Relationship between alternate bearing and apical bud development in cranberry (Vaccinium macrocarpon)

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.