Evaluation of Myanmar Rice Germplasms for Resistance to Bacterial Blight

Pathogenic diversity of Xanthomonas oryzae pv. oryzae from four major rice growing divisions of Myanmar was investigated. One hundred and thirty two isolates: 28 isolates from Ayeyarwady Division, 17 from Yangon Division, 42 from Bago Division and 45 from Mandalay Division, collected during 2004 and 2005 rice growing seasons were very diverse in virulence on 12 near-isogenic lines each of which carrying a specific resistance gene, Xa 1, Xa 2, Xa 3, Xa 4, xa 5, Xa 7, xa 8, Xa 10, Xa 11, xa 13, Xa 14, or Xa 21. The isolates were classified into 19 races based on their virulence. Among 19 races, Race 17 which consisted of 21.97% of the test isolates, was not only the most predominant race but also prevalent in 4 major rice growing divisions of Myanmar. It was also virulent on most of the differentials except IRBB 13 and IRBB 21. Race 7 and Race 11 fell into the second and third position in terms of predominance, respectively. However, Race 11 was found in four major rice growing divisions except Yangon Division, and Race 7 was detected in Bago and Mandalay Divisions only. Similarly, most of the other races found in one or two divisions were not detected in other divisions. The most predominant race in one division was also different from that of other divisions. Pathogenic diversity of four selected isolates collected from Hmawbi, Bogale, Paukkhaung and Kyaukse was confirmed by computer-assisted image analysis method in quantifying disease severity. The virulence of each of the four isolates on three near-isogenic lines, IRBB 3, IRBB 7 and IRBB 13 each carrying a specific resistance gene Xa 3, Xa 7, and xa 13, respectively, was qualitatively different from that of other isolates. One hundred and thirty-four Myanmar rice germplasms obtained from Seed Bank, Department of Agricultural Research, Yezin, were evaluated for their resistance to the representative isolates of four races. The test rice germplasms were divided into four groups, Group A, B, C and D, based on their reaction to four isolates. Two rice germplasms namely Mya Wut Yi and Talay were belonged to Group D and resistant to three representative isolates of the three most predominant races detected in four major rice growing divisions of Myanmar