Abstract
To obtain genetic resources of resistance to bacterial leaf blight of rice caused by Xanthomonas oryzae (Uyeda et Ishiyama) Dowson, many foreign and Japanese rice varieties were tested for the resistance to five different pathotypes, groups I, II, III, IV and V, existed in Japan. As the result, most varieties used in the experiment were classified into five varietal groups according to Kozaka's grouping system. Some varieties, however, were not belonged to any of the already-known varietal groups, Kinmaze, Kogyoku, Rantai Emas, Wase Aikoku and Java, because their reaction patterns to five different pathotypes of X. oryzae were different from those of five varietal groups. This paper describes two newly-discovered varietal groups of rice on the basis of their reaction patterns to five different pathotypes of X. oryzae existed in Japan. The isolates of X. oryzae used for the experiment were T7174 for group I, T7147 for group II, T7133 for group III, H75373 for group IV and H75304 for group V. Three weeks after inoculation, scoring was taken about the disease index number according to the standard proposed by Ezuka and Horino. The reaction was considered as S (susceptible) when the value was 2.0 and over, while considered as R (resistant) when the value was below 2.0. One of the newly-discovered varietal groups were S, R, R, S, R to the bacterial groups I, II, III, IV and V, respectively, while the other were S, R, R, S, S in the same way. In the conclusion, the former was termed “Elwee group”, while the latter was termed “Heen Dikwee group”. Three varieties, Elwee, IR 2071-636-5-5 and Dickwee-1, were included in Elwee group, while the other three varieties, Heen Dikwee-1, M104 and M304, were included in Heen Dikwee group. Both genotypes of the newly-discovered varietal groups, Elwee and Heen Dikwee, concerned in those reaction patterns to five different pathotypes of X. oryzae should differ from any one of the already-known five varietal groups. The meanings of the newly-discovered varietal groups were discussed from pathological and breeding points of view in relation to the resistance to bacterial leaf blight of rice.
