BACTERIAL DISEASES OF RICE .1. PATHOGENIC BACTERIA ASSOCIATED WITH SHEATH ROT COMPLEX AND GRAIN DISCOLORATION OF RICE IN THE PHILIPPINES

Surveys were made to determine if bacterial pathogens were associated with grain discoloration and leaf sheath rot of rice in the major rice -growing districts in the Philippines. In 1988 and 1989, 304 diseased plant and grain samples were collected from 16 different provinces, an d bacterial pathogens were found in 64 samples representing 12 of the provinces. In other cases, sheath rot or grain discoloration was attri buted to fungal disease, insects, or abiotic factors. Pathogenic bacte ria (204 strains) represented 3.6% of the total number of strains isol ated and tested. Inoculations into the leaf sheaths of seedlings or th e flag leaf sheaths produced symptoms characteristic of infection by B urkholderia glumae (formerly Pseudomonas glumae) and Pseudomonas fusco vaginae. None of the pathogens could be associated with distinctive sy mptoms. Strains of putative P. fuscovaginae were isolated from samples collected from the tropical lowland provinces of Laguna, Palawan, and Davao, and from the tropical highland (above 950 m) province of Ifuga o. Since bacterial pathogens were isolated from 21% of the collections with sheath rot or grain discoloration, bacteria appear important in these disease complexes in the Philippines.