Evaluation of the effect of potassium solubilizing bacterial strains on the growth of wheat (Triticum aestivum L.)

The present study was designed to isolate potassium solubilizing bacteria (KSB) and evaluate their capacity to mobilize available potassium (K) from soil to plants. Screening of KSB for plant growth-promoting (PGP) properties and K-solubilizing efficiency resulted in the selection of nine potential strains. Identification of the 16S rRNA gene of KSB confirmed that these isolates belong to the genera Bacillus and Pseudomonas. Optimization of physicochemical parameters revealed that pH 7 and 37 degrees C were the most suitable conditions for K solubilization by all test strains. The K-mobilizing activity was also observed at pH 7 and 25 degrees C, followed by pH 4 and 37 degrees C. However, the isolates did not solubilize K at pH 9 after incubation under the tested conditions (25 degrees C, 37 degrees C and 40 degrees C). The PGP effect of these strains was confirmed by an increase in root length of wheat seedlings by 16.0-40.0%. A significant enhancement (2-3 times) in biomass (both fresh and dry weight) was also observed in plants propagated from seedlings that were previously treated with KSB strains, in comparison with control plants. Apart from the growth enhancement, KSB strains mobilized 53.6-304.8% K from natural soil to wheat seedlings under optimized conditions in a greenhouse setup. However, the influx of K upon treatment with strains showing extreme mobilization capacity was negatively correlated with the chlorophyll content of the plants. Overall, four isolates, KSB9 (B. fungorum), KSB7 (P. aeruginosa), KSB20 (B. paramycoides), and KSB18 (P. aeruginosa) exhibited efficient PGP properties with optimum K-mobilizing potential.