Tesi sul tema "Nematode diseases of plants Genetic aspects"
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1
Williams, Kevin John. "Biological and genetic studies of wheat resistance to Heterodera avenae". Title page, summary and contents only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phw7238.pdf.
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Taylor, Sharyn Patricia. "The root lesion nematode, Pratylenchus neglectus, in field crops in South Australia". Title page, contents and summary only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09pht2462.pdf.
Abstract (sommario):
Includes bibliographical references (leaves 241-25). Aims to evaluate sampling procedures; assess the extent and magnitude of yield loss caused by Pratylenchus neglectus; assess the population dynamics of Pratylenchus neglectus in cereals; determine whether resistance occurs in field crops; and, assess whether variation occurs between geographically isolated species of Pratylenchus neglectus
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Vanstone, Vivien Alison. "The role of fungi and the root lesion nematode, Pratylenchus neglectus, in damaging wheat roots in South Australia". Title page, summary and contents only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phv281.pdf.
Abstract (sommario):
Includes bibliographical references (leaves 265-296). Pathogens associated with root damage were investigated in the Murray Mallee region of South Australia over the 1987-1989 growing seasons. Occurence of fungal species and the root lesion nematode (Pratylenchus neglectus) was assessed, and related to the appearance and severity of symptoms on the roots. Field experiments were supplemented with innoculation tests in the glasshouse and laboratory.
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Shrestha, Roshi. "A physiological and genetic mapping study of tolerance to root-knot nematode in rice". Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=24807.
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Maree, H. J. (Hans Jacob). "The expression of Dianthin 30, a ribosome inactivating protein". Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53633.
Abstract (sommario):
Thesis (MSc)--Stellenbosch University, 2003.ENGLISH ABSTRACT: Ribosome inactivating proteins (RIPs) are currently classified as rRNA N-glycosidases, but also have polynucleotide: adenosine glycosidase activity. RIPs are believed to have anti-viral and anti-fungal properties, but the exact mechanism of these proteins still need to be elucidated.The mechanism of resistance however, appears to be independent of the pathogen. For resistance the RIP terminates virus infected plant cells and stops the reproduction and spread of the virus. Transgenic plants containing RIPs should thus be resistant to a wide range of viruses. The ultimate goal of the larger project of which this forms part is the development of virus resistant plants. To monitor the expression of a RIP in a transgenic plant a detection method had to be developed. Antibody detection of the RIP was decided upon as the most cost effective method. The RIP, Dianthin 30 from Dianthus caryophyllus (carnation), was used and expressed in bacterial and insect expression systems. The bacterial expression experiments were done using the pET expression system in BL21(DE3)pLysS cells. The expression in this system yielded recombinant protein at a very low concentration. Expression experiments were also performed in insect tissue culture with the baculovirus vector BAC-TO-BAC™.With this system the expression was also too low to be used for the production of antibodies. A Dianthin 30 specific peptide was then designed and then produced by Bio-Synthesis. This peptide was then used to raise antibodies to detect Dianthin 30. These antibodies were tested on Dianthus caryophyllus proteins. To establish if this detection method was effective to monitor the expression in plants, tobacco plants were transformed with Agrobacterium tumefaciens containing Dianthin 30 in the pART27 plant expression vector. The putative transformed plants were analysed with peR and Southern blots.
AFRIKAANSE OPSOMMING: Tans word Ribosomale-inaktiverende proteïene (RIPs) geklassifiseer as rRNA N-glikosidase wat ook polinukleotied: adenosien glikosidase aktiwiteit bevat. Daar word geglo dat RIPs anti-virale en anti-fungus eienskappe bevat, maar die meganisme van beskerming word nog nie ten volle verstaan nie. Dit is wel bewys dat die meganisme van weerstand onafhanklik is van die patogeen. Virus geinfekteerde plantselle word deur die RIP gedood om die voortplanting en verspreiding te bekamp en sodoende word weerstand bewerkstellig. Transgeniese plante wat dan 'n RIP bevat sal dus weerstandbiedend wees teen 'n wye spektrum virusse. Die hoofdoel van die breër projek, waarvan die projek deel uitmaak: is die ontwikkeling van virusbestande plante. Om die uitdrukking van die RIP in die transgeniese plante te kontroleer, moes 'n deteksie metode ontwikkel word. Die mees koste effektiewe deteksie metode is met teenliggame. Die RIP, Dianthin 30 from Dianthus caryophyllus (angelier) was gebruik vir uitdrukking in bakteriele- en insekweefselkultuur. Die bakteriele uitdrukkingseksperimente was gedoen met die pET uitdrukkings sisteem III BL21(DE3)pLysS selle. Die uitdrukking in die sisteem het slegs rekombinante proteïene gelewer in uiters lae konsentrasies. Uitdrukkingseksperimente was ook gedoen in insekweefselkultuur met die baculovirus vektor BAC-To- BACTM. Met die sisteem was die uitdrukking ook veels te laag om bruikbaar te wees vir die produksie van teenliggame. Daar is toe 'n peptied ontwerp wat Dianthin 30 kan verteenwoordig vir die produksie van teenliggame. Die teenliggame is getoets teen Dianthus caryophyllus proteïene. Om vas te stel of die deteksiemetode wel die uitdrukking van Dianthin 30 sal kan monitor, is tabak ook getransformeer met Dianthin 30. Die transformasies is gedoen met die hulp van Agrobacterium tumefaciens en die pART27 plant uitdrukkings vektor. Die plante is getoets met die polimerase ketting reaksie en Southern klad tegnieke.
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Filkowski, Jody, e University of Lethbridge Faculty of Arts and Science. "The effect of pathogens on plant genome stability". Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences, 2004, 2004. http://hdl.handle.net/10133/254.
Abstract (sommario):
Resistance (R) genes, a key factor in determining the resistance of plants, have been shown often to be highly allelic entities existing in duplicated regions of the genome. This characteristic suggests that R-gene acquisition may have arisen through frequent genetic rearrangements as a result of transient, reduced genome stability. Tabacco plants transgenic for a recombination construct exhibited reduced genome stability upon infection with a virulent pathogen (tobacco mosaic virus). The reduced genome stability manifested as an increase in recombination events in the transgene. Such increases were observed following a virulent pathogen attack. This increase in recombination was shown to be systemic and was observed prior to systemic viral movement suggesting the presence of a systemic recombination signal. Further molecular analyses revealed that specific R-gene loci experience a large frequency of rearrangements following a virulent pathogen encounter. The possible targeting of instability to R-gene regions may be controlled through epigenetic processes, in particular, DNA methylation.xiii, 119 leaves ; 29 cm.
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Van, Eeden C. (Christiaan). "The construction of gene silencing transformation vectors for the introduction of multiple-virus resistance in grapevines". Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/53764.
Abstract (sommario):
Thesis (MSc)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: Viruses are some of the most important pathogens of grapevines. There are no effective chemical treatments, and no grapevine- or other natural resistance genes have been discovered against grapevine infecting viruses. The primary method of grapevine virus control is prevention by biological indexing and molecular- and serological screening of rootstocks and scions before propagation. Due to the spread of grapevine viruses through insect vectors, and in the case of GRSPaV the absence of serological screening, these methods of virus control are not always effective. In the past several methods, from cross-protection to pathogen derived resistance (PDR), have been applied to induce plant virus resistance, but with inconsistent results. In recent years the application of post-transcriptional gene silencing (PTGS), a naturally occurring plant defense mechanism, to induce targeted virus resistance has achieved great success. The Waterhouse research group has designed plant transformation vectors that facilitate specific virus resistance through PTGS. The primary focus of this study was the production of virus specific transformation vectors for the introduction of grapevine virus resistance. The Waterhouse system has been successfully utilised for the construction of three transformation vectors with the pHannibal vector as backbone. Each vector contains homologous virus coat protein (CP) gene segments, cloned in a complementary conformation upstream and downstream of an intron sequence. The primary vector (pHann-SAScon) contains complementary CP gene segments of both GRSPaV and GLRaV-3 and was designed for the introduction of multiple-virus resistance. For the construction of the primary vector the GRSPaV CP gene was isolated from RSP infected grapevines. A clone of the GLRaV-3 CP gene was acquired. The second vector (pHann- LR3CPsas) contains complementary CP gene segments of GLRaV-3. The third vector (pHann-LR2CPsas) contains complementary CP gene segments of GLRaV-2. The cassette containing the complementary CP gene segments of both GRSPaV and GLRaV-3 was cloned into pART27 (pART27-HSAScon), and used to transform N tabacum cv. Petit Havana (SRI), through A. tumefaciens mediated transformation. Unfortunately potential transformants failed to regenerate on rooting media; hence no molecular tests were performed to confirm transformation. Once successful transformants are generated, infection with a recombinant virus vector (consisting of PYX, the GFP gene as screenable marker and the complementary CP gene segments of both GRSPaV and GLRaV-3) will be used to test for the efficacy of the vectors to induce resistance. A secondary aim was added to this project when a need was identified within the South African viticulture industry for GRSPaV specific antibodies to be used in serological screening. To facilitate future serological detection of GRSPaV, the CP gene was isolated and expressed with a bacterial expression system (pETI4b) within the E. coli BL2I(DE3)pLysS cell line. The expressed protein will be used to generate GRSPaV CP specific antibodies.
AFRIKAANSE OPSOMMING: Virusse is van die belangrikste patogene by wingerd. Daar bestaan geen effektiewe chemiese beheer nie, en geen wingerd- of ander natuurlike weerstandsgene teen wingerdvirusse is al ontdek nie. Die primêre metode van beheer t.o.v. wingerdvirusse is voorkoming deur biologiese indeksering, en molekulêre- en serologiese toetsing van onderstokke en entlote voor verspreiding. As gevolg van die verspreiding van wingerdvirusse deur insekvektore, en in die geval van GRSPa V die tekort aan serologiese toetsing, is dié metodes van virusbeheer nie altyd effektief nie. In die verlede is metodes soos kruis-beskerming en patogeen-afgeleide weerstand (PDR) gebruik om virusweerstand te induseer, maar met inkonsekwente resultate. In onlangse jare is post-transkripsionele geenonderdrukking (PTGS), 'n natuurlike plantbeskermingsmeganisme, met groot sukses toegepas om geteikende virusweerstand te induseer. Die Waterhouse-navorsingsgroep het planttransformasievektore ontwerp wat spesifieke virusweerstand induseer d.m.v. PTGS. Die vervaardiging van virus spesifieke tranformasievektore vir die indusering van wingerdvirusweerstand was die primêre doelwit van hierdie studie. Die Waterhouse-sisteem was gebruik vir die konstruksie van drie transformasievektore, met die pHannibal vektor as basis. Elke vektor bevat homoloë virus kapsiedproteïen (CP) geensegmente, gekloneer in 'n komplementêre vorm stroom-op en stroom-af van 'n intronvolgorde. Die primêre vektor (pHann-SAScon) bevat komplementêre CP geensegmente van beide GRSPaV en GLRaV-3, en was ontwerp vir die indusering van veelvoudige-virusweerstand. Die CP-geen van GRSPa V was vanuit RSP-geïnfekteerde wingerd geïsoleer, vir die konstruksie van die primêre vektor. 'n Kloon van die GLRa V-3 CP-geen was verkry. Die tweede vektor (pHann-LR3CPsas) bevat komplementêre CP geensegmente van GLRaV-3. Die derde vektor (pHann-LR2CPsas) bevat komplementêre CP geensegmente van GLRa V-2. Die kasset bestaande uit die komplementêre CP geensegmente van beide GRSPaV en GLRaV-3, was gekloneer in pART27 (pART27-HSAScon), en gebruik om N tabacum cv. Petit Havana (SRI) te transformeer d.m.v. A. tumefaciens bemiddelde transformasie. Ongelukkig het potensiële transformante nie geregenereer op bewortelingsmedia nie; gevolglik was geen molekulêre toetse gedoen om transformasie te bevestig nie. Na suksesvolle transformante gegenereer is, sal infeksie met 'n rekombinante-virusvektor (bestaande uit PYX, die GFP geen as waarneembare merker en die komplementêre CP geensegmente van beide GRSPa V en GLRa V-3) gebruik word om die effektiwiteit van die vektore as weerstandsinduseerders te toets. 'n Sekondêre doelwit is by die projek gevoeg toe 'n behoefte aan GRSPaV spesifieke teenliggame binne die Suid-Afrikaanse wynbedryf geïdentifiseer is, vir gebruik in serologiese toetsing. Om toekomstige serologiese toetsing van GRSPa V te bemiddel, was die CP-geen geïsoleer en in 'n bakteriële uitdrukkingsisteem (PETI4b) uitgedruk, in die E. coli BL21(DE3)pLysS sellyn. Die uitgedrukte proteïne sal gebruik word vir die vervaardiging van GRSPa V CP spesifieke antiliggame.
