Laboratory and Pot Scale Performance Evaluation of Bacterial Consortium and Monoculture-Based Bioformulations for Zea mays Growth under Water Deficit Agro-condition

Abstract

This study evaluated the growth promoting performance of bacterial consortium and monoculture-based bioformulations on Zea mays under water deficit agro-condition. Rhizobacteria with plant growth promoting (PGP) traits [indole-3-acetic acid (IAA) production and/or phosphate solubilization (PS)] were isolated, characterized and identified using standard microbiological and molecular techniques. Preliminary PGP activity of the isolates was conducted via seed germination bioassay prior pot examination with the diverse formulations. The formulations were prepared by homogenizing 2 g of sterile oven-dried coir-dust with each standardized PGP-rhizobacteria inoculum, in the ratio 2:20 w/v. Pot study was conducted to evaluate the performance efficacy of the consortium and monoculture-based formulations, using shoot length (SL), root length (RL) and plant height (PH) of cultivated Zea mays seeds as comparative indices. Water deficit condition was simulated by no watering of the seeds throughout the 14 days duration of the pot experiment. Out of the 10 rhizobacteria isolated, isolate with the code RCE possessed the potential to produce IAA and solubilize phosphate, RPP tested positive for IAA production only, while RC tested positive for PS only. Also, 2 other rhizobacteria (RSW and RYE) in spite of testing negative to the screened PGP traits, expressed high growth promoting potential during the seed germination bioassay, and were used for bioformulations. Isolates RCE, RPP, RC, RSW, RYE, were identified as Priestia flexa, Klebsiella variicola, Bacillus altitudinis, Stretomyces herenosi, and Staphylococcus sp., respectively. At the end of the pot study, the bacterial consortium formulations (coir-dust +RSW+RC+RYE; coir-dust +RPP+RSW; and coir-dust +RCE+RSW+RPP) expressed better performance in growing and sustaining the inoculated seeds at days 7 & 14; mean RL (18.8 cm ±2.56 & 7.87 cm ±5.16 respectively), mean SL (4.53 cm ±0.42 & 2.77 cm ±0.35 respectively) & mean PH (47.83 cm ±2.76 & 36.4 cm ±7.93 respectively), relative to their un-inoculated control, in the same order; mean RL (12.6 cm ±0.0 & 3.5 cm ±0.0 respectively), mean SL (5.9 cm ±0.0 & 7.0 cm ±0.0 respectively) & mean PH (42.0 cm ±0.0 & 30.0 cm ±0.0 respectively), with significant difference at (P<0.05), compared to the bacterial monoculture bioformulations in the same order; mean RL (14.53 cm ±8.07 & 7.52 cm ±5.40 respectively), mean SL (4.75 cm ±0.75 & 4.67 cm ±1.75 respectively) & mean PH (48.3 cm ±11.43 & 34.2 cm ±7.0 respectively), relative to their un-inoculated control as stated above, with no significant difference (P>0.05). This study therefore projects bacterial consortium formulations as better and viable strategy for growing and sustaining plants under water deficit agro-condition.