Auswahl der wissenschaftlichen Literatur zum Thema „Cassava – Diseases and pests – South Africa“

Biotic constraints cause major crop losses and, hence, food insecurity in sub-Saharan Africa. This study documented the popularity, production constraints, pests and diseases, farmers’ perceptions on the severity of biotic constraints and the impact of related crop losses on household food security for the key root, tuber and banana (RTB) crops (cassava, potato, sweetpotato and banana). Farmer interviews were conducted in 2014 covering 811 households in Rwanda and Burundi. Farmers were asked to list their RTB crop production constraints, name insect pests and diseases of RTB crops, estimate crop loss due to pests and diseases, and mention if their household experienced any form of food insecurity due to pests and diseases. Cutworms and late blight in potato, banana weevils and banana Xanthomonas wilt in banana, cassava whitefly and cassava mosaic disease in cassava, sweetpotato weevils, and sweetpotato virus disease in sweetpotato were the most predominant pests and diseases reported. Crop losses due to pests and diseases for sweetpotato, banana, potato and cassava were estimated at 26%, 29%, 33%, and 36%, respectively, in Rwanda and 37%, 48%, 38%, and 37% in Burundi. Pests and diseases reduce the profitability of RTB crops, threaten food security, and constitute a disincentive for investment. Sustainable and affordable integrated pest management packages need to be developed.

AbstractCassava (Manihot esculenta Crantz) is one of the most important staple crops for small farmers in the tropics, feeding about 800 million people worldwide. It is currently cultivated in South and Central America, Africa and Asia. The genus Vatiga is widespread throughout the Neotropical region. Its species are sympatric and feed exclusively on cassava. The main objectives of this paper are: (1) to assess the potential distribution of Vatiga, one of the most relevant pests of cassava; (2) to project the resulting models onto the world; (3) to recognize areas with suitable and optimal climates (and thus, high probability) for future colonization, and (4) to compare this model with the harvested area of cassava analyzing the climatic variables required by both the host and the pest species. Species distribution models were built using Maxent (v3.3.3k) with bioclimatic variables from the WorldClim database in 2.5 arc min resolution across the globe. Our model shows that Vatiga has the potential to expand its current distribution into other suitable areas, and could invade other regions where cassava is already cultivated, e.g., Central Africa and Asia. Considering the results and the high host specificity of Vatiga, its recent appearance in Réunion Island (Africa) poses a serious threat, as nearby areas are potentially suitable for invasion and could serve as dispersal routes enabling Vatiga to reach the continent. The present work may help prevention or early detection of Vatiga spp. in areas where cassava is grown.

Cassava is one of the most important staple crops in Africa and its production is seriously damaged by viral diseases. In this study, we identify for the first time and characterize the genome organization of novel ampeloviruses infecting cassava plants in diverse geographical locations using three high-throughput sequencing protocols [Virion-Associated Nucleotide Acid (VANA), dsRNA and total RNA], and we provide a first analysis of the diversity of these agents and of the evolutionary forces acting on them. Thirteen new Closteroviridae isolates were characterized in field-grown cassava plants from the Democratic Republic of Congo (DR Congo), Madagascar, Mayotte, and Reunion islands. The analysis of the sequences of the corresponding contigs (ranging between 10,417 and 13,752 nucleotides in length) revealed seven open reading frames. The replication-associated polyproteins have three expected functional domains: methyltransferase, helicase, and RNA-dependent RNA polymerase (RdRp). Additional open reading frames code for a small transmembrane protein, a heat-shock protein 70 homolog (HSP70h), a heat shock protein 90 homolog (HSP90h), and a major and a minor coat protein (CP and CPd respectively). Defective genomic variants were also identified in some cassava accessions originating from Madagascar and Reunion. The isolates were found to belong to two species tentatively named Manihot esculenta-associated virus 1 and 2 (MEaV-1 and MEaV-2). Phylogenetic analyses showed that MEaV-1 and MEaV-2 belong to the genus Ampelovirus, in particular to its subgroup II. MEaV-1 was found in all of the countries of study, while MEaV-2 was only detected in Madagascar and Mayotte. Recombination analysis provided evidence of intraspecies recombination occurring between the isolates from Madagascar and Mayotte. No clear association with visual symptoms in the cassava host could be identified.

In this case study we successfully teamed the PDQeX DNA purification technology developed by MicroGEM, New Zealand, with the MinION and MinIT mobile sequencing devices developed by Oxford Nanopore Technologies to produce an effective point-of-need field diagnostic system. The PDQeX extracts DNA using a cocktail of thermophilic proteinases and cell wall-degrading enzymes, thermo-responsive extractor cartridges and a temperature control unit. This closed system delivers purified DNA with no cross-contamination. The MinIT is a newly released data processing unit that converts MinION raw signal output into nucleotide base called data locally in real-time, removing the need for high-specification computers and large file transfers from the field. All three devices are battery powered with an exceptionally small footprint that facilitates transport and setup. To evaluate and validate capability of the system for unbiased pathogen identification by real-time sequencing in a farmer’s field setting, we analysed samples collected from cassava plants grown by subsistence farmers in three sub-Sahara African countries (Tanzania, Uganda and Kenya). A range of viral pathogens, all with similar symptoms, greatly reduce yield or destroy cassava crops. Eight hundred (800) million people worldwide depend on cassava for food and yearly income, and viral diseases are a significant constraint to its production. Early pathogen detection at a molecular level has great potential to rescue crops within a single growing season by providing results that inform decisions on disease management, use of appropriate virus-resistant or replacement planting. This case study presented conditions of working in-field with limited or no access to mains power, laboratory infrastructure, Internet connectivity and highly variable ambient temperature. An additional challenge is that, generally, plant material contains inhibitors of downstream molecular processes making effective DNA purification critical. We successfully undertook real-time on-farm genome sequencing of samples collected from cassava plants on three farms, one in each country. Cassava mosaic begomoviruses were detected by sequencing leaf, stem, tuber and insect samples. The entire process, from arrival on farm to diagnosis, including sample collection, processing and provisional sequencing results was complete in under 3 h. The need for accurate, rapid and on-site diagnosis grows as globalized human activity accelerates. This technical breakthrough has applications that are relevant to human and animal health, environmental management and conservation.

