Phenotypic and marker assisted screening of rice genotypes inoculated with three widely available pathogenic strains of Xanthomonas oryzae pv . oryzae

The bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae is one of the most devastating pathogenic diseases responsible for extensive crop loss across different rice growing regions of the world. Presently, new X. oryzae strains have emerged which have managed to overcome the resistance conferred by major genes like xa5 and xa13 . Under such circumstances the current paper evaluates rice genotypes belonging to diverse origins, viz . high yielding varieties, indigenous landraces and IR24 near isogenic lines, in terms of their resistance against three widely available strains of X. oryzae in India vis-à-vis West Bengal. The genotypes were also screened using molecular markers which are tightly linked with four major resistance conferring genes, namely Xa4, xa5, xa13 and Xa21 . The overall analysis revealed that the three gene combination i.e. xa5 + xa13 + Xa21 was essential for maintaining stability in resistance against all the three pathogenic strains used for inoculation in the current study. A deviation from the above mentioned gene combination resulted in variable degree of pathogenesis, depending upon the Xoo strain used for inoculation. The investigation also identified the presence of dominant Xa4 gene among many of the popular cultivars in West Bengal, as well as in indigenous landraces like Kalabhat and Chamarmani; which showed strong resistance against the local Xoo strain. However, the genotypes failed to show any significant resistance against newly introduced strains indicating that the popular cultivars in West Bengal are still vulnerable towards new pathogenic strains of Xanthomonas oryzae . Thus, introgression of multiple resistance gene into popular cultivars in the region is necessary for ensuring durable resistance against the disease.