Genetic analysis of freezing tolerance in blueberry (Vaccinium section Cyanococcus)

An understanding of the genetic control of freezing tolerance (FT) in woody perennials is important for the effective selection and development of plants with a broader climatic adaptation. This study was undertaken to examine the inheritance and gene action of FT in segregating populations of a woody perennial blueberry (Vaccinium, section Cyanococcus). Two backcross populations were derived from interspecific hybrids of the diploid species Vaccinium backcross and Vaccinium caesariense, which are widely divergent in their FT. The bud FTs of uniformly cold acclimated plants of parental, F-1, and two backcross populations were evaluated with a laboratory controlled freeze-thaw regime, followed by a visual assessment of injury. FT (LT50) was defined as the temperature causing 50% of the flower buds to be injured. Data indicate that the two parents were homozygous for genes for low or high FT. Freezing-tolerance values of the parental and F-1 populations indicate that freeze-sensitivity is a partially dominant trait. Results from reciprocal crosses revealed that there was no significant maternal influence on freezing tolerance. Parental phenotypes were fully recovered in 40-42 plants of each testcross population, suggesting that FT is determined by relatively few genes. The degree of dominance and an analysis of generation means revealed that FT in blueberry is controlled largely by additive gene effects and, to a lesser degree, by dominance gene effects. Testing of various genetic models indicated that FT inheritance can be adequately explained by a simple additive-dominance model; however, two epistatic models involving additive-additive and dominance-dominance interactions also fit the data.