Two Methods for Assessing Frost Tolerance In Flowers of Highbush Blueberry Cultivars

Sensitivity of blueberry flowers to freezing temperatures differs among cultivars and stages of bud development.  Also, the frost testing technique and the duration at lethal temperature can have a dramatic effect on bud injury.  Artificial frost tests should duplicate the types of spring frosts in the field.  Freezing tests were conducted on detached shoots with open flowers in a controlled freezing glycol bath and on whole plants with flowers in a radiation frost chamber for ‘Bluecrop’, ‘Elliott’, ‘Hannah’s Choice’, ‘Murphy’, and ‘Weymouth’ highbush blueberries.  The freezing regimes enabled the expression of a range of frost damage symptoms in all the cultivars tested.  Damage score data showed a clear, bi-modality with either no damage or damage to corolla, stamen (anther sac and filament), style, and carpel.  The corolla was most sensitive to freezing temperatures, followed by anther filaments, style, ovary wall, and ovules.  Injury to all parts of flowers with expanded corolla occurred at higher temperatures than on flowers that were less developed (corolla unexpanded).  This study compared two methods for examining the effects of freezing temperatures on blueberry flower injury.  Convective and radiation freezing tests yielded similar results in assessing the susceptibility of blueberry cultivars and floral parts at different stages of development to freezing temperatures.  The cultivars were ranked for frost hardiness as follows: ‘Hannah’s Choice’ > ‘Murphy’ > ’Weymouth’ > ‘Bluecrop’ = ‘Elliott’.