Crop forecasting is a highly desirable tool for fruit production. For cranberry, early and accurate yield prediction would benefit handlers and processors to plan for crop volumes and fruit prices; most importantly, it would allow growers to customize inputs based on potential yield returns. The current yield prediction model for cranberry consists of evaluating the number of large apical buds per unit area in early fall; however, this model is highly inaccurate. Recently, DeVetter et al. (2015), in an effort to improve yield prediction, evaluated a model that included environmental and physiological factors, but they could only determine that berry number and size were the best predictors of yield. These factors are not useful for early crop forecasting, and large amounts of unexplained variations are associated with factors explaining the berry number (DeVetter et al., 2015).
Flower bud number and development are the most critical factors for accurate yield prediction (Aggelopoulou et al., 2011). Flower formation is a multistep process, from floral meristems differentiation to anthesis, and all of the steps are influenced by endogenous factors, such as resource allocation (Alvarez-Buylla et al., 2010; Liu et al., 2009; Polito et al., 2002). Previous studies examining cranberry bud floral differentiation focused on the timing of the first appearance of floral primordia in summer (Bolivar-Medina et al., 2019; DeVetter et al., 2013a; Goff, 1901; Lacroix, 1926; Roberts and Struckmeyer, 1943). Lacroix (1926) described the floral meristem development process of older cranberry cultivars; however, a more complete study has not been performed for current high-yielding cultivars. Furthermore, the extent of cranberry floral meristem development during fall and winter and its effect on fruit production during the following season have not been determined.
Cranberry is a perennial woody vine native to North America that produces vertical stems, known as uprights, which grow from long runners. Newly formed uprights arise from vegetative axillary buds of runners, whereas older uprights grow each season from mixed (vegetative and floral meristems) or vegetative apical buds of extant uprights. Fruiting uprights produce leaves, flowers, and, subsequently, fruit, whereas vegetative uprights do not bear any fruit. Both upright types have the potential to set a mixed apical bud in new cultivars (Roper and Vorsa, 1997; Trehane, 2004; Vorsa and Johnson-Cicalese, 2012). A wide range of terminal bud size has been observed, particularly in newer high yielding cultivars. However, the implications of bud size and the type of upright (i.e., vegetative or fruiting) have never been considered during cranberry crop forecasting, and they could potentially account for the large amount of unexplained variations in crop yield forecasting models.
The objectives of the present study were as follows: to describe the development of floral meristems in cranberry mixed terminal buds; to evaluate the extent of floral meristem development of small, medium, and large mixed buds of vegetative and fruiting uprights from fall to spring; and to evaluate the contributions of mixed bud sizes and upright types to fruit production.
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