VIEW ARTICLE

Resistance

Pathogenic Variability in Xanthomonas oryzae. O. R. Reddy, Former Research Fellow of The International Rice Research Institute (IRRI), Los Baños, The Philippines, Present address of senior author: All-India Coordinated Rice Improvement Project, Rajendranagar, Hyderabad-500 030, India; S. H. Ou, Plant Pathologist, The International Rice Research Institute (IRRI), Los Baños, The Philippines. Phytopathology 66:906-909. Accepted for publication 12 January 1976. DOI: 10.1094/Phyto-66-906.

Inoculations with 51 isolates of Xanthomonas oryzae (the causal organism of bacterial blight of rice) from 11 countries of Asia on 32 rice cultivars revealed wide difference in virulence of the pathogen and susceptibility of cultivars tested. Tall cultivars like BJ 1, Semora Mangga, Chinsurah Boro II, Hashikalmi, UCP-28, and semidwarf cultivars, such as Ratna and IR20, showed a broad spectrum of resistance to the isolates of the pathogen. The spectrum of resistance of breeding lines RP291-7-1 (A), RP633 (C), IR 1545-339, and IR 1514A-E666 was superior to that of their parents. Among the resistant group of rice cultivars and virulent strains of the pathogen differential reaction patterns were observed. The significantly different cultivar-isolate interaction suggested that a vertical pathotype exists in X. oryzae.