Variation among Highbush Blueberry Cultivars for Frost Tolerance of Open Flowers

Abstract

Injury of open flowers often occurs in fruit crops by late winter or early spring frosts and can result in significant reduction in yield. In this study, freezing tolerance of open flowers of five highbush blueberry cultivars, Bluecrop, Elliott, Hannah’s Choice, Murphy, and Weymouth, was determined using two freezing methods. Methods involved either placing whole plants in a radiation frost chamber or detached shoots in a glycol-freezing bath. In both methods, plants (or excised shoots) with opening flowers were exposed to temperatures ranging from –2 to –10 °C. After freeze treatments, several flower parts were evaluated for damage and the lethal temperature50 (LT50) determined. In order, from the most sensitive flower part to the least sensitive on average, were the corolla, filament, anther, style, exterior ovary, stigma, ovules, interior ovary, and placenta. A two-way analysis of variance (ANOVA) found no significant effect of the freezing method on the calculated freeze damage to most of the various flower parts. However, a significant genotype effect was found on freeze damage to the style, filament, anthers, and exterior ovary. Overall, ‘Bluecrop’ was the most sensitive to freezing, whereas ‘Hannah’s Choice’ and ‘Murphy’ were the most freezing-tolerant. In conclusion, genotypic variability in frost tolerance of open highbush blueberry flowers was detected, which can be exploited in breeding for more frost-tolerant cultivars.