Cold hardiness, ice nucleation, and growth modeling in the cranberry plant

We studied changes in cranberry plant cold hardiness during the spring, focusing on the relationship between changes in bud hardiness and morphology. Nonlinear regression was used to analyze bud regrowth capability after freezing. Bud hardiness changed dramatically both within and between bud stages. The largest changes occurred within tight and swollen stages (LT50 values from <-22 to 8.7°C and -18.2 to -7.4°C, respectively). Uprights at cabbagehead and later stages were very sensitive to freezing stress (LT50 values of -7.8 to -3.9°C for cabbagehead and to -2.4°C for early hook). Changes in bud and previous year leaf hardiness corresponded to fluctuations in minimum air temperature. Based on similar points in crop phenology, comparable shifts in bud hardiness occurred each year.;Using the ice-off date for the start of thermal time accumulation and corrected for daylength we developed a thermal model for predicting bud growth and development and frost hardiness. A 5°C base temperature for bud development and growth was estimated statistically and experimentally. Of five spring phenophases, 50% bud break and beginning of bloom were consistently predictable, while the timing the earliest phenophases (50% swollen and 50% cabbagehead) were not. However, the timing of hardiness changes and the development of early stages were demarcated by the accumulation of threshold amounts of thermal time. The largest shifts in tight bud hardiness and the appearance of swollen buds occurred around the accumulation of 100 degree days. After 240 degree days, cabbagehead and later stages developed and were highly frost sensitive.;The cranberry plant was used as a model system to study ice nucleation and propagation in fruit and leaves with infrared video thermography. We demonstrated the association of ice penetration into the leaf with the presence of stomata. Stomata in the remnant nectary of fruit were associated with the only observable location of ice propagation into fruit. Barriers to ice propagation in fruit exist at the fruit surface and the pedicel.;The results of the present study will be used to develop information and recommendations for growers to assist in better management of frost protection and water use.