FUNGITOXICITY OF RICE LEAF EXCRETION DUE TO ACTIVATED OXYGEN - CONTRIBUTION TO PARTIAL RESISTANCE TO BLAST DISEASE

The intact rice Oryza sativa L. plants of cultivars susceptible (Sha-t iao-tsao), vertically resistant (Zenith), and partially resistant (Shi mokita) to blast disease were studied. Drop diffusates collected from healthy or infected leaves of susceptible cultivars or from healthy le aves of vertically resistant cultivars slightly (by 10 - 30%) inhibite d fungal spore germination. The diffusates from infected leaves of ver tically resistant cultivars strongly inhibited the spore germination ( by 50 - 70%). The diffusates from healthy leaves of the partially resi stant cultivar also displayed high antifungal activity (40 - 60% inhib ition of spore germination), which increased to 60 - 90% after inocula tion. The fungitoxicity of a diffusate taken from partially resistant cultivars was prevented neither by long diffusate preincubation before spore treatment, by proteinase addition, nor by boiling. The toxicity action disappeared completely after diffusate dialysis. The toxicitie s of diffusates from the leaves of both resistant cultivars were elimi nated by catalase, a scavenger of hydroxyl radicals, or Fe3+ ion chela tor desferrioxamine. The superoxide dismutase was an effective protect or only in the case of the vertically resistant cultivar. This partial resistance appears to be accounted for by leaf diffusate fungitoxicit y mediated by active oxygen species (H2O2 and (OH)-O-., but not by O-2 (-)), their interconversion being catalyzed by iron ions.