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Ntushelo, Khayalethu. "Comparative studies on genetic variability and fungicide resistance in Tapesia yallundae". Thesis, Stellenbosch : Stellenbosch University, 1998. http://hdl.handle.net/10019.1/55834.
Abstract (sommario):
Thesis (MScAgric)--Stellenbosch University, 1998.ENGLISH ABSTRACT: Eyespot is an important disease of spring wheat (Triticum aestivum L.). Four species of Ramulispora are associated with this disease, of which Tapesia yallundae and T. acuformis. are common. This thesis investigates the broader subjects of genetic variability, reproductive dynamics and fungicide resistance in Tapesia yallundae. Each of the chapters treats specific but related topics. T. yallundae, which is the only species thus far reported from South Africa, has been associated with yield losses of up to 50%. To enable the implementation of more accurate and effective control measures, understanding the dynamics of reproduction and the genetics of the pathogen is of utmost importance. Of the many plant disease control measures such as cultural practices, sanitation, biological control, etc., fungicide application is the most commonly resorted to measure in eyespot control. This thesis investigates the broader subjects of genetic variability, reproductive dynamics and fungicide resistance of Tapesia yallzll7dae. Fungicide application, however, is not without problems. The pathogen can build up resistance to fungicides. The most commonly used fungicides in eyespot control include the benzimidazole carbendazim, triazoles such as flusilazole, tebuconazole, propiconazole, bromuconazole, flutriafol, fenbuconazole, triademinol, and the imidazole, prochloraz. Cases of resistance to the groups listed above have been reported. Frequent monitoring for resistance is thus crucial to prevent wastage of fungicide and unnecessary impregnantation of the environment with potentially ineffective chemicals. In chapter 2 of this thesis 300 isolates of T. yallundae from 15 fields were evaluated for resistance against carbendazim, flusilazole, tebuconazole, propiconazole, bromuconazole, flutriafol and fenbuconazole. These results indicated that to some triazoles, such as fenbuconazole, a high level of resistance was already present in field populations. In a sexually reproducing fungus such as T. yallundae, knowledge pertaining to its ability to pass resistance factors to offspring is equally important. Mating studies were, therefore, also conducted with parental strains that showed signs of triazole resistance. Three generations were subsequently tested for resistance to five triazoles, namely flusilazole, tebuconazole, propiconazole, bromuconazole and flutriafol. Results of this study showed variable sensitivity in progeny, which indicated quantitative inheritance of resistance to triazoles. Although the sexual stage has not yet been observed in the field in South Africa, this knowledge lays the foundation for the long-term understanding of the population dynamics of the fungus. The ability of a heterothallic ascomycete population to reproduce sexually is dependent on the availability of its two mating types, MATI-I and MATI-2, their distribution, and female fertility amongst other factors. In the UK. the teleomorph is commonly observed in the field, which is in contrast to the situation in South Africa, where it has only been induced in the laboratory. A comparative study between the South African and the UK. populations was therefore undertaken. Isolates representative of the two populations were mated with tester strains as both sperm recipients and as sperm donors. This allowed the percentage of hermaphrodites to be determined. No difference in terms of female fertility was observed between the South African and the UK. populations, with both populations showing low effective population numbers. These data suggested, therefore, that the teleomorph would also occur more frequently in South Africa if the climate was more indusive to its development. The overall results of this study indicated that eyes pot could still be controlled by means of fungicide application in South Africa. Although a shift in sensitivity was observed towards fenbuconazole and flusilazole, no resistance was detected towards carbendazim. The latter might be due to the absen<.:eof the sexual stage in the field, coupled by the monocyclic nature of the pathogen and sensible fungicide regimes. The absence of T. acujormis makes the disease situation less complicated in terms of fungicide application and management. Continuous surveys will have to be conducted, however, to monitor this situation in future.
AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die genetiese variasie, reproduksie dinamika en fungisied weerstand in Tapesia yallundae. Elke hoofstuk handel oor spesifieke maar verwante onderwerpe. Oogvlek is 'n belangrike siekte van lentekoring (Triticum aestivum L.). Vier spesies van Ramulispora word geassosieer met die siekte, waarvan Tapesia yallundae en T. acuformis mees algemeen voorkom. T. yallundae, wat tans die enigste spesie is wat in Suid-Afrika aangeteken is, het al verliese van tot 50% veroorsaak. Om meer akkurate en effektiewe beheermaatreels te implementeer, is dit noodsaaklik om die oorlewingsdinamika van die patogeen te verstaan. Van al die siektebeheermaatreels soos kulturele praktyke, sanitasie, biologiese beheer ens., bly fungisiedbehandeling die mees algemene maatreel vir die beheer van oogvlek. Fungisiedtoediening het egter ook verskeie probleme. Die patogeen kan weerstand opbou teen die fungisied. Die mees algemene fungisiedes wat vir oogvlekbeheer aangewend word sluit onder meer die benzimidasool karbendazim in, triasole soos flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol, fenbukonasool, triadimenol, en die imidasool, prochloraz. Weerstand is egter reeds teen hierdie middels bekend. Gedurige monitering vir weerstand is dus krities om die vermorsing van fungisied en besoedeling van die omgewing met oneffektiewe middels te beperk. In hoofstuk 2 van hierdie manuskrip word 300 isolate van T. yallundae van 15 lande geevalueer vir weerstand teenoor karbendazim, flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol en fenbukonasool. Resultate dui daarop dat teen sommige van hierdie triasole, soos bv. fenbukonasool, daar reeds 'n hoe vlak van weerstand teenwoordig was in veldpopulasies. In 'n seksueel reproduserende fungus soos T. yalluJ1dae, is dit noodsaaklik om te bepaal wat sy vermoe is om weerstandbiedenheid aan die nageslag oor te dra. Om die rede is paringstudies ook op ouers wat tekens van weerstand teenoor triasole getoon het uitgevoer. Drie generasies was gevolglik getoets vir weerstand teenoor vyf triasole, naamlik flusilasool, tebuconasool, propikonasool, brumukonasool en flutriafol. Resultate van die studie het 'n variasie in sensitiwiteit van die nageslag getoon, wat op 'n kwantitatiewe oorerwing van weerstand teen £riasole dui. Alhoewel die teleomorf nog nie in lande in Suid-Afrika opgemerk is nie, Ie hierdie kennis die fondament vir die langtermyn vertolking van die populasie dinamika van hierdie fungus. Die vermoe van 'n heterotalliese askomiseet populasie om seksueel voort te plant is afhanklik van die beskikbaarheid van sy twee paringstipes, MATI-I en MATl-2, hul verpreiding, vroulike vrugbaarheid en ander faktore. Alhoewel die teleomorf algemeen in lande in die Verenigde Koninkryk opgemerk word, is dit in kontras met die situasie in Suid-Afrika, waar hierdie stadium nog slegs in die laboratorium gelnduseer kon word. 'n Studie is dus onderneem om die Suid-Afrikaanse en V.K. populasies met mekaar te vergelyk. Isolate van die twee populasies is dus gepaar met paringsisolate as beide sperm ontvangers en sperm donors. Hierdie prosedure het dit moontlik gemaak om die persentasie hermafrodiete te bepaal. Geen verskille in vroulike fertiliteit is tussen die Suid-Afrikaanse en V.K. populasies bespeur nie, en beide populasies het ook 'n lae effektiewe populasie getal getoon. Hierdie data het dus voorgestel dat die teleomorf ook meer algemeen in Suid-Afrika sou voorkom as die klimaat meer geskik was vir teleomorf vormmg. Die resultate van hierdie studie het tot die slotsom gelei dat oogvlek steeds deur fungisiedbehandeling in Suid-Afrika beheer kan word. Alhoewel daar 'n merkbare verskuiwing in sensitiwiteit teenoor fenbukonasool en flusilasool was, was geen weerstand teenoor karbendazim waargeneem nie. Laasgenoemde kan dalk toegeskryf word aan die afwesigheid van die teleomorf in die veld, gekombineer met die monosikliese natuur van die patogeen en gebruik van alternerende fungisiedes. Die afwesigheid van T. acuformis maak die plaaslike siektetoestand minder gekompliseerd in terme van fungisied aanwending en bestuur. Voortdurende opnames sal egter uitgevoer moet word om hierdie situasie ook in die toekoms te monitor.
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Blignaut, Marguerite. "The molecular and biological characterisation of ORF5 of three South African variants of Grapevine Vitivirus A". Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2421.
Abstract (sommario):
Thesis (MSc (Genetics))--University of Stellenbosch, 2009.Grapevine Vitivirus A (GVA), genus Vitivirus, family Flexiviridae is a well characterised single-stranded RNA virus that has been implicated in the grapevine diseases, Kober stem grooving and Shiraz disease. The virus infects both its host, Vitis vinifera and the experimental model plant, Nicotiana spp.. Biological studies performed on the virus in its herbaceous host, Nicotiana benthami- ana, revealed that many divergent variants of the virus exists in South Africa and can induce di erent symptoms in the model plant. Further molecular analysis divided the variants into three molecular groups based on molecular heterogeneity and nucleotide identity. The establishment of an infectious full-length cDNA clone of GVA contributed towards the elucidation of gene functions for 4 of the 5 open reading frames (ORF's), and indicated ORF5 as the pathogenicity determinant within the genome. Further studies also showed that ORF5 encodes for a nucleic acid binding protein that exhibits suppression activity of a plants' natural virus silencing mechanism. Many proteins that have previously been identi ed as the pathogenicity determinant within a viral genome have been found to encode for suppression activity. Although suppression activity has been elucidated within the ORF5 of the Italian cDNA clone of GVA, IS 151, no such study has yet been performed on the divergent South African variants of GVA. Three variants, GTR1-1, GTR1- 2 and GTG11-1, which represent each of the molecular groups (Group III, II and I), were selected for this study. The aim of this study was to visually elucidate suppression activity of RNA transgene silencing by the ORF5's of GTR1-1, GTR1-2 and GTG11-1 in a transient expression assays in transgenic N. benthamiana (line 16c). Pathogenicity studies for these variants were also performed. The ORF5 of the infectious full-length clone, GVA118, which can also serve as an expression vector, was deleted and provided with restriction enzyme sites into which the respective ORF5s and the marker genes, GFP and GUS could be cloned directionally. Infectivity, symptom development and systemic movement were compared between the di erent full length clones after co-in ltration in N. benthamiana. Preliminary results obtained in this study failed to visually indicate any suppression activity encoded by the ORF5 of GTR1-1, GTR1-2 and GTG11-1. The deletion of ORF5 within GVA118 was successful and rendered the infectious full length clone asymptomatic. Directional cloning of the ORF5 of GTR1-1 into the unique restriction enzymes provided previously, resulted in much milder symptoms than those observe for GTR1-2 and GTG11-1. No GFP and GUS accumulation could be detected. This study has established an infectious full-length cDNA clone, pBINSN-e35SGVA118 ORF5-1-1-pA, that can possibly induce much milder symptoms in the herbaceous host, N. benthamiana. This construct can be further characterised as a possible expression vector of foreign proteins in herbaceous hosts and grapevine.
10
Behjatnia, Seyyed Ali Akbar. "Characterisation of DNA replication of tomato leaf curl geminivirus /". Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09ACP/09acpb419.pdf.
11
Galagedara, Nelomie Nayanathara. "Identification of Quantitative Trait Loci for Resistance to Tan Spot in Durum Wheat". Thesis, North Dakota State University, 2018. https://hdl.handle.net/10365/28765.
Abstract (sommario):
Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is a major foliar disease on wheat. The pathosystem involves three pairs of necrotrophic effector (NE) and host sensitivity (S) gene interactions, namely Ptr ToxA-Tsn1, Ptr ToxB-Tsc2 and Ptr ToxC-Tsc1. Additionally, genetic factors conferring race-nonspecific resistance have been identified. The objectives of this study were to map tan spot resistance QTL and investigate the role of NE-S interactions in disease in durum using association and bi-parental mapping. Evaluation of a worldwide collection of durum accessions allowed identifying highly resistant nineteen lines to multiple Ptr races. Association mapping revealed genomic regions on chromosomes 1A, 2B and 3B significantly associated with resistance to tan spot, which likely correspond to Tsc1, Tsc2 and racenonspecific resistance. Using a bi-parental population derived from Ben and PI 41025, we found that ToxA-Tsn1 interaction plays no significant role in disease, instead a major race-nonspecific QTL on chromosome 5A was identified.
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Presello, Daniel A. "Studies on breeding of maize for resistance to ear rots caused by Fusarium spp. and on the occurrence of viruses in maize in eastern Canada". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38260.
