Non random chloroplast DNA hypervariability in Medicago sativa

Two hypervariable regions of the alfalfa (Medicago sativa L) chloroplast genome were used to describe levels of genetic relatedness among populations. PCR primers were developed to amplify the hypervariable regions. The frequency of occurrence of fragments of like size between populations was used to develop a measure of genetic relatedness. Relationships among 135 alfalfa accessions were investigated with principal component and cluster analyses, based on the genetic distance measures. Distinct clusters were taken as an indication of genetically distinct lineages. The populations investigated represented collections from world regions defined as the centers of origin of specific alfalfa germplasm sources, or else represented collections of introduced, and naturally adapted, accessions from agriculturally advanced regions. In general, this analysis indicated that the accessions from regions of origin of germplasm sources were largely homogeneous, while accessions from areas of introduction were much more diverse. In some cases, the accessions from a region of origin formed distinct clusters, suggesting that divergence has resulted in genetically distinct lines persisting in the original region of origin. Investigation of the stability of the marker fragments through vegetatively, and sexually, propagated plants indicated stable transmission through the sexual phase. However, one of the two regions underwent a deletion of 145 bp of one copy of a tandemly repeated 146 bp region in the equivalent of 80 years of vegetative growth. Received: 18 November 1999 / Accepted: 31 March 2000