Made available in DSpace on 2017-07-25T19:29:54Z (GMT). No. of bitstreams: 1 Jose de freitas.pdf: 3442616 bytes, checksum: 5906555f02beebcd88aa23986b2f4865 (MD5) Previous issue date: 2012-07-20 / The main diseases occurring in soybean (Glycine max) in Brazil have a great damage potential, requiring additional expenses to control through measures available today, highlighting the fungicides spray. The objective of this study was to evaluate the effect of fungicides spray at different growth stages of soybean, cultivar CD 206, and verify the relation between the severity of powdery mildew (Erysiphe diffusa) and of asian soybean rust (Phakopsora pachyrhizi), on yield components. Two experiments were conducted on field one in Arapoti (experiment I) and another in Ponta Grossa (experiment II) in the region of Campos Gerais, Paraná. In both local the fungicide was sprayed trifloxystrobin + cyproconazole, in a rate of 56,4 + 24,0 mL a. i. ha-1, was added ajduvante methyl ester of soybean oil in a rate of 360,0 mL a. i. ha-1. The experimental design was randomized blocks with four replications. The treatments in a total of ten, were composed of fungicides spray in different numbers and growth stages: Experiment I, 1. Control (no spray); 2. R5.2; 3. R4 + R5.2; 4. R2 + R4 + R5.2; 5. V9 + R2 + R4 + R5.2; 6. V6 + V9 + R2 + R4 + R5.2; 7. V6 + V9 + R2 + R4; 8. V6 + V9 + R2; 9. V6 + V9 and 10. V6. Experiment II, 1. Control (no spray); 2. R5.1; 3. R3 + R5.1; 4. R1 + R3 + R5.1; 5. V8 + R1 + R3 + R5.1; 6. V5 + V8 + R1 +R3 + R5.1, 7. V5 + V8 + R1 + R3; 8. V5 + V8 + R1; 9. V5 + V8 and 10. V5. The treatments were composed in order to generate and compare different percentages of severity of powdery mildew and asian soybean rust obtained by the period of protection or exposure to these diseases. The severity of powdery mildew was evaluated experiment I growth stages R2, R4, R5.3 and R5.5 and in experiment II in R1, R3, R5.2, R5.3 and R5.5. The severity of asian soybean rust was evaluated experiment I in growth at stages R5.3, R5.4, R6 and R7.1, and in experiment II R5.1, R5.2, R5.3, R5.5 and R6. With the data of severity it was calculated the area under the disease progress curve. Were also evaluated defoliation, yield and their components (number of pods per plant, number of grains per plant, grain weight per plant and thousand grain weight). Powdery mildew showed low severity. The asian soybean rust was the disease predominant in high severity, with high damage potential. The fungicides spray reduced disease severity and there was a negative linear relationship with the yield. Long periods without protection of plants allowed rapid reinfection of powdery mildew and spray erradicativas resulted in low efficiency of control powdery mildew and asian soybean rust. The fungicides spray between growth stages R1 to R5.2 promoted protection since the beginning of the epidemic and residual effect, que resulted in less severity, less defoliation, increased grain yield and higher yield. / As principais doenças que ocorrem na cultura da soja (Glycine max) no Brasil apresentam grande potencial de dano, exigindo gastos adicionais para o controle através das medidas disponíveis atualmente, destacando-se as aplicações de fungicidas. O objetivo deste trabalho foi avaliar o efeito das aplicações de fungicidas em diferentes estádios de desenvolvimento da soja, cultivar CD 206, e verificar a relação entre a severidade do oídio (Erysiphe diffusa) e da ferrugem asiática da soja (Phakopsora pachyrhizi), sobre componentes de produtividade. Foram conduzidos dois experimentos de campo, um em Arapoti (experimento I) e o outro em Ponta Grossa (experimento II), na região dos Campos Gerais do Paraná. Em ambos os locais foi aplicado o fungicida trifloxistrobina + ciproconazol, na dose de 56,4 + 24,0 mL i. a. ha-1, adicionado de ajduvante éster metílico de óleo de soja na dose de 360 mL i. a. ha-1. O delineamento experimental utilizado foi o de blocos ao acaso, com quatro repetições. Os tratamentos em um total de dez, foram compostos de aplicações de fungicidas em diferentes números e estádios de desenvolvimento:Experimento I, 1. Testemunha (sem aplicação); 2. R5.2; 3. R4 + R5.2; 4. R2 + R4 +R5.2; 5. V9 + R2 + R4 + R5.2; 6. V6 + V9 + R2 + R4 + R5.2; 7. V6 + V9 + R2 + R4;8. V6 + V9 + R2; 9. V6 + V9 e 10. V6. Experimento II, 1. Testemunha (sem aplicação); 2. R5.1; 3. R3 + R5.1; 4. R1 + R3 + R5.1; 5. V8 + R1 + R3 + R5.1; 6. V5 + V8 + R1 + R3 + R5.1, 7. V5 + V8 + R1 + R3; 8. V5 + V8 + R1; 9. V5 + V8 e 10. V5. Os tratamentos foram compostos, a fim de gerar e comparar diferentes porcentagens de severidade de oídio e ferrugem asiática obtida pelo período de proteção ou exposição às estas doenças. A severidade do oídio foi avaliada no experimento I nos estádios de desenvolvimento R2, R4, R5.3 e R5.5 e no experimento II em R1, R3, R5.2, R5.3 e R5.5. A severidade da ferrugem asiática da soja foi avaliada no experimento I nos estádios de desenvolvimento R5.3, R5.4, R6 e R7.1, e no experimento II em R5.1, R5.2, R5.3, R5.5 e R6. Com os dados de severidade calculou-se a área abaixo da curva de progresso das doenças. Avaliouse também desfolha, produtividade e seus componentes (número de vagens por planta, número de grãos por planta, massa de grãos por planta e massa de mil grãos). O oídio apresentou baixa severidade. A ferrugem asiática foi a doença predominante em alta severidade, com alto potencial de dano. As aplicações de fungicidas reduziram a severidade das doenças e houve relação linear negativa com a produtividade. Longos períodos sem proteção das plantas permitiram reinfecção rápida do oídio e as aplicações erradicativas resultaram em baixa eficiência de controle do oídio e da ferrugem asiática. Aplicações do fungicida entre os estádios de desenvolvimento R1 a R5.2 promoveram proteção desde o início da epidemia e,efeito residual, resultaram em menor severidade, menor desfolha, maior massa de grãos e maior produtividade.

O meloeiro (Cucumis melo L.) é uma cultura de grande importância econômica para o comércio de exportação brasileiro e é cultivada principalmente na região Nordeste. A produção da cultura pode ser limitada por uma doença das partes aéreas, denominada oídio, sendo no Brasil, causada pelo fungo Podosphaera xanthii. Este patógeno apresenta diversas raças definidas com base na reação de um conjunto de cultivares diferenciadoras de meloeiro. Dentre estes genótipos, o acesso PI 414723 é resistente à maior parte das raças e a linhagem Védrantais é suscetível. O presente trabalho teve como objetivos: (i) estudar a herança da resistência às raças 1, 3 e 5 de P. xanthii em indivíduos da geração F2 do cruzamento PI 414723 x Védrantais e (ii) mapear os genes de resistência a estas raças com base em marcadores de polimorfismo de comprimento de fragmentos amplificados (AFLP), de repetições de sequências simples (SSR) e análogos de genes de resistência (RGA) também nesta população. A herança da resistência foi analisada em 87 indivíduos F2 cultivados em condições de casa-de-vegetação. As três raças foram inoculadas em seis regiões eqüidistantes da nervura central em quatro folhas de cada planta. Plantas foram classificadas como resistentes ou suscetíveis com base em avaliações visuais do desenvolvimento do fungo nas folhas. As plantas foram classificadas como suscetíveis quando houve reprodução abundante de conídios e resistentes quando a reprodução foi inexistente ou escassa. Frequências de indivíduos resistentes e suscetíveis indicaram que a resistência às três raças é controlada por um gene dominante de efeito maior. Um mapa genético foi construído compreendendo 1.469 cM, consistindo de 207 marcadores (139 AFLP, 47 SSR, 18 RGA e três fenotípicos) e com uma distância média de 7,4 cM entre marcadores distribuídos em 12 grupos de ligação. Análises de co-segregação com marcadores indicaram que os genes de resistência estão localizados no grupo de ligação II. Em adição a isto, as análises indicaram ligação completa entre os genes de resistência às raças 1 e 5, sendo este gene denominado Pm-x1.5. Já o gene de resistência à raça 3 (Pm-x3) foi localizado a 5,1 cM dos demais. Um marcador AFLP (H35M75_156) foi localizado entre os dois genes a 1,3 cM de Pm-x1.5 e 3,8 cM de Pm-x3. Este é o primeiro relato da localização genética de genes de resistência às raças 3 e 5 em PI 414723 e também o primeiro relato do mapeamento de marcadores RGA gerados pela técnica TRAP em meloeiro. / Melon (Cucumis melo L.) is a crop of great economic importance for the export trade in Brazil and is cultivated mainly in the Northeast. Crop yield can be affected by a disease of the aerial parts, called powdery mildew that in Brazil is caused by the fungus Podosphaera xanthii. This pathogen has several races characterized based on the reaction of a set of differential melon cultivars. Among these genotypes, the plant introgression PI 