|Karlson, Dale - WEST VIRGINIA UNIVERSITY|
|Byard, Stephanie - WEST VIRGINIA UNIVERSITY|
|Li, Jianhua - HARVARD UNIVERSITY|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 2009
Publication Date: March 1, 2010
Citation: Karlson, D., Byard, S., Wisniewski, M.E., Li, J. 2010. Interspecific analysis of xylem freezing responses in Acer and Betula. HortScience. 45:165-168. Interpretive Summary: Millions of dollars are lost annually by the fruit industry due to the adverse effects of freezing injury on tree vigor, longevity, and crop load. Many species of temperate woody plants, including fruit trees, exhibit the ability to avoid the freezing of specific tissues to very low sub-zero temperatures. This process is referred to as deep supercooling. The evolution and genetic regulation of this trait, however, is not well understood. The current study used differential thermal analysis to study the freezing response of a number of species in the maple and birch families of woody plants, and a genetic (phylogenetic) analysis of the birch family to determine whether or not this trait is present in the more primitive members of this family. Results indicated that all nine species of maple exhibited deep supercooling, while only 5 out of 15 species of birch exhibited deep supercooling. A genetic analysis of the birch data indicated that deep supercooling of xylem appears to be an ancestral trait. The results of this study indicate that a detailed analysis of supercooling in the species of Malus (apple) and Prunus (peach) may help to better understand the evolution and genetic regulation of this trait in fruit crops.
Technical Abstract: Temperate woody plants have evolved two methods for coping with seasonal exposure to sub-zero temperatures. Supercooling is a freeze-avoidance strategy where cells are able to resist the freezing of intracellular water below sub-zero temperatures. Non-supercooling is a freeze-tolerance strategy where the growth of extracellular ice crystals is promoted and intracellular water is withdrawn. Thus, non-supercooling species have also evolved adaptations to tolerate intracellular dehydration which results from the extracellular ice formation. The goal of our present study was to provide the first broad characterization of freezing responses within two representative woody genera (Acer and Betula) in an attempt to relate this to geographical distributions and the evolution of the freezing response trait. While all of the examined Acer species (9) exhibited xylem supercooling response, only 5 out of 15 Betula species were identified as supercooling species. In general, initiation temperatures for low temperature exotherms were in good correlation to ranges that are predicted by hardiness zones. As in Cornus, the supercooling freezing response is an ancestral trait in Betula.