A preliminary isozyme study in some Vigna species.

The taxonomy of the genus Vigna is of greatest interest not only for taxonomists, but also for geneticists and breeders, because some Vigna species carry important traits, for example resistance to biotic and abiotic stresses. A study was started using isozyme analysis, in order to assess taxonomic and phylogenetic relationships within the genus Vigna. This preliminary survey has involved seven species belonging to the subgenus Vigna, section Vigna (V. ambacensis, V. gracilis, V. heterophylla, V. luteola, V. marina, V. oblongifolia, and V. racemosa), plus V. unguiculata (subgenus Vigna section Catiang), and V. vexillata (subgenus Plectotropis, section Plectotropis). Among the nine enzymes tested, six were successful and revealed polymorphism in the species analyzed: AAT (Aspartate amino-transferase), ME (Malic enzyme), LAP (Leucine amino-peptidase), G6PDH (Glucose 6-phosphate), SOD (Superoxide dismutase) and MDH (Malate dehydrogenase). A total of 12 loci were identified and 49 alleles were assigned to the different loci, according to the literature published on Vigna isozymes. A pairwise comparison of the shared alleles between the species was carried out in order to have a preliminary idea of the genetic relationships among the studied species. V. vexillata was not taken into account because some of its zymograms were ambiguous. As expected, V unguiculata showed the lowest number of shared alleles, while V. luteola revealed to be more similar to V. marina, and V. ambacensis to V. oblongifolia. In the future, more enzyme systems will be analyzed, for a larger number of species, and for several accessions per species, in order to evaluate also intraspecific variation.