Forage yields of alfalfa populations derived from parents selected on the basis of molecular marker diversity

It is important to know if forage yields of alfalfa (Medicago sativa L.) cultivars could be improved by using a subset of genetically diverse parents selected from a larger population of parents for a synthetic cultivar. We used restriction fragment length polymorphisms to assess the level of genetic diversity among 93 alfalfa genotypes previously selected as parents for a potential commercial synthetic cultivar. On the basis of average pairwise genetic distances between genotypes, four synthetic populations (samples) were developed with 2, 4, 8, 12, 16, or 24 parents selected for genetic dissimilarity (DIS) or similarity (SIM). Resulting synthetic populations were evaluated for forage yield in replicated field trials at three locations for 2 yr. Forage yields of populations with low numbers of parents were highly variable among samples, and as number of parents increased, genetic diversity levels and yield variation decreased. No significant difference (P > 0.05) was detected between forage yields of DIS and SIM groups averaged over parent number and samples; however, yield variation among samples within parent number of DIS and SIM groups was highly significant (P < 0.0001). The SIM group had more sample variation than did the DIS group, and more SIM than DIS populations were among the lower yielding populations. The lack of significant differences between the forage yields of DIS and SIM populations may be due to linkage equilibrium in the population used for selecting parents and the inability to target heterozygosity to specific genome regions affecting yield.