Effective microorganisms: An innovative tool for inducing common bean (Phaseolus vulgaris L.) salt-tolerance by regulating photosynthetic rate and endogenous phytohormones production

Abstract

Effective microorganisms (EM) is a microbial inoculant containing many species of microorganisms’ e.g. photosynthetic bacteria, lactic acid bacteria, yeasts, actinomycetes, and fermenting fungi that can stimulate plant growth and improve soil fertility. The present study investigates the significance of EM application in alleviation of salinity stress in common bean by protecting photosynthesis apparatus. (Phaseolus vulgaris L. - cv. Nebraska) plants were treated or not with EM under different saline conditions [0.1 dS m–1 (non-saline), 2.5 and 5.0 dS m–1] and were sampled, 40 days after sowing. Plants grown in salty soils exhibited a significant decline in growth and yield components, photosynthetic pigments content, photochemical reactions of photosynthesis, net photosynthetic rate, transpiration rate, stomatal conductance, maximum quantum efficiency of PSII photochemistry, actual photochemical efficiency of PSII, electron transport rate, photochemical quenching coefficient, effective quantum yield of PSII photochemistry, activities of Rubisco, Rubisco activase, and carbonic anhydrase, seed carbohydrate content as well as leaf auxins, cytokinins and gibberellins concentration. EM application mitigated the inhibitory effect of salt stress and significantly improved the above parameters. Intercellular CO2 concentration, non-photochemical quenching coefficients, glycolate oxidase activity, and abscisic acid concentration were increased under soil salinization, whereas they were significantly decreased in salt-affected plants treated with EM. In sum, EM application mitigates salinity problems by regulating both mechanisms of photosynthetic apparatus adjustment and biosynthesis of endogenous phytohormone. EM application could be an effective approach to alleviate the harmful effects of salt stress and could be explored in an agricultural production system.