Orientadora: Maria Aparecida Pessôa da Cruz Centurion / Banca: Edson Lazarini / Banca: Ivana Marino Bárbaro / Resumo: Neste trabalho avaliou-se em duas cultivares de soja, uma de ciclo precoce e outra de ciclo médio (V Max e MG/BR-46 (Conquista)), os efeitos de doses reduzidas dos fungicidas azoxystrobina + ciproconazol (Priori Xtra®) + óleo mineral (Nimbus® 0,5% v/v) e tebuconazol (Folicur®), com dois intervalos de aplicação (10 e 20 dias), no controle da ferrugem asiática e sua interferência nas características agronômicas, produtividade, qualidade dos grãos e qualidade fisiológica das sementes. A avaliação da severidade da doença foi feita em intervalos de 10 dias, antecedendo as aplicações dos fungicidas, utilizando-se escala diagramática. Para a cultivar de ciclo precoce o uso de doses reduzidas de fungicidas teve pouco efeito sobre o patógeno em relação à severidade da doença. Para a cultivar de ciclo médio, essas não diferiram das doses recomendadas para o controle da ferrugem. Houve aumento na produtividade de grãos na cultivar MG/BR-46 (Conquista) com o uso de fungicidas, porém, na cultivar V Max, tal resultado não foi observado. Os testes de vigor indicaram que tanto as sementes da cultivar precoce como as da cultivar de ciclo médio foram classificadas como de baixa qualidade. A ocorrência da ferrugem asiática da soja comprometeu o desenvolvimento dos grãos na cultivar MG/BR-46 (Conquista), reduzindo seu tamanho, e, aumentando a quantidade de sementes retidas no fundo das peneiras. A qualidade do grão não foi influenciada pelas diferentes doses de fungicidas, mas a cultivar de ciclo médio MG/BR-46 (Conquista) apresentou maior porcentagem de grãos verdes e imaturos do que a cultivar V Max. / Abstract: This work was done to evaluate, in two soybean cultivars, one of early and the other of medium cycle (V Max and MG/BR-46 (Conquista)), the effects of reduced doses of the fungicides azoxystrobina + ciproconazol (Priori Xtra®) + mineral oil (Nimbus®) and tebuconazol (Folicur®), with two application intervals (10 and 20 days), on the control of soybean rust, as well as their effects on agronomics features, on yield, on grains and physiological seed quality. Disease severity assessment was done at 10 days intervals, before fungicide spraying, using a diagrammatic scale. For the early cultivar the use of reduced fungicide doses had little effect on the pathogen in relation to disease severity. For the medium cycle cultivar, reduced dose were not significantly different from the recommended doses for soybean rust control. There was yield increase on the cultivar MG/BR-46 (Conquista) with fungicide spraying; however, the same was not observed for the cultivar V Max. By the vigor tests, the both cultivars seeds presented a poor quality. On the cultivar MG/BR-46 (Conquista), the soybean Asian rust affected the grains development, reducing their size and increasing the discard. The quality of grain was not influenced by the different doses of fungicides, and the cultivar of medium cycle MG/BR-46 (Conquista) showed higher percentage of green and immature grains than cultivar V Max. / Mestre

O controle da ferrugem asiática é altamente dependente do tratamento com fungicidas. A decisão do momento correto da aplicação é fundamental para a eficiência do tratamento, visto que atrasos na efetuação do controle podem torná-lo tão ineficaz quanto à ausência de aplicações. O dano provocado pela ferrugem asiática é decorrente da redução da área foliar, devido à destruição do tecido vegetal e desfolha precoce. Tendo em vista a influência que o atraso no controle tem sobre a ferrugem asiática, e esta sobre a folhagem das plantas de soja, o dano pode ser melhor compreendido com o uso de variáveis que captem modificações na área foliar do hospedeiro. Com os objetivos de avaliar o efeito do atraso no controle da ferrugem asiática sobre o rendimento e os componentes do rendimento, a duração (HAD), a absorção da área foliar sadia (HAA) de plantas de soja e sobre a severidade da doença e examinar as relações entre o rendimento de soja com a duração, absorção da área foliar sadia e severidade da ferrugem asiática, foram conduzidos cinco experimentos no Centro de Pesquisa e Desenvolvimento Agrícola da Arysta LifeScience, em Pereiras-SP. Os experimentos envolveram um tratamento preventivo e tratamentos que corresponderam a atrasos crescentes na efetuação do controle químico. As relações entre os parâmetros citados acima foram avaliadas por meio de testes de comparação de médias (LSD) e regressões lineares e não lineares (p<=0,05). Os resultados mostraram que nas situações em que o início da ferrugem asiática da soja ocorre próximo à fase reprodutiva, o