Unraveling the interplay of temperature, plant genotype, and plant-growth-promoting bacteria inoculation on cowpea nodulation with native soil bradyrhizobia

Abstract

Background and Aims Climatic changes are impacting crop production worldwide. Among changes that will occur in future climatic scenarios, increasing temperatures by 4.8º C by the end of this century would be one of the most impactful situations for plants and their interaction with ecological partners. This study aimed to assess the impact of different temperatures and plant-growth-promoting bacteria inoculants on cowpea growth and the diversity of rhizobia associated with its root nodules. Methods Two cowpea genotypes were assessed at lower (min = 20º C and max = 33 ºC) and higher temperature regimes (min = 24.8º C and max = 37.8 ºC). Plants also were inoculated or not with Bacillus sp. ESA 402, a plant growth-promoting bacterium. The plants were assessed in terms of plant growth and the associated molecular diversity of bradyrhizobia. Results Higher temperatures reduced BRS Itaim nodulation. Two-hundred-thirty bradyrhizobial-like strains were obtained, and 186 were positive for amplifying nifH and nodC genes. Box-PCR genotyping clustered the collection into 47 groups. The higher temperatures reduced the number of the groups, but this negative influence was canceled by ESA 204 inoculation. Alpha-diversity metrics showed little influence on the experimental interactions however, this influence was evident for all factors and triple interaction when beta diversity was assessed. recA gene sequencing identified all strains as Bradyrhizobium spp. massively within the B. japonicum supercluster. Conclusions The diversity of the cowpea-Bradyrhizobium association is multifactorial under different temperature regimes, as is the presence/absence of Bacillus sp. ESA 402 as a plant-growth-promoting bacteria.