Abstract
Improvement of differential varieties is necessary, as the number of resistance genes used for breeding of blast resistance in rice increased. Establishment of new differential system is essential for population genetics and molecular genetics on host pathogen relationship. Blast fungus was collected from the ear necks of resistant varieties in several prefectures. Varieties from which the fungus was isolated were Kagahikari (Pi-i Pi-k" ) and Notohihari (('Pi-z" ) in Ishikawa Prefecture, Niigatawase ("Pi-z" or (Pi-a Pi-z" ) in Niigata Prefecture, Hatsuboshi ('Pi-i" ) in Fukushima Prefecture, Akiyutaka ((pi-k Pi-z" ) and Hanahikari ('Pi-i" ) in Yamagata Prefecture, and Yamahikari ('Pi-ta2) in Mie, Gifu and Nagano Prefectures. These isolates were tested for pathogenicity using twelve differential varieties, and 66 races (genotypes) were obtained. When plural nonrandom associations in interactions between avirulence loci were recognized in a field, two types of interactions (cross-type and noncross-type) were always found.
