Field performance of bacterial inoculants to alleviate water stress effects in wheat (Triticum aestivum L.)

Aims: Plant growth promoting bacteria (PGPB) containing 1-aminocyclopropane-1-carboxylate (ACC) deaminase can play an important role in abiotic stress tolerance in plants, particularly drought. The objective of this study was to evaluate bacterial strains Variovorax paradoxus RAA3, Pseudomonas palleroniana DPB16, Pseudomonas sp. UW4 for their ability to alleviate drought stress in wheat in field experiments under irrigated and rain-fed conditions in the Uttarkhand region of India. Methods: In this study, ACC deaminase producing bacterial strains Pseudomonas palleroniana DPB16, Pseudomonas sp. UW4 and Variovorax paradoxus RAA3 were evaluated for their efficiency in improving growth, nutrient content and yield of wheat varieties, HD2967 (drought sensitive) and PBW660 (drought tolerant) under rainfed (drought) and irrigated conditions. Results: Bacterial inoculants increased grain and straw yields at both sites, however the response to inoculation was considerably higher under rainfed conditions (64 to 90% increase with inoculation) compared to that observed under irrigated conditions (22 to 40% increase with inoculation). Of the three seed-coated inoculants tested, strain RAA3 maximally improved grain yield (28.2%, 47.4%), straw yield (11.2%, 26.0%) and harvest index (10.6%, 15.3%) under irrigated and rainfed conditions, respectively, compared to non-inoculated crops. The relative expression of the drought responsive gene aquaporin (TaTIP1;1), in response to inoculation, was significantly higher (3.34-fold) in the wheat variety PBW 660, as compared to the drought sensitive variety HD 2967 in which the expression level of aquaporin was unaffected. Under rainfed conditions, the relative mRNA level of the helicase gene WDH45 was significantly higher in HD 2967 (1.54-fold) than the PBW 660 (3.69-fold). Bacterial inoculation caused significant positive changes in plant biochemical and antioxidant properties compared to uninoculated plants. Conclusions: Overall, the results show that the selected PGPB containing ACC deaminase activity along with other plant growth promoting characteristics are effective inoculants for improving wheat yields in irrigated and rainfed field experiments.