Plants’ mechanisms for surviving freezing stresses are essential adaptations that allow their existence in environments with extreme winter temperatures. Although it is known that Vaccinium macrocarpon Ait. buds can acclimate in fall and survive very cold temperatures during the winter, the mechanism for survival of these buds is not known. The main objective of this study was to determine which of the two major mechanisms of freezing stress survival, namely, deep supercooling or freeze-induced dehydration, are employed by V. macrocarpon terminal buds. In the present study, no low-temperature exotherms (LTEs) were detected by differential thermal analysis. Furthermore, a gradual reduction of relative liquid water content in the inner portions of buds during magnetic resonance imaging (MRI) scans performed between 0 and −20 °C (where no damage was detected in controlled freezing tests (CFT)) indicates these buds may not deep supercool. The higher ice nucleation activity of outer bud scales and the appearance of large voids in this structure in early winter, in conjunction with the MRI observations, are evidence supportive of a freeze-induced dehydration process. In addition, the presence of tissue browning in acclimated buds as a result of freezing stress was only observed in CFT at temperatures below −20 °C, and this damage gradually increased as test temperatures decreased and at different rates depending on the bud structure. Ours is the first study to collect multiple lines of evidence to suggest that V. macrocarpon terminal buds survive long periods of freezing stress by freeze-induced dehydration. Our results provide a framework for future studies of cold hardiness dynamics for V. macrocarpon and other woody perennial species and for the screening of breeding populations for freezing stress tolerance traits.

Similar to other woody crops, cranberry (Vaccinium macrocarpon Ait.) exhibits alternate bearing or a tendency to produce heavier yields one year, followed by lighter yields the next year. Unfortunately, despite the occurrence in many fruit crops, this trait is not well understood. The variable differentiation of floral initials in cranberry uprights is a distinguishing characteristic associated with alternate bearing. This study evaluates bud morphology and the presence of floral initials through characterization of longitudinal sections of apical buds from vegetative and fruiting uprights of alternate and non-alternate bearing genotypes. Our results reveal that differentiation of floral initials in fruiting uprights only occurs in non-alternate bearing genotypes and after initiation in vegetative uprights. In addition, a strong positive correlation was found between the increase of bud width and the presence of floral initials. Lastly, uprights from the alternate bearing genotype exhibited significantly faster growth rates of the reproductive buds compared with the vegetative buds. In summary, our study shows marked differences in timing and growth rates of floral initials between uprights of the two genotypes, suggesting a possible correlation with resource allocation during the growth season, and thus could contribute to cultivar selection and management practices.

As the world population grows and resources and climate conditions change, crop improvement continues to be one of the most important challenges for agriculturalists. The yield and quality of many crops is affected by abscission or shattering, and environmental stresses often hasten or alter the abscission process. Understanding this process can not only lead to genetic improvement, but also changes in cultural practices and management that will contribute to higher yields, improved quality and greater sustainability. As plant scientists, we have learned significant amounts about this process through the study of model plants such as Arabidopsis, tomato, rice, and maize. While these model systems have provided significant valuable information, we are sometimes challenged to use this knowledge effectively as variables including the economic value of the crop, the uniformity of the crop, ploidy levels, flowering and crossing mechanisms, ethylene responses, cultural requirements, responses to changes in environment, and cellular and tissue specific morphological differences can significantly influence outcomes. The value of genomic resources for lesser-studied crops such as cranberries and grapes and the orphan crop fonio will also be considered.