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，研究了稻瘟病菌小种特异性激发子的产生与稻瘟病抗性表达的关系。在稻瘟病菌不亲和小种孢子萌发液存在的情况下，将预先接种稻瘟病菌亲和小种的关口朝日水稻叶鞘接种非病原菌或不亲和小种。接种后36小时，对接种后真菌在叶鞘细胞中的侵入和菌丝生长进行了研究，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 h后，对互隔孢霉或不亲和小种的侵入和菌丝生长均有明显的抑制作用。不亲和小种的sgf诱导健康叶鞘中的不可及性，而不预先接种与稻瘟病菌的亲和小种。此外，这种诱导的不可接近性也观察到处理与不兼容的小种的稻瘟病菌发芽的敏感品种Mohoto。以不亲和小种的孢子萌发液为材料，研究了其对稻瘟病菌孢子萌发的影响。稻瘟病菌在塑料平板上萌发，但未观察到上述诱导的不可接近现象。在120 ℃热处理20 min后，sgf的激发子活性没有受到破坏。凝胶过滤和透析试验表明，sgf的激发子分子量小于5000。有机溶剂萃取试验表明，该诱导子具有水溶性。这些结果表明，稻瘟病菌孢子产生的诱导子只对寄主组织产生诱导不可及性，而与品种和小种的亲和性无关。

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.