1990 Volume 56 Issue 1 Pages 1-9
This paper deals with the changes in aggressiveness of the isolate belonging to race 337 of rice blast fungus, Pyricularia oryzae Cavara, which was re-isolated after successive passage on rice cultivars with a different single true resistance gene. An isolate (race 337) with wide spectrum of virulence was used as original inoculum for successive passage. The authors measured the rate of susceptible lesion per total lesions produced on a leaf blade and the number of conidia formed on a unit area of lesion (10mm2) on leaf of 4 rice cultivars possessing the same or different true resistance gene from that of passed cultivars as indicants for the aggressiveness. As the results, many isolates re-isolated after successive passage enhanced the aggressiveness to the rice cultivars with the same true resistance gene as that of passed cultivars. On the other hand, many isolates decreased the aggressiveness to the rice cultivars with different true resistance gene from that of passed cultivars.