414723 is resistant to most races and the breeding line Védrantais is susceptible. This study aimed to: (i) study the inheritance of resistance to races 1, 3 and 5 of P. xanthii in the F2 generation from the cross PI 414723 x Védrantais, and (ii) map resistance genes to these races in this same population based on amplified fragment length polymorphism (AFLP), simple sequence repeat (SSR) and resistance gene analog (RGA) markers. The inheritance of resistance was analyzed on 87 F2 individuals grown under greenhouse conditions. The three races were inoculated simultaneously on four leaves of each plant. Plants were classified as resistant or susceptible based on visual assessments of fungal growth on the leaves. Plants were considered susceptible when there was abundant production of conidia and resistant when the production was scarce or non-existent. The frequencies of resistant and susceptible individuals indicated that resistance to all three races is controlled by a dominant major gene. A genetic map was constructed comprising 1469 cM, consisting of 207 markers (139 AFLP, 47 SSR, 18 RGA, and three phenotypic) with an average distance of 7.4 cM between markers distributed in 12 linkage groups. Co-segregation analysis with markers indicated that the resistance genes are located on linkage group II. Moreover, the analysis indicated complete linkage between resistance to races 1 and 5, and this gene was denominated Pm-x1.5. The gene for resistance to race 3 (Pm-x3) was located at 5.1 cM from Pmx1.5. An AFLP marker (H35M75_156) was located between the two genes at 1.3 cM from Pmx1.5 and 3.8 cM from Pm-x3. These is the first report on the location of resistance genes to races 3 and 5 in PI 414723, and also the first report of RGA markers mapping using the TRAP technique in melon.

Erysiphe necator (Schwein.) è l’agente causale dell’oidio della vite. Esso è in grado di svernare come ascospore all’interno di corpi fruttiferi, i chasmoteci, oppure come micelio in gemme infette. Le ascospore sono rilasciate nella primavera successiva e causano infezioni primarie che danno origine all’epidemia. Di conseguenza la riduzione dell’inoculo primario svernante potenzialmente riduce le epidemie nella stagione successiva. I primi sei capitoli di questa tesi riguardano nuove conoscenze sulla biologia, epidemiologia e modellistica del patogeno. Due nuovi modelli meccanicistici che simulano, rispettivamente, la maturazione e dispersione dei chasmoteci e le infezioni ascosporiche sono stati sviluppati ed è stata studiata approfonditamente la dinamica di maturazione e dispersione delle ascospore stesse. Nei restanti quattro capitoli il controllo del patogeno è stato riconsiderato in accordo con le linee guida della gestione integrata del vigneto. In particolare è stata valutata l’efficacia di diversi fungicidi, dell’iperparassita Ampelomyces spp. e di un olio minerale nel ridurre il numero di chasmoteci prodotti in autunno, nel distruggere gli stessi durante l’inverno e nel controllare le infezione primarie ascosporiche in primavera. / Erysiphe necator (Schwein.) is the causal agent of grapevine powdery mildew. It survives the winter in two ways: as ascospores in overwintering fruiting bodies, the chasmothecia, and as mycelium in infected buds. Ascospores that are repeatedly released and cause primary infections in the following grapevine growing season and trigger powdery mildew epidemics. Consequently, the reduction of the overwintering inoculum may reduce powdery mildew epidemics in the next season. In order to verify this statement and develop sanitation as a relevant strategy to be used in integrated management of grape powdery mildew, different studies were performed during this Doctorate. The first six chapters of this dissertation pertain to new findings about the biology, epidemiology and modeling of the pathogen. A new mechanistic model predicting maturation and dispersal of chasmothecia was developed, dynamics of ascospore maturation and dispersal were studied and another mechanistic model simulating ascosporic infections was developed. In the last four chapters the control of the pathogen was redrawn according to the Integrated Pest Management concept: the efficacy of fungicides, the hyperparasite Ampelomyces spp., and mineral oil in reducing chasmothecia production in fall, in killing chasmothecia before bud break, and in controlling ascosporic infections in spring was investigated.