rendimento cai à taxa de -31 kg ha-1 a -15 kg ha-1 por cada dia de atraso no controle, sendo o dano maior nos estádios mais jovens e menor nos estádios mais avançados. Na relação entre o atraso no controle da ferrugem asiática da soja e HAA, 10 MJ m-2 deixam de ser absorvidos por cada dia de atraso no controle. Na relação entre o atraso no controle da ferrugem asiática da soja e HAD, a duração da área foliar sadia diminui 2,4 a 1,4 dias por cada dia em que o controle é atrasado. Na relação entre o rendimento de soja e HAA, são ganhos 2 kg ha-1 para cada MJ m-2 absorvido pela área foliar sadia. Na relação entre o rendimento de soja e HAD, são ganhos de 13 a 9 kg ha-1 para cada dia de duração da área foliar sadia. A relação entre atraso no controle da ferrugem asiática da soja e severidade da doença é de 0,25% ponto percentual para cada dia de atraso no controle. A relação entre o rendimento de soja e severidade da ferrugem asiática é de -36 kg ha-1 por cada ponto percentual de severidade. A variável que melhor se relaciona com o rendimento de soja é a absorção da área foliar sadia (HAA). Tanto HAA quanto HAD são variáveis melhores do que a severidade para serem usadas na quantificação de danos provocados pela ferrugem asiática na soja. Nas situações em que o início da doença ocorre próximo à fase reprodutiva, atrasos no controle da ferrugem asiática superiores a 28 dias apresentam o mesmo resultado que a ausência de controle. Não há redução no rendimento de soja se o início da ferrugem asiática ocorrer a partir do estádio R5. / The control of the asian soybean rust is highly dependent of fungicides treatment. The decision of the correct moment of application is critical for the efficiency of the treatment, since delays in the control can become it so inefficacious as the absence of applications. The damage caused by asian soybean rust is decurrent of the reduction of the leaf area, due to vegetal tissue destruction and early defoliation. In view, the influence that the control delay has on the asian rust, and this on the foliage of the soybean plants, the yield loss can be better understood with the use of variable that catch modifications in the leaf area of the host plant. With the objectives to evaluate the effect of the delay in the asian soybean control on the yield and the yield components, the duration (HAD) and absorption of the healthy leaf area (HAA) of soybean plants and on the disease severity, and to examine the relationship between the soybean yield with the healthy leaf area duration, healthy leaf area absorption and asian soybean rust severity, were conducted five field experiments in Agricultural Research and Development Center of the Arysta LifeScience, in Pereiras-SP. The experiments had involved a preventive treatment and treatments that had corresponded the increasing delays in the chemical control. The relationship between the cited parameters above had been evaluated by averages comparison test (LSD) and linear and non linear regressions (p<=0,05). The results had shown that in the situations where the beginning of the asian soybean rust occurs next to the reproductive phase, the yield fall -31 kg ha-1 to -15 kg ha-1 per each day of control delay, being the loss bigger in youngest stadiums and lesser in oldier stadiums. In the relationship between control delay of the asian soybean rust and HAA, 10MJ m-2 does not absorbed per each day of control delay. In the relationship of the control delay of the asian soybean rust and HAD, the duration of the healthy leaf area reduced 2,4 to 1,4 days per each day where the control is delayed. In the relationship between soybean yield and HAA, were obtained 2 kg ha-1 for each MJ m-2 absorbed by the healthy leaf area. In the relationship between soybean yield and HAD, were obtained 9 to 13 kg ha-1 for each day of healthy leaf area duration. The relationship between control delay of the asian soybean rust and disease severity was of 0,25% percentile point for each day of delay in the control. The relationship between soybean yield and severity of the asian soybean rust were of -36 kg ha-1 for each percentile point of severity. The variable that better becomes related with the yield soybean was the healthy leaf area absorption (HAA). Even HAA as HAD are better variables than severity to be used in the yield losses quantification of the asian soybean rust. In the situations that the beginning of the disease occurs next to reproductive phase, control delay of asian soybean rust higher than 28 days show the same result that the control absence. It does not have reduction in the soybean yield if the beginning of the asian soybean rust occurs after the R5 stadium.

