Diversity and plant growth promoting activities of rice epiphytic bacteria

Abstract

Plant-associated bacteria have been known for their direct and indirect abilities to promote plant growth. Because of their benefits on plants, they are generally recognized as plant growth promoting bacteria (PGPB). In the present study, epiphytic bacteria were isolated from surfaces of roots, stems and leaves of rice plants that were grown in organic farms. Of 113 bacterial isolates, 68 and 45 isolates were stained Gram-positive and Gram-negative, respectively. Based on their cell shapes, 106 isolates were bacilli while seven isolates were cocci. The use of the 16S rRNA gene sequence analysis indicated that they were members of phyla Fimicutes (54.87%), Proteobacteria (38.05%) and Bacteroidetes ( 7. 08% ). All isolates were assessed for their abilities in nitrogen fixation, phosphate solubilization, siderophore production, auxin production and 1-aminocyclopropane-1-caboxylic acid (ACC) deaminase activity. The result showed that 91 isolates were tested positives for at least one activity. The antagonistic activity against the pathogenic fungus Pyricularia oryzae was also tested. Twenty-three isolates inhibited the growth of the fungal mycelia. The percentage of growth inhibition of these isolates against P. oryzae ranged from 73.10+3.24% to 100.00+0.00%. The protease and chitinase activities were found in 19 and 2 isolates, respectively. However, crude preparation of bioactive compounds from bacterial cultures yielded negative results. Based on the results obtained in this study, the surfaces of rice plants were colonized by various bacteria with potentials in plant growth promotion.