Mapping and validation of Alectra vogelii resistance in the cowpea landrace B301

Authors: Ohlson, Erik; TIMKO, MICHAEL - University Of Virginia

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2022
Publication Date: 10/27/2022
Citation: Ohlson, E.W., Timko, M.P. 2022. Mapping and validation of Alectra vogelii resistance in the cowpea landrace B301. Agronomy. 12(11). Article #2654. https://doi.org/10.3390/agronomy12112654.
DOI: https://doi.org/10.3390/agronomy12112654

Interpretive Summary: Cowpea, also known as black-eyed pea, is grown worldwide and is an important crops grown worldwide and is especially important in West and Central Africa. The parasitic weed Alectra vogelii, is an emerging threat to cowpea production throughout the African continent and genetic resistance is the most effective management strategy. Effective management is critical to prevent spread of Alectra locally and internationally. Introduction of parasitic weeds to the U.S., such as Striga asiatica, have caused devastating effects on growers. While several cowpea lines have been identified with Alectra resistance, no resistance genes have been reported, which has slowed cultivar development. In this study, we mapped two genomic intervals that confer complete immunity to Alectra parasitism to cowpea chromosomes 4 and 11. We also developed genetic markers that can be used to accelerate breeding. This research supports the development of cowpea cultivars with elite resistance to A. vogelii by cowpea breeders and will contribute towards food security in regions of Africa where cowpea is a primary source of protein.

Technical Abstract: Cowpea is the most important food legume in West and Central Africa and a valuable economic commodity in the region. Among the major biotic constraints to cowpea production are root parasitic weeds of which Alectra vogelii (Benth.) is of increasing importance. The cowpea landrace B301 was previously identified as a source of Alectra resistance, but neither the genes nor genomic loci conferring this resistance have been mapped. Therefore, to map and identify genetic markers linked to Alectra resistance for use in the molecular improvement of cowpea, we developed an F2 population from a cross of the susceptible variety 524B with B301. The population was phenotyped for resistance to A. vogelii and genotyped with a cowpea high density single nucleotide polymorphism (SNP) microarray. Putative resistance loci were mapped in F2 populations by categorical trait – multiple interval mapping and validated by selective genotyping. Selective genotyping indicated that the resistance loci on Vu04 (Rav1) and Vu11 (Rav2) were significantly associated with resistance (p = 0.01). Using marker assisted backcrossing, the two resistance loci were introgressed independently into the susceptible 524B genertic background. Phenotyping and genotyping of the segregating backcross families delineated Rav1 to a 10 cM on chromosome 4 and Rav2 to a 21 cM interval in chromosome 11. These two loci are desirable for breeding Alectra resistant cowpea varieties due to their simple inheritance and ability to independently confer complete immunity to the parasite.