Freeze resistance of pacific northwest strawberry flowers

Abstract

The roles of freeze avoidance and freeze tolerance in determining strawberry (Fragaria xananassa) flower freeze resistance were compared in laboratory freeze tests. Genotype, freezing point depression of expressed cell sap, and flower size were examined as potential sources of variation in freeze resistance. When ice was added as a nucleator to excised flowers, mean freeze damage was 97% at -3.0 °C, but in the absence of ice, flowers appeared to supercool and had only 15% damage at -4.0 °C. Without nucleation, cultivar differences in freeze damage were significant in three of four freezing temperatures, but the relative ranking of cultivar freeze damage was not consistent across temperatures. Cultivars that sustained the least amount of injury at -4 °C, were not necessarily the least injured at -7 °C. With an ice nucleator, damage occurred at warmer temperatures (-1.5 °C), but there was no relationship between percentage damage at -1.5 °C with nucleation and -4 °C without nucleation across cultivars. Freezing-point depression of expressed cell sap did not account for the variation in freeze resistance. In nucleated and nonnucleated treatments, larger flowers were more likely to be freeze damaged. Results of this research suggest that flowers of all cultivars are susceptible to freeze damage and survive spring frosts by freeze avoidance.