Grouping of rice cultivars based on reaction pattern to Philippine races of bacterial blight pathogen (Xanthomonas campestris pv. oryzae)

For identifying new sources of resistance to bacterial blight of rice, we inoculated rice cultivars from the International Rice Germplasm Center (IRGC) of International Rice Research Institute (IRRI) with races 1, 2, 3, and 4 of bacterial blight pathogen from Philippines. Based on the reaction patterns to the four races, rice cultivars were classified into eight groups. Four groups are based on single genes. (1) Java 14 group having resistance to four races with brownish margins around lesions. Cultivars of this group have Xa-3 for resistance. (2) TKM 6 group with resistance to race 1, moderate resistance to race 4 but susceptibility to races 2 and 3. Cultivars of this group have Xa-4. (3) DZ 192 group with resistance to races 1, 2 and 3 and moderate resistance to race 4. Cultivars of this group have xa-5. (4) CAS 209 group with resistance to race 2 only. Cultivars of this group have Xa-10. Four groups, each having two genes were recognized. These groups are: Mond Ba (Xa-4+Xa-10), DV85 (xa-5+Xa-7), Makhmal Mehi (xa-5+Xa-4), and BJ1 (xa-5+xa-13). Electrophoretic variation at isozyme loci was examined in a number of cultlvars belonging to different groups. These results suggest that the differentiation of BB resistance genes probably linked with the differentiation of cultivars into distinct ecotype