The severity of rice stem rot (Leptosphaeria salvinii) was decreased when the plant had been affected with "white tip", the rice nematode disease caused by Aphelenchoides besseyl. Both respiratio n rate and activity of respiratory enzymes (ascorbic acid oxidase, cytochrome c oxidase, polyphenol oxidase, catalase, and peroxidase) of rice plant were found to be promoted when the latter was affected by the white tip disease. When compared the activities of the two polyphenol oxidases of leaves it was found that laccase activity was stronger than that of tyrosinase, and the polyphenol oxidase activity of lower leaf of a plant was stronger than that of the upper. Considerin g the results12) that the severity of the stem rot was increased with the advance of the ripening of rice plants, it was concluded that the resistance against the stem rot of the white tip diseased plant was caused by the vigorous metabolism of the rice stem tissue, induced by the nematode invaded, during the season from tillering till harvest time.
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