Abstract
The occurrence of variants and change of predominant race of rice blast fungus, Pyricularia oryzae Cavara, during successive inoculation on rice plants were investigated using two isolates (race 337) which have wide spectrum of virulence and always sorted out some variants. Thus, the isolates were passed through the leaves of 6 susceptible rice varieties for 9 successive generations by punch-inoculation in a growth cabinet. In 4 among 12 combinations of 2 isolates and 6 rice varieties, predominant race changed until the 9th generation. On two varieties, Aichiasahi and Fujiminori with vartical blast resistance gene Pi-a, race 003 became predominant replacing the races 337 and 137 in 3 cases out of 4. Race 047 survived on Ishikari-shiroke with resistance gene Pi-i until the 9th generation. On the other hand, predominant race did not change in all combinations on Fukuyuki with resistance gene Pi-i and Kanto 51 and Kusabue with resistance gene Pi-k until the 9th generation.
These data suggested that race 337 sorted out many variants during the successive passage on rice leaves and some of the variants, race 003 or 047, survived and predominated in competition with others.
