Co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense in cowpea under salt stress ¹

Coinoculação com Bradyrhizobium ssp. e Azospirillum brasilense em feijão caupi sob estresse salino

HIGHLIGHTS:

Diazotrophic bacteria increase cowpea grain yield.

SEMIA 6462/6463 and SEMIA AbV5/AbV6 strains do not attenuate the deleterious effects of salinity on cowpea nodulation.

Bacterial co-inoculation may become a more sustainable alternative to obtain atmospheric nitrogen.

ABSTRACT

Plants grown under salinity are subject to many morphological and physiological disorders. In this context, practices that can enable the use of saline water are essential. The deleterious effects of salinity can be mitigated by using beneficial microorganisms, especially diazotrophic bacteria. In this context, this study aimed to evaluate the effect of bacterial inoculation and co-inoculation using Bradyrhizobium spp. and Azospirillum brasilense on the growth, nodulation and production of cowpea under salt stress. The experiment was conducted using a randomized block design, in a 4 × 5 factorial arrangement, corresponding to four nitrogen sources (N1 - without nitrogen and without inoculant; N2 - fertilization with mineral nitrogen and without inoculant; N3 - inoculation of Bradyrhizobium spp.; and N4 - co-inoculation of Bradyrhizobium spp. and Azospirillum brasilense) and five values of electrical conductivity of irrigation water - ECw (0.4, 1.9, 3.4, 4.9 and 6.4 dS m^-1), with five replicates. Co-inoculation with Azospirillum brasilense and Bradyrhizobium spp. favors the growth, production and nodulation of cowpea plants up to ECw of 0.4 dS m^-1. Increase in the electrical conductivity of irrigation water negatively affects the growth, production and nodulation of cowpea plants in Corujinha variety, regardless of the nitrogen source used.

Key words:
Vigna unguiculata L. Walp.; salinity; biological nitrogen fixation