Articles
CHANGES IN THE FREEZING STRESS RESISTANCE OF THE CRANBERRY LEAF, FLOWER BUD, AND FRUIT DURING GROWTH AND DEVELOPMENT
However, the critical frost killing temperatures for the various plant parts are not well established.
We investigated the frost resistance of Searles’ cranberry leaves, flower buds, and fruits by controlled freezing.
Freezing protocol used was: 1°C/h to reach -4°C, 2°C/h to reach -6°C, and then 4°C/h to reach -24°C. Ice nucleation was initiated at -1°C. Injury was assessed by visual observation and ion leakage.
A sharp increase (from -18°C to -2°C) was observed in the lowest survival temperature (LST) for the flower buds as they lost dormancy and started to open, between late April and early May.
A sharp decrease in the LST for newly formed flower buds in the last week of October was found and it reached the lowest LST measured of -22°C in early November.
Flowers and small fruits were very susceptible to freezing (no hardier than 0°C). The LST of the fruits changed from 0°C to -8°C and from 0°C to -3°C in 1986 and 1987, respectively, as the fruits changed from green to red stage of development.
Overwintering leaves lost their cold hardiness rapidly from late April to early May (from <-24°C to -7°C). Newly formed leaves changed their hardiness level from 0°C (very early in the growing season) to about -7°C in mid-July, to -24°C in mid-October, and then to <-24°C in mid-December.
Abbreviations: FRT, frost killing temperature, LST, lowest survival temperature.