The relevance of outcrossing for the dynamic management of genetic resources in predominantly selfing Triticum aestivum L. (bread wheat)

The mating system is of major concern for the dynamic management of genetic resources. We investigated the outcrossing rate of six experimental wheat populations, derived from two genetic pools (PA and PB) which have been cultivated at four French sites. The replicates of the two segregating populations have undergone 10 years of multiplication in isolation, with no artificial selection. For each population, 78 individuals were randomly sampled and genotyped for 25 codominant loci revealed by 15 restriction fragment length polymorphism (RFLP) probes. Outcrossing rates were estimated on the basis of the multilocus heterozygote deficiency. Estimates ranged from 2.4 to 10.1 %, depending on the population. The outcrossing rate appeared to be affected by the cultivation site, and also by the interaction between the genetic pool and the cultivation site. No significant pool effect was found over sites. The use of natural or modified outcrossing rates is suggested for the management of gene flows between the subpopulations of a metapopulation. Consequences of recombination events within and between populations are discussed in the context of short-term adaptive response of populations and long-term elimination of weakly deleterious mutations. (C) Inra/Elsevier, Paris