Abstract
In this paper, the authors report a new finding that an isolate of Xanthomonas campestris pv. oryzae became unexpectedly avirulent to a rice variety Kinmaze and some others. This isolate is the variant derived from Q6809 belonging to bacterial group III of X. campestris pv. oryzae. It was originally virulent to rice varieties belonging to Kinmaze, Kogyoku and Rantai Emas group and to IR 8, but has lost its virulence to japonica type rice varieties including Kinmaze group through successive transfers on artificial media. The virulence pattern of the variant is quite different from that of any of the already known bacterial groups.
