Abstract
The genes of IR 26 responsible for resistance to the five bacterial groups, I, II, III, IV and V of Xanthomonas campestris pv. oryzae (Ishiyama 1922) Dye 1978 from Japan were analyzed. The resistant variety IR 26, the susceptible variety Todorokiwase and their cross hybrids F1 and F2 plants were tested for resistance to each of the representative isolates of the five bacterial groups; T7174 for group I, T7147 for group II, T7133 for group III, H 75373 for group IV and H 75304 for group V.
Adult plants grown in the experimental paddy field were inoculated by double needle prick method. Three weeks later, the inoculated plants were scored for disease-index number according to the standard proposed by Ezuka and Horino (1974). With the disease-index number to bacterial groups I, II, III, IV and V, F1 and F2 means fell between the resistant and susceptible parents. F2 segregation, however, resulted in a continuous distribution with a wide range from 0.0 to 7.0 for bacterial groups I, II and III, from 0.0 to 6.0 for group IV, and from 0.0 to 5.0 for group V. This suggests that several multiple genes and/or polygenes are responsible for the resistance to bacterial groups I, II, III, IV and V.
The broad-sense heritabilities for resistance to bacterial groups I, II, III, IV and V in F2 generation were so high as estimated to be 0.892, 0.882, 0.877, 0.827 and 0.714, respectively, suggesting that the resistance to those five bacterial groups could successfully be selected. Besides, it was indicated that the differences among the estimates of heritability for resistance to bacterial groups I, II, III, IV and V most likely depended on the aggressiveness of the isolate used. Estimate of heritability for resistance to bacterial group V which is relatively weak aggressive isolate was somewhat lower than others.
On the other hand, there were also found in F2 generation high positive genotypic correlation coefficients (γG(B)=0.6-0.8) among the resistances to bacterial groups I, II, III, IV and V. These correlations are quite favorable for simultaneous selection of resistant plants to those five bacterial groups.
