, met toenemende gebruik van seevrag as vervoer keuse wat laer vervoer kostes en meer gunstige ‘koolstof voetspoor’ bevoordeel. Die oorsaak van loofblaarverbruining word sterk gekoppel aan ‘n koolhidraat stres wat uitgeoefen word deur die groot bloeiwyse op die loofblare, waar suiker-gebonde polifenoliese verbindings ensiematies of nieensiematies geoksideer word met die verwydering van die suiker verbinding. 'n Studie waar geoes was regdeur die seisoen, sowel as op geselekteerde dae om 08:00, 12:00, 15:00 en 17:00, het bevind dat die voorkoms van loofblaarverbruining in stele van Protea kv. Sylvia aansienlik geskil regdeur die seisoen, tussen jare en selfs met die oes tyd gedurende die dag. Die voorkoms van loofblaarverbruining het toegeneem vanaf Oktober en het hoog gebly tot en met Februarie, voordat dit gedaal het tot aanvaarbare laer vlakke teen Maart, tot en met Mei. Koolhidraat-en fenoliese inhoud sowel as die water status van die blare by oes was onsuksesvol om die voorkoms van die gepaardgaande loofblaarverbruining akkuraat te voorspel. Loofblaarverbruining was egter aansienlik laer as stele geoes later in die dag teenoor stele geoes in die oggend, ongeag die seisoen van oes. Lae sukrose en 'n hoë water inhoud geassosieer met hierdie oes-tye was positief gekorreleerd met ‘n hoë voorkoms van loofblaarverbruining. In 'n volgende studie waar die opname dinamika van glukose pulsing ondersoek was, is Protea kv. Sylvia stele geoes op verskillende tye dwarsdeur die dag, gedehidreer tot verskillende vlakke en met 'n toenemende reeks van glukose konsentrasies gepuls. Pulsoplossing opname per steel is sterk beïnvloed deur hierdie faktore, aangesien dehidrasie van die stele asook stele geoes later gedurende die dag die afname van steel waterpotensiaal veroorsaak het, terwyl die puls-oplossing opname versnel het binne ‘n bepaalde tyd. Die tyd van oes beïnvloed ook transpirasie, terwyl vaas oplossing opname afgeneem met 'n toename in glukose puls konsentrasie. Wanneer ‘Sylvia’ stele gepuls was voor stoor met 'n reeks van toenemende glukose konsentrasies, het nie net die puls van tussen 4.7 – 13.7% glukose aansienlik die voorkoms van loofblaarverbruining vertraag nie, maar dit het ook ‘n positiewe water balans langer in stele gedurende die vaas lewe behou. Nie etanol of asetaldehied dampe is bevind as geskikte alternatief vir glukose pulsing om die voorkoms van loofblaarverbruining in Protea kv. Sylvia te verlaag nie, alhoewel ‘n sinergistiese effek waargeneem was wanneer etanol in kombinasie met glukose gebruik was. ‘n Kommersieële bevestigingstoetsing het bevind dat Protea magnifica en ‘Pink Ice’ meer voordeel uit ‘n ethanoldamp behandeling kon trek teenoor ‘Sylvia’. Hierdie studie het bevestig die belangrikheid van koolhidraat beskikbaarheid in die Protea snyblom, vir beheer van loofblaarverbruining. Faktore wat die handhawing van hoë interne koolhidrate vlakke, soos bevorderde glukose puls opname of effektiewe vaas oplossing benutting sal bydra tot ‘n optimal beheer van loofblaarverbruining tydens vaas lewe na langtermyn koueopberging.
National Research Fund (NRF) for their financial support in 2009; Protea Producers of South Africa (PPSA) and Productschap Tuinbouw (PT) as well as the Frank Batchelor Will Trust Grant for the financial support.

