Use of Blueberry to Study Genetic Control of Chilling Requirement and Cold Hardiness in Woody Perennials

Received for publication 21 Apr. 1999. Accepted for publication 5 May 1999. This work was supported by the U.S. Dept. of Agriculture–Agricultural Research Service, West Virginia Univ.–Agricultural Experiment Station, and the U.S. Dept. of Agriculture–National Research Initiative grant No. 9401825. West Virginia Univ. Agricultural Experiment Station Publication No. 2679. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. The capacity of woody perennial plants to survive winter freezes is dependent on their entering a state of dormancy and developing cold hardiness (Powell, 1987). Once plants are in this winter dormant or “endodormant” state (Lang et al., 1987), a chilling period is required for vegetative and floral budbreak the following spring. This chilling requirement prevents growth from occurring during transitory periods of warm temperatures throughout a large portion of the winter and helps synchronize plant growth with exposure to favorable environmental conditions. Together, chilling requirement and cold hardiness levels determine to what degree temperate-zone fruit crops will survive the winter and early spring without shoot and flower bud damage. Chilling requirement and cold hardiness play critical roles in determining winter and early spring survival in woody perennials. Even though these traits are important to fruit crop industries, the inheritance of genes controlling chilling requirement and cold hardiness has not been well studied and little effort has been made to identify and map the genes involved. One of the reasons for this is the difficulty of conducting genetic research in woody perennials. Factors such as long generation times and problems associated with inbreeding depression often render use of recombinant inbred lines and, sometimes, even use of true backcross and F2 populations impossible for genetic and mapping studies. Another reason for the lack of progress in this area is that the induction of dormancy and the development of cold hardiness occur simultaneously and are triggered by some of the same stimuli, such as increasingly shorter photoperiods and lower temperatures. Thus, discerning if certain physiological changes or changes in gene expression are actually associated with dormancy and/or cold hardiness can be exceedingly difficult. We are using a combination of molecular, genetic, and physiological approaches to investigate genetic controls of chilling requirement and cold hardiness in blueberry (Vaccinium section Cyanococcus). In this paper, the term “cold hardiness” specifically refers to flower bud hardiness in the cold-acclimated state. The goals of our research are to: 1) construct a genetic linkage map of blueberry using diploid populations that segregate for chilling requirement and cold hardiness; 2) develop a better understanding of the modes of action of chilling requirement and cold hardiness genes, based on genetic analyses of gene action and quantitative trait loci (QTL) analyses, and tag genes controlling these traits. Concomitantly, we are trying to identify and isolate chilling/cold-responsive genes from blueberry and determine their relationship to dormancy and/or cold hardiness transitions. Here we describe the system (among blueberry populations) and the strategies used in our research, and discuss our progress in the research areas outlined above.