Abstract

                                Eighteen pathogenic isolates of Xanthomonas campestris pv. oryzae (Xco) were collected from seventeen locations in Tamil Nadu. Tetracycline exerted maximum inhibitory effect on the growth of all isolates. Isolate Isproduced the smallest lesion. Based on the leaf area blighted on the susceptible T(N) 1 rice variety, isolates, 11, 12 and Is were classified as most virulent, isolates 14.15,1617.19.110.111.12.16 and I18 as virulent and the isolates 13. Igand Isas least virulent. The reaction of the five international differential rice varieties have reacted to these 18 isolates differentially. Based upon the IRRI standard on the classification of race groups, Xco isolates. 13,Igand 115 are considered to belong to race group 2 and the rest of the 15 isolates belong to race group 3 of Philippines.

Key words : Pathogenic isolates, Bacterial blight