ACC-deaminase producing plant growth promoting rhizobacteria and biochar mitigate adverse effects of drought stress on maize growth.

Availability of good quality irrigation water is a big challenge in arid and semi arid regions of the world. Drought stress results in poor plant growth and low yield; however, the rhizobacteria, capable of producing 1-aminocyclopropane-1-carboxylate (ACC)-deaminase are likely to improve crop growth and productivity under drought stress. Similarly, biochar could also ameliorate the negative impacts of drought stress. Therefore, this pot experiment was conducted to evaluate the role of ACC-deaminase producing plant growth promoting rhizobacteria (PGPR) alone and in combinations with timber-waste biochar in improving maize growth under drought stress. The ACC-deaminase producing rhizobacteria, Pseudomonas aeruginosa, Enterobacter cloacae, Achromobacter xylosoxidans and Leclercia adecarboxylata were studied along with two rates (0.75 and 1.50% of the soil weight) of biochar under three moisture levels i.e., normal moisture, mild drought stress and severe drought stress. The E. cloacae in conjunction with higher rate of biochar produced a significant improvement i.e., up to 60, 73, 43, 69, 76 and 42% respectively, in grain yield plant-1, photosynthetic rate, stomatal conductance, chlorophyll a, total chlorophyll and carotenoids contents of maize as compared to the control under mild drought stress. Similarly, A. xylosoxidans with higher rate of biochar also enhanced grain yield plant-1, photosynthetic rate, stomatal conductance, chlorophyll a, total chlorophyll and carotenoids contents of maize up to 200, 213, 113, 152, 148 and 284%, respectively over control under severe drought stress. In conclusion, combination of ACC-deaminase containing PGPR, A. xylosoxidans and biochar (0.75%) proved an effective technique to improve maize growth and productivity under drought stress.