Construction of IAA-Deficient Mutants of Pseudomonas moraviensis and Their Comparative Effects with Wild Type Strains as Bio-inoculant on Wheat in Saline Sodic Soil

Abstract

Tryptophan role in microbial biosynthesis of Indole Acetic Acid (IAA) is very distinct. In present study IAA producing bacteria Pseudomonas moraviensis was applied on wheat for improving growth and physiology; in the presence or absence of L-tryptophan in saline sodic field. Aqueous solution of tryptophan was added to the rhizosphere soil at 10 mg L−1 with irrigated water. The survival efficiency of P. moraviensis measured in the presence of NaCl and mixture of salts. P. moraviensis increased P, NO3–N and K contents in soil by 18–35% and further 12–15% increase was recorded in the presence of tryptophan. There were 40–80% increases in indole acetic acid (IAA), abscisic acid (ABA) and gibberellic acid (GA) contents of rhizosphere soil, and 40–45% increase in leaves when tryptophan was added with P. moraviensis. In the second phase, IAA deficient mutants of P. moraviensis were constructed and tested for the conversion of tryptophan to IAA. In transposon mutagenesis, 1800 trans-conjugants were generated and tested for tryptophan conversion. Among these, 11 mutants were selected and inoculated into wheat to compare their growth responses to the wild type. P. moraviensis wild type served as PGPR under salinity, but IAA- deficient mutants of P. moraviensis were unable to produce IAA and halted plant growth.