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 pla nts with a broader climatic adaptation. This study was undertaken to examin e the inheritance and gene action of FT in segregating populations of a woo dy perennial blueberry (Vaccinium, section Cyanococcus). Two backcross popu lations were derived from interspecific hybrids of the diploid species Vacc inium backcross and Vaccinium caesariense, which are widely divergent in th eir FT. The bud FTs of uniformly cold acclimated plants of parental, F-1, a nd two backcross populations were evaluated with a laboratory controlled fr eeze-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. Da ta 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 recipro cal crosses revealed that there was no significant maternal influence on fr eezing tolerance. Parental phenotypes were fully recovered in 40-42 plants of each testcross population, suggesting that FT is determined by relativel y few genes. The degree of dominance and an analysis of generation means re vealed that FT in blueberry is controlled largely by additive gene effects and, to a lesser degree, by dominance gene effects. Testing of various gene tic models indicated that FT inheritance can be adequately explained by a s imple additive-dominance model; however, two epistatic models involving add itive-additive and dominance-dominance interactions also fit the data.