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

本研究基于基因换基因理论，研究了稻瘟病菌产生与抗性表达相关的种族特异性激发子。水稻的叶鞘。在稻瘟病菌亲和小种的孢子萌发液存在的情况下，用非病原菌或亲和小种分别接种关口朝日。接种36小时后，对接种后真菌在叶鞘细胞中的渗透和菌丝生长进行研究，发现不同孢子萌发液对真菌的侵染行为有较大差异。稻瘟病病菌不亲和小种的孢子发芽液（sgf）在水稻叶鞘上萌发24小时，显著抑制了交替稻瘟病菌和不亲和小种的渗透和菌丝生长。不亲和小种的sgf在不预先接种稻瘟病菌的情况下，诱导了健康叶鞘的不亲和性。用稻瘟病菌不亲和小种的sgf在敏感品种Mohoto上萌发，也观察到这种诱导不亲和性。不亲和种稻瘟病菌孢子发芽液（SGF）在塑料板上萌发时，未观察到上述诱导不可接近现象。在120℃下加热20 min后，sgf的激发子活性未被破坏。凝胶过滤和透析试验表明，激发子的分子量小于5000。有机溶剂萃取试验表明，萃取剂具有水溶性。结果表明，稻瘟病菌孢子产生的诱导子只对宿主组织产生诱导不可接近性，而与品种和菌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.