Plant Growth Promoting Traits of Phosphate Solubilizing Bacteria Isolated from Agricultural Lands in Sothern Sri Lanka

Inorganic phosphate solubilization by phosphate solubilizing bacteria (PSB) is known to be one of the major mechanisms associated with plant growth promotion. The use of plant growth-promoting bacteria as bio-inoculants/bio-fertilizers is thus considered to be an environmentally friendly approach of soil enrichment. Fifteen PSB from different agricultural lands including terrestrial, aqua and swamp regions of Southern Sri Lanka were isolated using serial dilution plating on NBRIP agar plates and screened for various plant growth-promoting traits. The highest phosphate solubilization (1127 μg/ml) was exhibited in PSB-14 which was identified as Enterobacter sp. IAA production was detected by 6 strains and among them,  bacterial isolate PSB-12 showed the highest IAA production (24.2 μg/ml) followed by PSB-7 and PSB-1 (21.3 and 20.9 μg/ml respectively). Except for PSB-8 and PSB-13 strains, all the other isolated strains showed a positive response for ammonia production. Except for PSB-2, PSB-7, PSB-10 and PSB-11, all the other studied isolates showed HCN production. PSB-3, PSB-9 and PSB-14 isolates were found to be strong HCN producers. All the strains showed catalase activity implying that they were capable of growing under stress conditions. PSB-1, PSB-12, PSB-14 and PSB-15 strains showed all the tested plant growth promotion traits.