Barley and wheat are the two most important crop species in Turkey. Molecular studies for increasing crop yield of these species are very important for the economic benefits of Turkey. Powdery mildew and yellow rust are the two main pathogens, infecting barley and wheat, respectively in our country and causing a great amount of yield loss each year. Till now, classical genetics studies were performed in order to develop resistant barley and wheat cultivars, but these studies have not been succesful. Therefore, molecular plant-pathogen interactions studies are starting to become the new tool to fight against pathogens. In this thesis, two important aspects of plant microbe interactions were investigated. In the first part, the role of microRNAs (miRNAs) in powdery mildew-barley pathosysytem, and yellow rust-wheat pathosystem were studied. The expression levels of miRNAs and their putative targets were investigated via miRNA microarray analysis and qRT-PCR, respectively, in response to virulent and avirulent pathogen infections. These data were used to establish a new model for powdery mildew-barley and yellow rust-wheat pathosystems. In the second part, functional analysis of a novel F-box gene, which was a ZTL-type F-box, was performed by using Barley Stripe Mosaic Virus mediated Virus Induced Gene Silencing. This F-box gene (HvDRF) (Hordeum vulgare Disease Related F-box) was induced upon yellow rust infection and we studied its role in powdery mildew infection. The results confirmed HvDRF as a positive regulator of race specific immunity and enlarged the roles of ZTL-type F-box proteins to biotic stress responses.

Barley is one of the most important crop species in Turkey and powdery mildew is one of the most common pathogen decreasing yield in barley. For this problem, agricultural biologists apply breeding technologies in order to select and propagate resistant barley cultivars. However, this is not a permanent solution since pathogens evolve rapidly to overcome plant resistance mechanisms. On the other hand, molecular plant pathologists are trying to understand basic mechanisms underlying plant-pathogen interactions by using molecular tools in order to develop long term solutions for preventing yield loss. In this thesis, miR159 mediated regulation of barley GAMyb transcription factor is studied. According to microRNA microarray results regarding to infection with powdery mildew pathogen Blumeria graminis f.spp hordei (Bgh) at different time points, miR159 expression level showed significant differences. Bioinformatics analysis revealed that miRNA159 targets GAMyb gene in barley. In order to investigate this relationsh&amp / #8223 / p, both miRNA and miRNA target were cloned into GFP containing expression vectors through Gateway cloning and resulting vectors were transformed into Nicotiana benthamiana through Agrobacterium mediated gene transfer. Observations based on GFP expression showed that miRNA159 targets and decreases the expression of GAMyb in vivo. v To conclude, this study can be evaluated as a distinctive study for two aspects / (i) it is the first study assessing a &ldquo / putative&rdquo / barley miRNA function biologically and (ii) developed a practical and effective functional assay for miRNA studies in plants.