Abstract (sommario):
Responses from pedigree selection for resistance to gibberella ear rot were assessed in four maize (Zea mays L.) populations, two selected after inoculation of Fusarium graminearum (Schwabe) macroconidia into the silk channel and two selected after inoculation into developing kernels. Responses were significant in both populations selected for silk resistance and in one of the populations selected for kernel resistance. Selection was more effective in later generations and genetic gains were associated with among-family selection but not with within-family selection. Results obtained here indicate that responses to selection could be more efficiently obtained by applying high selection intensities in advanced generations, by managing earlier generations as bulks and by reducing the number of plants per family. In another experiment, a wide sample of Argentine maize germplasm was evaluated for silk and kernel resistance to gibberella ear rot and to fusarium ear rot (caused by F. verticillioides (Saccardo) Nirenberg [=F. moniliforme (Sheldon)]. Several entries exhibited disease resistance in comparison with local check hybrids, particularly for fusarium ear rot, the most prevalent ear rot in Argentina. Results obtained in this study suggested the presence of general mechanisms controlling silk and kernel resistance to both diseases. In a supplementary study, viral diseases were surveyed in maize fields from the provinces of Ontario and Quebec in 1999 and 2000. Barley yellow dwarf was found in 1999. Sugarcane mosaic, maize dwarf mosaic and wheat streak mosaic were found in 2000. These diseases were not important for grain-maize planted in May, the most prevalent kind of maize crop in these provinces. Some of these diseases, such as sugarcane maize mosaic and maize dwarf mosaic were found important only in maize fields planted during or after the month of June, and this is of commercial relevance only for sweet corn.
13
Du, Preez Jacques. "The construction of an infectious clone of grapevine virus A (GV A)". Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/1012.
14
Huang, Chunyuan. "Mechanisms of Mn efficiency in barley". 1996, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phh8739.pdf.
Abstract (sommario):
Bibliography: leaves 131-153. This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels.
15
Mkhize, Thokozani M. "The detection of cherry leaf-roll nepovirus and the use of molecular markers for germplasm identification in walnuts (Juglans regia L.)". Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53624.
Abstract (sommario):
Thesis (MSc)--Stellenbosch University, 2003.ENGLISH ABSTRACT: The aim of this study was to combine two common diagnostic tools: serological kits and genetic fingerprinting to identify cherry leaf-roll nepovirus (CLRV), and to establish a marker system to characterize walnut germplasm. The detection of plant viruses is difficult. Restrictions are imposed for quarantine purposes on the importation of plant material from foreign countries. Modern techniques such as a PCR based screening method for CLRV are required to ensure material do not harbour viruses. A primer pair was designed to amplify a 430 bp non-coding homologous region. For the choice of primers, consensus sequences were considered and areas where the sequence data shared 98.5% homology, were chosen. The sensitivity of this detection method was 100-fold higher when compared to the ELISA. The PCR fragment was verified by nucleotide sequencing. AFLP technology was used to identify polymorphic fragments for 6 walnut cultivars and a rootstock, and SCARs were developed from AFLP specific bands. The AFLP technique distinguished all the walnut cultivars and the rootstock. However, conversion of AFLP fragments to SCAR markers for the development of a simple robust technique for cultivar discrimination, was not successful. Using 27 AFLP primer combinations, polymorphic fragments as high as 47.8% were scored. The reason for the lack of efficient conversion was as the result of the AFLP technique. The SCAR primers were generated from sequences internal to the AFLP primers but the specificity of the markers was in the AFLP primers not the internal sequence. In this study using AFLP, walnut cultivars were found to be closely related. The AFLP primer pairs used, provided polymorphic fragments. From these fragments, 7 SCAR markers were developed. It was expected that these SCARs derived from the AFLP markers would detect slight differences between cultivars. The Paradox SCAR marker was the only one that could divide the cultivars into two groups. When Chandler SCAR products were digested with the restriction enzyme Rsal, the same banding pattern as that of Paradox SCAR products was observed.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om twee algemene opsporingstegnieke te kombineer: serologiese toetsstelle en genetiese vingerafdrukke om cherry leaf-roll nepovirus (CLRV) te eien en om In merkersisteem te ontwikkel wat okkerneut kiemplasma kan karakteriseer. Die opsporing van plant virusse is baie moeilik. As gevolg van kwarantyn vereistes, word daar beperkinge geplaas word op die invoer van plant materiaal vanuit die buiteland. Moderne tegnieke soos hierdie een wat op PKR berus, word benodig om te verseker dat CLRV nie in plantmateriaal teenwoordig is nie. In Stel inleiers is ontwerp wat In 430 bp nie-koderende homoloë area amplifiseer. Hiervoor is konsensus volgordes bestudeer en slegs die volgordes wat 98,5% homologie getoon het, is gekies. In vergelyking met ELISA was die sensitiwiteit van hierdie deteksie metode 100 maal beter. DNA volgordebepaling is op die resulterende fragment gedoen om die PKR produk te verifieer. AFLP tegnologie is gebruik om polimorfiese fraqmente vir 6 okkerneut kultivars en 'n onderstok te identifiseer en SCARs is uit hierdie fragmente ontwikkel. Die AFLP tegniek kon tussen al die okkerneut kultivars en die onderstok onderskei. Die omskakeling van die AFLP fragmente in SCAR merkers om sodoende In eenvoudige kragtige tegniek vir kultivar onderskeiding te ontwikkel, was egter nie suksesvol nie. Met die gebruik van 27 AFLP inleier kombinasies, kon polimorfiese fragmente van so hoog as 47.8% verkry word. Die rede hoekom omskakeling onsuksesvol was lê by die aard van die AFLP tegniek. Die SCAR inleiers is ontwikkel uit volyordes intern tot die AFLP inleiers, maar die spesifisiteit van die merkers het juis in die AFLP inleiers gelê en nie in die interne volgordes nie. In hierdie studie, met die gebruik van AFLP, is gevind dat okkerneut kultivars baie naby verwant is. Die AFLP inleierstelle wat gebruik is, het polimorfiese fragmente gelewer. Uit hierdie fragmente is 7 SCAR merkers ontwikkel. Daar is verwag dat die SCARs wat uit die AFLP merkers ontwikkel is, klein verskille tussen kultivars sou opspoor. Dit was egter net die Paradox SCAR merker wat die kultivars in twee groepe kon verdeel. Restriksie ensiem vertering met Rsalop die Chandler SCAR produkte het dieselfde bandpatrone as die van die Paradox SCAR produkte gelewer.
16
Du, Min. "A greenhouse screening method for resistance to gray leaf spot in maize". Thesis, Virginia Tech, 1993. http://hdl.handle.net/10919/42953.
17
Becker, John van Wyk. "Plant defence genes expressed in tobacco and yeast". Thesis, Stellenbosch : University of Stellenbosch, 2002. http://hdl.handle.net/10019/2924.
18
Choe, Y. W. (Young Won). "DNA markers for cereal cyst nematode (Heterodera avenae Woll.) resistance gene in barley". 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phc545.pdf.
19
Choe, Y. W. (Young Won). "DNA markers for cereal cyst nematode (Heterodera avenae Woll.) resistance gene in barley / Y.W. Choe". Thesis, 1995. http://hdl.handle.net/2440/18680.
20
Vanstone, Vivien Alison. "The role of fungi and the root lesion nematode, Pratylenchus neglectus, in damaging wheat roots in South Australia / Vivien Alison Vanstone". Thesis, 1991. http://hdl.handle.net/2440/19581.
Abstract (sommario):
Includes bibliographical references (leaves 265-296).vi, 296 leaves, [14] leaves of plates : ill. (some col.), maps ; 30 cm.
Pathogens associated with root damage were investigated in the Murray Mallee region of South Australia over the 1987-1989 growing seasons. Occurence of fungal species and the root lesion nematode (Pratylenchus neglectus) was assessed, and related to the appearance and severity of symptoms on the roots. Field experiments were supplemented with innoculation tests in the glasshouse and laboratory.
Thesis (Ph.D.)--University of Adelaide, Depts. of Plant Science and Crop Protection, 1991
21
Farsi, Mohammad. "Genetic variation for tolerance and resistance to Pratylenchus neglectus / by Mohammed Farsi". 1995. http://hdl.handle.net/2440/18625.
Abstract (sommario):
Bibliography: leaves 318-347.ix, 347 [24] leaves : ill. (some col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
A major problem in the production of agricultural crops including wheat, is the damage caused by destructive plant parasitic nematodes, among these the root lesion nematode (Pratylenchus spp.) The association of P. neglectus with fungi in ceraeal root disease has been reported. Infection is associated with leaf yellowing, which reduces plant photosynthesis and grain yield. In nematode infested soil, well fertilized crops are usually less affected.
Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996?
22
Farsi, Mohammad. "Genetic variation for tolerance and resistance to Pratylenchus neglectus / by Mohammed Farsi". Thesis, 1995. http://hdl.handle.net/2440/18625.
Abstract (sommario):
Bibliography: leaves 318-347.ix, 347 [24] leaves : ill. (some col.) ; 30 cm.
A major problem in the production of agricultural crops including wheat, is the damage caused by destructive plant parasitic nematodes, among these the root lesion nematode (Pratylenchus spp.) The association of P. neglectus with fungi in ceraeal root disease has been reported. Infection is associated with leaf yellowing, which reduces plant photosynthesis and grain yield. In nematode infested soil, well fertilized crops are usually less affected.
Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996?
23
Williams, Kevin John. "Biological and genetic studies of wheat resistance to Heterodera avenae / by Kevin Williams". Thesis, 1994. http://hdl.handle.net/2440/21579.
Abstract (sommario):
Copy of author's previously published article inserted.Bibliography: leaves 60-75.
viii, 75, [40] leaves, [24] leaves of plates : ill. (some col.) ; 30 cm.
Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1995?
24
Asiedu, Robert. "A study of resistance to cereal cyst nematode (`Heterodera avenae Woll.`) located in the rye genome of triticale / by Robert Asiedu". 1986. http://hdl.handle.net/2440/21224.
Abstract (sommario):
Bibliography: leaves 133-152iv, 152 leaves, [47] leaves of plates : ill. (1 col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, 1987
25
Asiedu, Robert. "A study of resistance to cereal cyst nematode (`Heterodera avenae Woll.`) located in the rye genome of triticale / by Robert Asiedu". Thesis, 1986. http://hdl.handle.net/2440/21224.
26
Taylor, Christopher 1966. "Cytogenetic and molecular genetic markers for chromosome 6R of rye linked to CCN resistance / by Christopher Taylor". 1996. http://hdl.handle.net/2440/18939.
Abstract (sommario):
Includes bibliographies.xiv, 175, [96] leaves, [17] leaves of plates : ill. (some col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
This thesis reports on the generation of molecular tools for the analysis of chromosome 6R of rye and the application of these tools in structural analysis of 6RL. Results presented include physical and genetic maps of chromosome 6RL incorporating RFLP and PCR markers and CreR, the locus conferring resistance to cereal cyst nematode (CCN). The ability to detect small introgessions of rye chromatin in wheat is demonstrated.
Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1997
27
Mitchell, Aaron Thomas. "Genetic and molecular biological studies of annual ryegrass resistance to Anguina funesta / Aaron Thomas Mitchell". 2002. http://hdl.handle.net/2440/21972.
Abstract (sommario):
"December 2002"Corrections on back page.
Bibliography: leaves 118-129.
129 leaves : ill. ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Annual ryegrass toxicity (ARGT) occurs in grazing animals following the ingestion of seedheads of the annual ryegrass Lolium rigidum, infested with the corynetoxin-producing bacteria, Rathayibacter toxicus. Breaking the disease cycle, through the use of lines of L. rigidum resistant to the nematode Anguina funesta can be used to reduce th risk of ARGT outbreaks. In L. rigidum, resistance to A. funesta appears to be under the control of two unknown, but complementary genes. This study explored alternate approaches towards the allocation of genotype for lines of L. rigidum with respect to resistance to A. funesta.
Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2003
28
Hughes, Peter A. "Mode of action and protective effects of small basic protein toxins in transgenic plants". Phd thesis, 1997. http://hdl.handle.net/1885/145680.
29
Raisheed, Muhammad Saif-ur. "Tissue targeting signals of Tomato leaf curl virus". Thesis, 2007. http://hdl.handle.net/2440/63571.
Abstract (sommario):
The tissue and intracellular distribution of the monopartite Tomato leaf curl virus (TLCV) was investigated by in situ hybridization. contrary to the previous understanding of geminiviral localization, single stranded (SS) DNA of TCLV accumulated in the cytoplasm. TCLV ssDNA was also found in the nucleus, as were levels of replicative form doubl-stranded (ds)DNA.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2007
30
Gilbert, Brian M. "Characterization of the response mediated by the plant disease susceptibility gene LOV1". Thesis, 2012. http://hdl.handle.net/1957/34284.
Abstract (sommario):
Victoria blight, caused by fungus Cochliobolus victoriae, is a disease originally described on oats and recapitulated on Arabidopsis. Victoria blight is used as a model plant disease that conforms to an inverse gene-for-gene interaction. C. victoriae virulence is dependent upon its production of victorin, a host-specific toxin that induces programmed cell death in sensitive plants. In oats, victorin sensitivity and disease susceptibility is conferred by the Vb gene, which is genetically inseparable from the Pc-2 crown rust resistance gene. In Arabidopsis, victorin sensitivity and disease susceptibility is conferred by the LOCUS ORCHESTRATING VICTORIN EFFECTS 1 (LOV1) gene which encodes a NB-LRR protein, a type of protein commonly associated with disease resistance. LOV1-mediated cell death occurs when victorin binds Thioredoxin-h5 (TRX-h5) and LOV1 appears to "guards" TRX-h5. Together, these results suggest C. victoriae causes disease by inducing a resistance response.