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Fundação Oswaldo Cruz. Instituto Fernandes Figueira. Departamento de Ensino. Programa de Pós-Graduação em Saúde da Criança e da Mulher. Rio de Janeiro, RJ, Brasil.
As mucopolisacaridoses (MPS) são doenças geneticamente determinadas, causadas pela deficiência de enzimas lisossômicas, o que leva ao acúmulo de glicosaminoglicanos (GAGs) universalmente. As mielopatias cervicais ao nível da junção craniocervical são uma complicação frequente, grave e multifatorial das MPS. Este trabalho teve como principal objetivo o estudo das vias sensitivas e motoras centrais (cordão posterior e trato córtico-espinhal) em topografia medular cervical nos pacientes com mucopolissacaridoses (MPS), utilizando os potenciais evocados somatossensitivos e motores. Como objetivos específicos, a avaliação dos pacientes com MPS em fases distintas da doença, a demonstração da existência de comprometimento da condução nervosa nos trajetos das vias medulares na topografia já mencionada e o destaque do papel dos testes neurofisiológicos (funcionais) no diagnóstico, acompanhamento e na tomada de decisões terapêuticas nos pacientes com MPS. Foi realizado um estudo transversal, de uma série de casos, tendo como metodologia a revisão de prontuários, no Instituto Nacional de Saúde da Mulher, da Criança e do Adolescente Fernandes Figueira. Foram incluídos os pacientes com o diagnóstico de MPS, sem restrições quanto à idade, aos subtipos da doença ou ao fato de estarem ou não sob tratamento específico e excluídos aqueles pacientes com lesões graves do sistema nervoso central que impedissem a realização dos testes propostos. Os dados colhidos referiram-se à idade dos pacientes, o tipo de MPS, os achados do exame neurológico, os resultados dos estudos de imagem (ressonância magnética) da coluna cervical e os parâmetros neurofisiológicos encontrados nos potenciais evocados somatossensitivos (PESS) e motores (PEM), que incluiram as latências das ondas (N9, N13 e N20 nos PESS de membros superiores e N21 e P37 nos PESS de membros inferiores), os tempos de condução central (N20 – N13 e P37 – N21) e o tempo de condução motora central (nos PEM de membros superiores e inferiores). Foram analisados resultados de cinquenta e oito exames de potenciais evocados somatossensitivos e motores, realizados em vinte e oito pacientes com MPS. Todos os exames foram anormais, com alterações mais graves nos exames de PEM.
Mucopolysaccharidosis (MPS) are inherited metabolic diseases caused by deficiency of lysosomal enzymes leading to progressive accumulation of glycosaminoglycans (GAGs) in nearly all cell types, tissues and organs. Cervical myelopathy at the cranio-cervical junction is a frequent, severe and multifactorial complication of MPS. The first objective of the present study is the evaluation os the function of central neural pathways (brain stem and spinal cord posterior columns and corticospinal tract in patients with MPS using somatosensory evoked potentials (SEP) and motor evoked potentials (MEP). The secondary objectives are the evaluation of the patients in different periods of disease, the diagnostic of the lesions in cervical spinal cord and the remark of the role of these neurophysiological tests in diagnostic, follow-up and therapeutic decisions. This cross-sectional study included all patients with MPS of Instituto Nacional de Saúde da Mulher, da Criança e do Adolescente Fernandes Figueira, despite age, type of disease, enzyme replacement therapy or not, except the patients with severe central nervous system lesions in whom the neurophysiological evaluation became impossible. Data included the age of patients, type of disease, the findings in neurological examination, magnetic resonance imaging of cervical spinal cord and the neurophysiological parameters [the latencies of N9, N13 and N20 waveforms, central conduction time (upper limbs SEP), the latencies of N21 and P37 waveforms, central conduction time (lower limbs SEP), central motor conduction time (upper and lower limbs MEP)].Twenty-eight patients were enrolled and fifty-eigth tests (SEP and MEP, upper and lower limbs) were performed in these patients. All tests were abnormal with most severe functional impairment in MEP tests.