Blumeria graminis f. sp. hordei is a biotroph pathogen that causes powdery mildew disease in barley. In this study, Pallas01 and Pallas03 barley lines having Mla1, Ml (Al2) and Mla6, Mla14 R-genes were inoculated with Bgh103(64/01) race of the Blumeria graminis f. sp. hordei having avirulence and virulence to Pallas01 and Pallas03, respectively. The proteins were isolated from the three biological replicates of 12, 24, and 48 hpi samples following the method in Rampitsch et al., 2006. These there biological replicates of three time points together with the mock inoculated plant proteins were separated on 2D-PAGE using IPG strips of 4-7 pH values as three technical replicates, resulting 108 gels. The gels were analyzed using PdQuest (Bio Rad) in order to assess up- or down-regulated protein spots by comparing against controls and the samples having resistance or susceptible responses with each other. According to the analysis, 36 proteins were found to be differentiated and among them 18 proteins were found up-regulated and 8 proteins were found down-regulated. The spots were manually v excised and subjected to the nano-LC-ESI-MS/MS analysis (Proteome Factory, Germany). The MASCOT algorithm was used for identification of the possible proteins. The experimental pI and MW values were used for selecting the differentiated proteins from the mass results. The relative abundance of each of the 38 identified polypeptides was calculated in terms of spot intensity. The majority of the most abundant proteins were found to be carbohydrate metabolism related. The relative distribution of the proteins into four main functional categories was taken into consideration. Statistical tests (Students&amp / #8223 / T-test) were carried among the identified proteins in order to reveal statistically significant proteins throughout the study. By making a WoLF PSORT search, subcellular localization of the proteins was predicted. Accordingly, most of the proteins were found to be located in cytoplasm or chloroplast.

Blumeria graiminis f. sp. hordei (powdery mildew) is an obligate biotroph infecting hordeum vulgare (barley). It is one of the most devastating pathogens of barley, decreasing barley yield in great extent. In order to decrease barley loss, numerous studies are being conducted for overcoming the disease from the sides of both pathogen and host. However the pathogen is evolving very rapidly preventing the effective use of pesticides such as fungisides or development of resistant barley varieties by crossing race-specific resistance varieties, varieties having R genes, with susceptible but high yield producing varieties. In order to understand the mechanism of pathogen-host interactions, and producing enduring solutions for the problem of yield loss in barley molecular tools need to be used. In this thesis study, Amplified Fragment Length Polymorphism (AFLP) molecular marker method is used in order to reveal the molecular characterization of Turkish Blumeria graminis f. sp. hordei varieties collected from &Ccedil / ukurova region in Turkey. Thirty-nine samples were analyzed with eigth universal races, of which virulence genes are studied. AFLP studies were conducted on LI-COR 4300 DNA Analyzer system. Bioinformatics analysis was performed with NTSYS program. By the help of this Numerical Taxonomic System, similarity, dissimilarity, clustering, dendograms, two-dimensional scatter plots, and three-dimensional perspective plots were obtained. By the light of these analyses Turkish Blumeria graminis f. sp. hordei varieties together with universal races are grouped into three clusteres. In conclusion, studying Turkish Blumeria graminis f. sp. hordei isolates and comparing them with universal races is a unique study in terms of characterizing the Turkish Bgh isolates for the first time, and can be used as a frontier study for studying Resistance genes, by reverse genetic tools.

Immune systems are fundamentally based on the differentiation of self and non-self. Unlike mammals, plants have an innate immune system responding to the pathogen only at the site of attack. One of these pathogens is Blumeria graminis f. sp. hordei which is an obligate biotrophic pathogen causing powdery mildew disease and resulting in up to 30% yield loss for both cultivated and wild barley. In this study, Pallas-01 (P-01) and Pallas-03 (P-03) barley lines were inoculated with powdery mildew race Bgh103 (64/01) resulting incompatible and compatible interactions, respectively. 6, 12, 24, 48 and 72 hour-post-inoculation (hpi) samples were used in order to define the differential gene expression of NAD malic enzyme, chloroplast lipocalin, phosphoglyceromutase (PGM), Mg chelatase and 26S protease regulatory subunit 6B homolog. In the proteomics study previously conducted in the laboratory, except for the NAD-dependent malic enzyme, the other four proteins were shown to be involved in the incompatible interaction of P-01 and Bgh103 at protein level, whereas NAD-dependent malic enzyme was changing in the compatible interaction. The expression level for both proteomics and transcriptomics were assumed to be similar. However, the level of transcript would not always reflect its protein level or correlate with the level of proteins, due to complex cellular regulation processes. Post-transcriptional modifications such as synthesis, processing, degradation and post-translational modifications are changing the level of proteins expressed, thus a parallel correlation between the protein and mRNA levels can be lost. Other possible reasons for this variation can be changes in mRNA and protein stability, efficiency of translation and protein&rsquo / s turnover rate. The transcription level changes of the genes investigated in this study are found to be differentially expressed, supporting the proteomics data indicating that these genes are possibly involved in resistance. For further investigations, genetic tools such as gene silencing with RNAi and knockout experiments are required in order to elucidate the mechanism of these candidate genes in the plant-pathogen interaction.