Crop losses due to viral diseases and pests are major constraints on food security and income for millions of households in sub-Saharan Africa (SSA). Such losses can be reduced if plant diseases and pests are correctly diagnosed and identified early. Currently, accurate diagnosis for definitive identification of plant viruses and their vectors in SSA mostly relies on standard PCR and next generation sequencing technologies (NGS). However, it can take up to 6 months before results generated using these approaches are available. The long time taken to detect or identify viruses impedes quick, within-season decision-making necessary for early action, crop protection advice and disease control measures by farmers. This ultimately compounds the magnitude of crop losses and food shortages suffered by farmers. The MinION portable pocket DNA sequencer was used, to our knowledge globally for the first time, to sequence whole plant virus genomes. We used this technology to identify the begomoviruses causing the devastating cassava mosaic virus, which is ravaging smallholder farmers’ crops in sub-Saharan Africa.

Emerging pests and diseases are a major threat to food production worldwide. In a recent survey, Tomato torrado virus (ToTV) was identified on tomato crops in the Limpopo province of South Africa and a first report of the disease was published. In this follow-up study, the full genome sequence of a tomato-infecting isolate of ToTV from South Africa was elucidated. High-throughput sequencing was used to generate the full genome of ToTV infecting tomato crops in South Africa. The longest contig obtained for the RNA-1 and RNA-2 genome of ToTV was comprised of 7420 and 5381 nucleotides (nt), respectively. Blast analysis of the RNA-1 sequence of ToTV from South Africa (ToT-186) matched 99% to a Spanish and Polish isolate; the RNA-2 segment of ToTV from South Africa (ToT-186) matched 99% to ToTV isolates from Italy and Poland, respectively. The information presented in this study will go a long way towards better understanding the emergence and spread of ToTV and devising sustainable management of ToTV diseases.

With an increase in the global population, a protein-rich crop like soybean can help manage food insecurity in sub-Saharan Africa (SSA). The expansion of soybean production in recent years lead to increased land requirements for growing the crop and the increased risk of exposing this valuable crop to various pests and diseases. Of these pests, plant-parasitic nematodes (PPN), especially Meloidogyne and Pratylenchus spp., are of great concern. The increase in the population densities of these nematodes can cause significant damage to soybean. Furthermore, the use of crop rotation and cultivars (cvs.) with genetic resistance traits might not be effective for Meloidogyne and Pratylenchus control. This review builds on a previous study and focuses on the current nematode threat facing local soybean production, while probing into possible biological control options that still need to be studied in more detail. As soybean is produced on a global scale, the information generated by local and international researchers is needed. This will address the problem of the current global food demand, which is a matter of pressing importance for developing countries, such as those in sub-Saharan Africa.

This article focuses on the devastating hidden perils of agricultural pesticides repurposed by informal sellers in urban South African townships to kill rats and other unwanted pests. Drawing on collaborative research techniques, we investigate the causal relationship between child poisoning episodes and the household use of illegal street pesticides. Such pesticides are used to safeguard homes from pests in an attempt to protect children from the harmful consequences of rodent bites and vectorborne diseases. Here, we consider the social injustice and economic inequality of episodes of child pesticide poisoning in the Western Cape from three disciplinary perspectives: public health, medical anthropology and fine art. We ultimately seek to demonstrate the complex relationship between the political economy of sanitation, waste removal and insecure housing, and the proliferation of rodents and other pests in urban townships. As a contribution to the medical humanities, the paper leans into different disciplines to highlight the toxic layering at play in a child pesticide poisoning event. The public health perspective focuses on the circulation of illegal street pesticides, the anthropologists focus on the experiences of the children and caregivers who are victims of poisoning, and the fine artist centres the rat within a broader environmental context. While non-toxic methods to eliminate rats and household pests are critical, longer term structural changes, through environmental and human rights activism, are necessary to ameliorate the suffering caused by poisoning. The medical and health humanities is well poised to highlight creative ways to draw public attention to these challenges, as well as to bridge the divide between science and the humanities through collaborative research efforts. With this paper we set the stage for discussing and balancing perspectives when addressing pest control in poor urban communities.

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

Leaf diseases are an integral part of banana production. While currently not a cause for major concern in South Africa, many of these diseases van reach epidemic proportions and cause severe crop loss. To determine the present status of leaf diseases in South Africa, a survey was conducted in the five banana-growing regions of the country. The study indicated the following: Yello Sigatoka, caused by Mycosphaerella musicola was the most prevalent disease and occurred in all five the regions. Mycosphaerella speckle and Cordana leaf spot, caused by M. musae and Cornana musae respectively, were present in four regions. Cladosporium speckle, caused by Cladosporium musae, was found only in the Levubu area. Various other fungi, mainly saprobes and endophytes, were also isolated. The most commonly encountered species included Alternaria alternate, Colletrichum gloeosporioides, Nigrospora oryzae, N. sacchari, N. Spaerica, Pestalotiopsis sp., Phoma glomerata, Selenophoma asterina and S. juncea. Following morphological identification of the pathogenic species, monoconidial isolates were established from representative isolates of each and their virulence confirmed in artificial inoculation studies. The identity of M. musciola and Cladosporium musae was verified molecularly by means of species-specific primers and/or sequencing of the ITS region. Validation of the identity of Cladosporium musae constitutes the first report of Cladosporium speckle on banana in South Africa. Sequence data of the ITS region of isolates from Mycospaerella speckle lesions indicated that the symptoms are caused by two species, M. musae and one closely related to M. colombiensis, the latter previously described only from lesions on leaves of Eucalyptus urophylla in Colombia.
Dissertation (MSc (Microbiology))--University of Pretoria, 2002.
Microbiology and Plant Pathology
unrestricted

