Genetic analysis of cold hardiness and dormancy in alfalfa

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Abstract
Cold hardiness and fall dormancy in alfalfa (Medicago sativa L.) are positively associated, although this relationship is not always desirable for maximum production. The purpose of this study was to determine basic genetic information about cold hardiness and dormancy utilizing six parents differing in their cold hardiness and fall dormancy and their S0 and S1 progeny. A 6 × 6 diallel analysis was conducted to determine differences in general and specific combining abilities. Parent–offspring regression analyses were used to estimate heritabilities for cold hardiness and fall dormancy. Fall dormancy was measured as plant height 42 days after a final cut in September. Cold hardiness was measured using specific conductivity of exosmolyzed electrolytes of plant root tissues subjected to −8 °C. General combining abilities were significant for specific conductivity and height. Specific combining ability was also significant for specific conductivity. Mean values for S0 cross progeny were 11 to 13% higher than midparent values. Heritability estimates based on parent–offspring regression coefficients were 1.32 for specific conductivity and 0.72 for height.Significant positive phenotypic correlations were found for specific conductivity and fall growth for all generations except for height for S1 progeny. The correlations decreased with each successive generation. Genotypic correlations were positive, large, and increasing for each generation indicating large, negative, and decreasing environmental correlations. Linkage of these two traits is suggested. Selection for cold hardiness and fall growth would be rapid with proper breeding methods, but selection for high levels of both cold hardiness and fall growth would be difficult with the cultivars used in this study. Key words: cold hardiness, dormancy, alfalfa, Medicago sativa, conductivity, fall growth, phenotypic, genotypic.