Abstract
Anti-blast substances (S-1 and its derivatives) produced in blast-infected and UV-irradiated rice leaves of three cultivars showing different horizontal resistance were analyzed quantitatively, in order to clarify the role of these substances in disease resistance. The production of the substance was caused not only in the inoculated leaves, but also in UV-irradiated leaves where brown spots appeared. While, the production was not observed in case of symptomless highly resistance and chemical damages tested. Negative correlation was observed between the amount of the substances formed and the degree of horizontal resistance at 7th day after inoculation. These results seem to indicate that these substances could associate secondarily with the resistance and the production relates closely with browning of host cells in the destruction process. The final conclusion, however, should be drawn after studies at the infection site. UV-damages were severer in aged leaves (lower leaves) and the degree of the damages was different in each cultivar. The amount of the anti-blast substances formed closely correlated with the degree of UV-damages. So far as tested cultivars concerned, the damages were less in horizontally weak cultivar than that of strong cultivar. Further studies on this point with various cultivars were required.
