Pathogenic diversity of Xanthomonas oryzae pv. oryzae strains from Yunnan Province, China

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 Xal, 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 I 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.