Thesis (MSc)--Stellenbosch University, 2000.
Full text to be digitised and attached to bibliographic record.
ENGLISH ABSTRACT: The cultivation of citrus in the Vaalharts region is a fairly recent development. With the introduction of this crop, an insect pest complex has also developed in this region. The presence of these pests was studied in eleven orchards, planted with three citrus cultivars and of varying ages, distributed in the 300 square kilometer cultivation area. Each orchard was inspected for the presence of pests by making use of two weekly sampling techniques. Ten of the most important insect pests of citrus in the Vaalharts region are briefly described by refering to their general appearance, life cycles, feeding and pest status and economic threshold. For every pest various control options, including operational systems, crop cultivation, biological and chemical control, are discussed and, where applicable, illustrated by means of graphic presentations. The seasonal presence of the cirtrus pests in the Vaalharts region is tabulated and discussed individually. With these details as background, an insect pest management programme for citrus in the Vaalharts region is compiled.
AFRIKAANSE OPSOMMING: Die verbouing van sitrus in die Vaalhartsgebied is 'n redelik onlangse ontwikkeling. Gepaard met die nuwe gewas het daar ook 'n insekplaagkompleks in die gebied ontstaan. Die voorkoms van die plae is in elt .boorde, beplant met drie sitruskultivars en van verskillende ouderdomme, verspreid in die 300 vierkante kilometer verbouingsareaal, bestudeer. Elk van die boorde is weekliks ondersoek vir die aanwesigheid van plae deur van twee moniteringstegnieke gebruik te maak. Die tien belangrikste insekplae van sitrus in die Vaalhartsgebied word kortliks beskryf deur na hulle algemene voorkoms, lewenssiklus, voeding en plaagstatus en ekonomiese drempelwaardes asook die moniteringsmetodes wat gebruik is, te verwys. Vir elke plaag word beheeropsies, wat operasionele stelsels, gewasverbouing, bloloqlese en chemiese beheer insluit, bespreek wat, waar toepaslik, aan die hand van grafiese voorstellings gemustreer word. Die seisoenale aanwesigheid van die sitrusplae word in 'n tabel aangedui en individueel bespreek. Met die gegewens as agtergrond is 'n insekplaagbestuurprogram vir sitrus in die Vaalhartsgebied opgestel.

The South African Citrus Thrips, Scirtothrips aurantii Faure (Thysanoptera: Thripidae) has been a serious pest of the citrus industry of Southern Africa for over 70 years. It is indigenous to Africa and has no recorded parasitoids and, in most citrus-growing regions, predators are not economically effective. Firstly, in this study, the general ecology of thrips was reviewed along with the recorded history of S. aurantii and its control. Host plant relationships of S. aurantii were then examined and wild hosts were not found to be important in promoting citrus thrips outbreaks in the orchard after flowering. In addition, Scirtothrips dorsalis Hood, which attacks citrus in Asia, was collected for the first time in Africa, but from Castor Oil plant. It is therefore a potential pest of citrus here. Notes on its appearance compared to that of S. aurantii were prepared. Weekly sampling of S. aurantii adults was carried out from June 1984 to May 1990. Population fluctuations were then correlated with phenology of the citrus trees and the direct and indirect effects of weather. Temperature and rainfall were not found to be significantly directly correlated with thrips numbers recorded. However, the indirect effects of rainfall were important in promoting a large winter thrips population in certain years. Relatively high rainfall during March and April compared to that of the previous January and February stimulated atypical flushing of the citrus trees during autumn and the setting of out-of-season fruit. S. aurantii then exploited this unusual food source and high numbers were subsequently recorded in the following winter; as well as in spring. Thus the mild winter climate alone could not suppress thrips numbers at Letaba. Dispersal/Emergence traps, which are used in the U.S.A. for the monitoring of Scirtothrips citri, were evaluated over 24 months, and were effective in recording population peaks of S. aurantii. The emergence rate of adults in relation to second instar larvae trapped was 43.7%. 35.7% of adults caught after emerging from the soil were males and 64.3 were females. In contrast, yellow traps had recorded 59.1% males and 40.9% females over the same period. The yellow traps were subsequently found to be biased towards male catches when young fruit and/or soft flush was present on the citrus trees. Relative inhibition of female flight activity during times of food abundance is known in other thrips species. During times of food scarcity, the bias in the yellow trap results disappeared. At Letaba Estates, availability of food rather than the direct effects of weather was seen to be the most important factor in governing S. aurantii numbers. Because of the importance of soft flush in the promotion of S. aurantii population increase, it is recommended that more attention should be given to the control of thrips on, as well as conducting surveys for, this food source. As the climate at Letaba is so favourable for citrus thrips, even during winter, it is further recommended that trapping for S. aurantii is carried out throughout the year. Furthermore, males and females should be recorded separately in trapping results as the sex ratio gives an indication of the phenological state of the tree.

