Biodiversity of the Genus Medicago from Africa

Abstract

The genus Medicago has its primary center of diversity in the Caucasus, northwestern Iran and northeastern Turkey. It occurs widely in Africa, where it constitutes a rich and diversified heritage. In addition to their ecological importance, Medicago species are an important source of feed for livestock. These species show significant diversity in genetic composition, symbiotic interactions, and tolerance to abiotic and biotic stresses. At the morphological level, some species show a high diversity of biomass and flowering precocity. Characterization using molecular markers (isoenzymes, random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), single sequence repeats (SSR), etc.) shows significant variation within and among different populations. The differentiation of populations based on phenotypic traits and molecular markers emphasizes a role of the site of origin as the basis of natural selection. Furthermore, a broader-to-narrow symbiotic specificity is demonstrated, where some species are nodulated by both species of Ensifer meliloti and E. medicae while others are nodulated only by E. medicae or by a restricted group of E. meliloti. Different Medicago species show diverse levels of tolerance to biotic and abiotic stresses, which enable selection of lines displaying good agronomic performance. This review summarizes the current status of the characterization of the Medicago species in Africa and their use in breeding programs.