ORIGINAL PAPER V. Roussel L. Leisova F. Exbrayat Z. Stehno F. Balfourier SSR allelic diversity changes in 480 European bread wheat varieties released from 1840 to 2000 Received: 23 September 2004 / Accepted: 21 March 2005 / Published online: 11 May 2005 Ó Springer-Verlag 2005 Abstract A sample of 480 bread wheat varieties origi- nating from 15 European geographical areas and re- leased from 1840 to 2000 were analysed with a set of 39 microsatellite markers. The total number of alleles ran- ged from 4 to 40, with an average of 16.4 alleles per locus. When seven successive periods of release were considered, the total number of alleles was quite stable until the 1960s, from which time it regularly decreased. Clustering analysis on Nei’s distance matrix between these seven temporal groups showed a clear separation between groups of varieties registered before and after 1970. Analysis of qualitative variation over time in allelic composition of the accessions indicated that, on average, the more recent the European varieties, the more similar they were to each other. However, Euro- pean accessions appear to be more differentiated as a function of their geographical origin than of their reg- istration period. On average, western European coun- tries (France, The Netherlands, Great Britain, Belgium) displayed a lower number of alleles than southeastern European countries (former Yugoslavia, Greece, Bul- garia, Romania, Hungary) and than the Mediterranean area (Italy, Spain and Portugal), which had a higher number. A hierarchical tree on Nei’s distance matrix between the 15 geographical groups of accessions exhibited clear opposition between the geographical areas north and south of the arc formed by the Alps and the Carpathian mountains. These results suggest that diversity in European wheat accessions is not randomly distributed but can be explained both by temporal and geographical variation trends linked to breeding prac- tices and agriculture policies in different countries. Introduction There have been many reports recently on the impact of plant breeding on crop genetic diversity as determined by means of molecular markers. Some of the investigators have suggested that the reduction in genetic diversity accompanying plant improvement has been very limited. For example, with respect to cereal crops, Donini et al. (2000) analysed 55 UK wheat accessions released from 1934 to 1995 with six amplified fragment length poly- morphism (AFLP) and 14 simple sequence repeat (SSR) loci, while Koebner et al. (2003) studied 134 UK barley varieties registered over the period 1925–1995. Both au- thors reported that in the United Kingdom, plant breeding has resulted in a qualitative rather than a quantitative shift in the diversity of these crops over time. In contrast, Fu et al. (2003) analysed 96 Canadian oat cultivars released from 1886 to 2001 with 30 SSRs and detected a significant decrease in allele diversity at spe- cific loci after the 1970s. They linked these changes to breeding practices. More recently, Roussel et al. (2004) analysed 559 French bread wheat accessions (landraces and cultivars from 1800 to 2000) with a set of 42 mi- crosatellite markers and clearly demonstrated a signifi- cant decrease in allelic diversity at the end of the 1960s. In fact, as suggested by Fu et al. (2003), these differences gauging the effects of plant breeding could be explained both by the sample size of the accessions examined and the use of different molecular markers. As already demonstrated in oats, the evaluation of allelic diversity requires effective molecular tools such as SSR markers Electronic Supplementary Material Supplementary material is available for this article at http://dx.doi/10.1007/s00122-005-2014-8 Communicated by A. Charcosset V. Roussel F. Exbrayat F. Balfourier (&) Ame´lioration et Sante´ des Plantes (UMR 1095), INRA, 234 avenue du Bre´zet, 63039 Clermont-Ferrand, Cedex 2, France E-mail: balfour@clermont.inra.fr Tel.: +33-473-624346 Fax: +33-473-624453 L. Leisova Z. Stehno Research Institute of Crop Production, Drnovska Street 507, 16106 Praha 6-Ruzyne, Czech Republic Theor Appl Genet (2005) 111: 162–170 DOI 10.1007/s00122-005-2014-8