Bio-inoculation of Plant Growth-promoting Rhizobacterium Enterobacter cloacae ZNP-3 Increased Resistance Against Salt and Temperature Stresses in Wheat Plant (Triticum aestivum L.)

Abstract

Bacteria residing in the rhizosphere and capable of host plant growth stimulation (PGPR) through ACC-deaminase activity can ameliorate various biotic- and abiotic-stress conditions by decreasing the level of ‘stress ethylene’ in plants. The present study aimed to evaluate the effect of a PGPR strain Enterobacter cloacae ZNP-3 in augmenting wheat plant growth under salinity- and temperature-stress conditions. Among the plant growth-promoting (PGP) traits, the test organism produced ACC deaminase along with several other properties namely indole-3-acetic acid (IAA) production, mineral phosphate solubilization, hydrogen cyanide (HCN) and ammonia production. The test isolate illustrated its ability to function as a biocontrol agent as it displayed antagonistic activity against a wide range of bacterial and fungal pathogens. Its inoculation to wheat plant resulted in a considerable increase in growth parameters, biomass, and chlorophyll content under salinity stress. The inoculation also decreased the accumulation of Na+ and increased K+ uptake in shoots and roots, leading to maintenance of favorable K+/Na+ ratios in bacterial-treated plants for alleviating the toxic effect of salt stress. Moreover, application of ZNP-3 also stimulated the growth of wheat plants in terms of higher biomass and other growth parameters under temperature-stress conditions. Elevated levels of various compatible solutes following inoculation significantly alleviated the negative effect of salinity stress. The inoculation of isolate ZNP-3 also minimized salinity-induced oxidative damage by lowering H2O2 and O2 − contents. Moreover, the colonization behavior of the isolate illustrates its endophytic nature. The observed results indicate that the isolate Enterobacter cloacae ZNP-3 mitigates the detrimental effects of salinity and temperature stressors, and can be used as a promising bioinoculant to decrease the deleterious effects caused by salinity and other stressors.