Abstract: We produced buff mutants from a field isolate using UV-mutagenesis. Of 13 UV-induced buff mutants tested six were able to cause sporulating. lesions on rice plants. Buff cultures were recovered from lesions on CO 39, IR50 and IR36, suggesting that certain buff mutants have the ability to infect rice without nurmal melanin synthesis. Lesions derived from some buff mutants given conidial cultures with wild type pigment at frequencies ranging from 10% to 100%. White variants were also recovered from lesions caused by buff mutants. Pigment variants did not occur at frequency greater than 10^-3-10^-4 in plating experiments. Lesions obtained from IR50 coinoculated with a buff mutant and a wild type isolate gave predominantly buff cultures. In one case,a single lesion caused by a buff mutant gave both wild type and buff cultures. These data suggest that somatic changes might occur during interaction with rice plants.

Key words: Buff pigment mutants, Melanin synthesis, Magnaporthe grisea, UV-mutagenesis, Variant, Pigment, Somatic cell

摘要： 利用紫外光诱变，从来自菲律宾田间的一个具有广谱毒性的流行菌株PO6-6中获得一些浅黄色素突变株，并检测了它侵染水稻的频率；同时对利用浅黄色的表现型来研究体细胞变异的可能性进行了探讨。在所测试的13个浅黄色素突变株中，有6个能使水稻产生病斑，在品种CO39、IR50，IR36上能重新分离到浅黄色素突变株。由此表明，某些浅黄色的突变株具有侵染水稻的能力， 它们没有通常的黑色素合成。从一些浅黄色突变株引起的病斑上获得的单孢培养菌中，野生菌株(Wild type)色素的频率范围为10％～100％。由浅黄色突变株引起的病斑中也可重新获得白色的变异物。在室内培养试验中，出现色素变异的频率未超出l10^-3 ～10^-4 的范围。用一个浅黄色突变株和野生类型的分离菌株进行的相互接种中，从品种IR50的病斑上分离的单孢中，浅黄色菌株占绝对优势。在一次实验中， 由浅黄色素培养菌所引起的一个病斑中，同时获得了浅黄色和灰黑色的培养菌。这些结果表明，体细胞色素的变异也许表现在与寄主植物之间的互作。

关键词: 稻瘟病, 浅黄色素突变体, 紫外光诱变, 黑色素, 变异, 体细胞