Ecotypic differentiation in Medicago polymorpha L. along an environmental gradient in central Chile. RAPDs studies show little genetic divergence

Burr medic (Medicago polymorpha) is distributed in a wide range of bioclimatic and edaphic conditions throughout the mediterranean-climate region of Chile. Previous studies on populations of M. polymorpha collected along this gradient revealed a remarkable ecotypic differentiation in many adaptive traits. Random amplified polymorphic DNA (RAPD) was used to evaluate genetic divergence in 36 accessions collected along the entire gradient. Three Australian commercial cultivars were also included in the study, of which two originated in Chile. The 40 RAPD primers used revealed a high degree of polymorphism and generated a total of 295bands, of which 78% were polymorphic. Degrees of similarity, based on Nei's genetic distance, identified one group of accessions (22 of the 39studied) with an index of similarity = 100% centered in the semiarid and arid zones of the study region. The remaining 17 accessions (from more mesic zones and one commercial cultivar) were more diverse. Only 91%similarity was found for the combined 39 accessions, indicating a low degree of genetic divergence. Biogeographical and life history strategy aspects of the results are discussed, including the notion of a suite of ‘arid-adapted’ characteristics arising in annual legumes under arid /semiarid conditions. This revised version was published online in July 2006 with corrections to the Cover Date.