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CROP BREEDING, GENETICS & CYTOLOGY

Field Response to Selection in Alfalfa for Germination Rate and Seedling Vigor at Low Temperatures

Department of Agronomy, Iowa State University, Ames, IA 50011 USA

brummer{at}iastate.edu

Successful establishment of alfalfa (Medicago sativa L.) stands in early spring may require emergence and seedling growth at soil temperatures below 10°C. The objectives of this experiment were to evaluate changes in emergence and seedling height after laboratory selection in six cultivars at suboptimal temperature for (i) early germination (EG), (ii) high seedling vigor (HSV), (iii) EG + HSV, or (iv) late germination and low seedling vigor (LG + LSV). Cycles (C) 0 to 2 were evaluated for emergence 8 d after planting, seedling height (SH) 27 d after planting, forage dry matter yield, and other agronomic traits in field trials at Ames and Nashua, IA, in early spring 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 selection and 9% by EG selection; however, the response among cultivars was highly variable. Combined EG + HSV selection was less effective than HSV alone at increasing height. Selection for LG + LSV did not reduce seedling height in the field even though large decreases were previously observed in the laboratory. Most gain from selection was realized with C1, possibly because the variable seed production environment in the greenhouse may have limited more consistent responses in C2. Seedling height selection at suboptimal temperatures in the laboratory successfully improved seedling height in the field in some alfalfa populations without changing other agronomic characteristics.

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

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