Bacterial Diseases of Rice. I. Pathogenic Bacteria Associatedwith Sheath Rot Complex and Grain Discoloration of Rice in the Philippines. B. Cottyn, Project Scientist, International Rice Research Institute, Box 933, Manila, Philippines. M. T. Cerez, Research Assistant, M. F. Van Outryve, Project Scientist, and J. Barroga, Research Assistant, Entomology and Plant Pathology Division, International Rice Research Institute, Box 933, Manila, Philippines; J. Swings, Professor, Laboratorium voor Microbiologie, Universiteit Gent, K. Lede-ganckstraat 35, 9000 Gent, Belgium; and T. W. Mew, Plant Pathologist and Head, Entomology and Plant Pathology Division, International Rice Research Institute, Box 933, Manila, Philippines. Plant Dis. 80:429. Accepted for publication 13 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0429.

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, and bacterial pathogens were found in 64 samples representing 12 of the provinces. In other cases, sheath rot or grain discoloration was attributed to fungal disease, insects, or abiotic factors. Pathogenic bacteria (204 strains) represented 3.6% of the total number of strains isolated and tested. Inoculations into the leaf sheaths of seedlings or the flag leaf sheaths produced symptoms characteristic of infection by Burkholderia glumae (formerly Pseudomonas glumae) and Pseudomonas fuscovaginae. None of the pathogens could be associated with distinctive symptoms. 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 Ifugao. 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.