Abstract
Sporulation potentials of rice blast lesions formed on 22 rice cultivars differing in their degrees of field resistance to blast were compared by counting the number of spores produced per unit area in unit time, 10 days, after inoculation. Two isolates of blast fungus which are pathogenic to all the cultivars were used. Inoculation was made to the topmost leaves of the main stem and the primary tiller on the spots prepared by press-injuring with a specially designed punch. Lesion areas of resistant (R) cultivars were always larger than those on susceptible (S) ones at 10-leaf stage, and the difference in the sporulation potentials of lesions among the cultivars became distinct 10 days after inoculation. Sporulations of larger lesions were more abundant than those of smaller ones. Furthermore, sporulation potentials per 30mm2 of lesion areas conspicuously differed among the cultivars, i.e., lower in R cultivars, Todorokiwase and Yoneshiro, than in S cultivars, Kusabue and Aichi-asahi. Exceptionally, the potential was high on a R cultivar, Upland rice Norin 12, despite of its smaller lesion area. Differece in the sporulation potential was not enough clear at 5-leaf stage, became fairly distinct at 6-leaf stage, and prominent at 8-leaf stage.
