Growth of Soybean (Glycine max) Seeds Treated with Inoculums and Metabolites of Rhizobacteria

In recent years, traditional methods to boost crop yields, such as application of fertilizers, pesticides, and herbicides, are increasingly scrutinized due to their environmental and health impacts. This study was aimed at evaluating the impact of plant growth promoting rhizobacteria isolates on growth of soybeans. The study employed inoculums and metabolites of 15 bacterial isolates [Bacillus cereus (6), Bacillus thuringiensis (1), Serratia liquefaciens(2), Providencia rettgeri(4), and Providencia vermicola(2)]. The experimental groups included: inoculum + seed treatments, inoculum + soil treatments, metabolite + seed treatments, metabolite + soil treatments and water as control. Generally, seeds treated with certain inoculums, such as B. cereus (OP830500, OP830493, OP830502), P. rettgeri (OP830496), and S. liquefaciens (OP830504), showed significantly higher vigor indices, when compared to the control. Treatment with other strains, such as B. thuringiensis (OP830494) and P. rettgeri (OP830498), resulted in lower vigor indices. Germination rates, were however above 75% for all treatments. For soil-treated seeds, higher vigor indices were noted for strains like B. cereus (OP830493) and S. liquefaciens (OP830503), though some strains led to lower vigor indices without significantly affecting germination rates. In the case of the metabolite treatments, the seeds generally showed no significant differences in vigor indices, when compared to the control with the exception of treatments with B. cereus (OP830502) and P. rettgeri (OP830496), which recorded lower values. Germination rates were mostly unaffected by metabolite treatments. In soil applications of metabolites, significant differences in vigor indices were noted, with lower values for certain strains. Germination rates remained similar to controls across all treatments. The study revealed that that specific bacterial strains can positively influence soybean growth, suggesting that rhizobacterial inoculums could be viable alternatives to agrochemicals for sustainable agriculture.