Phenotypic Diversity of Xanthomonas oryzae pv. oryzae in Nepal. TIKA B. ADHIKARI, Former Research Fellow, Division of Plant Pathology, International Rice Research Institute (IRRI), P.O. Box 933, Manila, The Philippines. T. W. MEW, and P. S. TENG, Division of Plant Pathology, International Rice Research Institute (IRRI), P.O. Box 933, Manila, The Philippines. Plant Dis. 78:68-72. Accepted for publication 16 July 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0068.

Fifty-three strains of Xanthomonas oryzae pv. Oryzae collected from various rice-growing areas in Nepal were characterized for differences in biochemical and physiological characteristics, bacteriocin production, and virulence. Numerical analysis of phenotypic features revealed that all strains were associated at 82.4% similarity of coefficient (Ssm) in the dendrogram. No distinct phenons were observed, suggesting homogeneous populations of X. o. oryzae. Forty-four percent of the strains produced bacteriocin, and six bacteriocin groups were distinguished. Inoculation of X. o. oryzae strains on five IRRI differential rice cultivars (IR8, IR20, IR1545-339-2-2, Cas209, and DV85) and three Nepalese rice cultivars (Himali, Laxmi, and Sabitri) demonstrated significant cultivar-strain interaction. As a result, nine pathogenic races of X. o. oryzae were detected. Race I isolated from Nepal was similar to race 6 of the Philippines X. o. oryzae. No relationship was observed between virulence and physiological characteristics or bacteriocin production.

Keyword(s): bacterial blight of rice, differential interaction, epidemiology, Oryza saliva, pathogen variation