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

Influence of culture media and growth periods on the sporulation Septoria glycines

Com o objetivo de obter um meio de cultura que proporcione produção rápida e abundante de esporos de Septoria glycines (Hemmi), agente causal da mancha-parda-da-folha-da-soja, foi efetuado o presente trabalho. Inicialmente compararam-se fontes de carbono e de nitrogênio e substâncias reguladoras de crescimento. Posteriormente com base nos primeiros resultados alcançados, foram comparados os meios de cultura usados como testemunhas (Czapek ágar e BDA) agregados de fatores de crescimento nas doses que propiciaram a maior produção de esporos. Estes foram avaliados em cinco épocas de crescimento. Nos primeiros ensaios, os fatores de crescimento extrato de malte, extrato de levedura e tiamina foram superiores aos meios básicos. No ensaio final, mantiveram-se com a máxima produção de esporos, nas cinco diferentes épocas de leitura efetuadas ao longo de 25 dias, os tratamentos contendo o fator de crescimento extrato de levedura. A maior produção de esporos foi obtida, quando a cultura alcançou 25 dias de desenvolvimento, com o tratamento Czapec ágar + 4 g/l de extrato de levedura. The object of the present study was to find a new culture medium to provide rapid and abundant Septoria glycines (Hemmi) sporulation, the causal agent of brown spot disease on soybean leaves. First, carbon and nitrogen sources and growth regulators were compared. Later, based on the first results obtained, the culture media used as checks, associated with growth factors in doses which resulted in the greatest spore production, were compared (Czapek agar and PDA). These were evaluated in five growth periods. In the first trials, the malt extract, yeast extract and thiamine growth factors were greater than the basic media. In the final trial, the treatments containing the yeast extract growth factor continued with the greatest spore production in the five different periods observed during 25 days. The greatest spore production was obtained when the culture reached 25 days of development, with the Czapek agar medium + 4 g/l of yeast extract.

Dispersão vertical e horizontal de conídios de Stenocarpella macrospora e Stenocarpella maydis

Em experimentos conduzidos no campo, quantificaram-se a dispersão vertical e horizontal dos conídios de Stenocarpella maydis e S. macrospora liberados de palha de milho (Zea mays) naturalmente infetada. Verificou-se que 93% do número total de conídios de S. maydis e 88% de S. macrospora foram capturados durante o dia, diferindo estatisticamente do período noturno. O número de conídios de S. maydis e S. macrospora capturados no ar foi inversamente proporcional à distância da posição vertical e horizontal das armadilhas da fonte de inóculo. Os conídios foram capturados até uma altura de 2 m acima e distantes 120 m da fonte de inóculo. No entanto, em ambos experimentos, a freqüência e o número de esporos coletados foram maiores até 25 cm acima e 20 m distante da fonte de inóculo. Além disto, a dispersão dos conídios isolados ou agrupados no cirro, ocorreu livremente no ar, não necessitando estarem veiculados a gotículas d'água.Experiments were carried out in the field to quantify airborne dispersal of Stenocarpella maydis and S. macrospora conidia from naturally infected corn (Zea mays) straw. The data indicated that 93% and 88% of the total number of sampled conidia of S. maydis and S. macrospora, respectively, were trapped during the day, differing statistically from the night period. The number of sampled conidia of both fungi, was inversely proportional to the vertical and horizontal distance of spore traps from the inoculum source. Conidia were collected up to a height of 2.0 m and up to 120.0 m from the inoculum source. In both experiments, the frequency and the number of collected spores were the highest at a height of 25.0 cm and at a distance of 20.0 m from the inoculum source. Conidia was dispersed in the air as individual spores and/or grouped in cirri and not essentially associated to rain splashes