Foliar Application of Azospirillum brasilense Enhances Wheat Nutrition and Yield Under Tropical Savanna Conditions

Abstract

While soil inoculation is widely adopted, the mechanistic potential of foliar application of Azospirillum brasilense remains underexplored as an alternative delivery strategy that may reduce limitations associated with soil-mediated microbial establishment. This study evaluated the efficacy of foliar-applied A. brasilense (strains Abv-5 and Abv-6) in modulating the nutritional architecture and yield of two irrigated wheat cultivars grown under tropical savanna conditions. A randomized block design with six replications was used, and foliar inoculation (200 mL ha-1) was performed fifteen days after emergence, at the tillering stage, to evaluate foliar bacterial delivery independently of seed inoculation. The results revealed a pronounced and genotype-dependent response to foliar inoculation. In cultivar ‘CD1104’, the treatment promoted a coordinated increase in phosphorus, calcium, and iron concentrations, which was associated with a 9% increase in leaf chlorophyll index and a 12% increase in shoot biomass. In contrast, cultivar ‘CD150’ exhibited a distinct nutritional adjustment, characterized by higher concentrations of nitrogen, magnesium, and zinc. This targeted enhancement of plant mineral status culminated in a 9% grain yield increase for ‘CD1104’. By demonstrating that foliar application is a viable, high-efficiency alternative to soil delivery, our findings provide a strategic framework for optimizing wheat productivity and nutrient use efficiency in high-input tropical environments. These results also provide mechanistic evidence that plant responses to bioinoculants are strongly governed by host genotype. Consequently, agronomic recommendations should shift from generalized inoculation practices toward genotype-specific inoculant strategies.