Introgression Breeding in Cowpea [Vigna unguiculata (L.) Walp.]

Abstract

The narrow base of genetic diversity characteristic of cowpea can be attributed to it being self-pollinating, evolving from narrow wild germplasm and exhibiting very limited gene flow between wild and cultivated types. Backcrossing to introduce simply inherited desirable traits and utilization of improved breeding lines and varieties as parents in crossing programs further narrowed the genetic base of cowpea varieties. In most cowpea breeding programs, genes for resistance and market traits were pyramided into lines characterized by high levels of acceptance to farmers and consumers. Besides predisposing widely distributed improved varieties to genetic vulnerability, a narrow base of genetic variation may be contributing to the plateauing in cowpea grain yield, which compromises genetic gains. Cross compatible wild relatives have not been used in variety development because breeders shy away from them due to their tiny seed size, unattractive seed coat color and texture, pod shattering, and susceptibility to viruses. A number of wild cowpea relatives, both within and outside section Catiang of Vigna species, have been evaluated for their reaction to cowpea insect pests and diseases. Vigna vexillata lines were resistant to the legume pod borer (Maruca vitrata), the cowpea weevil (Callosobruchus maculatus), and Striga gesnerioides but are cross incompatible with cultivated cowpea. Some lines among the cross compatible wild relative V. unguiculata ssp. dekindtiana were found to be resistant to aphid in the seedling stage, while others showed good levels of drought and heat tolerance. Molecular markers are being generated to identify quantitative trait loci (QTL) with effects on some desirable attributes in cowpea. Modern breeding tools, including transgenics, can be applied for the improvement of cowpea, bypassing the natural barriers of traditional breeding. Transgenic cowpea with Bt gene cry1Ab showing resistance to M. vitrata has been released in Nigeria. Genome editing, a powerful emerging tool, can also be used for developing improved cowpea varieties with durable resistance to pests and diseases.

Molecular Fingerprinting and Hybridity Authentication in Cowpea Using Single Nucleotide Polymorphism Based Kompetitive Allele-Specific PCR Assay

“…Efficient and optimized breeding programs include routine QC to eliminate the false F 1 plants early enough to make the most impact with the resources available (PASSeL, 2019). With the advancements in genetics, molecular biology and tissue culture, plant breeding is now increasingly being carried out using molecular genetic tools (Tester and Langridge, 2010;Boukar et al, 2018Boukar et al, , 2020Khanna, 2018). Parental fingerprinting and hybridity tests, which are among the key aspects of QC in the breeding process can now be conducted using molecular markers (Weerasinghe et al, 2004;Wu et al, 2010;PASSeL, 2019;Osei et al, 2020).…”

Application of multi‐locus GWAS for the detection of bruchid resistance loci in cowpea (Vigna unguiculata)

“…In addition, biparental individuals do not allow for high resolution for the genomic regions discovered, making their future use in molecular breeding difficult (Korte & Farlow, 2013). According to Boukar et al (2020), cowpea's self-pollinating traits also result in low of cowpea genetic diversity, making it necessary to use diverse cowpea collections to establish mapping populations. Genome-wide association studies, a modern mapping technique that uses diverse populations with historical recombination, makes it possible to increase this genetic diversity and achieve more powerful QTL detection and better resolution.…”

Cross-compatibility of cultivated cowpea varieties and their wild relatives: Implications for crop improvement

“…Wild relatives of crop species are often sourcing of genes for disease and insect resistance, increased yield, improved product quality, earliness and wide adaptations (Khoury and Guarino, 2010). Wild forms and closely related species of cowpea, therefore, have great potential as an additional source of useful germplasm for cowpea improvement (Boukar et al, 2020). The first crossings between crop wild relatives and cultivars to obtain disease resistant varieties date back to the 1890's (Biodiversity International, 2012), with pest and disease resistance currently remaining the highest priority for breeders and CWR being used primarily for this purpose.…”

“…Moreover, authors have noted the narrow genetic base of cowpea despite large number of germplasm available in gene banks (Li et al, 2001, Boukar et al, 2020. This they attributed to cowpeas high self-pollinating characteristic and consistent improvement of the crop using elite lines.…”