Dissertation (PhD (Agric))--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma lanigerum (Hausmann) populations in apple orchards in the Western Cape Province of South Africa. The absence of cornicles and the presence of a vulva could be used to identify 1st instar nymphs and adults respectively. Body length, body width and length of the hind femur are useful for separating 2nd , 3rd and 4th instars. However, separation of 2nd from 3rd instar nymphs was very unreliable. Maximum population growth rate was at 23°C while at 30 °C population growth was zero. The estimated minimum and maximum threshold temperatures for development were 4.32 and more than 30°C respectively. Numbers of underground E. lanigerum in soil samples taken using mechanical and hand augers were similar. However, numbers of aphids in samples were influenced by the distance from the trunk at which the samples were taken and the presence and the type of root material in the samples. More aphids were recorded close to the trunk, and at a given distance from the trunk more aphids were recorded if there was root material in the sample, especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the winter rainfall was high. These cycles coincided with the nitrogen cycles in the roots. Embryos were also present in all instars throughout the year. There were more embryos in the 4th instar and adult aphids than in the other instars. The highest number of embryos in the 4th instar and adult aphids occurred during spring, which coincided with peak nitrogen levels in the roots of apple trees. Nitrogen levels in root material adjacent to galls and in ungalled roots were higher than in root galls. A number of entomopathogenic fungi, including species of Conidiobolus, Hirsufella and Beauveria were found. Their present contribution to biological control is not known. A straw mulch suppressed subterranean E. lanigerum population levels at least as well as the soil insecticide, imidacloprid, currently in use.
AFRIKAANSE OPSOMMING: 'n Studie van die basiese biologie van ondergrondse bevolkings van , Eriosoma lanigerum (Hausmann) is in appelboorde in die Weskaap Provinsie van Suid-Afrika uitgevoer. Die afwesigheid van kornikels en die aanwesigheid van 'n vulva kon gebruik word om die 1ste instar nimfe en volwassennes onderskeidelik te identifiseer. Liggaamslengte, liggaamsbreedte en die lengte van die agterste femur kon gebruik word om die 2de , 3de en 4de instars van mekaar te onderskei. Onderskeiding tussen 2de en 3de instar nimfe was egter baie onbetroubaar. Maksimum bevolkingsgroei het by 23°C plaasgevind, terwyl dit nul was by 30 °C. Die beraamde minimum en maksimum temperature vir ontwikkeling was by 4.32 en meer as 30°C onderskeidelik. Getalle van ondergrondse E. lanigerum in grondmonsters wat geneem is met gebruik van meganiese en hand bore was eenders. Getalle plantluise in monsters is egter beïnvloed deur die afstand vanaf die stam waarby die monsters geneem is en die teenwoordigheid van wortelmateriaal in die monsters. Meer plantluise is aangeteken as daar wortelmateriaal in die monsters was, en veral as daar galle op die wortels was. Die appelbloedluis was dwarsdeur die jaar ondergronds aktief. Bevolkingsvlakke het gedurende die vroeë somer (November, Desember) en vroeë herfs (Februarie, Maart) toegeneem, en gedurende die winter afgeneem, veral as die winterreënval hoogwas. Embrio's was ook teenwoordig dwarsdeur die jaar. Daar was meer embrio's in die 4de instar en volwasse plantluise as in die ander instars. Die hoogste aantal embrio's in die 4de instar en volwasse plantluise het in die lente voorgekom, wat saamgeval het met piek stikstofvlakke in die wortels van appelbome. Stikstofvlakke in wortelmateriaal aangrensend aan wortels en in wortels sonder galle was hoër as in wortelgalle. Talle entomopatogeniese swamme, insluitend spesies van Conidiobolus, Hirsufella en Beauvaria IS gevind. Hulle huidige bydrae tot biologiese beheer is nie bekend nie. 'n Strooideklaag het ondergrondse bevolkingsvlakke van E. lanigerum tot ten minste dieselfde mate as die grondinsektedoder, imidacloprid, wat tans in gebruik is, onderdruk.

