Rice cultivar groups in Myanmar based on reaction to bacterial blight

Abstract

Rice cultivars from Myanmar were evaluated for resistance to four Philippine races of bacterial blight pathogen (Xanthomonas campestris pv. oryzae) with clipping inoculation method (KAUFFMAN et al. 1973). Out of 1473 cultivars screened at seedling stage. 337 cultivars were initially categorized into five groups by their differential reactions to races 1, 2, 3, and 4 e.g. SRSS, RSSM, RRSM, RRRM (or RRRR) and MMMM. The MMMM reaction at seedling stage was further classified either into RRRR with browning reaction around lesions or moderately resistant cultivars (non-classified) on the basis of repeated tests at adult stage. As discussed by OGAWA et al. (1991), the RRRR reaction with the browning around the lesions is similar to that of Java 14 group. The cultivars of this group were considered to have Xa-3 for resistance. The reactlon SRSS is similar to that of CAS 209 (Xa-10) group. Likewise, the reaction patterns of RSSM, RRSM, and RRRM (without browning) resembled the reaction patterns of TKM 6 (Xa-4), Mond Ba (both Xa-10 and Xa-4), and DZ 192 (xa-5) groups, respectively. Out of 337 cultivars screened at adult stage, 218 were susceptible. Of the 119 resistant cultivars, 44 were placed in CAS 209 group, 33 in TKM 6, 4 in Mond Ba group, 9 in DZ 192 group, 3 in Java 14 group, and 26 as non-classified cultivars. The raction of the cultivars of each group was compared with that of each of the near-isogenic lines having a specific gene for the cultivar groups. Homogeneity of each group was confirmed through variance analysis over three seasons. Thus, the cultivars of CAS 209 and TKM 6 groups were predominant with a small number of cultivars belonging to Java 14 and DZ 192 groups.