Thesis (MSc)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Grapevine virus E (GVE) is a newly identified virus that has been detected in an established vineyard in South Africa. This virus is a member of the genus Vitivirus, family Flexiviridae. Members of this genus are known to infecte grapevine and are associated with various disease complexes, such as the Rugose wood complex (RWC) and Shiraz disease (SD). However, the role and impact of GVE in South African vineyards are still unknown. It is important to study these viruses to determine how they infect and the possible impact they may have on vine health. The accurate and early detection of grapevine viruses is the first important step in disease management. In this study, reverse transcription-polymerase chain reaction (RT-PCR), double antibody sandwich enzyme linked immunesorbent assay (DAS-ELISA) and quantitative (q)RT-PCR were used for the detection of GVE in the vineyard (Vitis vinifera cv Merlot) where GVE was first identified in South Africa. Reverse transcription-PCR was used for detection and determining the incidence of GVE. The incidence was as low as 3% in the vineyard surveyed. All the GVE positive plants were co-infected with GLRaV-3 and no disease association could therefore be made. Evaluation of the Bioreba Grapevine virus A (GVA) DAS-ELISA kit showed that it did not detect GVE. No cross-reactivity occurred with epitopes of GVE, confirming this kit to be a valid and specific assay for GVA infection. The relative virus titer of GVE was calculated over the growing season of 2010/2011, using qRT-PCR. No fluctuation in virus titer was observed during that growing season. Transmission experiments were performed in an attempt to transfer GVE from grapevine to an alternative host. Three different transmission buffers as well as nine different herbaceous plant species, that have shown to be susceptible to several plant viruses in previous studies, were evaluated. In these experiments, GVE could not be transmitted to any of the herbaceous species. To further characterize GVE, chimeric clones were constructed with GVA. The ORF2 and ORF5 of GVE were cloned into previously constructed GVA ORF2 and ORF5 deletion mutants. Construction of the chimeric clones, 35S-GVA-GR5-ΔORF2-GVE-ORF2 and 35S-GVA-118-ΔORF5-GVE-ORF5 were successful and they were evaluated for their infectivity in N. benthamiana. The 35S-GVA-GR5-ΔORF2-GVE-ORF2 chimera was able to infect and replicate in these plants and disease symptoms such as yellowing of veins and leaf curling were observed. Virus, derived from this vector, was detected by TPIA, RT-PCR and DAS-ELISA. The 35S-GVA-118-ΔORF5-GVE-ORF5 chimeric vector was not able to infect N. benthamiana as no disease symptoms were observed in any of the infiltrated plants and virus was not detected with serological analysis and RT-PCR. This study was aimed at further characterizing the recently identified virus GVE. Here, insight is given into the prevalence of this virus in the vineyard where it was first identified and attempts to biologically characterize GVE were made.
AFRIKAANSE OPSOMMING: Grapevine virus E (GVE) is „n nuut geïndetifiseerde virus wat onlangs in „n gevestigde wingerd in Suid Afrika opgespoor is. Hierdie virus vorm deel van die genus Vitivirus, familie Betaflexiviridae. Spesies in hierdie genus is bekend vir wingerdinfeksies en word met „n verskeidenheid wingerd siektes geassosieer, soos bv. Rugose wood complex (RWC) en Shiraz siekte (SD). Die rol en impak van GVE is nog onbekend. Dit is dus belangrik om die virus te bestudeer om te bepaal hoe dit infekteer en of dit enige impak het op wingerd gesondheid. Akkurate en vroeë opsporing van virusse is die eerste belangrike stap vir virussiekte beheer. In hierdie studie word tru-transkripsie (TT) – polimerase ketting reaksie (PKR), dubbel teenliggaam (DAS) -ensiem gekoppelde immuno-absorberende analise (ELISA) en qTT-PKR gebruik vir die opsporing van GVE in die wingerd (Vitis vinifera cv Merlot) waar dit vroeër in Suid Afrika geïdentifiseer was. Vir opsporing en bepaling van verspreiding is TT-PKR gebruik. Daar is bepaal dat 3% van die wingerd met GVE geïnfekteer is. Al die GVE-positiewe stokke het ook positief getoets vir GLRaV-3 en geen assosiasie met siekte simptome kon gemaak word nie. Evaluering van die Bioreba GVA DAS-ELISA met GVE positiewe stokke het nie GVE opgespoor nie. Geen kruisreaktiwiteit het plaasgevind met epitope van GVE nie en dus is die DAS-ELISA ʼn betroubare toets vir GVA infeksie. Die relatiewe virus titer van GVE was ook bepaal oor die groeiseisoen van 2010/2011 deur qTT-PKR te gebruik. Geen fluktuasie in virus titer gedurende die groeiseisoen is waargeneem nie. Transmissie eksperimente is gedoen om GVE vanaf wingerd na ʼn alternatiewe gasheer oor te dra. Drie verskillende transmissie buffers en tien verskillende sagteplant spesies, wat voorheen vatbaarheid vir plantvirusse getoon het, is gebruik. In die transmissie eksperimente kon GVE nie na enige van die sagteplante oorgedra word nie. Om GVE verder te karakteriseer is hibried-virusse met GVA gemaak. Die leesraam (ORF) 2 en ORF5 van GVE gekloneer in GVA ORF2 en -ORF5 delesie konstrukte, 35S-GVA-GR5-ΔORF2 en 35S-GVA-118-ΔORF5, onderskeidelik (Blignaut, 2009; Du Preez, 2010). Klonering van die hibried konstrukte, 35S-GVA-GR5-ΔORF2-GVE-ORF2 en 35S-GVA-118-ΔORF5-GVE-ORF5, was suksesvol en is in N. benthamiana geëvalueer. Virus afkomstig van die 35S-GVA-GR5-ΔORF2-GVE-ORF2 hibried konstruk, kon plante suksesvol infekteer en kon repliseer binne hierdie plante. Siektesimptome soos vergeling van die are en rolblaar is ook waargeneem in plante geïnfekteer met hierdie hibried konstruk. Plante is getoets met weefsel afdruk immuno analise (TPIA), TT-PKR en DAS-ELISA en is positief gevind vir virus afkomstig van hierdie konstruk. Die 35S-GVA-118-ΔORF5-GVE-ORF5 hibried kon nie N. benthamiana infekteer nie en geen siektesimptome is waargeneem in enige van die plante geïnfiltreer met hierdie konstruk. Serologiese analise en TT-PKR het ook nie virus in die N. benthamiana plante opgespoor nie. Die doel van hierdie studie was om GVE te karakteriseer. In hierdie studie word insig gegee oor die verspreiding van hierdie virus in Suid Afrika en pogings is gemaak om GVE biologies te karakteriseer.

