Unraveling the Role of Auxin-Producing Plant Growth Promoting Rhizobacteria by Modulating L-Tryptophan on Yield and Growth Components of Maize

Plant growth promoting rhizobacteria own diverse mechanisms, like synthesis of plant growth regulators (auxin), which play a vital role in regulating plant growth. L-Tryptophan (L-TRP) is renowned precursor of auxin biosynthesis. The present study was conducted under field conditions to explore the potential of soil microbes that synthesize plant hormones (auxin) with and without substrate (L-TRP) in maize crop. Glasshouse screening of auxin-producing bacterial strains i.e. Gluconacetobacter diazotrophicus, Pseudomonas fluorescens, Azospirillum baldaniorum, and Serratia proteamaculanswere was evaluated alone and in combinations in the presence and absence of L- Tryptophan. Azospirillum baldaniorum (2.18 mgL-1), and Serratia proteamaculans (2.11 mgL-1) showed maximum hormone production in the presence of substrate as compared to other strains. Maximum plant height (235 cm), fresh biomass of plants (55 g), number of grains per cob (620), 1000 grain weight (268 g) and straw yield (14.5 g) due to the combined application of Azospirillum baldaniorum + Serratia proteamaculans in presence of L-TRP was observed as compared to other alone and absence of L-TRP treatments. Nutrient uptake, net photosynthesis, transpiration rate, stomatal conductance and water use efficiency were also improved in Azospirillum baldaniorum + Serratia proteamaculans along with L-TRP application over un-inoculated control. The results showed that substrate induced auxin biosynthesis enhanced the hormone production of microbes that ultimately lead to increased crop physiological and yield parameters.