Intensidade do oídio Microsphaera diffusa Cke. & Pk. em cultivares de soja [Glycine max (L.) Merr.] sob diferentes temperaturas e períodos de molhamento foliar

Abstract

RESUMOObjetivou-se, neste trabalho, verificar o efeito da temperatura e do período de molhamento foliar no progresso da severidade do oídio Microsphaera diffusa Cke. & Pk., nas cultivares de soja Conquista e Suprema [Glycine max (L.) Merr.]. As plantas foram inoculadas em casa-de-vegetação por agitação de plantas doentes sobre plantas sadias no estádio vegetativo V 3 . Em seguida foram colocadas, ao acaso, em câmaras de crescimento vegetal, nas temperaturas de 15, 20, 25 e 30°C e períodos de molhamento foliar de 0, 6, 12, 18 e 24 h. Dados da severidade foram utilizados para avaliar o progresso da doença e integrados ao longo do tempo por meio da área abaixo da curva de progresso da severidade (AACPS). Modelos de regressão não-linear foram ajustados para AACPS. O progresso da intensidade do oídio (AACPS) nas cultivares Conquista e Suprema foi favorecido por temperaturas próximas a 23ºC e 24ºC, respectivamente. Períodos de molhamento foliar de 8h proporcionaram o progresso máximo da severidade da doença na cultivar Conquista sob temperatura de 23ºC. Temperaturas próximas de 30ºC e de 15ºC reduziram a intensidade da doença.Termos para indexação: Severidade, epidemiologia, doença. ABSTRACTIn this study the effects of temperature and leaf wetness period in the severity progress of Powdery Mildew Cke. & Pk. in soybean cultivars Conquista and Suprema [Glycine max (L.) Merr.] were evaluated. Plants at the V3 stage were inoculated in greenhouse. Subsequently, they were conditioned into growth chambers at temperatures of 15, 20, 25 and 30°C and leaf wetness periods of 0, 6, 12, 18 and 24 hours. Severity data were integrated in time by the disease progress curve for severity (AUDPCS). Nonlinear regression models were adjusted for the disease intensity. Temperatures near 23ºC and 24ºC favored the powdery mildew intensity progress (AUDPCS) in Conquista and Suprema cultivars, respectively. Leaf wetness period of 8 h allowed the maximum progress of the disease in Conquista at temperatures of 23ºC. Temperatures near 30ºC and 15ºC reduced powdery mildew intensity.

Microclimate in agrosilvopastoral system enhances powdery mildew severity compared to agropastoral and non-integrated crop

“…In the present work, a smaller temperature difference was observed in the ASP, with similar nighttime and daytime temperatures. The average daytime temperature observed in the ASP (26.5°C) was lower than in the other treatments and closer to the best temperatures reported for M. diffusa in Brazil (Alves et al 2009).…”

“…Although B. graminis develops in a wide range of temperature, the optimum temperature for spore germination is 20°C (Cherewick 1944;Manners and Hossain 1963). Enhanced growth of M. diffusa on soybean plants was observed at temperatures of 23 and 24°C in Brazil, depending on the cultivar (Alves et al 2009), in agreeing with previous report (Mignucci 1989).…”

“…Leaf wetness was also the microclimatic characteristic most related with PM on soybean (Table 2). This may be a key factor for increased PM severity in this production system, as the leaf wetness has been shown to be harmful to conidial germination for different species that cause PM (Grainger 1947;Manners and Hossain 1963;Schnathorst 1965;Sivapalan 1993;Alves et al 2009). Higher temperatures were observed during the overnight period in the ASP system, which explains lower dew due to condensation (Hughes and Brimblecombe Fig.…”

“…In addition to providing shorter leaf wetness, temperature changes provided by the trees in ASP may have contributed directly to greater PM severity. It was demonstrated that low variation in temperature favors M. diffusa (Phillips 1984;Alves et al 2009;Pap et al 2013), while greater variation reduces infection. In the present work, a smaller temperature difference was observed in the ASP, with similar nighttime and daytime temperatures.…”

“…If colonies were kept for a second day after wetting, the sporulation returned to normal, so there seemed to be no permanent damage due to wetting on germination. In soybean eight hours of leaf wetness was the ideal period for PM (Microsphaera diffusa Cooke & Peck) in Brazil (Alves et al 2009).…”