QTL Mapping of Ineffective Nodulation and Nitrogen Utilization‐Related Traits in the IC‐1 Mutant of Cowpea

Abstract

ABSTRACT Biological nitrogen fixation is a valuable component of sustainable agriculture. Improved understanding of nodulation pathways can facilitate enhancement of nitrogen utilization‐related traits. Previously, a cowpea [ Vigna unguiculata (L.) Walp.] mutant, ‘IC‐1’, with ineffective nodules was identified. Heritability studies indicated that ineffective nodulation in IC‐1 was controlled by a single gene designated cpi . To map cpi , F 2 mapping populations were developed from crosses between IC‐1 and two commercial cowpea cultivars. The F 2 populations were evaluated for leaf and nodule color, nitrogen content, dry plant weight, nodule number, and nodule fresh weight. Nitrogen content, aboveground plant dry weight, and nodule fresh weight were each significantly lower in individuals with ineffective nodulation, whereas nodule number was significantly higher. Ninety individuals from one population were selected and genotyped with the Cowpea iSelect Consortium single‐nucleotide polymorphism (SNP) array. In total, 6083 polymorphic SNPs were used for linkage map construction and quantitative trait loci (QTL) analysis. A major QTL accounting for nearly 50% of the phenotypic variance was identified on linkage group (LG) 4 associated with all traits except nodule fresh weight, whereas a minor QTL for nodule fresh weight was mapped to LG 6. The major QTL was validated in a second F 2 population with several polymerase chain reaction markers. Identification of these QTL provides a foundation for future identification of the cpi gene and potential loci for targeted improvement of nitrogen‐related traits in cowpea.