Assessment of Plant Growth Promoting Activities of Phosphorus Solubilizing Bacteria

Plant growth promoting traits like production of indoleacetic acid (IAA), ammonia, hydrogen cyanide (HCN), siderophore, and like the enzyme activities of catalase, ACC deaminase, cellulase, chitinase and protease were assayed in vitro for twenty one phosphorus solubilizing bacteria isolated from soil isolates. Except SPP-5 and SPP-15 strains, all the other isolated strains produced IAA in various amounts of 10 to $23{\mu}g\;ml^{-1}$. All strains showed positive response for ammonia production and ACC deaminase activity implying that they are capable of growing in a N-free basal medium. Catalase activity was found to be superior in SPP-2, SPP-7, SPP-12 and SPP-17 compared to the other strains tested. HCN production was detected by 15 strains and among them SPP-9, SPP-15, SAph-11, and SAph-24 were found to be strong HCN producers. Except the isolates SPP-10, SPP-12, SPP-13 and SPP-14, all the other isolates produced more than 80% siderophore units. None of the strains showed cellulose and chitinase activity. SAph-8, SAPh-11, SAPh-24 and SPP-15 strains showed 35.84, 50.33, 56.64 and 34.78 U/ml protease activities, respectively. SPP-1, SPP-2, SPP-3, SPP-11, SPP-17, SPP-18, SAph-11 and SAph-24 strains showed positive response for all the tested plant growth promotion traits except cell wall degrading enzyme activities. According to the results, all the tested phosphorus solubilizing isolates could exhibit more than three or four plant growth promoting traits, which may promote plant growth directly or indirectly or synergistically. Therefore, these phosphorus solubilizing strains could be employed as bio-inoculants for agriculture soils.