A soja é a cultura agrícola com maior extensão de área plantada no Brasil, país que se destaca no cenário mundial como o segundo maior produtor e exportador desta oleaginosa. A ferrugem asiática (FA), causada pelo fungo Phakopsora pachyrhizi, apresenta-se como um dos mais graves problemas fitossanitários da cultura da soja no Brasil, principalmente por não existirem, até o presente momento, cultivares com níveis de resistência satisfatórios. Com o objetivo de melhor se conhecer a biologia de Phakopsora pachyrhizi e alguns fatores relacionados ao processo infeccioso em soja, no presente trabalho foram avaliados: (1) Métodos de preservação de urediniósporos; (2) Influência da descontinuidade do molhamento foliar no processo infeccioso dos urediniósporos; (3) Influência da luminosidade e da superfície foliar no processo infeccioso de urediniósporos de P. pachyrhizi; (4) Influência do estádio fenológico da soja na infecção de P. pachyrhizi. Os resultados obtidos mostraram que a desidratação dos esporos proporcionou maior viabilidade destes ao longo do tempo, para todas as condições de armazenamento testadas. No deep freezer foi possível preservar os esporos por até 231 dias, independente da sua condição de hidratação. No ambiente, os esporos não desidratados e desidratados permaneceram viáveis por 16 e 22 dias, respectivamente. A reversão de dormência dos esporos foi efetiva ao empregar hidratação (24h de câmara úmida) seguida ou não por choque térmico (40&#176;C/5 minutos). Em todos os tratamentos onde se aplicou molhamento foliar descontínuo, a severidade de FA foi sempre inferior quando comparada ao molhamento contínuo, principalmente quando a interrupção do molhamento se deu após 4 horas de câmara úmida inicial. A interrupção temporária do molhamento afetou os esporos que haviam germinado, pois os mesmo não foram aptos a infectar após novo período de molhamento. Com relação à luminosidade, os urediniósporos foram aptos a infectar plantas de soja tanto na luz quanto no escuro. Porém, severidade maior foi observada quando se inoculou a superfície adaxial, com posterior incubação das plantas no escuro. Os experimentos in vitro mostraram que, na ausência de luz, houve maior germinação e maior formação de apressórios. O teor de cera epicuticular e o seu aspecto ultra-estrutural não apresentaram diferenças entre as superfícies adaxial e abaxial no cultivar BRS 154. Os cultivares BRS 154 e BRS 258, no estádio fenológico reprodutivo, R5, apresentaram menor severidade em relação aos estádios V3 e R1. O período latente médio (PLM) da FA foi 8 e 9 dias para os cultivares BRS 154 e BRS 258, respectivamente. O PLM não se diferenciou em função do estádio fenológico para ambos cultivares. Quanto à influência da idade da folha na suscetibilidade à FA, a folha 1, considerando-se o sentido base-ápice da planta, mostrou maior suscetibilidade e freqüência de infecção de P. pachyrhizi . Os resultados apresentados são essenciais, tanto por disponibilizarem informações sobre a biologia e epidemiologia do fungo, quanto por servirem como base para novos estudos, nas mais diversas áreas sobre este importante patossistema. / Soybean is the agricultural crop with the largest planted area in Brazil. The country stands out in the world scenario as the second-largest producer and exporter of this oilseed crop. The Asian rust (AR), caused by the fungus Phakopsora pachyrhizi, is one of the most serious phytosanitary problems of soybean in Brazil, especially because no cultivars exist so far with satisfactory resistance levels. In order to acquire better knowledge about the biology of Phakopsora pachyrhizi and some factors related to its infectious process in soybean, the following were evaluated in the present work: (1) Uredospore preservation methods; (2) Influence of leaf wetness discontinuity on the infectious process of uredospores; (3) Influence of luminosity and leaf surface on the infectious process of P. pachyrhizi uredospores; (4) Influence of phenological stage of soybean on infection by P. pachyrhizi . The results obtained showed that spore dehydration provided greater spore viability with time, in all storage conditions tested. Spores could be preserved for up to 231 days in the deep freezer, regardless of their hydration condition. At room temperature, non-dehydrated and dehydrated spores remained viable for 16 and 22 days, respectively. Spore dormancy reversion was effective when hydration was used (24h in humid chamber), followed or not by thermal shock (40&#176;C/5 minutes). In all treatments where