Yield and Nutraceutical Value of Lettuce and Basil Improved by a Microbial Inoculum in Greenhouse Experiments

Members of <i>Bacillus</i> spp. have been widely used to enrich the soil/root interface to provide plant growth promoting activities. A new isolate, namely to <i>Bacillus</i> sp. VWC18, has been tested under greenhouse conditions in lettuce (<i>Lactuca sativa</i> L.) pots at different concentrations (10³, 10⁵, 10⁷, and 10⁹ CFU·mL⁻¹) and application time (single inoculum at transplant and multiple inoculum every ten days) to evaluate the best application dose and frequency. Analysis of foliar yield, main nutrients, and minerals evidenced a significant response for all applications. The lowest (10³ CFU·mL⁻¹) and the highest doses (10⁹ CFU·mL⁻¹), applied every ten days until harvest, had the greatest efficacy; the nutrient yield (N, K, P, Na, Ca, Fe, Mg, Mn, Cu, and B) increased more than twice. A new randomized block design with three replicates was then performed in lettuce and basil (<i>Ocinum basilicum</i> L.), with the two best performing concentrations applied every ten days. In addition to previous analysis, root weight, chlorophyll, and carotenoids were also examined. Both experiments confirmed the previous results: inoculation of the substrate with <i>Bacillus</i> sp. VWC18 promoted plant growth, chlorophyll, and mineral uptake in both crop species. Root weight duplicated or triplicated compared to control plants, and chlorophyll concentration reached even higher values. Both parameters had a dose-dependent increase.