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Evaluation of PGPR strains in multiple crop hosts and predictability of growth promotion efficacy by PGPR traits

Anthony Adesemoye: University of Nebraska Lincoln

<div>Plant growth-promoting rhizobacteria (PGPR) can increase plant growth and yield by facilitating nutrient availability, stimulating plant growth via hormone production, and inhibiting plant pathogens. The objectives of this study were to (a) assess plant growth promotion properties of twelve spore-forming bacteria on sweetcorn, wheat, and soybean and (b) determine which physiological traits are predictive of growth-promotion efficacy. The bacterial strains were isolated from wheat (<em>Tritium aestivum</em>) rhizospheres and identified via 16S rDNA sequence analysis as species of<em> Bacillus</em>, <em>Paenibacillus</em> and <em>Lysinibacillus</em>. Greenhouse pot experiments with the three test crops grown in a raw field soil-sand potting mix were conducted to assess each strain’s growth-promotion potential. The strains were screened <em>in vitro</em> for traits associated with plant growth promotion, including antagonism against bacteria and fungi, mineral nutrient conversion, and growth hormone production. Seed treatment with <em>Bacillus megaterium</em> R181, <em>B. safensis </em>R173, <em>B. simplex </em>R180, and <em>Paenibacillus graminis</em> R200 increased the growth of all test crops compared to water-treated controls. The four strains increased shoot mass by 93-126% compared to the controls and increased root mass by 127-197%. Seven other strains increased growth only on sweetcorn. Results of <em>in vitro</em> physiological traits showed that no strain was strongly positive for antagonism against Gram-negative bacteria, chitinase activity, or nitrogen-fixation. Strains R173, R180, and R181 differed as to the number and type of traits each expressed, while R200 was negative for all traits tested. Therefore, no single trait was found to be predictive of growth-promotion efficacy of the bacterial strains.</div>