Abstract
Occurrence or disappearance of abnormality in normal or abnormal isolates of Rhizoctonia solani anastomosis group 4 (AG4) by several treatments were examined. Abnormality has not disappeared by heat (40∼60C) treatment, chemical (streptomycin sulfate, oxytetracycline, chloramphenicol, cycloheximide, ethidium bromide, acriflavine) treatment, hyphal tip or mass transfer, and single protoplast isolation of abnormal isolates. On the other hand, abnormal isolates occurred from healthy isolates by single protoplast isolation and hyphal tip transfer with low frequency of 0.9% and 0.2%, respectively. These results showed that agent(s) stimulating abnormality had already existed in healthy isolates. Development of abnormality was also highly seen when normal isolates were dipped into a culture broth or macerated suspension of abnormal isolates. However, it was not seen in the case of a culture broth or macerated suspension filtrated through membrane (0.45μm). Lethal isolates which produced brown-black pigment in medium and could not survive after transfer were obtained both from normal and abnormal isolates. Besides agent(s) stimulating abnormality, the existence of lethal agent(s) has been suggested.
