FUNGITOXIC RESPONSES OF RICE LEAVES AND CALLI AS RELATED TO BLAST RESISTANCE

The toxicity of rice cell exometabolites to blast spores was studied. The cultivars represented the host susceptibility or resistance (complete, partial or mixed). Diffusates collected from intact leaves of the susceptible cultivar, 1 or 2 days after inoculation, was found to inhibit spore germination weakly whereas this ability was significantly stronger in all resistant cultivars. Active oxygen (AO) species (H2O2 or.OH) may be involved in the toxicity since the latter was abolished by appropriate scavengers. The contribution of radical O2 to the toxicity was large in completely resistant cultivars and absent in the partially resistant ones. Cultivars with mixed type of resistance were intermediate in this respect. So, the leaf diffusate fungitoxicity was likely indicative of the resistance. Analogous antifungal responses were found in rice callus cultures, with the similar specificity to fungus strains as in intact plants from which the cultures were derived. Diffusates of spore-inoculated calli were weakly if any fungitoxic in compatible combinations but strongly toxic in incompatible ones. The reaction depended on Ca2+ ions. During the first hours after inoculation, the toxicity of callus diffusates was mediated by AO and then by other substances formed as a result of AO production. Therefore, rice cells in a callus culture retain fungitoxic responses characteristic of the varietal resistance and peculiar to intact plants.