The work presented here aimed to determine if the response mediated by LOV1 is functionally related to a resistance response. We genetically characterized the response mediated by LOV1 with virus-induced gene silencing. We determined SUPPRESSOR OF THE G2 ALLELE OF SKP1 (SGT1), a gene required for the function of many resistance genes, is required for victorin sensitivity and involved in LOV1 protein accumulation. We screened a normalized library and identified six genes that suppressed victorin-mediated cell death and cell death induced by expression of the RESISTANCE TO PERONOSPORA PARASITICA PROTEIN 8 (RPP8) resistance gene: a mitochondrial phosphate transporter, glycolate oxidase, glutamine synthetase, glyceraldehyde 3-phosphate dehydrogenase and the P- and T-protein of the glycine decarboxylase complex. Silencing the latter four also inhibited cell death induced by the expression of an autoactive form of the resistance gene PTO, and reduced PTO-mediated resistance to Pseudomonas syringae pv. tabaci. These results provide evidence that victorin-mediated cell death is functionally similar to a resistance response, further supporting the hypothesis that a resistance response is exploited by C. victoriae for pathogenesis in Victoria blight.
Resistance function of LOV1 was evaluated by observing Pseudomonas syringae pv. tomato virulence upon LOV1 activation. The LOV1 response pathway in Arabidopsis was adapted to activate upon infection with Pseudomonas syringae pv. tomato expressing the type III-dependent effector protein AvrRpt2, a well-characterized protease. We developed a construct to express a beta-glucuronidase (GUS) and TRX-h5 fusion protein separated by an AvrRpt2 proteolytic cleavage site, in which GUS sterically inhibits TRX-h5 function in LOV1-mediated cell death. The fusion is cleaved upon infection by P. syringae pv. tomato expressing avrRpt2, thereby leading to TRX-h5-mediated activation of LOV1 in the presence of victorin. However, when this strain was inoculated with victorin into transgenic LOV1 trx-h5 plants expressing the GUS/TRX-h5 fusion protein, no decrease in pathogen virulence was observed. Technical shortcomings likely prevented observable LOV1 resistance function.
���Graduation date: 2013
Access restricted to the OSU Community at author's request from Oct. 9, 2012 - Oct. 9, 2013
31
"Disease resistance related genes co-regulated in bacterial leaf blight near isogenic lines, Xa2, Xa12 and Xa14". 2004. http://library.cuhk.edu.hk/record=b5891981.
Abstract (sommario):
Shuk-man Chow.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references (leaves 171-186).
Abstracts in English and Chinese.
Thesis committee --- p.i
Statement --- p.ii
Abstract --- p.iii
Acknowledgement --- p.viii
General abbreviations --- p.x
Abbreviations of chemicals --- p.xi
List of figures --- p.xii
List of Tables --- p.xiii
Table of contents --- p.xv
Chapter 1. --- Literature review
Chapter 1.1. --- General introduction to rice disease --- p.1
Chapter 1.1.1. --- Pathogenesis of Bacterial Leaf Blight (BLB) --- p.1
Chapter 1.1.2. --- Pathogenesis of rice blast --- p.2
Chapter 1.1.3. --- Control of rice diseases --- p.3
Chapter 1.2. --- Plant defense mechanisms --- p.4
Chapter 1.2.1. --- Basal resistance in plants --- p.4
Chapter 1.2.2. --- Wound induced defense response --- p.5
Chapter 1.2.3. --- Pathogen induced host defense response --- p.6
Chapter 1.3. --- Structure of R gene products --- p.7
Chapter 1.4. --- Recognition between R and Avr proteins in rice --- p.8
Chapter 1.5 --- Current knowledge on Xa resistance and AvrXa avirulence protein --- p.9
Chapter 1.6 --- Current knowledge on Pi resistance and AvrPi avirulence protein --- p.10
Chapter 1.7 --- Pathogen induced signal transduction cascade --- p.12
Chapter 1.7.1. --- R gene mediated signal transduction cascade --- p.12
Chapter 1.7.2. --- Signal events of G-protein activation --- p.12
Chapter 1.7.3. --- Signaling events for the accumulation of Ca2+ in cytosol --- p.13
Chapter 1.7.4. --- Signaling events for oxidative burst --- p.14
Chapter 1.7.5. --- MAPK cascade in defense signaling --- p.15
Chapter 1.7.6. --- Transcriptional regulation of disease resistance related genes --- p.16
Chapter 1.7.7. --- Translational regulation of disease resistance related genes --- p.17
Chapter 1.8. --- Defense responses and defense related genes --- p.19
Chapter 1.8.1. --- Pathogenesis related (PR) proteins --- p.20
Chapter 1.8.2. --- Phytoalexins --- p.21
Chapter 1.9. --- Disease resistance related genes common between rice blast and BLB resistance --- p.22
Chapter 1.10. --- SA induced signal transduction pathway in rice --- p.23
Chapter 1.11. --- Important tools facilitating the identification of disease resistance related genes from BLB resistant rice lines --- p.24
Chapter 1.12. --- Hypothesis --- p.26
Chapter 1.13. --- Project objective --- p.26
Chapter 2. --- Materials and Methods --- p.27
Chapter 2.1. --- Plant Materials --- p.27
Chapter 2.2. --- Pathogen Inoculation --- p.27
Chapter 2.3. --- RNA extraction --- p.29
Chapter 2.4. --- Denaturing gel electrophoresis --- p.29
Chapter 2.5. --- Subtraction libraries construction --- p.30
Chapter 2.5.1. --- Cloning of disease resistance related genes --- p.32
Chapter 2.5.1.1. --- pBluescript II KS (+) T-vector preparation --- p.32
Chapter 2.5.1.2. --- Ligation --- p.32
Chapter 2.5.1.3. --- Transformation --- p.32
Chapter 2.5.1.4. --- Colony picking --- p.33
Chapter 2.5.1.5. --- PCR amplification of DNA inserts --- p.33
Chapter 2.5.1.6. --- Purification of PCR products --- p.34
Chapter 2.6. --- Gene chips printing --- p.34
Chapter 2.7. --- Probes synthesis and gene chips hybridization --- p.35
Chapter 2.8. --- Standard-RNAs synthesis --- p.35
Chapter 2.9. --- Data collection and analysis --- p.36
Chapter 2.10. --- Sequencing --- p.36
Chapter 2.11. --- cDNA synthesis --- p.37
Chapter 2.12. --- RT-PCR --- p.38
Chapter 2.13. --- DNA gel electrophoresis --- p.39
Chapter 3. --- Results --- p.58
Chapter 3.1. --- Construction of BLB gene chips --- p.58
Chapter 3.1.1. --- Preparation of cDNA clones for gene chips construction --- p.58
Chapter 3.1.2. --- Purification of PCR products on microtiter plate --- p.59
Chapter 3.1.3. --- Gene chips construction --- p.59
Chapter 3.1.4. --- DNA immobilization --- p.62
Chapter 3.1.5. --- Probe synthesis --- p.62
Chapter 3.1.6. --- Gene chip analysis --- p.65
Chapter 3.1.6.1. --- Scanning --- p.65
Chapter 3.1.6.2. --- Data analysis --- p.65
Chapter 3.2. --- "Identification of disease resistance related genes commonly regulated by Xa2, Xal2 and Xal4 BLB resistance loci" --- p.70
Chapter 3.2.1. --- "Signal perception, transduction and regulatory elements" --- p.71
Chapter 3.2.1.1. --- Proteins involved in reversible phosphorylation cascade --- p.71
Chapter 3.2.1.2. --- Proteins potentiate signal transduction through specific protein-protein interaction --- p.72
Chapter 3.2.1.3. --- Other signal transduction components --- p.73
Chapter 3.2.2. --- Transcriptional and translational regulatory elements --- p.74
Chapter 3.2.2.1. --- Proteins involved in transcriptional regulation --- p.74
Chapter 3.2.2.2. --- Proteins involved in post-transcriptional regulation --- p.75
Chapter 3.2.2.3. --- Proteins involved in translational regulation --- p.76
Chapter 3.2.3. --- "Oxidative burst, stress, apoptotic related genes" --- p.77
Chapter 3.2.3.1. --- Stress related proteins --- p.77
Chapter 3.2.3.2. --- Proteins involved in induction of oxidative burst --- p.78
Chapter 3.2.3.3. --- PR proteins --- p.79
Chapter 3.2.3.4. --- Proteolysis related proteins --- p.79
Chapter 3.2.4. --- Cell maintenance and metabolic genes --- p.80
Chapter 3.2.4.1. --- Antioxidant --- p.80
Chapter 3.2.4.2. --- Metabolic genes --- p.81
Chapter 3.2.4.3. --- Molecular chaperone --- p.82
Chapter 3.2.4.4. --- Cell cycle regulators --- p.82
Chapter 3.2.4.5. --- Cell wall maintenance --- p.83
Chapter 3.2.4.6. --- Proteins involved in protein transport --- p.83
Chapter 3.2.5. --- Unclassified/others --- p.84
Chapter 3.3. --- Expression analysis of disease resistance related genes --- p.88
Chapter 4. --- Discussion --- p.141
Chapter 4.1. --- Differential expression of disease resistance candidates --- p.141
Chapter 4.2. --- Disease resistance signal transduction components --- p.143
Chapter 4.2.1. --- Reversible phosphorylation cascade --- p.143
Chapter 4.2.2. --- Signal transduction potentiated by protein-protein interaction --- p.144
Chapter 4.3. --- Other signaling molecules --- p.145
Chapter 4.3.1. --- PRL1-interacting factor G --- p.145
Chapter 4.3.2. --- Vacuolar-type H+-ATPasen subunit G --- p.146
Chapter 4.4. --- Regulation of expression of disease resistance candidates --- p.146
Chapter 4.4.1. --- Transcriptional regulation of disease resistance related genes --- p.146
Chapter 4.4.1.1. --- G-box binding protein --- p.147
Chapter 4.4.1.2. --- MYB TF --- p.147
Chapter 4.4.2. --- Post-transcriptional modification of disease resistance candidates --- p.148
Chapter 4.4.2.1. --- RNA splicing factor --- p.148
Chapter 4.4.2.2. --- Glycine rich RNA binding proteins --- p.149
Chapter 4.4.3. --- Translational regulation of disease resistance related genes --- p.149
Chapter 4.5. --- Induction of oxidative burst --- p.150
Chapter 4.6. --- PR proteins --- p.151
Chapter 4.7. --- Cell maintenance --- p.152
Chapter 4.7.1. --- Protein folding --- p.152
Chapter 4.7.2. --- Protein degradation --- p.153
Chapter 4.7.3. --- ROS scavenging --- p.154
Chapter 4.7.4. --- Regulation of cell cycle --- p.154
Chapter 4.8. --- "Confirmation and profiling of disease resistance related candidates commonly regulated in Xa2, Xal2 and Xal4 BLB resistance NILs at different time points" --- p.155
Chapter 4.8.1. --- Basal resistance related genes --- p.156
Chapter 4.8.2. --- General disease resistance related genes --- p.161
Chapter 4.8.3. --- Pathogen responsive genes --- p.164
Chapter 4.8.4. --- Prediction of novel genes functions --- p.168
Chapter 4.9. --- Future prospect --- p.169
Chapter 4.10. --- Conclusion --- p.169
References --- p.171
Appendix --- p.187
32
Behjatnia, Seyyed Ali Akbar. "Characterisation of DNA replication of tomato leaf curl geminivirus / Seyyed Ali Akbar Behjatnia". Thesis, 1997. http://hdl.handle.net/2440/14766.
Abstract (sommario):
Bibliography: leaves 133-152.xi, 152 leaves : ill. (some col.), col. map ; 30 cm.
Studies biological relatedness of strains of tomato leaf curl virus and cross-interaction with the replication-associated protein requireed for DNA replication.
Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1997
33
Wilson, Ryan. "Functional studies of the Cf-9/Avr9 interaction". Phd thesis, 2003. http://hdl.handle.net/1885/151590.
34
Sow, Mounirou El-Hassimi. "Genetic diversity of Oryza species in Niger ; screening and breeding for resistance to rice yellow mottle virus (RYMV)". Thesis, 2012. http://hdl.handle.net/10413/8520.
