Fotossíntese de folhas de soja infectadas por Corynespora cassiicola e Erysiphe diffusa.

RESUMO: A estimativa visual da severidade de doenças em plantas nem sempre se correlaciona com o efeito desta sobre a atividade fotossintética do hospedeiro. O objetivo do trabalho foi avaliar a interferência dos fungos Corynespora cassiicola e Erysiphe diffusa, causadores da mancha-alvo e do oídio na cultura da soja, respectivamente, na eficiência fotossintética de folhas infectadas. A fotossíntese foi relacionada com a área foliar doente por meio da equação Px/Po=(1-x)β. Os parâmetros β (± erro padrão) estimados foram 2,78 (± 0,28) (p1) indica que houve redução da eficiência fotossintética no tecido lesionado e em parte do tecido verde remanescente, enquanto que os valores obtidos para E. diffusa (β≤1) indicam que a estimativa visual da severidade da doença é um bom indicador do efeito do fungo na taxa fotossintética do hospedeiro. ABSTRACT: The visual estimate of the disease severity in plants does not always correlate with its effect on the host?s photosynthetic activity. The aim of this study was evaluate the interference of the fungi Corynespora cassiicola and Erysiphe diffusa, causal agents of target spot and powdery mildew on soybeans, in the photosynthetic efficiency of infected leaves. Photosynthesis was related to the diseased leaf area by the equation Px/Po = (1-x)β. The estimated parameters β (± standard error) were 2.78 (± 0.28) (p1) indicates that there was a reduction in the photosynthetic efficiency in the injured tissue and in part of the remaining green tissue, while the values obtained for E. diffusa (β≤1) indicate that the visual estimate of the disease severity is a good indicator of the effect of the fungus on the photosynthetic rate

Sensitivity of Corynespora cassiicola from soybean to carbendazim and prothioconazole.

The incidence of target spot disease on soybean has increased in recent years in Brazil even with intensive use of fungicides, and fungal resistance has been reported in recent studies. The objective of this study was to determine the fungicide sensitivity to carbendazim and prothioconazole in a sample of 24 isolates of Corynespora cassiicola from soybean collected from 1996 to 2011 in the states of Paraná, Mato Grosso and São Paulo (Brazil) and Corpus Christi (Paraguay). The 50% effective concentration (EC50) values were estimated by the relative mycelium growth reduction on fungicide-amended medium with the doses of 0, 0.5, 1, 10, 100 and 1000 µg of active ingredient/ mL. For carbendazim, four highly resistant isolates (EC50 > ou = 50 µg/mL) were observed from samples collected from Mato Grosso in 2008 and from Paraná and Mato Grosso in 2011. The EC50 values for prothioconazole ranged from 0.47 µg/mL to 26.44 µg/mL (mean: 5.02 µg/mL). The results reinforce the occurrence of C. cassiicola resistance to benzimidazole in Paraná and Mato Grosso states

Efeito da severidade de oídio e crestamento foliar de cercospora na produtividade da cultura da soja.

Ensaios de campo foram conduzidos na safra 2002/03, com as cultivares de soja (Glycine max) BRS 133 e BR 16, visando quantificar o efeito das doenças foliares na produtividade da cultura. O delineamento experimental foi blocos ao acaso com seis tratamentos (diferentes níveis de doença) e quatro repetições, sendo cada repetição formada por parcelas de 18 m2. Diferentes épocas e números de aplicações de fungicida (difenoconazole + propiconazole) foram utilizados para criar um gradiente de doença. Foram realizadas avaliações semanais da severidade de doenças e do índice de área foliar, utilizando o analisador de dossel (Li-Cor®). A produtividade foi quantificada nos 4 m2 centrais das parcelas. As doenças predominantes no ensaio foram oídio e crestamento de cercospora. A severidade de doença, nos estádios R6 (vagens com sementes verdes que preenchem totalmente a cavidade), e R7 (início a 50% de amarelecimento de folhas e vagens) apresentou uma correlação negativa significativa com a produtividade, utilizando-se regressão linear. As variáveis integrais área abaixo da curva de progresso da doença (AACPD), obtida a partir da integração das curvas de progresso das doenças, e duração da área foliar sadia (DAFS), obtida a partir da integração do índice de área foliar sadia, foram relacionadas à produtividade, havendo correlação negativa com AACPD, utilizando-se regressão linear (R2=0,67 para BRS 133 e 0,69 para BR16) e positiva com DAFS, utilizando-se o modelo monomolecular (R2=0,76 para BRS 133 e 0,62 para BR 16)

Sensitivity monitoring of Phakopsora pachyrhizi populations to triazoles in Brazil.

