Auxin and 1-Aminocyclopropane-1-Carboxylate Deaminase Activity Exhibiting Rhizobacteria Improved Maize Quality and Productivity under Drought Conditions

Abstract

Drought, the major characteristic of arid regions, exerts drastic effects on crop productivity. Rhizobacteria equipped with 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole-3-acetic acid producing activity (IAA) assist plants to cope with drought stress. From the arid regions (Multan and Bahawalnagar) of Southern Punjab, a total of 95 bacterial morphotypes were isolated, out of which, 32 isolates showed acetylene reduction activity (ARA), 43 were positive for phosphate (P) solubilization activity and 30 bacterial isolates produced IAA in culture medium. Of the total 95 bacterial morpho-types, 34 showed catalase activity and 25 were positive for ACC deaminase activity. Two potent bacterial isolates MD-23 and BN-5 with highest ARA, phosphate solubilizing, IAA production and positive for ACC deaminase activity were selected and tested for exopolysachharide (EPS) secretion. Significantly higher amount of sugars, (7163 µg g-1 and 7081 µg g-1), protein (988 µg g-1 and 925 µg g-1) and uronic acid (0.87 µg mg-1 and 0.82 µg mg-1) were detected in EPS of BN-5 and MD-23, respectively as compared to non-inoculated control. In two years field study, maize seeds inoculated with these bacterial isolates were grown in field under drought stress at vegetative and tasseling stages {(~50% field capacity (FC)} while well-watered conditions (~75% FC) throughout the season were taken as control. Results disclosed that both strains (BN-5, MD-23) reduced the excised leaf water loss, increased the relative leaf water contents, chlorophyll contents and grain yield both under well-watered and drought conditions over their respective non-inoculated control. The grain quality parameters like carbohydrate, protein and oil contents of bacterial inoculated plants were enhanced over their respective non-inoculated control under well-watered and drought stress at both growth stages in both years of study. Moreover, grain yield and quality parameters were significantly lower in non-inoculated control compared with bacterial inoculation under drought stress imposed at vegetative and tasseling stages. In conclusion, the PGPR strains equipped with ACC deaminase and IAA producing activity and EPS secretion improved the yield and quality of maize under well-watered and drought stressed conditions.