Abstract (sommario):
Rice is a staple food in many West African countries, including Niger. However, both regional and national rice production have failed to meet demand due to several constraints, among which is the Rice yellow mottle virus (RYMV). Moreover, attempted intensification of rice cultivation and the introduction of modern cultivars are encouraging farmers towards abandoning local landraces for high yielding, but often susceptible varieties. The study was primarily oriented towards rice pre-breeding, and identifying priorities for rice breeding in Niger in relation to farmers' preferences and their environment. A secondary aim was the development and evaluation (for release at the regional level) of new breeding lines with resistance to RYMV. This study aimed to: 1) Establish farmers' perception of rice varieties as well as the main constraints on rice production in Niger and particularly those posed by RYMV; 2) Create a collection of rice species from Niger for ex- situ conservation, and to determine the phenotypic variability within this collection; 3) Determine the genetic diversity and population structure of the collection; 4) Screen the collection for resistance to RYMV, so that new sources of resistance could be detected; 5) Improve five elite varieties from West Africa for resistance to RYMV using marker-assisted selection (MAS). The germplasm collection and PRA of this study were conducted in 2008 and 2009 in Niger, while the field and the laboratory researches were conducted in 2008 and 2009 at the Africa Rice Center (AfricaRice) in Benin. For the PRA, data was obtained from a semi-structured group discussion carried out in 14 villages, individual questioning of 153 farmers and visits to farmers' field and storage facilities. The local farmers' union was the only formal seed dissemination system. Seed exchanges between farmers and the use of seeds from previous harvests were important. The RYMV and the bacterial leaf blight (BLB) were cited as the prevalent biotic stresses in the irrigated agrosystem, where the varieties IR1529-680-3 and Waihidjo were found to be the most popular. Flood, birds and hippopotamus were the most damaging agents in the lowland cropping system, and the landrace Degaulle/ D5237 was the preferred variety. Apart from the yield, farmers preferred varieties with good grain quality (milling quality and good taste), high market value, stress tolerance (drought, flood, disease, birds, rodents), and those recommended by the local farmers' association. These findings should be included in breeding goals, seed production and dissemination systems. During collection, a total of 270 rice accessions were assembled, comprising the two cultivated rice species Oryza sativa L. and O. glaberrima Steud. and its two wild relatives Oryza barthii A. Chev. and O. longistaminata Chev. et Roehr. The region of the Niger River and its tributary (the Dallol Maouri) provided the majority (80.7%) of the accessions. Apart from a few wild O. barthii accessions, the accessions found around Lake Chad and the Komadougou river (South-East) were also collected in the Niger River area. Farmers' naming and ecological classification of rice varieties was generally consistent. Three major phenotypic groups were found during the field trials, and the overall phenotypic variability of the collection (as measured by the Shannon-Weaver Diversity Index) was relatively high. There was no significant difference in diversity between the main eco-geographical zones of collection, as well as between the identified phenotypic groups, suggesting a high level of germplasm exchange between the regions in Niger.
From the collection, 264 accessions were genotyped from the collection using 18 well distributed SSR markers and two main genetic compartments were detected, comprising O. sativa subsp. indica varieties and O. glaberrima and its wild relative O. barthii and O. longistaminata. The O. sativa group in Niger was divided into irrigated and floating rice, bound by lowland rice. The wild progenitor O. barthii was widespread but without any clear genetic differentiation from O. glaberrima, probably due to the presence of admixtures within the collected samples of O. barthii. Allelic diversity was relatively high, despite the geographical distance from the centre of domestication of African rice, and the points of entry of Asian rice to Africa. The findings reflect the underuse of Niger's rice landraces genetic potential for rice breeding, given that all the "improved" varieties released during the last 25 years in Niger were clustered together on the dendrogram. The response of a set of the rice collected from Niger and some accessions from Mali to inoculation by RYMV was evaluated using five different virus isolates from Niger (3), Benin (1) and Burkina Faso (1). All rice varieties were susceptible to the disease. However, depending on the virus strain, a few O. glaberrima accessions displayed partial resistance, similar to the highly resistant TOG5681. Allelic research based on primers derived from the RYMV1 gene revealed one accession with allele rymv1-3, and two accessions with allele rymv1-4, and one accession with a different resistance gene. The implications of the finding were discussed and a strategy proposed for breeding varieties with a comprehensive resistance to RYMV.
After three generations of backcrossing, the major resistance gene of the variety Gigante was successfully introgressed into five elite rice varieties of West Africa by Marker-Assisted Backcross (MABC). The newly developed BC3F3 progenies were screened for resistance to RYMV in farmers' fields in Guinea and Mali and also under controlled conditions in a screenhouse in Benin. As shown by low virus content and level of disease incidence, low tiller number and plant height reduction, the transferred gene was fully functional in the new genetic background. Moreover, some lines also displayed a high level of resistance to rice blast (Pyricularia oryzae) and stem borer infestation in Guinea. Four of those lines are in the second year of multi-location trial in seven West African countries. Therefore, effective deployment of the newly developed varieties, coupled with good cultural practices, should reduce the damaging effects of RYMV in lowland and irrigated rice cropping systems and thereby increase the income of small scale farmers from rice cultivation.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
35
Mweshi, Mukanga. "Genetic improvement of Zambian maize (Zea mays L.) populations for resistance to ear rots and a survey of associated mycotoxins". Thesis, 2009. http://hdl.handle.net/10413/519.
Abstract (sommario):
Maize ear rots are among the most important impediments to increased maize production in Africa. Besides yield loss, they produce mycotoxins in their host whose contamination has been linked to several human and animal mycoses. The main objectives of the studies reported on in this thesis were (i) to investigate farmer perceptions of maize ear rot disease and prospects for breeding for host plant resistance in Zambia; and (ii) to establish the levels of incidence and extent of maize ear rot infection as well as the level of mycotoxins in the maize crops of smallholder farms in central and southern Zambia; (iii) to appraise the field inoculation techniques and assess them for their suitability for the Zambian environmental conditions, (iv) to determine the combining ability of Zambian maize populations for resistance to ear rot and investigate the genetic basis of this resistance; and (v) to investigate both direct and indirect responses to full-sib selection for ear rot resistance in Zambian maize populations. A participatory rural appraisal (PRA) was conducted in four communities, involving a total of 90 farmers. Participatory methods were used, such as focused group discussions, group interviews, participant scoring and ranking. Farmers ranked and scored the various constraints affecting their maize production in general and the maize ear rots in particular. Ear rots were ranked as the third most important biotic stress and it was evident that although farmers were aware of the disease, they were not aware of mycotoxins. This was reflected in the way they disposed of rotten maize: either by feeding livestock or eating it in periods of hunger. The survey of ear rots and mycotoxins was carried out in the Southern and Central Provinces of Zambia. A total of 114 farms were covered in the survey: maize samples were collected and both ear rot fungi and mycotoxins were isolated. Fusarium and Stenocarpella were the most frequently isolated fungi from smallholder farms. The levels of fumonisins on these farms ranged from 0.05 to 192 ppm, while those of aflatoxins were between 1.5 and 10.6 ppb. In 50% of the farmsteads surveyed, the mycotoxins, i.e. fumonisins and aflatoxins, exceeded the recommended FAO/WHO 1limits of 2 ppm and 2 ppb, respectively. Five field inoculation techniques namely, colonised toothpick, leaf whorl placement, ear top placement, spore suspension spray, and silk channel injection, were evaluated over three seasons in a series of experiments. It was found that the leaf whorl placement of inoculums, followed by colonized toothpick method, gave a constant ranking of genotypes across locations and years compared to the other three methods. In addition, the use of a mixture of ear rots as inoculum was as effective as its principal single species constituents. In the population diallel analysis, five broad-based maize populations were crossed in a diallel and evaluated under artificial ear rot inoculation using an inoculum mixture of three ear rot fungi, Aspergillus flavus, Fusarium verticilloides and Stenocarpella maydis at four locations in Zambia. The purpose was to estimate general (GCA) and specific combining ability (SCA) and investigate genotype x environment interaction. GCA effects were found not to be significant for disease severity but were significant for grain yield across environments. Populations with a strong GCA effect for disease severity across sites included PRA783244c3, Pop25, MMV600, and ZUCASRc2. Across sites, the F1 combinations, MMV600 x Pop25, ZUCASRc2 X Pop25, and Pop25 x PRA783244c2 had strong SCA effects for root lodging, ear drooping, husk cover and ear insect damage. In a related diallel analysis of 10 full-sib families derived from these populations, it was observed that resistant x susceptible families and their reciprocal crosses performed better than their resistant parents, suggesting an over dominant expression of resistance. Both maternal and non maternal effects were observed to be influencing resistance to ear rots. There was a preponderance influence of non-additive gene action. A response to full-sib recurrent selection was conducted in four locations in Central Zambia. Out of the 343 families created in 2005/6 season, 10% were selected from each population and recombined to create five new populations. These, with the original populations, were evaluated in four sites during the 2007/8 season. There was a net reduction in ear rot incidence and rot severity in the new synthetic population. Pop10 had the largest reduction in disease severity. The predicted gain per cycle was -4.1% and realized gain was -2.5% for disease incidence, and 0.19% and 19.4% for grain yield. Genetic variability was maintained though with low heritability estimates. Negative but at times strong association between grain yield and ear rot disease severity was detected suggesting that in general selecting for ear rot resistance would enhance grain yield in the five populations. Overall the importance of the ear rots and mycotoxins in compromising yield and health of the communities in Zambia, respectively, were confirmed and support the call to improve maize varieties for resistance to ear rots. The results indicate that the five populations could be enhanced for ear rot resistance through population improvement procedures such reciprocal recurrent selection that exploit both additive and non-additive variation. Selection might be compromised by the large genotype x environment interaction effects, and large reciprocal effects and their interaction with the environments. To enhance repeatability genotypes should be artificially inoculated, by placing the inoculum in the leaf whorl followed by colonized toothpick inoculation, and screened in many environments to identify genotypes with stable resistance to ear rots.Thesis (Ph.D) - University of KwaZulu-Natal, Pietermaritzburg, 2009.
36
Barker, Claire Louise. "An Examination of the signalling capacity of the tomato Cf-9 disease resistance protein". Phd thesis, 2002. http://hdl.handle.net/1885/148656.
37
Chakrabarti, Apratim. "Structure-function analysis of Cf-9 and Cf-9B resistance proteins from tomato (Lycopersion [i.e. Lycopersicon] esculentum Mill.)". Phd thesis, 2005. http://hdl.handle.net/1885/149669.
38
Panter, Stephen Neil. "Functional domains, expression and potential dimerisation of the Cf-9 and Cf-9B fungus resistance proteins of tomato (Lycopersicon esculentum Mill.)". Phd thesis, 2001. http://hdl.handle.net/1885/151625.
39
Huang, Chunyuan. "Mechanisms of Mn efficiency in barley / by Chunyuan Huang". Thesis, 1996. http://hdl.handle.net/2440/18731.
Abstract (sommario):
Bibliography: leaves 131-153.xiii, 153 leaves : ill. (some col.) ; 30 cm.
This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels.
Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996
40
Moodley, Vaneson. "Development of a pepper (Capsicum annuum L.) hybrid variety with resistance to potato virus Y (PVY) using molecular breeding". Thesis, 2013. http://hdl.handle.net/10413/10829.
Abstract (sommario):
Pepper (Capsicum annuum L.) is an important vegetable crop grown and consumed worldwide. Potato virus Y (PVY) is a globally economically important pathogen which significantly reduces the yield and quality of cultivated pepper. The virus is considered as a major limiting factor to the economic production of pepper in the province of KwaZulu-Natal (KZN) in the Republic of South Africa (RSA). Many applied practices to control the spread of PVY are ineffective to mitigate the losses incurred by many farming communities across the KZN province. Therefore, the objectives of this study was to determine the full genome sequence of a PVY isolate from KZN, to identify resistance alleles in commercially available pepper varieties in KZN and to develop a pepper hybrid variety with resistance to PVY using a molecular breeding strategy
The first part of the study was conducted to determine the first full genome sequence of a PVY isolate (JVW-186) infecting pepper from KZN. The complete genome sequence of JVW-186 was assembled from overlapping RT-PCR clones using MEGA 5 software. Individual ORFs were identified using the nucleotide data base NCBI and aligned using CLUSTALW. RDP4 software was used to identify recombination junctions in the sequence alignment of JVW-186. CLC Main Workbench 6 software was used to determine the nucleotide sequence similarity of recombinant and non-recombinant fragments of JVW-186 in conjunction with ten PVY parental isolates. Based on sequence data, virus morphology and the coat protein size as determined by SDS-PAGE analysis, the identity of the isolate JVW-186 was confirmed as PVY. Phylogenetic trees were constructed from all recombinant and non-recombinant segments of the sequence by the maximum likelihood method using MEGA 5 software. The full length sequence of JVW-186 consisted of 9700bp. Two ORF’s were identified at position 186 and 2915 of the sequence alignment encoding the viral polyprotein and the frameshift translated protein P3N-PIPO, respectively. RDP4 software confirmed two recombination breakpoints at position 343 and 9308 of the sequence resulting in four segments of the genome. At each recombination event, a 1021-bp fragment at the 5’
end in the region of the P1/HC-Pro protein and a 392-bp fragment in the region of the coat protein shared a high sequence similarity of 91.8 % and 98.89 % to the potato borne PVYC parental isolate PRI-509 and the PVYO parental isolate SASA-110 respectively. The non-recombinant fragment 1 clustered within the C clade of PVY isolates; however the large 7942-bp fragment 3 did not cluster within any of the clades although it shared > 80% nucleotide sequence similarity to other PVY isolates used in this study. Our results suggest that isolate JVW-186 is a novel recombinant strain of PVY that could have evolved due to the dynamics of selection.