Asian soybean rust (ASR), reported for the first time in 2001 in South America, spread quickly to the major Brazilian soybean-producing regions and is considered one of the most important diseases of the crop in Brazil. Fungicides for ASR control belong to QoI (strobilurins) and SBI (azole) compounds. A lower efficiency of straight azole fungicides has been observed since 2006–2007. Embrapa Soybean Researcher Center started a sensitivity monitoring program for P. pachyrhizi in 2008–2009 to detect changes in the EC50 values (half maximal effective concentration) of the fungi population to triazoles. The bioassay has been carried out according to FRAC (Fungicide Resistance Action Committee) methodology. In the 2010–2011 growing season, leaf samples infected with P. pachyrhizi were sent from nine Brazilian states, in a total of 54 populations, and the spores collected were inoculated in detached leaves treated with the fungicides cyproconazole, metconazole, tebuconazole (0, 0.16, 0.45, 1.3, 3.8, 11, and 32 ppm), and prothioconazole (0, 0.02, 0.06, 0.164, 0.5, 1.4, and 8 ppm). Disease severity was evaluated 15 days after inoculation and only 16 bioassays showed ASR severity above 5%. The EC50 values were estimated by Proc Probit, SAS. The averages of EC50 were 0.59 for cyproconazole, 0.37 for metconazole, 0.33 for tebuconazole, and 0.1 for prothioconazole. These values were similar to the average values estimated in 2008–2009 and 2009–2010

Models and applications for risk assessment and prediction of Asian soybean rust epidemics.

Asian rust of soybean [Glycine max (L.) Merril] is one of the most important fungal diseases of this crop worldwide. The recent introduction of Phakopsora pachyrhizi Syd. & P. Syd in the Americas represents a major threat to soybean production in the main growing regions, and significant losses have already been reported. P. pachyrhizi is extremely aggressive under favorable weather conditions, causing rapid plant defoliation. Epidemiological studies, under both controlled and natural environmental conditions, have been done for several decades with the aim of elucidating factors that affect the disease cycle as a basis for disease modeling. The recent spread of Asian soybean rust to major production regions in the world has promoted new development, testing and application of mathematical models to assess the risk and predict the disease. These efforts have included the integration of new data, epidemiological knowledge, statistical methods, and advances in computer simulation to develop models and systems with different spatial and temporal scales, objectives and audience. In this review, we present a comprehensive discussion on the models and systems that have been tested to predict and assess the risk of Asian soybean rust. Limitations, uncertainties and challenges for modelers are also discussed

Models and applications for risk assessment and prediction of Asian soybean rust epidemics

Asian rust of soybean [Glycine max (L.) Merril] is one of the most important fungal diseases of this crop worldwide. The recent introduction of Phakopsora pachyrhiziSyd. & P. Syd in the Americas represents a major threat to soybean production in the main growing regions, and significant losses have already been reported. P. pachyrhizi is extremely aggressive under favorable weather conditions, causing rapid plant defoliation. Epidemiological studies, under both controlled and natural environmental conditions, have been done for several decades with the aim of elucidating factors that affect the disease cycle as a basis for disease modeling. The recent spread of Asian soybean rust to major production regions in the world has promoted new development, testing and application of mathematical models to assess the risk and predict the disease. These efforts have included the integration of new data, epidemiological knowledge, statistical methods, and advances in computer simulation to develop models and systems with different spatial and temporal scales, objectives and audience. In this review, we present a comprehensive discussion on the models and systems that have been tested to predict and assess the risk of Asian soybean rust. Limitations, uncertainties and challenges for modelers are also discussed