Iron (Fe) deficiency affects more than 3 billion of the global population. The objectives of this study were to (1) determine the genetic and environmental variation of seed Fe concentration and food matrix factors that govern Fe bioavailability in field peas (Pisum sativum L.) grown in North Dakota, USA in 2010 and 2011, and (2) determine the genetic variation of Fe uptake by field pea grown under greenhouse conditions with different Fe treatments. Seed Fe concentration in field pea samples from the field study ranged between 46-53 mg/kg with a mean of 51 mg/kg. Mean concentrations of the food matrix factors in those field peas were as follows: phytic acid=5.1 mg/g, xanthophyll=17.3 mg/100 g, canthaxanthin=86.8 mg/100 g, beta-carotene=516.8 ?g/100 g, kestose=1697 mg/100g, quercetin=54.3 mg/100 g, and ferulic acid=46.9 mg/100 g. DS Admiral and CDC Golden showed high concentrations of Fe promoter compounds and low concentrations of phytic acid. DS Admiral showed high Fe uptake with increasing Fe fertilizer rates in the greenhouse study. Therefore, DS Admiral and CDC Golden could be potential field pea genotypes for future Fe biofortification efforts.

Data for this study were collected by the US Forest Service and the Pennsylvania Bureau of Forestry on nearly 600 plots in central Pennsylvania. Tree and stand characteristics recorded between 1978 and 1985 include estimates of percent defoliation on individual trees. Logistic regression using maximum likelihood estimation was employed to model individual-tree mortality of 15 species in central Pennsylvania that had been defoliated by the gypsy moth. Defoliation was estimated to the nearest ten percent for individual trees. Other variables used for prediction included stand basal area and an individual-tree relative basal area index. Success ranged from no fit for three of the species to an R value (a derivation of Akaike's information criterion) of .613 for white oak. The inclusion of defoliation in the models had a varied effect. For four of the species percent defoliation was not significant. For hickory and white oak respectively, percent defoliation raised the R value by .305 and .290 percentage points. As many as five models for each species were developed: one or two models with no defoliation measure in the model and one each for one, two or three consecutive years of defoliation measures. A beta and gamma function were used to model individual· tree basal area growth for the same 15 species. The models were fit using nonlinear least squares. Variables used include the relative basal area index, stand basal area, site index and a defoliation index that incorporated three years of individual-tree, percent defoliation. The beta and gamma functions fit equally well with values of (1 - relative mean square error) ranging from .1967 to .6290. Results for both models are presented for each species. The defoliation index was a significant variable for five of the fifteen species: white, chestnut, red, and black oak and sassafras.
Master of Science

The effects of gypsy moth defoliation on acorn production (the seed source for oak regeneration), and the forest floor regeneration environment were investigated. Parameters measured included: acorn quantity, weight, development, and viability; litterfall; and forest floor depth and biomass. Nineteen plots in north-central Virginia and western Maryland on which trees suffered heavy, moderate, or no defoliation were monitored over a two-year period.

Master of Science

Deoxynivalenol (DON), a mycotoxin produced in cereal grains infected by Fusarium Head Blight produced by Fusarium graminearium and Deoxynivalenol-3-?-D-glucopyranoside (DON-3G), were studied during processing using LC-MS-MS and GC. DON reduced significantly (P<0.05) 61.8% during milling into flour. Therefore, DON was concentrated mostly in the bran and germ. DON increased 40.8% during the fermentation stage of baking. DON increased in dough more than flour and mixed dough. Milling reduced by 23.7% but fermentation did not. But bread was significantly lower in DON-3G at 0.15 ppm than flour and dough at 0.31 ppm. The baking increased DON and decreased DON-3G showing a difference in stability of the mycotoxins during processing. Enzyme hydrolysis on DON using ?-amylase, cellulase, protease, and xylanase, showed a significant increase with cellulase (20.8%), protease (11.4%), and xylanase (35.6%) compared to wheat composite. DON may be bound to the cell wall or protein component of the kernel.