Chilling Injury of Sweet Cherry Flower Buds with and without Freezing

Flower buds of sweet cherry (Prunus avium L. cv. Satohnishiki) exposed to critically low temperatures were investigated in relation to browning of pistils, with and without freezing, developmental stage (size) of buds, and their temperatures within buds (bud temperatures). Half of the buds chilled below -1.5°C initiated the freezing process. Thirty to 40 percent of buds freezing at -1.5 to -2.5°C of bud temperatures were injured, resulting in browning of pistils. Even pistils of supercooled buds, browning occurred when the bud temperatures were maintained below -1.5°C for 1 to 2 hours. Hence, pistils were damaged without ice formation when supercooled to subzero temperatures. These supercooled buds were more susceptible to chilling injury during their early stages of development, indicating that some structural and/or physiological changes in developing flower buds are related to the damage.