Use of Genetic Diversity on SSR Markers to Increase Forage Yield in Timothy (Phleum pratense L.)

Molecular markers may provide a tool to overcome the forage yield plateau in timothy (Phleum pratense L.) breeding. The relationship between marker-based genetic distance (GD) estimates and yield was investigated in various mating-designs such as synthetic populations, polycross progenies, and top-cross progenies. GDs were estimated using Dice coefficients framed by 28 simple sequence repeat markers. In the case of synthetic populations, parents with high general combining ability (GCA) from two contrasting first-generation synthetic strains (exhibiting high and low yields) were compared. These differences indicated that GD may be partially the basis for contrasting yields. For polycross progenies, GDs among 40 parents of a polycross were used for calculating general genetic distance (GGD), which is an indicative of their allelic complementation. Analyses revealed a significant (P < 0.01) moderate correlation (r) between GGD and GCA for yield (r = 0.45) and a significant (P < 0.01) residual mean square for the regression of yield on GGD, suggesting that considerable non-additive effects were associated with GCA. In the experiments with top-cross progenies between a tester ‘Aurora’ and 51 clones, a significant correlation (r = 0.68, P < 0.001) was found between yields of top-cross progenies and GDs among the parents. These results showed that GD estimation could be utilized for yield improvement. In addition, simulations of selection procedures based on these results lead to apply the reciprocal recurrent selection in “clone and strain synthesis” development where strains are synthesized by combining two top-cross progenies.