An improved breeding strategy for autotetraploid alfalfa (Medicago sativa L.)

Alfalfa cultivar development will be enhanced by breeding strategies which utilize the full potential of autotetraploid population genetic structures. This study evaluates the effectiveness of an allelic selection scheme. which was developed to overcome limitations of inbreeding depression and to exploit general and specific combining ability effects in autotetraploid populations. Allelic selection entails the minimization of non-additive genetic effects by selecting among full-sib families (F1) which are at uniform levels of heterozygosity. Such F1 lines are developed by crossing individuals from two unrelated random mating populations. Selected F1 lines were intercrossed to form an improved population. Eight random mating populations of alfalfa were developed to study the effectiveness of allelic selection. Selection for increased dry matter yield resulted in alfalfa populations with 38 percent greater yield than the parent populations. Two cycles of intercrossing, among selected F1 lines, did not dissipate the gain from selection. This result has important implications for synthetic cultivar development in which a major limitation is the decline in productivity with advancing generations of seed increase. A positively correlated response to selection for dry matter yield was observed for plant height and stem diameter. The results of this research indicate that continued testing of the allelic selection scheme is warranted and could have a significant impact on the breeding of autotetraploid alfalfa, particularly for synthetic cultivar development.