Introduction. Chitosan and plant growth promoting rhizobacteria are recognized as agricultural biostimulants for the biological benefits they provide to plants. Objective. To evaluate the combined application of chitosan concentrations and the Azofert-S¨ inoculant on soybean seeds, on the survival of Bradyrhizobium elkanii and the vegetative growth of the plants. Materials and methods. The research was developed in the plant growth room of Plant Physiology and Biochemistry Department of the Instituto Nacional de Ciencias Agricolas, Cuba, in 2016. The effect of chitosan and Azofert-S¨ inoculant applied to soybean seeds was determined on the number of viable bacteria in seeds and the behavior of morphoagronomic and physio-biochemical indicators related to the nodulation and vegetative development of plants. Results. The chitosan concentrations evaluated in the compatibility test did not affect the number of viable cells in the seeds, except for 500 and 1000 mg l-1, which improved the bacteria survival at the beginning of the test and 500 mg l-1 at ten days of seed storage. The latter concentration also benefited root and stem length, leaf area, and nitrate reductase enzymatic activity in leaves. The combined application of Azofert® - chitosan and seed inoculation alone enhanced the concentration of nitrogen and other nutrients in nodules and trifoliolus. The concentration of flavonoids and total phenols increased with the concentration of 10 mg l-1 of chitosan, although it decreased the concentration of total soluble and reductive carbohydrates in leaves. Conclusion. The biostimulants were compatible when applied on seeds at the time of sowing and benefited the nodulation, nutrition, and vegetative development of soybeans plants, depending on the concentration of the polymer.

Plant growth-promoting bacteria (PGPB)-based inoculants represent a promising alternative to mineral fertilizers. However, their application may be limited by constraints associated with the use of living microorganisms, particularly under field conditions. The objective of this study was to select a bacterial strain and a suitable carrier for the inoculation of rice cv. Selección 1. The effect of inoculation with 3 Rhizobium spp. strains on rice growth was evaluated under greenhouse conditions, enabling selection of the most promising strain. This strain was further characterized based on its motility, production of indolic compounds in the presence of tryptophan, and antagonistic activity against 3 rice phytopathogenic fungi. In addition, the effects of culture media based on aqueous extracts of soybean and rice seeds on bacterial growth and chemotactic response were evaluated, along with the shelf-life stability of the resulting inoculant formulations. Rhizobium sp. strain 5P1 significantly increased plant height (33%), root length (21%), shoot dry weight (30%), and root dry weight (17%) of rice cultivar Selección 1 under greenhouse conditions. The strain exhibited motility predominantly via swarming and twitching, produced indolic compounds (23.9 ± 0.8 µg mL⁻¹), and showed antagonistic activity against Magnaporthe oryzae (32.5% radial growth inhibition at 16 days), Curvularia oryzae (20.0%), and Bipolaris oryzae (6.6%) under in vitro conditions. Culture media based on molasses and soybean or rice seed extracts did not enhance bacterial growth relative to the conventional medium; however, they elicited a stronger chemotactic response. Formulations supplemented with sodium alginate and carboxymethylcellulose maintained cell viability above 10⁸ CFU mL⁻¹ after 105 days of storage at 4 °C. These findings propose Rhizobium sp. strain 5P1 and a molasses-based carrier formulation as strong candidates for the development of an effective bioinoculant for rice in Ferric Gleysol soils.