âEpidemiologia do mofo-cinzento (Amphobotrys ricini Buchw.) da mamoneira" / "Epidemiology of gray mold of castor bean"

AUTOR(ES)

Angelo Aparecido Barbosa Sussel

DATA DE PUBLICAÇÃO

2008

RESUMO

The gray mold of castor bean, caused by Amphobotrys ricini, promotes rapid and complete destruction of castor bean bunches under high relative humidity and temperatures around 25 ÂC. Currently, it is the most important disease of the crop in some regions of Brazil. Thus, the objectives of this work were: to characterize cultures of A. ricini from different regions of Brazil; to assess the effects of conidial concentration, temperature and wetness duration on the progress of the disease in growth chambers; to evaluate the effect of the environment in the aerobiology and on the spatial and temporal progress of the gray mold in the field; and to develop a diagrammatic scale to assess the severity of the disease. Eight isolates from the states of Minas Gerais, SÃo Paulo and Rio Grande do Sul were assessed. The isolates, even those of the same origin, showed differences on the mycelial growth, sporulation, germination of conidia and formation of sclerotia on PDA under different temperatures of incubation. The sclerotia ranged in size (0.5 to 5.0 mm) and color (gray white to black). The optimum temperature for mycelial growth, sporulation and conidial germination ranged from 20.7 to 33.7 ÂC, 20.6 to 22.1 ÂC and 16.1 to 22.3 ÂC, respectively. There was significant interaction between temperature and wetness duration on the progress of gray mold under controlled conditions. Increases of conidial concentration, wetness duration and temperature resulted in higher disease incidence and severity. There was no manifestation of symptoms in the absence of wetness under temperatures below 20 Â C. The disease was more severe at 28 Â C and 72 hours of wetness duration. There was greater dependence of wetness duration when temperatures were below 20 ÂC. Under low rainfall and low relative humidity in the field, the monomolecular model fitted better to explain the incidence and severity progress and the spatial distribution pattern of the aggregated diseased plants. During periods of increased rainfall and relative humidity, the Gompertz model fitted better to the progress curves and the diseased plants were randomly distributed in the field. The concentration of conidia in the air was higher during the period of higher relative humidity and rainfall, resulting in higher incidence and severity of the gray mold. There was correlation between all environmental variables evaluated and the progress of epidemics and the inoculum concentration in the air. The diagrammatic scale to assess the gray mold severity was made of ten levels of severity (3, 5, 8, 12, 25, 50, 76, 86, 94, and 99%). Its use has enabled precise and accurate evaluations of the severity of the gray mold in bunches of castor bean.

ASSUNTO(S)

ciÃncias agrÃrias spatio-temporal progress temperature climatic variables inoculumÂs dinamic leaf wetness period cultural caracterization progresso espaÃo-temporal variÃveis climÃticas dinÃmica de inÃculo temperatura perÃodo de molhamento foliar caracterizaÃÃo cultural

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