Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the major production constraints especially in irrigated and rainfed lowland ecosystems. Fifty two isolates of Xoo collected from different rice growing areas of Andhra Pradesh were characterized for their virulence and genetic profile. Virulence analysis carried out on a set of rice differentials revealed that different NILs with single genes were susceptible to about 53–84% of the isolates except IRBB 13 which showed susceptible phenotype to about 23% of the isolates used in the study. Among the two genes combination, combination of Xa4 and xa 5 showed susceptibility to many pathotypes. Based on the virulence pattern, the isolates were categorized into 10 pathotypes. Among these, pathotypes 21 and 22 were highly virulent and were individually virulent on differentials having xa13 and Xa21 genes. Pathotype 7 was most common and was present in all the locations surveyed. Molecular analysis of variability among the isolates was carried out through PCR analysis using multi-locus primer Jell and Jel2 (based on the repeat element ISll12 in the Xoo genome). A high level of genetic polymorphism was detected among the isolates. Using the genotypic data of selected isolates from different pathotype groups, we clustered them based on genetic similarity. Afairly good correlation was obtained where most of the isolates virulent on BB resistance genes xa13 or Xa21 or both grouped together. The results ofthe study revealed that gene combinations like xa5 + xa13, xa13 + Xa21, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 can give broad spectrum durable resistance to this important disease of rice.
Xanthomonas oryzae pv. oryzae, rice, bacterial blight, resistance
