Article

The genetic structure of plant poplliations is deterrnined by severa I factors, from selection processes to histori ca l events (i.e. bottlenecks). Mating system is one of the most inportant factors due to its direct inOuence on thc way progcny genotypes are generated and on the reco!l1binational potential. In self-pollinating species, indi viduals are predo!l1inantly hO!l1ozygous and consequentl y effecti ve recombination is very low. As a consequence strong allelic disequilibri a arise among linked and lInlinked loci , in particular if se1ec tion is in volved, and hence mllitilocus assoc iations. The distribution of multilocus associations suggests that natural selec tion could be involved in their maintenance in some habitats, so they could represent coadaptated gene compl exes. Another criticai point for genetic variability and population structure is the polyploidy Ievel, because in self-pollinating polyploids the loci can be maintained throllghout generations in an heteroallelic state, which is phenotypycally equivalent to the heterozygote. ll1e ex ampie of Avena is taken to illustrate these points, and the consequences that the genetic structure ha ve when planning the collection and conservation of genet ic resources in Ihis species are discusscd.