Comparison of two differential systems for distinguishing pathogenic groups of Xanthomonas campestris pv. oryzae

Two differential systems for distinguishing pathogenic groups of Xanthomonas campestris pv. oryzae, the causal organism of bacterial leaf blight of rice, have been developed in Japan and at IRRI independently of each other. This experiment was designed to make a comparative study of both differential systems. The needle pricking method alone was adopted for inoculation in this study, because a highly significant correlation was observed between the scores based on the needle pricking method and the clipping method developed in Japan and at IRRI, respectively. Five rice differentials from Japan : Kinmaze, Kogyoku, Te-tep, Wase Aikoku 3 and Java 14, and five from IRRI : IR8, IR20, IR1545-339, DV85 and Cas 209, with specific genes for resistance identified in respective countries were evaluated at reproductive stage against the Japanese and the Philippine isolates. Japanese differentials Kogyoku and Te-tep were as susceptible as Kinmaze to all the Philippine isolates. Wase Aikoku 3 and Java 14, however, were resistant to all of them. IRRI differentials showed different reactions to the Japanese isolates. IR8, carrying no functional major gene for resistance to the four Philippine groups, was resistant to the Japanese groups, II, III and IV. IR20 was resistant to Japanese groups I and V, but susceptible to groups II, III and IV. IR1545-339 and DV85 were resistant to all the five Japanese groups. Cas 209, which was resistant to the Philippine group II, was susceptible to all the five Japanese groups. The results indicated that rice differentials developed in Japan and at IRRI were individually distinct in their reaction to the groups of both countries. Forty-nine varieties of japonica and indica rices were evaluated for their resistance to four Philippine groups. Reaction patterns of the forty-nine varieties to four Philippine groups did not coincide with their respective Japanese varietal groups classified according to five Japanese groups. Virulence of sixty-two isolates in the Philippines were evaluated on the ten rice differentials of Japan and IRRI. Sixty-one out of sixty-two were similar to isolate T7133 (Japanese group III) on Japanese differentials, but showed different reaction to IRRI differentials. It appears that the viulence of the Philippine isolates was not comparable to any group of Japan