Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 2008
Publication Date: December 1, 2008
Citation: Rowland, L.J., Ogden, E.L., Ehlenfeldt, M.K., Arora, R. 2008. Cold Tolerance of Blueberry Genotypes throughout the Dormant Period from Acclimation to Deacclimation. HortScience. 43:1970-1974. Interpretive Summary: The blueberry industry in the United States suffers from a lack of cold hardy cultivars. Cold injury in plants can occur with fall freezes, severe mid-winter freezes, or early spring frosts. Flower buds must survive these freezes in order to produce berries the next season. Up until now, no one has studied the blueberry plant’s response to some of these freeze conditions systematically. To develop blueberry cultivars for specific regions of the country, a comprehensive understanding of blueberry cold hardiness is needed throughout the period when buds are vulnerable, from fall to early spring. Here we report cold hardiness measurements throughout this period for several different blueberry varieties. We found significant differences in varieties’ responses which lead us to believe that different varieties have genes that could be important in breeding for good fall frost tolerance, spring frost tolerance, or even mid-winter hardiness. This information will be of value to breeders to use in developing cultivars that should be more tolerant from fall through spring.
Technical Abstract: Cold hardiness in woody perennials is determined by complex interacting factors: the timing and rate of cold acclimation; the degree of cold tolerance attained; the maintenance of cold tolerance during the winter; and the rate of loss of cold tolerance or deacclimation upon resumption of spring growth. For highbush blueberry, the degree of winter freezing tolerance and susceptibility to spring frosts have been identified as the most important genetic limitations of current cultivars. Depending on the winter and the location, both winter freezes and spring frosts can cause damage to floral buds or flowers resulting in substantial losses in yield. In order to identify genotypes that are particularly slow or late to deacclimate and thus may be useful in breeding for spring-frost tolerant cultivars, we compared deacclimation kinetics under controlled laboratory and field conditions among several blueberry genotypes with diverse genetic backgrounds. Clear genotypic differences in timing and rate of deacclimation were found. In the field study, the species Vaccinium constablaei Gray was identified as particularly late to deacclimate, and ‘Little Giant’, a 50:50 hybrid of V. constablaei and V. ashei Reade, was nearly as late to deacclimate as 100% V. constablaei. Recently, we extended our cold tolerance measurements from October through midwinter, comparing acclimation kinetics and maximum cold tolerance levels among genotypes. Although all genotypes appeared to reach maximum cold tolerance about mid-December, genotypic differences were detected in other aspects, including initial cold tolerance, rate of acclimation, maximum cold tolerance, and length of the plateau. ‘Little Giant’ and ‘Northsky’, a 75:25 hybrid of V. corymbosum L. and V. angustifolium Ait., were very early to acclimate and were hardier than the other genotypes both initially and when maximum cold tolerance was reached. Understanding how cold tolerance levels change throughout the dormant period should help us to develop cultivars better suited to their environments.