The second part of the study aimed to evaluate different pepper lines for resistance to PVY. Two recessive alleles (pvr21 and pvr22) located on the pvr2-elF4E locus are known to confer resistance to the virus. To this end, six pepper lines were challenged with PVY infected Nicotiana tabacum cv. Xanthi leaf material using mechanical inoculation under greenhouse conditions. Each line was assessed for resistance to PVY by visual screening for disease severity and quantitative enzyme linked immunosorbent assay (ELISA) for virus load. Pepper lines were further characterized using tetra-primer ARMS-PCR (amplification refractory mutation system polymerase chain reaction) to identify and differentiate the presence of homozygous/heterozygous resistance alleles that confer PVY resistance. Evaluations revealed two resistant pepper lines (Double Up and Cecelia) and varying levels of susceptibility in the other four pepper lines challenged with PVY. The most susceptible pepper line was Benno, although high levels of susceptibility were observed in three other lines (IP, Mantenga and Excellence). The pvr2+ allele was positively identified in all the susceptible pepper lines using the T200A tetra-primer which confirms that the presence of this allele is dominant for PVY susceptibility. Double Up and Cecelia were genotyped homozygous pvr21/pvr21 and pvr22/pvr22 respectively, and remained asymptomatic throughout the trial which indicates that these alleles confer resistance to the isolate of PVY used in this study. The information generated in this study can be incorporated into breeding programs intended to control PVY on pepper in KZN.
The final part of the study focused on the development of resistant varieties as the best alternative to manage PVY diseases on pepper. Homozygous F2 pepper lines were
developed from local germplasm carrying PVY resistance genes (pvr21 and pvr22) using marker assisted selection (MAS). The F1 progeny was obtained by crossing a homozygous pvr21 (resistant) ‘Double Up’ cultivar with a heterozygous susceptible (pvr2+/pvr22) ‘Benno’ cultivar. F1 and F2 generations were assessed for the presence of PVY resistance/susceptibility alleles (pvr2+/pvr21/pvr22) at the pvr2-elF4e locus using the tetra primer amplification refractory mutation system – polymerase chain reaction (ARMS-PCR) procedure. Negative selection was carried out using the tetra-primer T200A marker to detect the pvr2+ (susceptible) allele. All F1 progeny displaying the pvr2+ allele were eliminated from further study. All 302 plants belonging to 29 F2 families expressing homozygous recessive traits were tested via mechanical inoculation for their response to PVY infection and resistance to PVY was confirmed in all selected families based on symptomatology in greenhouse house screens using double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA). These results show that ARMS-PCR can be used to successfully screen pepper genotypes for alleles that confer PVY resistance thereby contributing to the improvement of pepper production using molecular breeding approaches.Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
41
Mengesha, Wende Abera. "Genetic diversity, stability, and combining ability of maize genotypes for grain yield and resistance to NCLB in the mid-altitude sub-humid agro ecologies of Ethiopia". Thesis, 2013. http://hdl.handle.net/10413/10935.
Abstract (sommario):
Maize (Zea mays L.) is the third most important cereal crops in the world after wheat
and rice. In Ethiopia, maize remains the second largest food security crop after tef
[Eragrostis tef (Zucc.) Trotter.]. The mid-altitude, sub-humid agro-ecology (1000 to 1800
m above sea level) is the most important maize producing environment in Ethiopia.
However, productivity of maize is low, due to several biotic and abiotic constraints.
Among the biotic constraints, Turcicum leaf blight disease of maize caused by
Exserohilum turcicum Pass Leonard & Suggs shows high incidence of 95-100% and
inflicts significant grain losses in the country. Therefore, high yielding, Turcicum leaf
blight resistant and farmers-preferred maize varieties and their production technologies
should be developed and made available to growers to enhance maize production and
to achieve food security.
The objectives of this study were to: (1) assess farmer’s preferences, and production
constraints for maize in the mid-altitude, sub-humid agro-ecology of western Ethiopia,
(2) determine the genetic variability among elite maize inbred lines and select promising
parents for resistance to E. turcicum, (3) determine diversity among the elite germplasm
lines using SSR markers, (4) determine combining ability and heterosis among elite
maize inbred lines and their hybrids, and (5) investigate genotype x environment
interaction and yield stability of experimental maize hybrids developed for the midaltitude
sub-humid agro-ecology of Ethiopia.
A participatory rural appraisal (PRA) research was conducted involving 240 maize
farmers in three representative maize growing zones of western Ethiopia; West Shoa,
East Wollega and West Wollega, each represented by two districts and two subdistricts.
Maize was ranked number one both as food and cash crop by 82.9% of
respondents. Turcicum leaf blight was ranked as number one devastating leaf disease
by 46% of respondents. Breeding for improved disease resistance and grain yield,
enhancing the availability of crop input and stabilizing market price during harvest time
were recommended as the most important strategies to increase maize production by
small-scale farmers in western Ethiopia. Fifty inbred lines were evaluated for reaction to Turcicum leaf blight during the main
cropping seasons of 2011 and 2012. Inbred lines were clustered into resistant
(CML202, 144-7b, 136-a, 139-5j, 30H83-7-1, ILOO’E-1-9, SZYNA-99-F2, and 142-1-e),
and susceptible (CML197, CML464, A7033 , Kuleni C1-101-1-1, CML443, SC22-430
(63), (DRB-F2-60-1-2) – B-1-B-B-B, Pool9A-4-4-1-1-1). Inbred lines (CML312, CML445,
Gibe-1-158-1-1-1-1, CML395, and 124-b (113)) had intermediate response to the
disease. Overall, inbred lines such as CML202, 30H83-7-1, ILOO’E-1-9-1, CML312,
CML395 CML445 and 142-1-e were selected with better agronomic performance and
resistance to leaf blight for breeding. Twenty selected elite parental inbred lines were
genotyped with 20 polymorphic SSR markers. The genotypes used were clustered into
five groups consistent with the known pedigrees. The greatest genetic distance was
identified between the clusters of lines CML-202 and Gibe-1-91.
Eighteen selected inbred lines were crossed using the factorial mating scheme and 81
hybrids developed to determine combining ability effects and heterosis. Inbred lines with
high GCA effect (CML 202, CML395, 124-b (113), ILOO’E-1-9 and CML 197) were
selected as best combiners for hybrid development. Additionally five high yielding novel
single cross hybrids with grain yield of > 8 t ha-1 and high SCA effects were identified
such as CML395 X CML442, DE-78-Z-126-3-2-2-1-1 X CML442, ILOO’E-1-9-1-1-1-1-1
X CML312, X1264DW-1-2-2-2-2 X CML464 and SC22 X Gibe-1-91-1-1-1-1. These
experimental hybrids are recommended for direct production or as hybrid testers for
hybrid development.
Genotype x environment interaction (GEI) effects of 81 newly developed and three
check maize hybrids were evaluated across 10 locations in the mid-altitude sub-humid
agro-ecologies of Ethiopia. The AMMI-3 and GGE biplot models were used to determine
stability. Hybrids such as G68, G39, G37, G77, G34 and G2 were identified as the most
stable and high yielding at favorable environments such as Bako, Jima, Arsi Negelle
and Pawe in Ethiopia. The genotype and genotype by environment interaction (GGE)
biplot clustered the 10 environments into three unique mega-environments. Environment I included Bako, Jima, Asossa, Ambo, Finote Selam, Haramaya and Pawe
while environment II represented by Arsi-Negelle and environment III Areka and
Hawassa.
In general, the study identified valuable maize inbred lines with high combining ability
for breeding and novel single cross hybrids for large-scale production or as testers for
hybrid development at the mid-altitude, sub-humid agro-ecologies of Ethiopia or similar
environments in sub-Saharan Africa.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
42
Mariote, David. "Response to selection for downy mildew (Peronosclerospora sorghi) and maize streak virus resistance in three quality protein maize populations in Mozambique". Thesis, 2007. http://hdl.handle.net/10413/748.
43
Ibaba, Jacques Davy. "Characterization of potato virus Y (PVY) isolates infecting solanaceous vegetables in KwaZulu-Natal (KZN), Republic of South Africa (RSA)". Thesis, 2009. http://hdl.handle.net/10413/613.
Abstract (sommario):
Potato virus Y (PVY) is an economically important virus worldwide. In South Africa, PVY has been shown to be a major limiting factor in the production of important solanaceous crops, including potato (Solanum tuberosum L.), pepper (Capsicum annuum L.), tomato (Lycopersicon esculentum Mill.) and tobacco (Nicotiana spp). The variability that PVY displays, wherever the virus occurs, merits the study of the isolates occurring in KwaZulu-Natal (KZN) in the Republic of South Africa (RSA). This characterization will provide a clear understanding of strains/isolates from local vegetables and how they relate to the other PVY strains already identified, as well as information that can be used to manage the diseases they cause. Hence, the aim of this project was to study the biological and genetic properties of PVY isolates infecting potato, tomato and pepper in KZN. Enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies and reverse transcription polymerase chain reaction (RT-PCR) using primers specific to all PVY strains were used to detect the virus in plant material showing PVY-like symptoms collected from various locations in KZN. A total of 39 isolates (18 isolates infecting tomato, 12 infecting potato and 9 infecting pepper) were further differentiated into strains by means of ELISA using strain specific antibodies and RT-PCR using primers specific to the different strains of PVY identified around the world. All PVY isolates infecting tomato and pepper tested positive for the ordinary PVYO strain with both ELISA and RT-PCR. PVY isolates infecting potato were more diverse and comprised the PVYN, PVYNTN and PVYNWilga strains, with mixed infections noted in some cases. The biological properties were studied by mechanically inoculating Chenopodium quinoa, Nicotiana tabacum cv Xanthi, N. tabacum cv Samsun, N. glutinosa, and N. rustica with leaf extracts from plants infected with the different PVY strains detected in this study. All inoculated C. quinoa plants did not show symptoms. All tobacco plants showing symptoms were tested for the presence of PVY by means of ELISA using monoclonal antibodies targeting all strains and electron microscopy using the leaf dip technique. Not all the inoculated tobacco tested positive with ELISA. The symptoms observed were therefore divided into PVY-related and PVY non- related. PVY-related symptoms included vein clearing, mosaic chlorosis, stunting, and vein necrosis. PVY non-related symptoms included wrinkles and leaf distortions. Potyvirus-like particles of about 700 nm were observed under the transmission electron microscope (TEM) from plants showing PVY-related symptoms while rod shaped viral particles of sizes varying between 70 and 400 nm were observed from plants showing non-PVY related symptoms. A portion of the virus genome (1067 bp) covering part of the coat protein gene and the 3’ non-translated region (NTR) of three PVYO isolates infecting tomato, one PVYO isolate infecting pepper and one PVYNWilga isolate infecting potato were amplified, cloned and sequenced. The 5’ NTR, P1, HC-Pro and part of P3 regions (2559 bp) of a PVYN isolate infecting potato were also amplified, cloned and sequenced. Sequence data was compared with selected PVY sequences from different geographical locations around the world. These were available on the NCBI website and subsequently used for phylogenic analyses. The sequenced genomic regions of the PVYN isolate were found to be 99% similar to the New Zealand PVYN isolate (GenBank accession number: AM268435), the Swiss PVYN isolate CH605 (X97895) and the American PVYN isolate Mont (AY884983). Moreover, the deduced amino acid sequence comparison of the genomic regions of the PVYN isolate revealed the presence of five distinct amino acids residues. The three amino acid residues (D205, K400, and E419), which determine the vein necrosis phenotype in tobacco, were also identified. The coat protein and 3’ NTR sequences of all KZN PVYO isolates infecting pepper and tomato were closely similar to each other than to KZN PVYNWilga isolate infecting potato. The phylogenic analysis clustered the KZN PVYN isolate with the European sublineage N, PVYNWilga isolate infecting potato with the American PVYO isolate Oz (EF026074) in the O lineage and all PVYO isolates infecting tomato and pepper in a new sublineage within the O lineage. Taken together, these results point to the presence of PVY in solanaceous vegetables cultivated in KZN and they lay the foundation for the formulation of effective control measure against PVY diseases in KZN.Thesis (M.Sc.) - University of KwaZulu-Natal, Pietermaritzburg, 2009.
44
Kam, Honore. "A study of the diversity of Burkina Faso rice landraces and identification of source of resistance to rice yellow mottle virus (RYMV)". Thesis, 2011. http://hdl.handle.net/10413/8518.
