Genetic Diversity among Cowpea (Vigna unguiculata (L.) Walp.) Landraces Suggests Central Mozambique as an Important Hotspot of Variation

Abstract

Cowpea is a multiple-purpose drought-tolerant leguminous pulse crop grown in several dry tropical areas. Its domestication center is thought to be East or West Africa, where a high level of genetic diversity is apparently still found. However, detailed genetic information is lacking in many African countries, limiting the success of breeding programs. In this work, we assessed the genetic variation and gene flow in 59 Vigna unguiculata (cowpea) accessions from 10 landraces spanning across six agro-ecological zones of Mozambique, based on nuclear microsatellite markers. The results revealed the existence of high genetic diversity between the landraces, even in comparison to other world regions. Four genetic groups were found, with no specific geographic pattern, suggesting the presence of gene flow between landraces. In comparison, the two commercial varieties had lower values of genetic diversity, although still close to the ones found in local landraces. The high genetic diversity found in Mozambique sustains the importance of local genetic resources and farm protection to enhance genetic diversity in modern varieties of cowpea worldwide.

Diversity of Cowpea [Vigna unguiculata (L.) Walp] Landraces in Mozambique: New Opportunities for Crop Improvement and Future Breeding Programs

“…However, according to our results, Mozambican cowpea landraces retain a high level of morphological diversity, corroborating a previous genetic analysis that showed a high degree of genetic admixture [17]. The two cultivars also showed no clear differentiation with the wild accessions collected in the landraces suggesting that the genetic diversity of these two commercial varieties were still close to that of the wild accessions.…”

“…However, it can be misleading if used alone, mainly to track intra-landrace variation [32]. For instance, a previous genetic study on cowpea landraces found no specific genetic clustering in the different AEZs [17], in accordance also with the morphological results found here. However, that study, although based on a small sample size, revealed the existence of four different genetic groups that we did not find here: one cluster was predominant and grouped all accessions from North Zambezia and most accessions from Sofala and Central Manica; the second cluster characterized Central and South Zambezia accessions; the third clustered accessions from North Manica as well as Central Sofala; the fourth cluster was exclusively composed of accessions from South Manica.…”

“…The fact that most of the traits measured were uniform across landraces, except the ones related to seed (seed length, width, thickness, and weight), suggests the existence of gene flow between landraces. In fact, a low genetic differentiation was previously found in these landraces due to crossbreeding between individuals coupled with seed exchange promoted by farmers [17]. Over the long rural distances in Africa, certified commercial seeds do not reach all farmers and, as they are expensive, farmers tend to recycle varieties between them [27].…”

“…Six accessions were collected in the AEZ R10, in the Zambeze highlands, i.e., the Gurué District. AEZ R10 is a high altitude zone covering the Zambezia, Tete, and Manica highlands [17]. Also, in the Zambezia province, 12 additional accessions were collected in three communities of the AEZ R7, a medium altitude zone spanning across Zambezia and Tete provinces in Central Mozambique and Nampula, Niassa and Cabo Delgado provinces in Northern Mozambique.…”

“…A significant pool of cowpea genetic resources is thought to be available, but the limited detailed information about the diversity of its germplasm makes it difficult for breeding programs to thrive. In this region, most smallholders relay on local landraces which harbor a great genetic potential for cowpea improvement [17], including the presence of tolerant genotypes [18]. Unlike commercial varieties, landraces maintained by farmers usually have high levels of genetic variability as they have evolved from years of uncontrolled crossregional and infield genetic exchange, even between previously released and discontinued open pollinated varieties [19].…”