discontinuous leaf wetting was applied, AR severity was always lower when compared with continuous wetting, especially when wetting was interrupted after 4 hours of initial treatment in the humid chamber. Temporary wetness interruption affected spores that had already germinated, as these were not able to infect after a new wetness period. As to luminosity, uredospores were capable of infecting soybean plants both in the light and in the dark. However, higher severity was observed when the adaxial surface was inoculated, with later incubation of the plants in the dark. The in vitro experiments showed that there was greater germination and greater formation of appressoria in the absence of light. Epicuticular wax content and its ultrastructural aspect did not show differences between the adaxial and abaxial surfaces in cultivar BRS 154. At the R5 reproductive phenological stage, cultivars BRS 154 and BRS 258 showed smaller severity in relation to stages V3 and R1. The AR mean latent period (MLP) was 8 and 9 days for cultivars BRS 154 and BRS 258, respectively. MLP differences due to phenological stage were not detected in any of the cultivars. As to the influence of leaf age on AR susceptibility, leaf 1 showed greater susceptibility and frequency of infection by P. pachyrhizi, considering the plant base-apex direction. The results herein presented are essential, either because they make information available on the biology and epidemiology of the fungus, or because they serve as a foundation for new studies on the most diverse areas about this important pathosystem.

O custo ferrugem que engloba gastos com fungicidas, os custos operacionais das aplicações, perdas de produção, e redução na arrecadação de impostos representa um elevado valor para sojicultura mundial. Assim, a ferrugem asiática da soja apresenta-se como um dos grandes desafios para a pesquisa agrícola nos próximos anos, pois o controle químico da doença é alternativa obrigatória enquanto não se dispõe de cultivares resistentes. Porém a prática representa aumento considerável no custo de produção. No Brasil estima-se que este custo, para duas aplicações gire, em torno de US$ 40,00.ha-1, sem contar os gastos operacionais com máquinas e combustível, ou seja, gasto apenas o fungicida. Considerando o exposto, este trabalho tem como objetivo avaliar duas fontes de resistência à ferrugem asiática da soja (PI 200487 e PI 459025A), e verificar se os genes responsáveis pela reação ao patógeno já foram descritos na literatura, ou seja, identificar seus respectivos grupos de ligação. A estratégia de segregantes agrupados (Bulked segregant analysis) foi utilizada para mapear os genes de interesse. Os resultados obtidos permitiram chegar as seguintes conclusões: a) a técnica BSA foi eficiente para detectar locos relacionados com a resistência à ferrugem asiática da soja; b) a PI 459025 (Bing Nam) apresenta o gene de resistência Rpp4 localizado no grupo de ligação G e c) A PI 200487 (Kinoshita) apresenta um gene diferente daqueles descritos na literatura, sendo este localizado no grupo de ligação N. Este gene pode ser denominado de Rpp5. / The costs due to Asian soybean rust, which consists of fungicides, operational application costs and reduction in paid taxes, represent severe losses for worldwide soybean production. Thus, Asian soybean rust represents one of the most challenging problems for agricultural research in the future, since chemical control of the disease is the obligated alternative while resistant cultivars are unavailable. However, fungicide application significantly increases production costs. In Brazil, it is estimated that the costs of two applications are of approximately US$ 40,00.ha-1, aside the operational costs incurred due to machinery and fuel, that is, the figure represents solely fungicide costs. Taking into account the previous considerations, the present work aims to evaluate two sources of resistance to Asian soybean rust (PI 200487 and PI 459025A), and to verify if the genes involved in pathogen-responses have already been described in previous work, by identifying their respective linkage groups. Bulked segregant analysis was used to map the genes of interest. The results allowed the following conclusions: a) BSA was effective to detect loci associated to Asian soybean rust resistance; b) PI 459025A (Bing Nam) carries the resistance gene Rpp4 mapped to the linkage group G and c) PI 200487 (Kinoshita) has a novel resistance gene mapped to the linkage group N. The identified gene is denominated Rpp5.

