Comparison of Bud Development Across Traditional and New Cranberry Cultivars

Growers and industry predict yield of cranberry (Vaccinium macrocarpon Ait.) via visual assessments of terminal buds.  This qualitative approach assumes large and round buds are mixed and consequently contain flower initials that contribute to next season’s crop.  Small and narrow buds, in contrast, are assumed to be vegetative and non-yield contributing.  Despite widespread use of this method, the margin of error between predicted and actual yields can exceed 15%.  Such a large margin of error leads to questions about the reliability of this metric.  An additional complication with this approach to yield prediction is the recent release of cultivars that have been reported to differ in bud development.  The objectives of this project were to: 1) characterize bud development and flower initiation throughout two growing seasons; 2) compare bud development across several cultivars, including traditional and recently-released cultivars; and 3) determine the relationship between external appearance of buds and the presence/absence of flower initials.  Samples of plant material were collected from commercial beds located in central Wisconsin during the 2011 and 2012 growing seasons.  Cultivars sampled include Searles, Stevens, HyRed, and Crimson Queen.  Collected material was separated based on growth type.  Buds were subsequently dissected and analyzed for presence/absence of flower initials using light and scanning electron microscopy (SEM).  Growth degree days (GDD) were calculated and used to determine the timing of floral initiation.  Presence of flower initials was first observed 29 July 2011 and 10 July 2012.  These dates coincide with 290 and 322 GDD, respectively.  Dates of flower initiation did not differ across cultivars and types of uprights.  Searles, the oldest cultivar included in the study, was the only exception to this finding.  Lack of initiation data in ‘Searles’ was due to high mortality of buds during both years of the study.  Analysis of descriptive bud data showed wider buds had a greater probability of containing flower initials and bud width was greater among recently released cultivars.  Noteworthy was the discovery that biennial bearing tendencies were minimal among recently released cultivars.  These new cultivars exhibited “rebud,” which is an important trait that circumvents biennial bearing and has not been widely documented in the literature.  Based upon the qualitative nature of bud appearance and variation observed across cultivars, we conclude visual appearance of buds is not a robust metric for yield prediction.  Future work should consider quantifiable metrics when attempting to develop improved methods of yield prediction.