Non random chloroplast DNA hypervariability in Medicago sativa

Two hypervariable regions of the alfalfa (Medicaga sativa) chloroplast geno me were used to describe levels of genetic relatedness among populations. P CR primers were developed to amplify the hypervariable regions. The frequen cy of occurrence of fragments of like size between populations was used to develop a measure of genetic relatedness. Relationships among 135 alfalfa a ccessions 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 r epresented collections from world regions defined as the centers of origin of specific alfalfa germplasm sources, or else represented collections of i ntroduced, and naturally adapted, accessions from agriculturally advanced r egions. In general, this analysis indicated that the accessions from region s of origin of germplasm sources were largely homogeneous, while accessions from areas of introduction were much more diverse. In some cases, the acce ssions from a region of origin formed distinct clusters, suggesting that di vergence has resulted in genetically distinct lines persisting in the origi nal region of origin. Investigation of the stability of the marker fragment s through vegetatively, and sexually, propagated plants indicated stable tr ansmission through the sexual phase. However, one of the two regions underw ent a deletion of 145 bp of one copy of a tandemly repeated 146 bp region i n the equivalent of 80 years of vegetative growth.