Inoculation of rizobacteria in a hydroponic system in nutrition, production and quality of American lettuce

Abstract

Several researches have reported the multiple mechanisms of action and benefits of plant growth-promoting bacteria (BPCP) for Agriculture, however research in hydroponic systems is rare. Thus, it is believed that in a hydroponic system, inoculation with Azospirillum brasilense, Pseudomonas fluorescens and Bacillus subtilis can also increase the efficiency of use and accumulation of nutrients in the plant, reduce the concentrations of nitrate in the leaves and increase the lettuce fresh mass productivity. In addition, given the lack of information on this interaction of these bacteria (unprecedented research), there may be a synergistic effect between the use of A. brasilense, P. fluorescens and B. subtilis. Therefore, the objective of this research will be to evaluate the effect of inoculation with Azospirillum brasilense, Bacillus subtilis and Pseudomonas fluorescens in isolation and/or combined, in the nutrition, production and quality of American lettuce in NFT hydroponic cultivation. In addition to verifying the contribution of these BPCPs in agronomic biofortification with Fe and Zn, and reduction of nitrate concentration in lettuce leaves. For this, four experiments will be carried out in a randomized block design, with five replications. Each bench will receive a treatment. In all experiments, the inoculants of each BPCPs species will be applied in the nutrient solution at the time of transplanting the lettuce seedlings and at 10 days after transplanting, according to each experiment: experiment 1: inoculation with Azospirillum brasilense strains AbV5 and AbV6 (guarantee of 2x108 UFC mL-1), with doses of 0; 8; 16; 32 and 64 mL of the liquid inoculant for every 100 liters of nutrient solution; experiment 2: inoculation with Bacillus subtilis strain CCTB04 (1x108 UFC mL-1 guarantee), with doses of 0; 7.8; 15.6; 31.2 and 62.4 mL of the liquid inoculant for every 100 liters of nutrient solution; experiment 3: inoculation with Pseudomonas fluorescens strain CCTB03 (2x108 UFC mL-1 guarantee), with doses of 0; 8; 16; 32 and 64 mL of the liquid inoculant for every 100 liters of nutrient solution; experiment 4: will be carried out last, with the inoculation combined of BPCPs according to the optimal dose obtained for each inoculant in experiments 1, 2 and 3. The six treatments will be the following: a) control (without inoculation); b) inoculation with Azospirillum brasilense; c) Azospirillum brasilense + Bacillus subtilis; d) Azospirillum brasilense + Pseudomonas fluorescens; e) Bacillus subtilis + Pseudomonas fluorescens; f) Azospirillum brasilense + Bacillus subtilis + Pseudomonas fluorescens. Evaluations will be carried out: 1) fresh and dry lettuce production; 2) concentrations and accumulations of N, NO3-, P, K, Ca, Mg, S, B, Cu, Fe, Mn and Zn in the shoots and roots of the lettuce; 3) calculation of the nutrient efficiency use; 4) physiological assessments with IRGA; 5) economic analysis of the production systems according to the treatment application. (AU)