Molecular elucidation of race-cultivar specificity in rice blast disease by using the rice mutants.

本研究基于基因对基因理论，对稻瘟病菌产生与抗性表达相关的小种特异性激发子进行了研究。在稻瘟病菌不亲和小种孢子萌发液存在的情况下，用非病原菌或不亲和小种接种预先接种稻瘟病菌亲和小种的关口朝日品种水稻叶鞘。在接种36h后观察接种后真菌在叶鞘细胞中的穿透和菌丝生长情况，发现不同孢子萌发液中真菌的侵染行为存在较大差异。稻瘟病菌不亲和小种的孢子萌发液在水稻叶鞘上萌发24小时后，对赤霉菌或不亲和小种的侵染和菌丝生长均有明显的抑制作用。不亲和小种的SGF在没有预接亲和小种的情况下导致健康叶鞘不能获得。此外，在感病品种Mohoto上萌发的稻瘟病菌不亲和小种的SGF处理也观察到了这种诱导不可达性。而在塑料平板上萌发的稻瘟病菌不亲和小种孢子萌发液(SGF)中，未观察到上述诱导不可及现象。SGF的激发子活性不受120℃热处理20min的破坏。凝胶过滤和透析实验表明，诱导子的相对分子质量小于5,000。有机溶剂提取试验表明，诱导子是水溶性的。这些结果表明，稻瘟病菌孢子只在寄主组织上产生与诱导不可及有关的激发子，而与品种和真菌小种之间的亲和性无关。

In this study, the production of race-specific elicitors by M.grisea relating to expression of resistance based on gene-for-gene theory in rice blast disease was investigated. Rice leaf-sheaths of cv.Sekiguchi-asahi which had been pre-inoculated with a compatible race of M.grisea were inoculated with a nonpathogen or an incompatible race in the presence of the spore germination fluids from incompatible race of M.grisea. When the penetration and hyphal growth of post-inoculated fungi in leaf-sheath cells were investigated 36 hr after post-inoculation, there is a large difference in infection behaviors of fungi among spore germination fluids. In the case of the spore germination fluid (sgf) from incompatible races of M.grisea germinated on rice leaf-sheaths for 24 hr, penetration and hyphal growth of A.alternata or incompatible race were significantly inhibited. The sgf from incompatible race induced inaccessibility in healthy leaf-sheaths without pre-inoculation with the compatible race of M.grisea. Further, such induced-inaccessibility was also observed by treatment with the sgf from the incompatible race of M.grisea germinated on the susceptible cultivar Mohoto. In the case of spore germination fluid (SGF) from incompatible race of M. grisea germinated on plastic plates, however, above mentioned induced-inaccessibility phenomena were not observed. The elicitor activity of the sgf was not destructed by heat treatment at 120 C for 20 min. From gel filtration and dialysis tests, it was suggested that molecular weight of the elicitors were smaller than 5,000. From extraction test with organic solvents, it was demonstrated that the elicitors were water-soluble. These results indicate that M.grisea spores produce the elicitors concerning to induced inaccessibility only on host tissues regardless of the compatibility between cultivar and fungal race.