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

Alfalfa cultivar development will be enhanced by breeding strategies whichutilize the full potential of autotetraploid population genetic structures. Thisstudy evaluates the effectiveness of an allelic selection scheme, which wasdeveloped to overcome limitations of inbreeding depression and to exploitgeneral and specific combining ability effects in autotetraploid populations.Allelic selection entails the minimization of non-additive genetic effects byselecting among full-sib families (F1) which are at uniform levels ofheterozygosity. Such F1 lines are developed by crossing individuals fromtwo unrelated random mating populations. Selected F1 lines wereintercrossed to form an improved population. Eight random matingpopulations of alfalfa were developed to study the effectiveness of allelicselection. Selection for increased dry matter yield resulted in alfalfapopulations with 38 percent greater yield than the parent populations. Twocycles of intercrossing, among selected F1 lines, did not dissipate the gainfrom selection. This result has important implications for synthetic cultivardevelopment in which a major limitation is the decline in productivity withadvancing generations of seed increase. A positively correlated response toselection for dry matter yield was observed for plant height and stemdiameter. The results of this research indicate that continued testing of theallelic selection scheme is warranted and could have a significant impact onthe breeding of autotetraploid alfalfa, particularly for synthetic cultivardevelopment.