Thesis (MScAgric)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Cydia pomonella (codling moth), Thaumatotibia leucotreta (False codling moth), Thaumatotibia batrachopa (Macadamia nut borer), Grapholita molesta (Oriental fruit moth), Cryptophlebia peltastica (Litchi moth), Epichoristodes acerbella (Pear leafroller/Carnation worm) and Lozotaenia capensana (Apple leafroller) are the most economically important tortricids affecting various crops in South Africa. The correct identification of these species, especially of the larval stage, is of great importance in pest management. Using available literature, augmented by additional morphological studies, an interactive identification key (Lucid key) for larval and adult stages of the seven species was developed. The colour and markings of the head, characteristics of the prothoracic and anal shields, the position of the prespiracular setae (L-group) relative to the spiracle on the prothoracic segment, the position of the spiracle on the eighth abdominal segment and L-group on the ninth abdominal segment, as well as the presence or absence of the anal comb are key characteristics for larval identification. For adult identification, wing pattern and genitalia are the most important features. However, the use of genitalia for moth identification might be difficult for the lay user, as the dissection and mounting of these structures requires certain skills and specialized equipment. Thus, genitalia have not been included in the Lucid Key. Differences in the morphological characteristics of most pupae were so minute that this stage was also not included in the Lucid key. However, the pupae of E. acerbella and L. capensana are easily distinguished from those of the other species by the presence of acremaster. This study also included the first morphological description of the pupa of L. capensana, which can be distinguished from that of E. acerbella by various features of the cremaster, antennae, spiracle shape, number of setae on abdominal segments A5-7, the size of spines on A3-7, and the presence/absence of spines on A9. A previous study by Timm (2005) indicated that geographically isolated populations of T. leucotreta tend to be genetically distinct. This raised the question of whether speciation/subspeciation has occurred or is occurring. Male moth genitalia are thought to evolve rapidly and are often the only features that can reliably distinguish similar species. Hence, variation in the shape of the valvae of T. leucotreta was used to determine whether divergence has occurred between populations of T. leucotreta. Elliptical Fourier analysis was used to analyze the valvar variation in three different populations. Although some variation in valvar shape was detected among mean population values for certain traits, no clear pattern emerged. Principle component analysis also showed no distinct clustering of valvae shape among populations, providing no evidence for divergence in male genitalia and therefore no morphological evidence of incipient speciation.
AFRIKAANSE OPSOMMING: Cydia pomonella (Kodlingmot), Thaumatotibia leucotreta (Valskodlingmot), T. batrachopa (Makadamianeutboorder), Grapholita molesta (Oosterse vrugtemot), Cryptophlebia peltastica (Lietsjiemot), Epichoristodes acerbella (Peerbladroller/Angelierrusper) en Lozotaenia capensana (Appelbladroller) is die mees ekonomies belangrike tortrisiede van die vrugtebedryf in Suid-Afrika. Die juiste identifikasie van hierdie spesies, veral van hulle larwale stadium, is van groot belang by plaagbestuur. Deur gebruik te maak van beskikbare literatuur, aangevul deur bykomstige morfologiese studies, is ‗n interaktiewe uitkenningssleutel (―Lucid key‖) vir die larwale en volwasse stadia van die sewe spesies ontwikkel. Die kleur en tekening van die kop, kenmerke van die prothorakale en anale skild, die ligging van die prespirakulêre setae (L-groep) relatief tot die spiraculum op die prothorakale segment, die ligging van die spirakulum op die agste abdominale segment en L-groep op die negende abdominale segment, asook die aan- of afwesigheid van die anale kam is sleutel kenmerke vir larwale uitkenning. Vir die volwassenes is die vlerktekening en genitalia die mees belangrike kenmerke. Die gebruik van die genitalia vir motuitkenning kan egter vir die leek gebruiker moeilik wees omdat die disseksie en montering van hierdie strukture bepaalde vaardighede en gespesialiseerde toerusting vereis. Vir die rede is die genitalia nie in die Lucid-sleutel ingesluit nie. Verskille in die morfologiese kenmerke van meeste papies is klein en die stadium is gevolglik ook nie in die sleutel ingesluit nie. Die papies van E. acerbella en L. capensana kan egter maklik van die ander spesies onderskei word deur die aanwesigheid van ‗n cremaster. Hierdie studie sluit ook die eerste morfologiese beskrywing van die papie van L. capensana in, wat van dié van E. acerbella onderskei kan word deur gebruik te maak van kenmerke van die cremaster, antennae, spirakulêre vorm, aantal setae op abdominale segmente A5-7, die grootte van stekels op A3-7, en die aan- of afwesigheid van stekels op A9. ‗n Vroeëre studie (Timm 2005) het aangedui dat geografies geïsoleerde bevolkings van T. leucotreta neig om geneties verskillend te wees. Dit het die vraag laat ontstaan of spesiasie/subspesiasie moontlik plaasgevind het of steeds plaasvind. Manlike mot genitalië word geag om vinnig te ontwikkel en is dikwels die enigste kenmerke wat betroubaar tussen soortgelyke spesies kan onderskei. Dus is die variasie in die vorm van die valvae van T. leucotreta gebruik om te bepaal of divergensie wel tussen bevolkings van T. leucotreta plaasgevind het. Elliptiese Fourier ontleding is gebruik om die valvae se variasie by drie verskillende bevolkings te ontleed. Alhoewel enkele variasie in die vorm van die valvae bespeur is by die gemiddelde bevolkingswaardes vir bepaalde eienskappe, kon geen duidelike patroon bespeur word nie. Hoofkomponentontleding het ook geen duidelike groepering van valvae se vorm tussen bevolkings getoon nie, wat geen bewys lewer van divergensie in die manlike genitalia en dus geen morfologiese bewys van beginnende spesiasie.

