Phytoalexin Production Elicited by Pyricularia oryzae Infection and Its Hyphal Wall-Component Treatment in Rice Leaves

Abstract

Infection of the rice blast fungus Pyricularia oryzae elicited the diterpenoid phytoalexin (PA) production in rice leaves. Striking difference in the time course of PA production was observed between incompatible and compatible race-cultivar relations. The PA production was firstly observed at 36-48hr, in general, after inoculation in incompatible case and no production was observed at this time in compatible case. The production was sometimes detected at 12hr in incompatible case. Such difference, however, disappeared in the case of the treatment with heat-killed spores of the fungus and PA production was observed at 48hr in incompatible and compatible cases. No elicitation of PA production was documented at the treatment with protoplasts originated from the hyphal cells of Pyricularia oryzae. Hyphal cell-wall components, especially water insoluble fraction, obtained by the fractionation of the fungal cells of compatible and incompatible races elicited excellently PA production. These results clearly verified the existence of the elicitor in hyphal cell wall.