Biostimulant potential of lactic acid bacteria in hydroponic lettuce production: growth and nutritional quality

Abstract

The use of microbial biostimulants has become an important strategy for improving the productivity and quality of soilless vegetable production systems. However, the potential role of lactic acid bacteria (LAB) in hydroponic crop production remains insufficiently explored. This study evaluated the effects of three LAB strains, namely Lactiplantibacillus plantarum (LP), Levilactobacillus brevis (LB), and Pediococcus pentosaceus (PP), their combined mixture, and a commercial PGPR-based product, Rhizofill, on the growth, yield, physiological performance, and nutritional quality of lettuce grown in a floating hydroponic system. The experiment was conducted under greenhouse conditions using Batavia-type lettuce cv. ‘Caipira’ in a randomized complete block design with four replications. Bacterial suspensions were applied to the nutrient solution at 7-day intervals. Bacterial inoculations significantly improved plant growth, yield, SPAD chlorophyll index, leaf sap EC, and antioxidant-related quality traits compared with the untreated control. Among the tested treatments, LP showed the strongest overall performance, increasing plant fresh weight and total yield by 34.0% and 36.0%, respectively, compared with the control. LP also enhanced total phenolic, flavonoid, and L-ascorbic acid contents, indicating a simultaneous improvement in productivity and nutritional quality. LB was particularly effective in promoting root fresh weight and produced the lowest nitrate accumulation among all treatments. Compared with Rhizofill, LP showed equal or superior performance in several growth and quality parameters, suggesting that selected LAB strains may provide an effective alternative to conventional PGPR-based microbial biostimulants. Overall, the findings highlight the potential of LAB, particularly L. plantarum, as emerging microbial biostimulants for sustainable hydroponic lettuce production.