Thesis (PhD(Agric))--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: The purpose of this study was to characterize the race and vegetative compatibility of Fusarium oxysporum f. sp. melonis (FOM) isolates collected in the major melon producing areas, to report on their geographical distribution, and their possible relatedness to isolates from other countries. Seventy two FOM isolates obtained from 30 fields in 17 melon producing regions were race-typed using the differential cultivars Topmark (susceptible to all races), Doublon (Fomi), CM 17187 (Fom2) and Perlita (Fom3) and grouped by means of vegetative compatibility. All isolates belonged to vegetative compatibility group 0134, indicating a high degree of genetic homogeneity among the South African FOM population. Fifty four isolates were identified as race 0, eight as race 1, and 10 as race 2. Race 0 occurred in 15 of the regions whereas race 1 was sporadically recovered. Race 2, on the other hand, was obtained only from four fields located in one geographical region. Perlita plants (carrying the gene Fom3) inoculated with local isolates ofrace 0 and race 2 and reference isolates of race 0 became stunted, their leaves turned yellow, and became thickened and brittle. These results suggested that Fom3 in Perlita confers a tolerant reaction compared to the resistant reaction of gene FornI in Doublon. The disease reaction of cultivar Perlita to FOM was therefore reinvestigated. Twenty isolates, including the four FOM races (0, 1, 2, and 1,2) obtained from different countries, were used. The differential cultivars were included to verify virulence of the isolates. Perlita plants inoculated with three isolates of race 2 remained asymptomatic. The remaining race 2 and 0 isolates, induced severe stunting of Perlita plants, but mean percentage stunting values did not differ significantly (P = 0.05) and ranged between 25.1 and 50.0. Leaves of stunted plants were chlorotic, thickened and brittle. Disease reaction of Perlita was verified at a lower inoculum concentration with two race 2 (pipette method) and two race 0 isolates (root dip method). Results proved that Fom3 does not confer similar resistance towards race 0 and some race 2 isolates as FornI in Doublon. Cultivars possessing Fom3, should therefore be considered tolerant to FOM races 0 and 2. The ability of a nit mutant isolate, generated from FOM race 0 which belongs to VCG 0134, to change its virulence during infection of melon plants, was investigated under quarantine. Seedlings of melon cultivars Imperial 45 and Early Sweet (no resistance genes), Amber (Fom2) and Fiata (FomI, Fom2) were consecutively grown in two cement troughs in a gauzehouse. Each planting was terminated when plants had advanced Fusarium wilt or after the fruit were harvested. In the first planting, Imperial 45 seedlings were transplanted and artificially inoculated with the nil mutant isolate. In the consecutive plantings, seeds were sown in the infested soil to enable natural infection. For each crop, representative plants showing Fusarium wilt were selected for isolation. All F. oxysporum isolates recovered were single-spored and their nit mutant and VCG status verified. Virulence of the labelled isolates was determined using differential cultivars. In trough A, all plants of the susceptible cultivars Imperial 45 and Early Sweet crops showed Fusarium wilt. The labelled isolates recovered from the selected plants were all designated race O. In the first crop (planting No.5) of the resistant cultivar Amber, 6.7% of the plants developed Fusarium wilt. In the second Amber crop the disease incidence increased to 56.6%, and to 81.8% in the final crop. Contrary to the susceptible cultivars, only race 2 isolates were obtained from the symptomatic Amber plants. Similar data were found with the susceptible cultivar Imperial 45 and the resistant cultivar Amber in trough B. Planting of Fiata caused a dramatic reduction in Fusarium wilt incidence in trough B. However, 1.2% of plants were affected by Fusarium wilt in the first Fiata crop (planting No.6), whereas 4% of the plants were symptomatic in the final planting. From these symptomatic Fiata plants only race 1,2 isolates were obtained. These findings, and the fact that the symptomatic plants represented a substantial proportion of the first Amber (approximately 7-15%) and Fiata (approximately 2%) crops, provedthat changes in the race structure of this fungal pathogen occurred rapidly when confronted with a resistant cultivar. The potential of RAPD analysis to differentiate between the isolates displaying virulence changes was evaluated. Four F. oxysporum f. sp. niveum isolates were included as an outgroup. A histopathological study was conducted to verify whether these isolates retain their ability to behave as true vascular pathogens. The three primers used clearly distinguished the 12 FOM isolates from the four F. oxysporum f. sp. niveum isolates. However, the primers showed a highly conserved and characteristic banding pattern for the FOM isolates which represented three physiological races (race 0, race 2, race 1,2), indicating that RAPD analysis cannot detect race-specific groupings in FOM. Disease reactions on the three differential cultivars confirmed the virulence of FOM isolates. The histopathological data furthermore proved that the two FOM races (race 2, race 1,2), which derived from the race 0 parent isolate, retained their ability to behave as true vascular pathogens.
AFRIKAANSE OPSOMMING: DIE KARAKTERISERING EN PATOGENESITEIT VAN SUID-AFRIKAANSE ISOLATE VAN FUSARIUMOXYSPORUMF. SP.MELONIS Die doel van die studie was om Fusarium oxysporum f. sp. melonis (FOM) isolate wat in die hoof spanspekproduserende gebiede versamel is, volgens ras en vegetatiewe verenigbaarheid te karakteriseer, en hul geografiese verspreiding en verwantskap met isolate van ander lande aan te dui. Twee en sewentig FOM isolate afkomstig vanaf 30 landerye wat 17 spanspekproduserende areas verteenwoordig, is gebruik. Die differensiële kultivars Topmark (vatbaar vir alle rasse), Doublon (Forni), CM 17187 (Fom2) en Perlita (Fond) is gebruik om die rasbepalings te doen asook om die vegetatiewe verenigbare groepe (VVG) te bepaal. Al die isolate is as VVG 0134 geklassifiseer, wat 'n hoë mate van genetiese homogenesiteit binne die Suid-Afrikaanse populasie aandui. Vier en vyftig isolate is as ras 0, agt as ras 1 en 10 as ras 2 geklassifiseer. Ras 0 is vanaf 15 gebiede afkomstig, terwyl ras 1 sporadies voorgekom het. Ras 2 is vanuit vier landerye binne dieselfde geografiese gebied verkry. Plante van die kultivar Perlita wat met plaaslike isolate van ras 0 en 2, asook verwysings-isolate van ras 0 geïnokuleer is, het verdwerg voorgekom. Die blare van die plante het vergeel, verdik en bros voorgekom. Hierdie siekte reaksie het aangedui dat Fond in Perlita toleransie bewerkstellig in teenstelling met die weerstandbiedende reaksie van geen Fomi in Doublon. Die siekte reaksie van Perlita teenoor FOM is dus verder ondesoek. Hiervoor is 20 isolate wat al vier FOM rasse insluit (0, 1, 2, en 1,2), en van verskillende wêrelddele afkomstig is, gebruik. Die virulensie van die isolate is met die differensiële kultivars bevestig. Drie van die ras 2 isolate het geen siektesimptome op Perlita veroorsaak nie. Die ander ras 2 isolate, en al die ras 0 isolate, het egter die Perlita plante aansienlik verdwerg en die blare vergeel en verdik. Laasgenoemde groep isolate het 'n gemiddelde verdwergingsindeks van tussen 25.1% en 50.0% veroorsaak. Die siekte reaksie by Perlita is verder bevestig deur plante teen 'n laer inokulumdigtheid van twee ras 2 (pipet metode), en twee ras 0 (wortel-doop metode) isolate, te inokuleer. Uit die resultate was dit duidelik dat die weerstand wat Fom3 teenoor ras 0 en sommige ras 2 isolate verskaf, van FornI verskil. Kultivars wat oor die weerstandsgeen Fom3 beskik moet dus as tolerant beskou word. 'n Ondersoek is geloods na die vermoë van 'n nil mutant isolaat, genereer vanaf die wilde ras 0 isolaat van FOM (VVG 0134), om onder kwarantyn sy virulensie gedurende infeksie van spanspekplante te verander. Saailinge van die spanspekkultivars Early Sweet (geen weerstandsgene), Amber (Fom2) en Fiata (FornI, Fom2) is opeenvolgens in twee sement trêe in 'n gaashuis verbou. Die afsonderlike aanplantings is beëindig sodra gevorderde Fusarium-verwelksimptome verkry is, of nadat vrugte ge-oes is. Vir die eerste aanplanting is oorgeplante Imperial 45 saailinge kunsmatig met die nil mutant isolaat geïnokuleer. Tydens die opeenvolgende aanplantings is saad direk in die besmette grond gesaai ten einde natuurlike infeksie te verkry. Met elke aanplanting is isolasies gedoen vanaf verteenwoordigende plante wat Fusarium-verwelksimptome getoon het. Alle F. oxysporum isolate wat verkry is, is ge-enkelspoor en hul nit mutant status en VVG is bevestig. Virulensie van die gemerkte isolate is bepaal deur inokulasie van die differensiële kultivars. Alle plante van die vatbare Imperial 45 en Early Sweet kultivars wat in trog A geplant is, het Fusarium-verwelksimptome getoon. Die gemerkte isolate wat vanaf die verteenwoordigende plante verkry is, is almal as ras 0 geklassifiseer. Tydens die eerste aanplanting van die weerstandbiedende kultivar, Amber (aanplanting No.5), het 6.7% van die plante Fusarium-verwe1ksimptome ontwikkel. Tydens die tweede en derde aanplanting van Amber het die frekwensie van siektevoorkoms verhoog na 56.6% en 81.8 %, onderskeidelik. In teenstelling met die vatbare kultivars, is slegs ras 2 vanuit die Amber plante met siektesimptome verkry. Soortgelyke resultate is met Imperial 45 en Amber in trog B verkry. Aanplanting van kultivar Fiata het egter 'n dramatiese verlaging in die voorkoms van Fusarium-verwelk bewerkstellig. Tydens die eerste Fiata aanplanting (aanplanting No.6) het 1.2% plante Fusarium-verwelksimptome ontwikkel, en 4% tydens die laaste aanplanting. Vanaf hierdie plante is slegs ras 1,2 isolate verkry. Hierdie bevindings, en die feit dat 'n aansienlike hoeveelheid van die Amber (ongeveer 7-15%) en Fiata plante (ongeveer 2%) siektesimptome getoon het, bewys dat FOM vinnig van virulensie verander wanneer die patogeen 'n weerstanbiedende kultivar infekteer. Die vermoë van RAPD analise om tussen isolate wat in virulensie verander het, te onderskei, is ondersoek. Vier isolate van F. oxysporum f. sp. niveum is as 'n buite-groep ingesluit. Om te bevestig dat die isolate wat van ras verander het wel egte vaskulêre patogene is, is 'n histopatologiese ondersoek gedoen. Die drie inleiers wat gebruik is, het die 12 FOM isolate duidelik van die vier F. oxysporum f. sp. niveum isolate onderskei. Die 12 FOM isolate wat drie fiosologiese rasse (ras 0, ras 2, ras 1,2) verteenwoordig het, is egter saam gegroepeer, wat aandui dat hierdie metode nie tussen rasse van FOM kan onderskei nie. Inokulasiestudies met die differensiële kultivars het die virulensie van die isolate bevestig. Die histopatologiese ondersoek het verder bewys dat beide FOM rasse (ras 2, ras 1,2) wat vanaf die wilde tipe ras ° isolaat ontstaan het, hul vermoë behou het om as egte vaskulêre patogene op te tree.

