Abstract
The effects of momilactones A (M-A) and B (M-B) extracted from rice husks, and of their derivatives, momilactone A alcohol (M-A-OH) and momilactone B acetate (M-B-Ac), upon the spore germination, germ tube growth and appressorium formation of rice blast fungus, Pyricularia oryzae Cavara were investigated. Three or six isolates belonging to 3 pathogenic race groups of this fungus were used in this study. The chemicals used were suspended in water containing 0.1% of Tween 80 and adjusted to the concentrations of 10-3, 10-4 and 10-5 M, respectively. All chemicals used inhibited spore germination and germ tube growth, but the inhibition % reduced with the elapse of incubation time during treatment. The antifungal activity was highest in M-B, followed by M-B-Ac and M-A-OH, and was least in M-A. The inhibitory activities differed considerably with the isolates used. The ED50 values in M-A and M-B of the inhibition of germ tube growth at 9 hr treatment were about 10-410-3 M and about 10-510-4 M, respectively. Only M-A stimulated the appressorium formation.