Soybean (Glycine max (L.) Merr.) occupies an important position in the world economy of the feedstock of high quality protein and vegetable oils. However, its production is threatened by, Asian soybean rust (ASR), caused by the rust fungus Phakopsora pachyrhizi Syd. & P. Syd. This fungus is highly dependent on environmental conditions, has a wide range of hosts, and evolves rapidly into novel races, making it difficult to control. In addition, most commercial varieties are susceptible to rust, the rust has already developed resistance to triazole fungicides, and most small-scale farmers cannot afford expensive systemic fungicides to control the disease. The use of resistant varieties is the most viable, long-term option to manage ASR, especially in the small-holder soybean farming sector. This study was therefore designed to undertake the following goals: (i) to identify farmers’ preferred varieties and desired traits, their knowledge of ASR, and other key constraints affecting soybean production in Kenya; (ii) to evaluate soybean accessions for rust resistance, and to determine the correlation of rust resistance with other agronomic traits; (iii) to determine the mode of inheritance for ASR resistance and selected agronomic traits; and (iv) to determine yield stability of soybean advanced lines at multiple sites in Central and Eastern Kenya. To understand farmers’ preferred varietal characteristics, knowledge of ASR and other key constraints to soybean production, a survey was conducted using a structured questionnaire in the major soybean growing areas of Kenya. The farmers preferred local varieties because of their desirable characteristics, which included high yields, early maturity, drought tolerance and seed availability. Although the majority of the participating farmers expressed a willingness to grow improved varieties, financial limitations, seed unavailability and lack of information were the major barriers to their use of improved varieties. High yield, early maturity, adaptability and grain quality were the traits that most farmers sought in an ideal soybean variety. Knowledge of the cause of ASR was limited, and its occurrence was largely attributed to environmental factors, poor soil fertility conditions, poor agronomic practices, physiological maturity and specific species of weeds. Their investments in control methods were minimal due to a lack of technical knowledge, poor access to fungicides, and limited resources. Other constraints faced by soybean farmers included: lack of access to grain markets; lack of knowledge in processing and utilization of soybean grain; the unavailability of seeds; losses to pests and diseases; the lack of inputs such as fertilizers; frequent dry spells; and low yielding varieties. A total of 110 soybean accessions were evaluated for their rust reactions and correlations with selected agronomic traits. These included plant introductions possessing single rust resistant genes (Rpp1-4), tolerant lines, gene bank accessions, commercial varieties and advanced lines. Soybean genotypes varied significantly in their reactions to rust severity, sporulation, lesion type and area under disease progress curve (AUDPC) values. Genotypes possessing Rpp4 (G10428) and Rpp2 (G8586) resistant genes, and non-characterized genotypes MAK BLD 11.3, GC 00138-29 and Namsoy 4M, were the most resistant accessions, as indicated by low rust severity scores, low AUDPC values, red brown lesions and low sporulation scores. Other genotypes with known resistant genes including G7955 (Rpp3), G58 and Tainung 4 (Rpp1), a few tolerant lines, and one advanced line (BRS Sambaiba) were moderately resistant. All the other advanced lines, commercial varieties, gene bank accessions and collections from the farmers’ fields were highly susceptible to rust. Rust severity was positively correlated with rust sporulation, indicating that reduction of sporulation made a significant contribution towards rust resistance. An F2 population was generated from a half diallel mating design, involving 4 resistant, 2 moderately resistant and 2 susceptible genotypes selected as parents. The F2 populations along with their parents were evaluated in two environments to determine the type of gene action for rust resistance and other quantitative traits in soybeans. The results revealed that both general combining ability (GCA) and specific combining ability (SCA) were significant for most of the traits studied, indicating that both additive gene action and non-additive gene action played a major role in the inheritance of rust resistance and selected agronomic traits. The GCA/SCA ratio was close to unity for