Geographical patterns of genetic variation in two species of Stylosanthes Sw. using amplified fragment length polymorphism

Understanding the extent and distribution of genetic diversity within a spe cies is essential for the development of effective conservation strategies. The objective of this study was to assess genetic variation using amplifie d fragment length polymorphisms (AFLP) in two species of the tropical legum e genus Stylosanthes Sw. Annual, S. humilis (2n = 20) and perennial, S. vis cosa (2n = 20) are found throughout tropical America, and are sympatric for much of their range of distribution. One hundred and eleven accessions, co vering a wide geographical range, were selected for AFLP analysis. Binary d ata matrices derived from DNA banding patterns were analysed using the soft ware programs NTSYS-PC and ARLEQUIN. Several accessions were found to be mi sidentified. Of the S. humilis accessions, the overall average similarity v alue was (0.72) slightly higher than the value obtained for S. viscosa (0.6 7). Cluster analysis and principal coordinate analysis grouped accessions f rom both species by geographical origin, with a few exceptions. Analysis of molecular variance (AMOVA) in S. humilis revealed 59.4% of the variation a mong groups formed from the cluster analysis. This was highly significant ( P < 0.001). For S. viscosa AMOVA also revealed more variation among than wi thin groups (66.5%). This was also highly significant (P < 0.001). The majo rity of accessions of both species conserved ex situ are of Brazilian and V enezuelan origin. This study has identified areas in Central America and Me xico for which novel genetic variation may be found and where conservation activities should be focused.