Thesis (MScAgric)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Lucerne is the most important pasture and fodder crop in the winter rainfall area of South Africa. Various pests are known to cause damage to this crop. The use of the sweep net for monitoring pests is a cheap, easy and quick technique. If the sweep net is suitable for the lucerne pests in South Africa, potential pest status can be determined easily and quickly and the necessary precautionary measures taken to prevent crop losses. From a managerial point of view, it is also important to know the composition of the insect community in order to follow practices in which the number of beneficial insects can be increased and the injurious insects decreased. Therefore a study was done to quantify the use of the sweep net as a survey technique for monitoring pests on established lucerne stands. Insect diversity was also determined to obtain information on the insect families and guilds on lucerne. The redlegged earth mite, due to its importance as a pest, and the Anystis mite, important as a predator, were also included. The sweep net proved to be suitable for the sampling of the main lucerne pests. If a 29 cm diameter sweep net is swiped once per pace for six long paces, twelve systematically chosen sampling units are recommended for the lucerne earth flea and aphids. It is not necessary to differentiate amongst the three aphid species, or between the winged and unwinged aphids. Actual counts should be used instead of absence-presence data. Instead of counting all the insects in a sample, sub-samples can be taken. Operational characteristic curves can be used to determine the risk involved in the decision not to intervene, for example by spraying or grazing. Recommendations for monitoring and the accuracy of control decisions for the redlegged earth mite, Sitona weevil and lucerne butterfly can only be made after threshold values have been determined. The pea aphid, bluegreen aphid and lucerne earth flea showed peaks in their population levels during spring. Peak numbers of the spotted alfalfa aphid occurred during late summer and autumn. The Sitona weevil and lucerne butterfly numbers reached peak levels during late spring and early summer. For all pests population levels were dramatically reduced after grazing or cutting of the plantings. Therefore, these cultivation practices provided good control. The herbivores made up more than 85% of the insect community in lucerne. The largest herbivorous families, in terms of the number of individuals per family, were the Aphididae and Sminthuridae. These two families contain the main lucerne pests, the pea aphid, bluegreen aphid, spotted alfalfa aphid and the lucerne earth flea. The largest predatory family was the Anystidae, represented by the Anystis mite, the most important predator of the red legged earth mite and lucerne earth flea. Another well represented predatory family was the Coccinellidae, containing natural enemies of the aphids. The dryland plantings had a higher percentage of predators than the irrigated lucerne. The most important parasitaids were those in the superfamily Chalcidoidea and in the family Braconidae. The main detritivores were springtails in the suborder Arthropleona, insects in the families Mycetophilidae on irrigated lucerne, and Mycetophagidae on dryland lucerne. The most abundant visitors were in the families Chironomidae, Drosophilidae and Tephritidae. The dryland plantings had a lower percentage of visitors than the irrigated plantings. The number of insect families, as well as the number of individuals per family, was lower at the dryland plantings than at the irrigated plantings. The vast majority of insect families found on lucerne were collected during the one-year sampling period. A lower diversity was found where grazing was more severe, and there was a negative relationship between diversity and evenness.
AFRIKAANSE OPSOMMING: Lusern is die belangrikste wei- en voergewas 10 die winterreëngebied van Suid- Afrika. Hierdie gewas word deur 'n verskeidenheid plae aangeval. Die gebruik van die swaainet vir die monitering van plae is 'n goedkoop, maklike en vinnige tegniek. lndien die swaainet geskik is vir die betrokke plae in Suid-Afrika, kan potensiële plaagstatus van die plae dus maklik en vinnig bepaal word en die nodige voorsorgmaatreëls getref word om verliese te voorkom. Vanuit 'n bestuursoogpunt is dit ook belangrik om te weet wat die samestelling van die insekgemeenskap is sodat praktyke gevolg kan word waardeur die getal voordelige insekte verhoog en nadelige insekte verlaag word. Gevolglik is 'n studie uitgevoer om die gebruik van die swaainet te kwantifiseer as 'n monsternemingsmetode vir die monitering van plae op gevestigde lusernstande. Insekdiversiteit is ook bepaal ten einde inligting te bekom oor die insekfamilies en -gildes op lusern. Die lusernerdvlooi en swartsandmyt, vanweë hul belang as plae, en die Anystis-roofmyt, vanweë sy belang as predator, is ook ingesluit. Die swaainet blyk geskik te wees vir die monitering van die. vernaamste lusernplae. Wanneer 'n 29 cm deursnee swaainet vir ses lang treë een keer per tree geswaai word, word 12 sistematies gekose steekproefnemingseenhede vir die lusernerdvlooi en plantluise aanbeveel. Daar hoef nie onderskeid tussen die plantluisspesies en tussen gevleuelde en ongevleuelde plantluise getref te word nie. Daar moet gebruik gemaak word van werklike insektellings en nie van aanwesigheid-afwesigheid data nie. In plaas van om al die insekte in 'n monster te tel, kan submonsters geneem word. Operasionele karakteristieke kurwes kan gebruik word om die risiko verbonde aan die besluit om nie op te tree, deur byvoorbeeld te spuit of bewei nie, te bepaal. Vir die swartsandmyt, Sitona-snuitkewer en lusernskoenlapper moet drempelwaardes eers vasgestel word voordat aanbevelings vir monitering en die akkuraatheid van besluite rakende beheer, gegee kan word. Vir die ertjieluis, blougroenluis en lusernerdvlooi het die bevolkingsvlakke 'n piek in die lente bereik. Die gevlekte lusernluis se piekgetalle was hoofsaaklik in die laat somer en herfs. Die Sitona-snuitkewer en lusernskoenlapper het piekgetalle gehad in die laat lente en vroeë somer. Vir al die plae het bevolkingspieke drasties afgeneem nadat die aanplantings bewei of gesny is. Hierdie verbouingspraktyke blyk dus goeie beheer te verskaf. Die herbivore op lusern het meer as 85% van die insekgemeenskap beslaan. Die grootste herbivoorfamilies, in terme van aantal individue per familie, was die Aphididae en Sminthuridae. Hierdie twee families bevat die vernaamste lusernplae, naamlik die ertjieluis, blougroenluis, gevlekte lusernluis en lusernerdvlooi. Die grootste predatoriese familie was die Anystidae, wat verteenwoordig is deur die Anystis-roofmyt. 'n belangrike predator van die swartsandmyt en lusernerdvlooi. Nog 'n predatoriese familie wat goed verteenwoordig was, was die Coccinellidae, natuurlike vyande van plantluise. Die droëland aanplantings het 'n hoër persentasie predatore gehad as die besproeide lusern. Die belangrikste parasitoïede aanwesig was dié in die superfamilie Chalcidoidea en familie Braconidae. Die vernaamste detritivore was erdvlooie in die suborde Arthropleona, insekte in die families Mycetophilidae by besproeide lusern, en Mycetophagidae by droëland lusern. Die volopste besoekers was lede van die families Chironomidae, Drosophilidae en Tephritidae. Die droëland aanplantings het 'n laer persentasie besoekers gehad as die besproeide lusern. Die aantal insekfamilies, asook die aantal individue per familie, was laer by die droëland aanplantings as by die besproeide aanplantings. Die oorgrote meerderheid insekfamilies wat op lusern voorkom, is gedurende die een jaar opnameperiode waargeneem. 'n Laer insekdiversiteit is gevind waar beweiding strawwer was, en daar was 'n negatiewe verband tussen diversiteit en gelykmatigheid.

False codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is considered the most important indigenous pest of citrus in southern Africa. Major concerns such as progressive insecticidal resistance, the negative impact of insecticides on the environment, as well as the influence of consumers opposed to chemical residues on fruit, created opportunities for biological control methods such as Sterile Insect Technology (SIT). This technology is now established in the Western and Eastern Cape provinces of South Africa as an effective, sustainable alternative to conventional FCM control methods. Due to the prevalence of the pest in all citrus producing areas of South Africa, potential for SIT to expand is enormous. Success of an SIT programme is highly dependent on efficient application of the technology to achieve its objectives in a timeous manner. The aim of this study was to advance the application of SIT for control of FCM on citrus in South Africa, by investigating the effect of certain critical stages in the process. The effect of long-distance transportation on fitness of irradiated FCM was determined, showing reduced performance with cold-immobilized transport. A significant decrease in flight ability and longevity of irradiated FCM was found, although critically, realized fecundity was not affected. The effect of two different insecticides in the pyrethroid and organophosphate chemical groups were investigated for their residual effect on mortality of released irradiated FCM, to determine if these pest control programmes could be integrated. Both chlorpyrifos and tau-fluvalinate were effective in killing irradiated FCM for a number of days after application, after which degradation of the active ingredient rendered it harmless. This effect was found to be similar for irradiated and non-irradiated males, consequently ratios of sterile : wild male FCM should be retained regardless of whether sprays are applied or not. The modes for release of sterile FCM in an SIT programme were investigated. Efficacy of ground and aerial release platforms were tested by evaluating the recovery of released irradiated male FCM in these orchards. More irradiated FCM were recovered in orchards released from the ground compared to air. However, an economic analysis of both methods shows application of irradiated insects over a large geographical area is more cost-effective by air. Depending on the terrain and size of the target area, a combination of both methods is ideal for application of SIT for control of FCM in citrus. Development of application technology for advance of the programme is discussed and recommendations for future research and development are offered.

Chocolate is the center of a massive global industry worth billions of dollars annually, yet its future in our modern world is currently under threat. Here, Dale Walters discusses the problems posed by plant diseases, pests, and climate change, looking at what these mean for the survival of the cacao tree. Walters takes readers to the origins of the cacao tree in the Amazon basin of South America, describing how ancient cultures used the beans produced by the plant, and follows the rise of chocolate as an international commodity over many centuries. He explains that most cacao is now grown on small family farms in Latin America, West Africa, and Indonesia, and that the crop is not easy to make a living from. Diseases such as frosty pod rot, witches’ broom, and swollen shoot, along with pests such as sap-sucking capsids, cocoa pod borers, and termites, cause substantial losses every year. Most alarmingly, cacao growers are beginning to experience the accelerating effects of global warming and deforestation. Projections suggest that cultivation in many of the world’s traditional cacao-growing regions might soon become impossible. Providing an up-to-date picture of the state of the cacao bean today, this book also includes a look at complex issues such as farmer poverty and child labor, and examines options for sustainable production amid a changing climate. Walters shows that the industry must tackle these problems in order to save this global cultural staple and to protect the people who make their livelihoods from producing it.