Abstract (sommario):
The main goals of this study were to ascertain farmers' preferred traits in rice landraces and their perception of Rice yellow mottle virus, to collect rice landraces across Burkina Faso, investigate their genetic diversity, and to exploit this diversity in a search for varieties resistant and tolerant to RYMV, for their utilisation in rice breeding. Farmers' preferred traits, approaches to crop management, and disease perceptions were assessed using a Participatory Research Appraisal (PRA) approach. In the main rice growing regions of Burkina Faso, 330 rice landraces were collected. The agro-morphological diversity of the germplasms was evaluated in the field with 20 quantitative and 30 qualitative agro-morphological parameters. Thereafter, 22 Simple Sequence Repeat molecular markers were used to assess the genetic diversity and the population structure of the collection. Finally, the rice landraces were screened against four RYMV isolates to assess the susceptibility, tolerance and resistance of the landraces in the collection using visual assessment and Enzyme Linked Immunosorbent Assay. The PRA identified sweet taste, grain expansion when cooking, easy cooking and yield as paramount selection criteria in rural rice farming communities in Burkina Faso. Drought and disease resistance are characters that farmers wish to have in their varieties. The PRA also highlighted that farmers are conscious of RYMV disease in their fields. However, they are unaware about the epidemiology of the disease.
An agro-morphological study of the phenotypic diversity of the collection confirmed the presence of the two cultivated rice species: O. glaberrima and O. sativa. There were more O. sativa accessions than O. glaberrima landraces. There were 48 O. glaberrima and 282 O. sativa accessions in the collection. Both species were divided into four clusters, reflecting the richness of the collection. The underlying genetic diversity of the collection was confirmed by the use of 22 Simple Sequence Repeat molecular markers. The neutral markers confirmed the existence of two substructures, namely O. glaberrima and O. sativa, and the presence of admixture varieties. However, a core collection of 52 individuals was developed. This included 13 O. glaberrima and 39 O. sativa accessions. It reflects the genetic diversity of the sub-clusters present in each species. This core collection contains 89% of the allelic richness of the collection. Its small size will facilitate the maintenance and active use of diversity of germplasm in the core collection. The entire collection was utilised to search for varieties resistant and tolerant to RYMV disease. The screening of the collection with different RYMV isolates exposed the susceptibility of most of the accessions in the collection. Most of the O. sativa indica accessions were highly susceptible. However, ten O. glaberrima accessions displayed a delay of symptom expression, and moderate resistance. However, their resistance was overcome later by a particularly virulent RYMV isolate BF1. Remarkably, a single moderately resistant cultivar, BM24, showed that partial resistance and tolerance to RYMV can be found in an O. sativa variety. Serological evaluation of this local variety in comparison with the partially resistant variety, Azucena, showed that BM24 and Azucena expressed similar resistance patterns. A genetic profile of both varieties showed that both had an identical allele status at RM101, which is a marker bracketed in the same zone as the QTL12.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
45
Bucheyeki, Tulole Lugendo. "Characterization and genetic analysis of maize germplasm for resistance to northern corn leaf blight disease in Tanzania". Thesis, 2012. http://hdl.handle.net/10413/8730.
Abstract (sommario):
The majority of farmers in Tanzania have not yet adopted modern maize varieties and still
cultivate landraces and open pollinated varieties (OPVs) with low production potential and
susceptible to diseases like maize streak virus (MSV), grey leaf spot (GLS) and northern corn
leaf blight (NLB). The NLB disease is among the major causes of low yield and has been
reported in all 21 maize growing regions in Tanzania. Breeding for host plant resistance with
high yielding potential and involving the community in the breeding process is expected to
address the problem of low yield, NLB disease susceptibility and low rate of F1 hybrid adoption.
Therefore, the study was conducted to obtain additional sources of resistance to NLB disease,
high yielding cultivars with community acceptable traits adapted to Tanzanian conditions. The
main objective was to contribute to increased maize productivity in the western zone of
Tanzania. The specific objectives of this study were therefore to : 1) investigate maize
production limiting factors for smallholder farmers in western Tanzania, 2) identify farmers and
stockist perceptions, opinions and maize variety selection criteria in western Tanzania, 3)
establish NLB disease status in farmers’ fields of western Tanzania, 4) determine the genetic
relationships among landraces and assess maize landraces as sources of breeding materials,
5) determine the combining ability and heterosis for NLB disease resistance of eleven maize
inbred lines adapted to Tanzanian conditions, and 6) determine the gene action and inheritance
of resistance to NLB disease in five maize inbred lines adapted to Tanzanian conditions. The
study was conducted from 2008-2011 in three diverse environments which represent all the
maize growing regions in the country
The participatory rural appraisal (PRA) was conducted in three districts to investigate farmers’
and stockists preferred traits for maize selection in western Tanzania, determine maize
production constraints facing farmers and assess NLB disease prevalence in the same area. A
focus group of 30 farmers was selected in each of the three villages. Transect walks, wealth
ranking and historical profiles were used in an informal survey. One hundred and fifty
questionnaires were used in a formal survey. The recorded yield was only 1 t haˉ¹. Thirteen
major maize production constraints, 13 insect pests and vermin and, 11 diseases were
recorded. The NLB disease was reported to be increasing in severity in all farmers’ fields.
Farmers’ preferred traits included resistance to abiotic and biotic stresses, early maturity,
preferred milling qualities, high storage qualities and high yielding potential. Stockists mentioned
12 preferred maize variety traits which included high yielding, disease and insect pest
resistance, heavy grain, large cob size and large grain sizes. Similarity between farmers and
stockist variety preference ranking were found to exist.
The occurrence and distribution of northern leaf blight (NLB) disease study was conducted to
assess the incidence and severity of NLB disease in farmers’ fields in seven districts. The study
was conducted for two seasons. In each season, 175 fields with 5600 plants were sampled.
There were sixteen varieties grown with wide NLB disease reaction variation. Gembe, a
landrace, was among the three observed resistant varieties. The NLB disease has changed its
distribution pattern affecting all districts of the western zone. The disease incidence in season
two (2009/2010) significantly increased from season one (2008/2009) t= -3.25 (348), P= 0.001.
About 30% of both means of blight incidence and severity were recorded in the area.
Characterization and screening of maize landraces for northern leaf blight disease resistance was
conducted to determine the genetic relationships among landraces, assess maize landraces as
sources of NLB disease resistance and assess important agronomic traits for future maize
improvement. Ninety breeding materials consisting of 71 landraces and 19 commercial varieties
were evaluated. The average yield of landraces under research management was 2.3 t haˉ¹.
Landrace TZA 3075 was identified as NLB disease resistant. Yield potential, dent grain texture,
white endosperm and husk cover were important agronomic traits observed among landraces.
There were high variations in terms of morphology and NLB disease resistance among the
landraces. Five principal components contributed to 71.98 % of total variation. Clusters analysis
revealed five distinct groups of landraces. Leaves/plant, infested leaves/plant, lesion number,
lesion length, lesion width and NLB disease incidence traits highly contributed to variation and
grouping of landraces.
Combining ability analysis for northern leaf blight disease resistance was conducted to estimate
the combining ability for NLB disease resistance of 11 maize inbred lines adapted to Tanzanian
conditions, determine maternal effects which are involved in NLB disease resistance in maize
germplasm, and determine the heterosis in the F1 hybrids. A full 11 x 11 diallel cross was
performed. All top ten experimental hybrids in each of the three sites had negative midparent
heterosis for NLB disease severity. The overall mid-parent heterosis means for yield across
sites was 152%. The mean sum of squares for GCA was highly significant (P< 0.001) on
disease severity indicating additive gene action effects. Mean sum of squares for SCA were
highly significant for disease severity and yield implying non-additive gene action effects.
The mean squares for reciprocal effects were highly significant on yield and non-maternal sum
of squares had significant effect (P<0.05) on yield. The GCA contribution was high for disease
severity (91%) and lesion number (85%). Almost, all GCA effects for NLB disease resistance
were negative implying contribution to disease resistance. Due to preponderance of the additive
gene action, recurrent selection could be used to improve the resistance of inbred lines while
the non-additive gene action could be exploited in breeding for disease resistant hybrids.
Generation mean analysis of northern leaf blight disease resistance was conducted to
determine the mode of gene action involved in the inheritance of resistance to NLB disease in
five inbred lines adapted to Tanzania at contrasting environments, estimate heterosis and
heritability in five tropical inbred lines. Generation mean analysis was conducted using a six
parameter model comprising P1, P2, F1, F2, BCP1 and BCP2 generation progenies. The mean
sum of squares for environment, replication with the nested environment, generations,
generations x environment interactions were highly significant (P<0.001). The full model of
additive, dominance, additive x additive and additive x dominance epistatic effects was highly
significant (P<0.001). Nonetheless, the additive gene effects were predominant ranging
between 57% and 89% which was matched by large heritability (54%-85%). The average
degree of dominance ranged between -0.52 and 0.88 supporting observations of partial
dominance. The NLB disease severity showed a continuous distribution in all three sets for F2,
BCP1 and BCP2 populations which is an indication of quantitative nature of inheritance and
additive gene effects. The mid parent heterosis ranged from -19 to 1%. Therefore, resistance to
NLB disease could be improved through selection by exploiting the additive gene effects. The
epistatic gene effects would cause less complications because they were negligible (<25%).
The client oriented breeding for maize northern leaf blight disease resistance was carried out to
perform farmers and stockists assessment on the 110 F1 experimental maize hybrids and
compare them with breeders selection criteria. Breeders selection criteria ranked 10 top high
yielding experimental hybrids. Farmers developed 14 while stockists developed 13 selection
criteria. The most preferred hybrids by farmers were VL 05616 x CML 159, CML 159 x KS03-
0B15-47 and EB04-0A01-304 x CML 442 while stockists preferred VL 05616 x CML 395,
EB04-0A01-304 x CML 442 and VL 05616 x CML 159. Two F1 experimental hybrids EB04-
0A01-304 x CML 442 and CML 159 x CML 442 appeared in all top five ranked hybrids by
breeders, farmers and stockists. Generally, findings showed that, farmers, stockists and
breeders coincide in some selection criteria but also differ in other cases.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
46
Mhora, Terence Tariro. "Genomics of quantitative resistance to brown rust (Puccinia melanocephala) in a sugarcane breeding population". Thesis, 2012. http://hdl.handle.net/10413/10036.
Abstract (sommario):
The Sugarcane Industry contributes approximately 400 000 jobs and ZAR 8 billion annually to South Africa’s economy. Due to climate change and the subsequent threat posed by disease, these figures have been on the decline. Brown rust, a contributor to this decline is caused by the basidiomycete Puccinia melanocephala Syd. and P. Syd., which previously resulted in 50% yield losses in susceptible varieties. This highlighted the need for improved screening and breeding techniques which will result in the replacement of susceptible varieties.
The objectives of this study were to:
a) Adopt and optimise a glasshouse whorl inoculation screening technique applicable for mass screening of large populations.
b) Develop a rapid and cost effective rust resistance screening technique using detached leaves.
c)Utilise two flanking marker sets (R12H16 and 9O20-F4-PCR primers) for the rust resistance Bru1 gene in a diagnostic polymerase chain reaction (PCR) to identify rust resistant genotypes lacking Bru1 and possessing either quantitative resistance or an alternative major qualitative resistance gene.
d) Correlate rust phenotypic data to AFLP marker data for the Linkage Disequilibrium (LD2) mapping population.
e) Utilise suppression subtractive hybridization (SSH) profiling on rust challenged genotypes to discover differentially expressed genes between susceptible and resistant (susceptible Bru1 negatives taken away from resistant Bru1 negatives); and resistant genotypes (resistant Bru1 positives taken away from resistant Bru1 negatives). 4
Results from the glasshouse whorl inoculation trials showed the technique could be reliably used to screen large populations, as two independently conducted pot trials showed highly correlated rust ratings. A visually assessed detached leaf assay (DLA) was developed using selected genotypes. Chlorophyll fluorescence and SPAD readings were used in the DLA to determine the leaf photochemical efficiency (PIABS) with relation to chlorophyll content, resulting in reduced assessment time of at least two days. PCR diagnostics revealed 31% of LD2 did not possess either flanking marker, 8% had one or the other marker, and 61% had both markers. The overall rust phenotypic ratings (rating scale of 0-10) and Bru1 status of the genotypes was used to group the population, with the Bru1 negative genotypes containing all three rating categories (resistant 0-3.5; intermediate 3.51-6.5; susceptible 6.51-10); while the Bru1 positive genotypes were all resistant. The phenotypic data was correlated to AFLP data using the Pearson product-moment correlation coefficient and stepwise multiple linear regression employed to build marker based models to use for predicting non-Bru1 mediated resistance. SSH analysis was then subsequently conducted on genotypes selected on the basis of Bru1 status and AFLP correlation data. Two subtraction cDNA libraries were constructed and the cDNA inserted into electro-competent Escherichia coli cells. PCR on transformed cells revealed cDNA inserts ranging from 200- 1300bp. BLAST analysis of the cDNA sequences indicated the presence of high proportions of disease and drought stress related sequences in the libraries. Analysis of the sequences in both libraries showed that the resistant Bru1 negative genotypes contained oxidative stress related sequences which were however absent in the Bru1 positive resistant genotypes. The library comparing the Bru1 negative resistant genotypes against the Bru1 negative intermediate and susceptible genotypes showed a higher proportion of differentially expressed sequences coding for putative disease resistance proteins, highlighting their presence in the resistant genotypes. Both subtraction libraries also contained high proportions of a leucine rich repeat protein coding cDNA which contained a conserved domain homologous to that of a disease resistance protein conferring resistance to Pseudomonas syringae in Arabidopsis thaliana. The outcomes of this study will subsequently enable an improved understanding of sugarcane-rust resistance mechanisms and improved breeding and screening techniques for sugarcane by identifying SSH and AFLP markers linked to rust resistance QTLs or alternative R genes.Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
47
Mafu, Nothando Fowiza. "Marker-assisted selection for maize streak virus resistance and concomitant conventional selection for Downy Mildew resistance in a maize population". Thesis, 2013. http://hdl.handle.net/10413/10023.
