Studies on Genetics and Breeding of Resistance to Bacterial Leaf Blight in Rice. : II. Newly-Discovered Wase Aikoku Group Varieties Native to Japan

To obtain genetic resources of resistance to bacterial leaf blight 0f rice caused by Xan-thomonas oryzae (Uyeda et Ishiyama) Dowson, 34 Japanese native varieties were tested for the resistance to five different pathotypes existing in Japan, groups I, II, lll, IV and V. As the result, 15 Japanese native varieties were newly found to express the reaction pattern of Wase Aikoku group to five different pathotypes of X. oryzae. Adult plants grown in the paddy field were provided for the experiment. The isolates of X. oryzae used for the inoculation were T 7174 for group I. T 7147 for group II, T 7133 for group lll, H 75373 for group IV and H 75304 for group V. Sixteen fully developed leaves per combination of rice variety with bacterial isolate were inoculated at their central part by double needle pricking method. Two weeks after inoculation, scoring was taken abuot the disease index number according to the standard proposed by EZUKA and HORINO (1974). The resistance degree was evaluated on the basis of the mean value of the disease indices of sixteen leaves, and graded as R (resistant) or S (susceptible) depending on whether the value was 2.O and below or over 2.O.