rust severity, rust sporulation, days to flowering, days to maturity and plant height. This indicated that additive gene action played a more significant role in the inheritance of these traits than non-additive gene action. Non-additive gene action was only predominant for soybean grain yield. Parental lines G10428, G8586 and Namsoy 4M were the best general combiners for improving rust resistance across the environments. The most promising parents for early flowering were G7955, G8586 and G58. Parent Maksoy 1N was the best general combiner for early maturity while parents Maksoy 1N, G58, G7955 and Nyala contributed effectively towards reduced plant height. Yield stability analysis was conducted for 30 genotypes in 6 environments, using additive main effects and multiplicative interaction (AMMI), genotype main effect and genotype x environment interaction (GGE) biplot analyses. Genotypes 916/5/19 and G7955 were identified as the high yielding and most stable across the environments. On the other hand, genotypes BRS MG46 and Sable were high yielding but unstable and specifically suitable for the environments EM2 and MW2, respectively (both environments have long rainy seasons). Environment EM2 was identified as the most discriminating and representative among the six environments. Environments IG1 and MW1 (short rainy seasons) were less informative on genotypes tested, as confirmed by short environment vectors. Environment EM1 was better for discriminating genotypes but was a poor representative of the test environments, hence it should only be utilized for developing specifically adapted genotypes. Further analysis using GGE biplot approach grouped the environments into three putative mega-environments in Central and Eastern Kenya. Overall, this study established the need to educate farmers on the cause of ASR, to develop ASR resistant varieties, and to incorporate farmers’ desired traits in the breeding programme, especially by the use of participatory breeding approaches. The resistant and moderately resistant genotypes identified in this study could be used as sources of resistant genes to develop ASR resistant varieties in Kenya. This study also established that genetic improvement for ASR resistance and selected agronomic traits in soybeans is possible based on the use of recurrent selection breeding procedures that result in the accumulation of additive gene effects. Selection of late segregating generations would be effective for soybean grain yield improvement. This study identified potential parents for ASR resistance and selected agronomic traits, but they require further breeding to improve on farmers’ desired traits. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi Syd., is a real threat to soybean crops in South Africa. Its ability to spread rapidly and its potential to severely reduce yields have earned it the reputation as the most destructive foliar disease of soybeans. SBR has been reported in South Africa every year since its arrival in 2001. While extensive research had been done on the epidemiology and fungicide application requirements in South Africa, no work into the long term climatic vulnerability of soybean production areas to SBR had been done. This meant soybean producers do not know whether SBR is a threat in their areas. Through this research a SBR algorithm was developed using readily available climate data, viz. temperature and rainfall, to create a daily index specifying the climatic vulnerability of SBR infection. The algorithm was applied to a 50 year historical climate database, and a series of maps was created illustrating the long term vulnerability of different areas to SBR infection. These maps allow soybean producers to understand the climatic vulnerability of their area to SBR infection. Time series graphs were created for selected key soybean production areas to allow soybean producers to distinguish periods of high and low climatic risk during the season. This may help with decisions regarding the planting times, the maturation rate of different cultivars as well as the timing and application of fungicides. The framework for a near real time forecasting system was created outlining how the system could amalgamate recently recorded and forecasted weather data, run it through the SBR algorithm and provide a near real time, as well as forecasted vulnerability, based on the climatic conductivity for SBR infection. Anticipated limitations and difficulties on developing the forecasting system are also outlined. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Abstract not available. / Thesis (Ph.D)-University of KwaZulu-Natal, Pietermaritzburg, 2008.