ACTIVE OXYGEN MEDIATES HEAT-INDUCED RESISTANCE OF RICE PLANT TO BLAST DISEASE

Fragments of rice leaves taken from a cultivar susceptible to blast disease were incubated after inoculation either at low (23-degrees-C) or high (28-degrees-C) temperature for 24 h. In the latter case the leaves acquired some resistance, exhibited as a lower frequency of susceptible type lesions. Generation of superoxide radicals (assayed with epinephrine) in diffusates of healthy or infected leaves increased with heating. Simultaneously toxicity of diffusates to Pyricularia oryzae spores was enhanced. The toxicity was eliminated with superoxide dismutase or catalase, indicating a participation of O2- and H2O2 in exerting an antifungal action. Addition of these antioxidative enzymes to inocula completely prevented the heat-induced resistance to blast. It is concluded that this resistance is caused (at least partly) by increased production of fungitoxic oxygen species on the leaf surface.