Abstract
The strains of Xanthomonas oryzae pv. oryzae collected in Yunnan province, China, during the period from 1994 to 1996 were polymorphic for virulence to the 12 near-isogenic lines harboring the resistance genes Xa1, Xa2, Xa3, Xa4, xa5, Xa7, xa8, Xa10, Xa11, xa13, Xa14 and Xa21, and the 3 check varieties, IR24, Toyonishiki and Sigadagabo. One hundred and thirty-eight strains were classified into 10 pathogenic groups (tentatively designated as pathotypes A to J) based on their pathogenicity. These 10 pathotypes were classified into 3 large groups based on the pathogenic range to the differentials; group 1 with a very narrow pathogenic range was virulent to only 2 differentials, group 2 with an intermediate pathogenic range was virulent to 4 to 7 differentials and group 3 with the widest pathogenic range was virulent to 9 to 12 differentials, respectively. Groups 1 and 2 were distributed in the northern and central parts of Yunnan province where various kinds of Japonica rice varieties are cultivated. On the other hand, Group 3 was distributed mainly in the southern part, where Indica rice varieties including hybrid rice are widely cultivated. In this study, we showed that 2 differentials, IRBB13 (xa13) and IRBB21 (Xa21), were resistant to all the strains tested, while IRBB5 (xa5) was susceptible only to 6 strains (4.3%). These resistance genes could be used for a breeding program for resistance to BLB in Yunnan province.
