Isolation, characterization and screening of phosphate (P) solubilizing actinomycetes and exploring its potency in finger millet (Eleusine coracana L.)

Abstract Background Phosphorus (P) bioavailability, a major problem in acidic agro-ecosystem due to its fixation in clay lattices. Bioavailability of insoluble P is enhanced by phosphate solubilizing microorganisms (PSMs). Therefore, the current study was carried out to evaluate the phosphate solubilizing efficiency of isolated actinomycetes from different acid soils. Methods Isolation of actinomycetes from native soils and its potency was studied in a pot experiment with fourteen treatments, laid out in completely randomized design. Results A total of 54 actinomycetes strains were isolated out of which six strains showed the ability of P solubilization and tested positive for biochemical tests like urease, methyl red, ammonia production and decomposition of esculin, starch, casein, hippurate. Three isolated actinomycetes strains (S18,S19,S16) performed better in in-vitro P solubilization and in measurement of optical density, IAA production and pathogen test. Pot experiment with the best three microbial strains of actinomycetes was studied to evaluate the potency in test crop finger millet with a set of treatments comprising of with and without inorganic phosphorus. Growth parameters like, plant height(cm) varied from 56.11 ± 2.86 to 72.89 ± 1.43 cm, root length was in range of 36.89 ± 2.44 to 65.44 ± 2.89 cm. Root dry weight(g) varied from 8.16 ± 0.41 to13.96 ± 0.78 and shoot dry weight(g) from 6.72 ± 0.74 to 13.80 ± 1.68. Photosynthetic activity like chlorophyll content (SPAD) varied from 18.36 ± 0.49 to 28.24 ± 0.13. Root volume was also influenced by combination of isolated actinomycetes stains with inorganic P fertilizers. Highest phosphorous uptake of shoot and root (mg pot− 1) were 30.15 ± 6.31; 13.80 ± 2.65 respectively in the best performed strain S18 followed by S19,S16 and control pots. Conclusions Based on biochemical and genomic studies, three best isolated microbial strains viz. S18 (Streptomyces cellostaticus), S19 (Streptomyces durhamensis) and S16 (Streptomyces longiwodensis) were confirmed as actinomycetes. Findings on pot experiment resulted that use of isolated actinomycetes strains along with 75% inorganic P fertilizer in finger millet crop can be recommended for enhancing P use efficiency under acidic Inceptisols.