Development and Field Evaluation of a Prototype Bacterial Inoculant for Cuban Rice Under Reduced Nitrogen Fertilization

Rice is a priority crop in Cuba, and bacterial inoculants could help sustain productivity under reduced mineral fertilizer inputs. However, evidence describing the main stages involved in developing these bioproducts in the country remains limited. This study aimed to evaluate the suitability of a bacterial strain as the active microbial ingredient of a prototype rice inoculant for application under reduced nitrogen fertilization. Three promising bacterial strains were evaluated for their effects on rice yield components under field conditions at 60% of the recommended N fertilization rate. The taxonomic affiliation of the selected strain was assessed by multilocus phylogenetic analysis of the recA, rpoB, and glnII genes. The microbiological stability of inoculant formulations supplemented with CaCl2 or sodium alginate was evaluated during storage at 4 °C and room temperature for 231 days. Inoculant production was scaled up to working volumes of 30 and 300 L, and the resulting prototype was evaluated in a second field experiment at 30% of the recommended N fertilization rate. Among the inoculated treatments, strain Rpd16 produced the highest numbers of panicles per square meter and total and filled grains per panicle. This strain was selected as the active microbial ingredient and was phylogenetically affiliated with the Agrobacterium pusense lineage. After 231 days at 4 °C, all formulations contained viable cell concentrations above 108 CFU mL−1. Compared with the uninoculated treatment receiving the same N fertilization rate, seed bio-priming with the prototype inoculant, provisionally named Azofert-A, was associated with higher tiller number (5.6%), plant height (10.7%), flag leaf length (9.9%), flag leaf dry weight (41.2%), and grain yield (20.4%), providing preliminary evidence of its agronomic potential under reduced N fertilization. This study integrates the main stages involved in developing a prototype bacterial inoculant for rice under Cuban conditions.