Field response to selection in alfalfa for germination rate and seedling vigor at low temperatures

Successful establishment of alfalfa (Medicago sativa L.) stands in early sp ring may require emergence and seedling growth at soil temperatures below 1 0 degrees C. The objectives of this experiment were to evaluate changes in emergence and seedling height after laboratory selection in six cultivars a t suboptimal temperature for (i) early germination (EG), Oil high seedling vigor (HSV), (iii) EG + HSV, or (iv) late germination and low seedling vigo r (LG + LSV), Cycles (C) 0 to 2 were evaluated for emergence 8 d after plan ting, seedling height (SH) 27 d after planting, forage dry matter yield, an d other agronomic traits in field trials at Ames and Nashua, IA, in early s pring 1998. Emergence was improved in all selected populations at Ames but not at Nashua; HSV and EG + HSV selection were most effective at improving emergence, After two cycles, seedling height was increased 21% by HSV selec tion and 9% by EG selection; however, the response among cultivars was high ly variable. Combined EG + HSV selection was less effective than HSV atone at increasing height. Selection for LG + LSV did not reduce seedling height in the held even though large decreases were previously observed in the la boratory. Most gain from selection was realized with C1, possibly because t he variable seed production environment in the greenhouse may have limited more consistent responses in C2. Seedling height selection at suboptimal te mperatures in the laboratory successfully improved seedling height in the f ield in some alfalfa populations without changing other agronomic character istics.