DIVERSITY OF PSEUDOMONAS-FUSCOVAGINAE AND OTHER FLUORESCENT PSEUDOMONADS ISOLATED FROM DISEASED RICE

Fluorescent pseudomonads associated with sheath brown rot of rice were isolated from rice at low and high elevations in various geographic a reas and analyzed for pathogenicity and phenotypic and genetic diversi ty by biochemical tests and restriction fragment length polymerphism ( RFLP) analysis of polymerase chain reaction (PCR)-amplified 16S-rDNA g enes. Standard strains of various Pseudomonas species of rRNA homology group I were analyzed along with field-collected isolates. Biochemica l characterization revealed 23 groups characterized by different nutri tional features. Nineteen of thirty-five rice isolates were identified as P. fuscovaginae (biochemical group G1). Using PCR-RFLP, 25 composi te 16S-rDNA haplotypes were found. Parsimony analysis revealed that th e P. fuscovaginae isolates were distributed in four 16S-rDNA haplotype s, but they formed a cluster that differentiated them from other rRNA group I Pseudomonas species. All field isolates were pathogenic on ric e when introduced by injection. Inoculation of rice without wounding a t the booting stage showed that only the four haplotypes of P. fuscova ginae and isolates with haplotypes 7, 9, and 17 were pathogenic. Thus, populations of rice-associated fluorescent pseudomonads comprised bot h phylogenetically different pathogenic isolates and opportunistic iso lates pathogenic on rice only after wounding.