Genetic analysis for biological nitrogen fixation (BNF) in cowpea

Abstract

This work aimed to estimate the genetic parameters of biological nitrogen fixation (BNF) in cowpea to guide the development of efficient cultivars in N2 fixation. Inoculation was performed with a mix of three Bradyrhizobium strains. Two soil inoculations were performed with 1mL of the inoculum, at sowing and at five days after seedlings emergence. Plants were harvested and evaluated at 40 days after sowing. The means and variances of parents F1 and F2 and the BCs IC-1 (inefficient) × BRS Marataoã (efficient) (cross 1) and IC-1 × BRS Pujante (efficient) (cross 2) were analyzed. Segregation analyses for efficient and non-efficient plants indicate that BNF is controlled by two genes with dominant-recessive epistatic effect. Narrow-sense heritability estimates for crosses 1 and 2 were, respectively, 90% and 78% for shoot dry matter (SDM); 78% and 58%, for number of nodules/plant (NN); 86% and 58%, for nodule fresh matter (NFM); and 85% and 71%, for accumulated nitrogen (AN). Gene number estimates for SDM, NN, NFM, AN ranged from two to nine by the Mather and Jinks' method, and from one to two, by the Lande's method, in both crosses. SDM x NFM and NFM x AN had significant and positive correlations, while NN showed significant negative correlation with AN and SDM. BNF efficiency in cowpea can be easily achieved using autogamous breeding methods.