Indu？？o de resistência à brusone em folhas de arroz por isolado avirulento de Magnaporthe oryzae

the induction of disease resistance can be activated in plants with biotic and abiotic agents such as avirulent isolates of pathogens. the objective of this investigation was to determine the concentration of inducer isolate and the time required between the inoculation with inducer (avirulent isolate) and virulent isolate of magnaporthe oryzae, for the induction of resistance in rice leaves. eighteen-day-old plants of rice cultivars metica-1 and cica-8 were sprayed in a greenhouse with an avirulent isolate utilized as inducer, at the concentrations of 0, 105, 3x105 and 6x105 conidia ml-1; sprayed 24, 48, and 72 hours prior to inoculation with virulent isolate. the induction of resistance was manifested in the reduction of leaf area affected and lesion type. the degree of induced resistance was greater in cultivar metica-1 than in cultivar cica-8 in relation to respective controls. the induction of resistance was superior in cica-8 in treatments where inducers were applied 48 hours prior to inoculation with the virulent isolate, at concentrations of 6x105 and 3x105 conidia ml-1. on the other hand, the induction in metica-1 was significantly higher in relation to control, at all concentrations and all periods of application of the inducer, and did not show differences between treatments.