Efeitos e transmissão de Amphobotrys ricini em sementes de mamona

Abstract

The gray mold of castor bean, caused by the fungus Amphobotrys ricini, has become an important disease due to the growth of the crop in the country, encouraged by the Biodiesel Program (PNPB).The aim in this study was to evaluate theeffects of that pathogen on seed performance and to quantify the transmission rate of this fungus in seeds of castor bean under controlled conditions.The work was carried out usingseeds of two castor cultivars (IAC Guarani e Al Guarany 2002), two strains of the fungus, two environment temperatures ( 20 ° and 25 ° C) being the seeds inoculated by the osmotic conditioning method in which seeds are exposed to fungal colonies for variables periods of times:36, 72 and 108 h, meaning different inoculum potentials.The transmission of the pathogen in seeds occurred in very low percentages in the cultivars usedand the rate did not increase with increasing inoculum potential. The presence of the fungus in artificially inoculated seeds did not affect the growth and initial development of the plant, except the dry weight of plants which presented a decrease. At 20 ° C, the speed of emergence index (IVE) and stand of plants were lower than at 25 °C. The germination percentages showed low values, which may be explained by the specific structure of castor bean, making difficult seed germination. The electrical conductivity test showed higher values than the control treatment. By "blotter test" the incidence of A. ricini, was high reaching 100% in one strain at the highest inoculum potential (108 h exposure of seeds to the fungus).