Exploring plant growth-promoting Streptomyces spp. for yield and nutrition traits in pearl millet hybrids

The present study aimed to demonstrate the use of two strains of Streptomyces albus (CAI-24 and KAI-27) and one strain of S. griseus (MMA-32) for plant growth-promotion (PGP) and improving pearl millet yield and nutrient content under greenhouse and field conditions. Two hybrids, a low-Fe (PA-9444; non-biofortified hybrid) and high-Fe (ICMH-1201; biofortified hybrid), treated with selected Streptomyces strains, significantly enhanced a range of traits including grain yield in the glasshouse (13-23%) and field (9-12%) over the control. In the greenhouse experiments an enhanced stover and grain nutrient concentrations were observed in ICMH-1201 (Fe 53% and 40%; Zn 15% and 10%; Ca 11% and 29%) over the control, while such nutrition augmentations were not found in PA-9444. The field harvested stover and grain nutrient concentrations were also increased over the control in both hybrids. A higher stover nutrient concentration was found in ICMH-1201 while PA-9444 had an increase in grain nutrient concentration indicating the significance of these Streptomyces strains' PGP role in the non-biofortified hybrid. Based on this study, strains KAI-27 and MMA-32 significantly improved shoot weight, root weight and grain yield while CAI-24 and MMA-32 improved nutrient concentrations including Fe contents (up to 49%) in grain as well as in stover. Further, the stover samples of pearl millet contained a higher Fe concentration (150-200%) compared to grain samples. This study confirms that the selected Streptomyces strains have the potential for enhancing PGP and stover and grain nutrient concentrations in pearl millet and can complement the existing conventional biofortification strategies.