The Origin, Evolution, and Genetic Diversity of Alfalfa

Abstract

AbstractAlfalfa is one of the earliest domesticated forage crops that played an important economic and cultural role in the history. Cultivated alfalfa (Medicago sativa ssp. sativa) is a perennial, outcrossing, and autotetraploid (2n = 4x = 32) forage crop selected from M. sativa species complex that includes both diploid and tetraploid interfertile subspecies. There are two putative centers of diversity and origin suggested for alfalfa, Asia Minor/Caucasia (a region that contains Northwestern Iran, highlands of Armenia, Georgia, and Eastern Turkey) and Central Asia (Kazakhstan, Uzbekistan, and highland of Afghanistan). As being member of a relatively comprehensive complex, the evolution of alfalfa and the allied taxa can be traced using morphological traits as well as the cytogenetic state of ploidy and subsequent hybridization among the taxa. As the most prominent morphological traits to deduce the evolution of alfalfa, flower color and pod shape were used extensively. The purple flower color occurs in a limited number of taxa and was regarded as a rather recent evolutionary event and linked to alterations in pollinators’ behaviors while the evolution of the coiled pods was reported to be the result of a selective evolution in a restricted region around Caucasia to adapt to the seed chalcid (Bruchophagus roddi) infestation. Both of these events possibly resulted in genetic isolation and subspeciation. Similarly, autotetraploidy within the complex has been linked to the evolution of alfalfa and allied taxa. Despite the recent efforts to unveil genetic diversity and clustering pattern in cultivated and wild alfalfa, the population genomics studies that are aiming to tackle domestication history of alfalfa and the effect of domestication and subsequent selection on the alfalfa genome lagged behind the other major crops. Recently two tetraploid alfalfa accessions and a diploid accession were sequenced, assembled, and annotated providing a great access to study population genomics of alfalfa and other members of the complex.KeywordsAlfalfaOriginEvolutionResourceGenetic diversity