In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%, respectively, of area under maize production, but grain yield is compromised by downy mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal) Shaw), and lack of appropriate varieties, especially hybrids. Among other factors, productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding than open pollinated varieties. Development of a viable hybrid-breeding programme requires knowledge of genetic effects governing yield and DM resistance in inbreds, and effective germplasm management requires heterotic groups and heterotic patterns to be established. In addition, knowledge of farmer-preferred traits is required. Currently, such information is not available to the hybrid-breeding programme in Mozambique. The objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and major production constraints, ii) to determine combining ability effects of inbred maize S4 lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic patterns among the elite inbred maize lines, and iv) to investigate gene effects governing resistance to DM in breeding source inbred maize lines from the breeding programme in Mozambique. During 2007/08, 142 households were involved in a survey conducted in three districts representing two maize agro-ecological zones in Mozambique. Formal surveys and informal farmer-participatory methods were employed and data subjected to analysis in the SPSS computer programme. Results indicated that there was a low utilization of improved varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of the major production constraints and could discriminate constraints according to their importance for their respective communities. For the lowland environment, farmers identified downy mildew, drought, and cutworm and stem borer damage as the main constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among the major constraints limiting productivity. The most important variety selection criteria were grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the breeding programmes for the lowland and mid altitude environments in Mozambique. To determine combining ability for downy mildew resistance, heterotic groups and heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at two sites under DM. Preponderance of GCA effects indicated that additive gene effects were more important than non-additive gene effects in governing both grain yield and downy mildew resistance in the new maize lines. Based on specific combining ability (SCA) data, lines for yield were classified into two heterotic groups, S and Z; whereas based on heterosis data, lines were fitted into three heterotic groups (S, Z and SZ). Further heterotic patterns and gene action for yield were determined by subjecting nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The diallel crosses, three hybrid checks and the two testers were evaluated in six environments in Mozambique. Results revealed that non-additive gene effects were predominant for yield components. In addition, high levels of heterosis for yield was observed and three heterotic groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred elite maize lines were observed. Topcrosses with yield levels comparable to single cross hybrids were also identified, and these would be advanced in the testing programme with potential for deployment as alternative cheaper and sustainable technology to conventional hybrids for the poor farming communities in Mozambique. To determine gene effects for downy mildew resistance in potential breeding lines, two maize populations were derived from crosses between downy mildew susceptible line LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies (BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of the populations were evaluated at two sites under downy mildew infection. A generation mean analysis was performed in SAS. It was revealed that downy mildew resistance was influenced by genes with additive and dominance effects, plus different types of epistatic effects such as additive x additive, and dominance x dominance. Overall results indicated that genes with predominantly non-additive effects controlled resistance in DRAC, whereas resistance in Suwan-L1 was largely influenced by additive gene effects. These findings have serious implications on the effective use of these downy mildew resistance sources in breeding programmes that aim to generate varieties with downy mildew resistance. Overall, results suggested that inbreeding and selection within heterotic groups, followed by hybridization between inbreds within and across heterotic groups would be effective to generate new hybrids. The breeding programme will consider development of conventional hybrids, such as single crosses and three way crosses, and top crosses. Implications of the findings of the study and recommendations are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

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.