Genetic diversity and relationship between wild and cultivated cowpea [Vigna unguiculata (L.) Walp.] as assessed by allozyme markers

In Cameroon, cowpea plays an important role in traditional agroecosystems. Genetic variation in wild and cultivated cowpea in Cameroon has not yet been documented. Allozyme markers because of their codominance and polymorphism are useful tools for studying genetic variation and disparity in plant species. The present study was undertaken to elucidate the relationship between wild and cultivated cowpea from Cameroon. Ten enzyme systems encoding nineteen isozyme loci were used on 62 cowpea germplasm (45 wild and 17 cultivated). A total of thirty-two alleles were found. One allele was only found in cultivated samples (Enp⁹⁸). Eight alleles were specific only to wild plant (Amp₂⁹⁸, Amp_3a¹⁰³, Amp₄⁹⁶, Fdh¹⁰⁴, Idh₂⁹⁵, Pgi₃⁹², Pgm₂⁹⁵ and Sdh⁹⁵). Twenty-three alleles were common to both wild and cultivated accessions. Amp₂¹⁰² (z = −4.633, p < 0.001) and Fle₃⁹⁶ (z = −2.858, p < 0.010) were significantly more represented in cultivated compared to wild cowpea forms. The mean number of alleles per locus in wild (1.632 alleles/locus) cowpea were significantly higher (t = 2.805, p < 0.010) compared to cultivated (1.263 alleles/locus) cowpea. Also, the proportion of polymorphic loci (P = 52.63%) and average Nei’s genetic diversity (He = 0.126) were important in wild, compared to the cultivated plants: P = 26.31% and He = 0.063, respectively. The low level of diversity found in domesticated accessions compared to wild can be attributed to a major genetic bottleneck that probably happened during the domestication process. Cluster analysis revealed by UPGMA dendrogram separated the 62 accessions into three clusters. Although an admixture of both wild and cultivated accessions within the same cluster were found, the dendogram, however, highlighted a visible separation between wild and cultivated cowpea. Wild cowpea with many more private alleles indicates an untouched resource available for future breeding.