High Temperatures and Bacillus Inoculation Affect the Diversity of Bradyrhizobia in Cowpea Root Nodules.

Abstract

Future climatic scenario predictions indicate a substantial temperature increase, reducing crop production worldwide and demanding the development of adaptations in agriculture. This study aimed to assess the impact of high temperatures and amendments with Bacillus on nodulating bradyrhizobia. Two cowpea genotypes were evaluated at low (min = 20.0°C, max = 33.0°C) and high-temperature regimes (min = 24.8 C, max = 37.8°C). Plants were also inoculated with Bacillus sp. ESA 402, a plant growth-promoting bacterium. The molecular diversity of the bradyrhizobia isolated from cowpea nodules and plant growth was assessed. High temperatures reduced nodulation of the BRS Itaim cowpea genotype. One hundred and eighty-six were genotyped, clustering the collection into 45 groups. The high temperatures reduced the number of groups, but this negative influence was diminished by Bacillus inoculation. Alpha diversity showed little impact on the experimental interactions. However, this influence was evident for all factors and the interaction of the three factors when beta diversity was assessed. 16S rRNA and constitutive gene sequences identified all strains as Bradyrhizobium spp. mainly within the B. japonicum supercluster. Cowpea-Bradyrhizobium association diversity is multifactorial under different temperature regimes, as is the presence or absence of the plant-growth-promoting bacteria Bacillus sp. ESA 402.