Abstract
Seven isolates of Pyricularia oryzae Cav. were tested for their dependency of sporulation on substrates or near UV irradiation. All the isolates exhibited poor sporulation on PDA medium in the darkness. Even in the darkness, 2 out of the 7 isolates produced conidia abundantly on autoclaved rice leaf pieces and also on rice leaf powder medium. Another 5 isolates responded to the near UV irradiation with the sporulation 10 to 40 times as much as that in the darkness. Therefore, there exist two types of sporulating ability in P. oryzae, one mainly depends on a substrate and the other on near UV light. The presence of leaf powder of rice and Italian ryegrass stimulated the sporulation of all isolates, whereas that of bean, raddish and potato stimulated only very slightly and the degree of stimulation differed according to the isolates tested. The water or ethanol extract from rice leaf tissues induced sporulation of blast fungus and the activity of both extracts is not inactivated by autoclaving. The active substances in the hot water extract are adsorbed by ion exchanger of anion, but not of cation. The extract which is not adsorbed by the cation exchanger stimulated sporulation at concentrations higher than 10μg/ml.
