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CROP BREEDING, GENETICS & CYTOLOGY

Response of Six Alfalfa Populations to Selection under Laboratory Conditions for Germination and Seedling Vigor at Low Temperatures

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011 USA

brummer{at}iastate.edu

Alfalfa (Medicago sativa L.) seeded in early spring often germinates and emerges under cold temperatures. We conducted this study to determine if phenotypic recurrent selection improved germination time and seedling growth under cool temperatures in the laboratory. Four selection methods were conducted in the laboratory for two cycles within six commercial alfalfa cultivars: 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 evaluated in controlled environmental chambers. Two cycles of selection for rapid germination at 5°C decreased germination time (GT) by 29%. Response 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°C by 15%. In some cultivars, selection for high seedling vigor was effective at increasing SH in the laboratory and further increases may be expected. Selection for high seedling vigor increased GT, indicating an association between these traits under laboratory conditions. The mean realized heritability 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 in GT of 29% with no effect on SH after two cycles, but combined selection against 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.

Abbreviations: EG, early germination • HSV, high seedling vigor • LG, late germination • LSV, low seedling vigor • GT, germination time • SH, seedling height

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