Beans in Europe: structure of genetic diversity in common bean (Phaseolus vulgaris L.) for AFLPs.

The variation of European common bean germplasm is the result of adaptations to different growing environments of germplasm introductions from both .the Andean and the Meso-American domestication Centres. Distinctive patterns of phaseoline are largely used to assess the presence of germplasm from the two domestication centres but, on this basis, the relative contribute of these two gene pools to the evolution of bean genome in Europe cannot be established. In this study a “core collection” of 202 accessions of common bean European germplasm, obtained on the basis of random sampling stratified by country of origin and phaseoline patterns, was compared with 47 domesticated bean accessions from the two American Centres using fluorescent AFLP markers and automated data analysis. A total of 169 AFLP markers across all material were scored using two EcoRI/MeI primer combinations: 101 were from E-AGT/M-GAC and ranged from 62 bp to 364 bp, 68 were from EAGT/ M-GTA and ranged from 76 bp to 372 bp. All markers where polymorphic within European and 155 within the American germplasm. Genetic distances between accessions among European and among American accessions (Dice 1945; Nei and Li 1979) were separately estimated and the resulting matrixes were used for a UPGMA cluster analysis. Relationship among individual accessions showed a clear separation of ‘S’ phaseoline type accession from ‘T’ and ‘C’ accessions in both American and European germplasm. Genepools were separated from each other at an average genetic distance of about 0.97 in the American set and about 0.94 in the European one. In the germplasm from America classification on the base of country of origin as obtained from passport data in some cases does not match with the observed phaseoline type. Moreover, in the American set, 6 markers, 3 from E-AGT/M-GAC, with frequencies 71%, 71% and 83%, and 3 from E-AGT/M-GTA (25%, 25% and 21%) were associated only with Mesoamerican type ‘S’ phaseoline but this association was not observed in the analyses European germplasm. In the European dendrogram some large clusters associated to ‘C’, ‘T’ and ‘S’ phaseoline types and some relation to the European region of origin were observed. AFLP analysis revealed a high degree of variation in the European germplasm and confirms the expected history of gene exchange among germplasm introduced in Europe from different domestication Centres.