Rafael Moreira Soares

Development of classification criteria for resistance to soybean rust and differences in virulence among Japanese and Brazilian rust populations

Nos ultimos anos a ferrugem asiatica, causada pelo fungo Phakopsora pachyrhizi tornou-se uma das mais serias ameacas a producao de soja Brasileira. Linhagens melhoradas e variedades tem sido selecionadas para a resistencia a ferrugem da soja na Asia, entretanto para a selecao e utilizacao dessas fontes de resistencia, diferencas de virulencia entre populacoes Asiaticas e Brasileiras desse fungo devem ser consideradas. Neste trabalho sugerimos um criterio para se distinguir resistencia de susceptibilidade pela analise de quatro caracteres de resistencia: frequencia de lesoes contendo uredias, numero de uredias por lesao, frequencia de uredias abertas e nivel de esporulacao determinados pela utilizacao de 63 genotipos. Sob condicoes controladas em câmaras de crescimento, treze variedades de soja foram expostas a tres populacoes de fungos - uma populacao proveniente do Japao e duas populacoes provenientes do Brasil-e avaliadas quanto aos caracteres de resistencia mencionados acima. As populacoes Brasileiras diferiram entre si claramente quanto a virulencia e em relacao a populacao de isolados do Japao. Apenas dois genes de resistencia, Rpp4 presente na variedade PI459025 e Rpp5 presente na variedade Shiranui conferiram resistencia as tres populacoes da ferrugem. O numero de variedades ou genes resistentes uteis em ambos os paises parece ser limitado. Assim, um cultivar universalmente efetivo contra a ferrugem da soja deveria ser desenvolvido pela piramidacao de genes maiores de resistencia e pela introducao de resistencia horizontal.

Ineficiência de acibenzolar-S-methyl na indução de resistência de feijoeiro comum à murcha-de-Curtobacterium

O efeito da inducao de resistencia promovido por acibenzolar-S-methyl foi avaliado em tres cultivares de feijoeiro (Phaseolus vulgaris), com diferentes niveis de resistencia a murcha-de-Curtobacterium, em dois ensaios distintos, sob condicoes de casa de vegetacao. O primeiro ensaio visou avaliar a acao do acibenzolar-S-methyl na inducao de resistencia a murcha-de-Curtobacterium e o segundo, objetivou avaliar a acao deste produto na atividade das enzimas peroxidase e polifenoloxidase e no nivel de proteinas totais soluveis, em amostras de folhas e caule, sem inoculacao do patogeno. Em ambos os ensaios o indutor foi pulverizado na dosagem de 100 µg i.a./ml, cinco dias apos o transplante das plantas para vasos. O acibenzolar-S-methyl foi ineficiente, tanto para controlar a doenca na cultivar suscetivel (IAC Carioca), quanto para incrementar os niveis de resistencia das cultivares resistentes (IAC Carioca Akyta e IAC Carioca Pyata). A peroxidase apresentou maior atividade nas plantas pulverizadas com o indutor, tanto na folha, como no caule. A polifenoloxidase mostrou maior atividade apenas no caule das plantas pulverizadas. O nivel de proteinas totais soluveis foi maior no caule das plantas pulverizadas do que nas nao-pulverizadas, porem nao diferiu na folha. As enzimas e proteinas avaliadas apresentaram maiores niveis na folha do que no caule das plantas de feijoeiro avaliadas.

Escala diagramática para avaliação da severidade da mancha alvo da soja

A mancha alvo da soja, causada pelo fungo Corynespora cassiicola, e encontrada em praticamente todas as regioes de cultivo de soja do Brasil e pode causar perdas economicas. Esse trabalho teve como objetivo elaborar e validar uma escala diagramatica para avaliacao da severidade da mancha alvo da soja. Para tal, foram coletados foliolos de soja com sintomas da doenca, onde se mediu a severidade, determinando-se os limites minimos e maximos, e os niveis intermediarios da escala de acordo com a lei do estimulo visual de Weber-Fechner. A escala elaborada apresentou sete niveis de severidade: 1, 2, 5, 9, 19, 33 e 52%. A validacao foi realizada por oito avaliadores, sem experiencia em quantificar essa doenca, que estimaram a severidade de 40 foliolos com diferentes niveis de severidade da mancha alvo, sem e com o auxilio da escala. A utilizacao da escala diagramatica resultou em melhor acuracia e precisao das estimativas realizadas, sendo uma ferramenta de facil e rapida utilizacao, que pode ser adotada para auxiliar na avaliacao da severidade da mancha alvo da soja.

Ferrugem-asiática da soja no Brasil: passado, presente e futuro

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi , is the most severe disease of the crop and can cause yield losses of up to 90%. The disease was first reported in Brazil in 2001. Epidemics of the disease are common in the country, where the fungus can survive year‑round. Regulatory measures to reduce the inoculum between seasons and avoid late-season soybean have been adopted to manage the disease. Disease control has relied mainly on chemical control, but a lower sensibility of the fungus to fungicides has been reported in Brazil. Major‑resistance genes have been mapped and incorporated into the cultivars. With the reduced efficacy of the fungicides, the adoption of integrated measures to control the disease will be important for the sustainability of the crop. This review presents the main changes in the soybean crop system caused by the introduction of the fungus in Brazil, the current management strategies adopted to avoid losses, and the new trends that, together with biotechnological strategies, can improve management in the future.

