Evaluation of bacteria isolated from rice for plant growth promotion and biological control of seedling disease of rice

Of 102 rhizoplane and endophytic bacteria isolated from rice roots and stem s in California, 37% significantly (P <= 0.05) inhibited the growth in vitr o of two pathogens, Achlya klebsiana and Pythium spinosum, causing seedling disease of rice. Four endophytic strains were highly effective against see dling disease in growth pouch assays, and these were identified as Pseudomo nas fluorescens (S3), Pseudomonas tolaasii (S20), Pseudomonas veronii (S21) , and Sphingomonas trueperi (S12) by sequencing of amplified 16S rRNA genes . Strains S12, S20, and S21 contained the nitrogen fixation gene, nifD, but only S12 was able to reduce acetylene in pure culture. The four strains si gnificantly enhanced plant growth in the absence of pathogens, as evidenced by increases in plant height and dry weight of inoculated rice seedlings r elative to noninoculated rice. Three bacterial strains (S3, S20, and S21) w ere evaluated in pot bioassays and reduced disease incidence by 50%-73%. St rain S3 was as effective at suppressing disease at the lowest inoculum dens ity (10(6) CFU/mL) as at higher density (10(8) CFU/mL or undiluted suspensi on). This study indicates that selected endophytic bacterial strains have p otential for control of seedling disease of rice and for plant growth promo tion.