Abstract (sommario):
Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila, Naude), and maize downy mildew (DM) disease caused by Peronosclerospora sorghi (Weston and Uppal) Shaw, are major contributing factors to low maize yields in Africa. These two diseases threaten maize production in Mozambique, thus the importance of breeding Mozambican maize varieties that carry resistance to these diseases. Marker-assisted selection (MAS) was employed to pyramid MSV and DM disease resistant genes into a single genetic background through simultaneous selection. Firstly, it was essential to determine the genetic diversity of MSV disease resistance in 25 elite maize inbred lines to aid in the selection of suitable lines for the introgression of the msv1 gene; and subsequently, to introduce the msv1 resistance gene cluster from two inbred lines, CM505 and CML509, which were identified as the ideal parental lines for the introgression of MSV disease resistance into a locally adapted Mozambican inbred line LP23 that had DM background resistance. Pyramiding the resistance genes by the use of simple sequence repeat (SSR) molecular markers to track the MSV gene cluster was investigated in 118 F3 progeny derived from crosses of CML505 x LP23 and CML509 x LP23. High resolution melt (HRM) analysis using the markers umc2228 and bnlg1811 detected 29 MSV resistant lines. At the International Maize and Wheat Improvement Centre (CIMMYT) in Zimbabwe, MSV disease expression of the 118 F3 progeny lines was assessed under artificial inoculation conditions with viruliferous leafhoppers and the effect of the MSV disease on plant height was measured. Thirty-seven family lines exhibited MSV and DM (DM incidence ≤50) disease resistance. Individual plants from a total of 41 progeny lines, that exhibited MSV disease severity ratings of 2.5 or less in both locations within each of the F3 family lines, were selected based on the presence of the msv1 gene based on SSR data, or field DM disease resistance, and were then advanced to the F4 generation to be fixed for use to improve maize hybrids in Mozambique for MSV resistance. Simultaneous trials were run at Chokwe Research Station in Mozambique for MSV and DM disease assessment, under natural and artificial disease infestation, respectively. Thus the MSV and DM genes were effectively pyramided. Lines with both MSV and DM resistance were advanced to the F4 generation and will be fixed for use to improve maize hybrids in Mozambique for MSV and DM resistance, which will have positive implications on food security in Mozambique. This research discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. It was concluded that a conventional maize breeder can successfully use molecular markers to improve selection intensity and maximise genetic gain.Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
48
Gichuru, Lilian Njeri. "Breeding investigations on utility of maize streak virus resistant germplasm for hybrid development in the tropics". Thesis, 2014. http://hdl.handle.net/10413/10694.
Abstract (sommario):
Maize (Zea mays L.) supports millions of livelihoods in sub-Saharan Africa (SSA) in terms of
food and feed. Production of the crop is however limited by several factors, among these, maize
streak virus (MSV) disease. Although extensively studied, MSV remains a serious problem in
SSA due to several challenges in breeding MSV resistant maize varieties. These include
integration of MSV resistant germplasm from different backgrounds, reliance on a few resistant
sources, and genotype x environment interactions. This study was designed to assess the
breeding potential of several MSV resistant lines in hybrid combinations. Understanding
architecture of genetic divergence and background of these genotypes would greatly aid in
breeding high yielding and stable MSV resistant hybrids. Experiments were conducted during
2010 to 2012 seasons in Kenya. Diallel crosses and SSR markers were used to characterize
MSV resistant maize inbred lines from three programs of CIMMYT, KARI and IITA.
In general, this study revealed that MSV is still an important problem in Kenya with high
incidence and severity levels in the farmers’ fields. The levels of MSV resistance in locally
grown hybrids needs to be improved. Farmers challenged breeders to develop new hybrids that
combine early maturing, high yield potential and MSV resistance.
The study was successful in identifying the best eight inbred lines for use in breeding new maize
hybrids with MSV resistance. The nature of gene effects was established for the first time, in
particular the role of epistasis and G x E in conditioning MSV resistance in hybrids. Results
indicate serious implications for previous models that ignored epistasis in studying MSV
resistance in maize. The inbreds Z419, S558, CML509 and Osu23i, displayed high levels of
epistasis for MSV resistance. Unless strong sources of MSV resistance, such as MUL114 and
CML509, are used, breeding resistant hybrids will require parents that carry dominant
resistance genes. The additive-dominance model was adequate to explain northern leaf blight
(NLB) resistance in hybrids, indicating fewer complications in breeding NLB resistant hybrids.
The study also reveals that SSR genetic distance data can be used to predict hybrid
performance, especially when the correct set of markers is used. Many previous studies have
not found any significant relationship between genetic distance and heterosis, due to large
G x E and use of a wrong set of markers. The diallel analysis and SSR data established the
important heterotic groups, which will be exploited for efficient development of MSV resistant
maize hybrids. These strategies will be recommended to programs that emphasize MSV
resistance in maize hybrids.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
49
"Studies on brown rust (Puccinia melanocephala) of sugarcane in South Africa". Thesis, 2009. http://hdl.handle.net/10413/2625.
Abstract (sommario):
The first serious outbreak of brown rust of sugarcane caused by Puccinia melanocephala Syd. & P. Syd. was reported in India in 1907. It was first reported in South Africa (SA) in 1941 on the variety Co301 and is now present in almost all the sugarcane growing areas of the world. In SA, it is now described as an important disease of sugarcane, causing yield losses of up to 26% in susceptible varieties. Within the SA sugar industry, rust is controlled through the use of resistant varieties as it is the most economical method of control. However, most of the newer varieties that are being released have an intermediate resistance rating for rust. An integrated management approach for the control of rust is therefore being investigated. Aspects investigated in this study included environmental conditions required for development of the disease i.e. epidemiology, the use of silicon (Si) as a cultural control method against brown rust and identification of gene sequences expressed in response to brown rust infection.
For the epidemiology study, inoculated plants were incubated in a dew chamber at different temperatures and leaf wetness periods. The choice of leaf wetness duration and temperature was based on urediniospore germination studies. The optimum temperature for urediniospore germination and disease development at > 98% relative humidity was found to be between 20 and 25°C with nine hours of leaf wetness. Silicon has been shown to reduce the incidence of diseases and pests in a number of crops. The ability of sugarcane to accumulate Si and the location of Si deposition was established using two uptake and deposition trials. Different concentrations of Si were applied to the plant and accumulation in the roots, stalks, old leaves and young leaves was determined using inductively coupled plasma optical emission spectrometry, with accumulation found to be roots > old leaves > stalks > young leaves. Silicon deposition in the leaves was determined using energy dispersive X-ray mapping on freeze dried specimens and significant differences were found between the upper epidermis, lower epidermis and mesophyll with the most Si being deposited in the lower epidermis. For
disease severity, plants were naturally infected with rust and rated weekly. A significant decrease in disease severity and area under disease progress curve was noted when the Si concentration increased, indicating that Si has potential in reducing rust incidence. Currently, the most reliable and economical method of managing brown rust is with the use of resistant varieties. Identification of resistance within breeding lines is therefore important. For this part of the study, suppression subtractive hybridization was used as a tool to identify differentially expressed genes between a susceptible and resistant variety and a susceptible and intermediate variety, in response to brown rust infection. Two efficient subtracted cDNA libraries were generated and differentially expressed sequences were identified within each library. The results of this study show potential for the development of molecular markers which could be used for the early identification of brown rust resistance during the breeding process. This study forms a firm basis on which an integrated management strategy, for the management of brown rust in the SA sugar industry, could be designed. The cDNA sequences identified could be further investigated and used to develop molecular markers to select for rust resistant varieties, the epidemiology results together with further field data could be used to develop a disease prediction model and Si has potential in the field to reduce brown rust severity.Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.
50
Chikoti, Patrick Chiza. "Development of cassava (Manihot esculenta Crantz) cultivars for resistance to cassava mosaic disease in Zambia". Thesis, 2011. http://hdl.handle.net/10413/8402.
Abstract (sommario):
Despite the increasing number of farmers growing cassava in Zambia, yield per hectare has
remained low at 5.8 t ha-1. The major constraints contributing to low yields are pests and
diseases of which cassava mosaic disease (CMD) caused by East Africa cassava mosaic virus
(EACMV), Africa cassava mosaic virus (ACMV) and South Africa mosaic virus (SACMV) is the
most important. Breeding of cassava is restricted by limited information on viruses and
associated satellites, and farmer preferences. Most of the farmers cannot manage to institute
control strategies that require buying of chemicals. The most feasible option remains improving
existing cultivars through resistance breeding. The study therefore was conducted to: i)
establish farmers’ perception and knowledge of CMD; ii) to identify viruses of cassava occurring
in Luapula province; iii) evaluate the performance of local and improved cultivars for agronomic
traits; iv) evaluate the performance of F1 progenies for CMD resistance; and v) determine
general combining ability and specific combining ability for CMD resistance. The studies were
carried out between 2008 and 2011 at different locations in Zambia. The information generated
was important in formulating a local breeding strategy for CMD resistance.
A participatory rural appraisal and a structured survey was conducted in Mansa, Samfya and
Mwense districts in Luapula province involving farmers to ascertain farmers’ perceptions of
CMD. The results of the study showed that the majority of the respondents (97.6%) were not
aware of CMD. Most of the farmers grew landraces on small pieces of land. Although, the
cultivars (local and improved) were widely grown, they were susceptible to CMD. The farmers
preferred cultivars with high yielding and early bulking characteristics among others.
A CMD survey conducted between April and May 2009 in Samfya, Mansa, Mwense,
Kawambwa and Nchelenge districts in Luapula province established East Africa cassava
mosaic virus (EACMV), and Africa cassava mosaic virus (ACMV) as the most prominent viruses
in the area. Symptoms of satellites were also observed in the farmers’ fields in most of the areas
visited. Satellite II and III were detected in leaf samples. The CMD incidence (59.1%) and
severity (2.4) was moderate across the districts surveyed. The CMD symptoms on the cassava
plants were variable with plants showing mild and severe symptoms characterised with
narrowing and reduced leaf blades. The transmission of CMD infections was mainly through
cuttings rather than via whitefly infection which means that most of the planting materials used
by the farmers were infected.
Evaluation of cassava cultivars for CMD resistance was conducted in 2009/2010 and 2010/11
seasons at Mansa Research Station in Luapula province using a 4 x 4 α lattice design. Both
introduced and locally grown cultivars had significant (P<0.001) differences in their reaction to
CMD. Bangweulu, Namuyongo, Kalaba, Chikula, Mwakamoya, Chila7 and Chila11 were the
most susceptible genotypes. Mweru, Tanganyika, and Nalumino were moderately tolerant to
CMD.
Eight hundred F1 genotypes developed using a North Carolina II mating design were evaluated
in a 4 x 5 α lattice design in 2011 at Mansa Research Station, Luapula province to determine
combining ability for reaction to CMD, yield and yield components. The plants were harvested 7
months after planting (MAP). Significant (P<0.001) general combining ability and specific
general combining ability were recorded for CMD. The SCA effects were more important for
CMD than GCA effects suggesting that non-additive gene action was more prominent than the
additive gene action in determining CMD reaction. Parent lines with desired significant, negative
GCA effects for reaction to CMD were Bangweulu, Kampolombo, Nalumino and TME2.
In general, the survey and participatory rural appraisal established CMD as one of the
constraints to cassava production and created a basis for the research study. The findings
indicate opportunities that exist in creating genotypes with tolerance to CMD. The study
identified cassava lines with resistance to CMD. The lines that expressed the above trait should
be selected and tested further for release to the farmers in Zambia. Since the clonal evaluation
trial was harvested at 7 MAP, there is need to investigate further for earliness trait in best
performing lines in different locations.Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.