First report of Curtobacterium flaccumfaciens pv. flaccumfaciens on soybean in Brazil

Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) causes bacterial wilt on beans (Phaseolus vulgaris) and bacterial tan spot on soybeans (Glycine max). Cff was detected on beans in Brazil in 1995. Plants of commercial and experimental fields of soybean with typical symptoms of the disease were collected in the State of Parana, Brazil, during the 2011/2012 growing season. The causal agent was identified as Cff by isolation from symptomatic leaves on CNS semi-selective medium, artificial inoculation test and re-isolation in soybean and bean, Gram staining test, solubility in KOH, and by PCR. This is the first report of Cff on soybean in Brazil.

Genetic control of soybean (Glycine max) yield in the absence and presence of the Asian rust fungus (Phakopsora pachyrhizi)

Soybean is one of the most important crops in Brazil and continuously generates demands for production technologies, such as cultivars resistant to diseases. In recent years, the Asian rust fungus (Phakopsora pachyrhizi Syd. & P. Syd 1914) has caused severe yield losses and the development of resistant cultivars is the best means of control. Understanding the genetic control and estimating parameters associated with soybean (Glycine max) resistance to P. pachyrhizi will provide essential information for cultivar selection. We investigated quantitative genetic control of P. pachyrhizi and estimated parameters associated to soybean yield in the absence and presence of this phytopathogen. Six cultivars and their 15 diallel derived F2 and F3 generations were assessed in experiments carried out in the absence and presence of P. pachyrhizi. The results indicated that soybean yield in the presence and absence of P. pachyrhizi is controlled by polygenes expressing predominantly additive effects that can be selected to develop new cultivars resistant or tolerant to P. pachyrhizi. These cultivars may prove to be a useful and more durable alternative than cultivars carrying major resistance genes.

Utilização de glifosato para o controle de ferrugem da soja

The objective of this work was to evaluate the effect of glyphosate on the germination of Phakopsora pachyrhizi spores, and on soybean rust control; applications were either preventive or eradicative under controlled conditions. The germination of spores was evaluated by pouring spores solutions on culture medium, with different concentrations of glyphosate (0, 100, 1,000, 10,000 and 20,000 ppm) and fungicides. For the rust control evaluation, plants were sprayed with glyphosate, varying doses and moments, and estimating the disease severity. The product reduced spores germination. Plants sprayed in greenhouse conditions, showed effect of the product on rust, when applied preventively, but with short protection period and lower fungus toxicity than tebuconazole fungicide. The use of glyphosate, evaluated in this trial, must not be taken as a rust management measure, and should not interfere in usual practices for soybean rust control.

Development of Sclerotium rolfsii sclerotia on soybean, corn, and wheat straw, under different soil temperatures and moisture contents.

The objective of this work was to evaluate the effect of moisture and temperature on the development of Sclerotium rolfsii on soybean, corn, and wheat straw. Wheat straw produced the lowest number of sclerotia. Intermediate soil moisture level (70% of field capacity), and temperatures ranging between 25-30oC favored sclerotia development. No sclerotia were formed at temperatures between 30-35oC, on any type of straw.

Plant-to-seed transmission of Curtobacterium flaccumfaciens pv. flaccumfaciens on soybean

Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) causes bacterial tan spot on soybeans (Glycine max), which was detected in Brazilian crops in 2012. The objective of this study was to determine the Cff transmission rate from plant to seeds in soybean cultivars with different levels of resistance to bacterial tan spot. For this, two assays were conducted under greenhouse and laboratory conditions. Inoculation in soybean plants was performed by the stem puncture method in the first assay and the toothpick method in the second assay. The Cff transmission to seed was checked by plating the suspensions extracted from seeds of the inoculated plants on semi-selective medium. Molecular identification of Cff amongst the obtained isolates was performed by PCR. The susceptible cultivars, BRS 284 and NS 5858 RR, showed zero to 1% Cff seed transmission, while the moderately resistant cultivar, BRS 388RR, showed 0% seed transmission. We concluded that Cff can be transmitted to soybean seeds of susceptible cultivars at low rates.

Eficácia de Fusarium spp. no controle da murcha-de-curtobacterium do feijoeiro

Embrapa Soja, Rodovia Carlos João Strass Distrito da Warta, 86001-970 Londrina, PR, Brasil Faculdade de Ciências Agronômicas, FCA/UNESP, Rua José Barbosa de Barros no 1780, 18610-307 Botucatu, SP, Brasil. *Parte da tese de doutorado do primeiro autor apresentada à FCA/UNESP. Autor para correspondência: Rafael Moreira Soares (rafael.soares@embrapa.br) Data de chegada: 25/08/2016. Aceito para publicação em: 07/08/2017 10.1590/0100-5405/168402