Effect of Rhizobium-Azospirillum coinoculation on nitrogen fixation and yield of two contrasting Phaseolus vulgaris L. genotypes cultivated across different environments in Cuba

Azospirillum spp. have shown potential to enhance nodulation and plant growth of legumes when coinoculated with Rhizobium. The effect of Azospirillum on the Rhizobium-legume symbiosis is, however, dependent on the host genotype used. Previous greenhouse experiments identified two genotypes of common bean (Phaseolus vulgaris L.), BAT477 and DOR364, contrasting in nodulation response to Azospirillum when coinoculated with Rhizobium. Genetic analysis revealed a genetic basis (Quantitative Trait Loci) on the bean genome related to the differential responsiveness to Azospirillum between the two bean genotypes. In this study, on-station and on-farm field experiments in different regions in Cuba were conducted to evaluate the agronomic relevance of the differences in response to Azospirillum-Rhizobium coinoculation between the two genotypes BAT477 and DOR364. It was observed that Azospirillum-Rhizobium coinoculation as compared to single Rhizobium inoculation increased the amount of fixed nitrogen and the yield of DOR364 across all sites. For BAT477, on the contrary, a negative effect of Azospirillum-Rhizobium coinoculation on yield and nitrogen fixation was observed on most of the sites as compared to single Rhizobium inoculation. The modified stability regression equations resulting from this study may contribute to predict how a combination of genotype and inoculum will perform at a certain environmental setting. This study highlights the importance of genotype x inocula interactions in agricultural outputs and establishes a link between greenhouse phenotype, genetic background and performance in the field.