Response of six alfalfa populations to selection under laboratory conditions for germination and seedling vigor at low temperatures

Alfalfa (Medicago sativa L.) seeded in early spring often germinates and em erges under cold temperatures. We conducted this study to determine if phen otypic recurrent selection improved germination time and seedling growth un der cool temperatures in the laboratory. Four selection methods mere conduc ted in the laboratory for two cycles within six commercial alfalfa cultivar s: 5454, Alfagraze, Amerigraze 401+Z, Innovator +Z, Magnum IV, and WL252HQ ranging in fall dormancy class from two to four. Cycles 0, 1, and 2 were ev aluated in controlled environmental chambers. Two cycles of selection for r apid germination at 5 degrees C decreased germination time (GT) by 29%. Res ponse to selection was greatest in the first cycle. Two cycles of selection for high seedling vigor increased seedling height (SH) after 45 d at 10 de grees C by 15%. In some cultivars, selection for high seedling vigor was ef fective at increasing SH in the laboratory and further increases mag be exp ected. Selection for high seedling vigor increased GT, indicating an associ ation between these traits under laboratory conditions. The mean realized h eritability estimates were 0.49 for GT and 0.18 for SH. Selection for both early germination and high seedling vigor resulted in an average decrease i n GT of 29% with no effect on SH after two cycles, but combined selection a gainst both traits increased GT by 162% and decreased SH by 18%. Laboratory selection for decreased GT and increased SH under low temperatures can be successful, but the amount of improvement is population dependant.