Bud development, return bloom, and external bud appearance differ among cranberry cultivars

Abstract

Recent cultivar releases of cranberry (Vaccinium macrocarpon) have been reported to differ in terminal bud development, biennial bearing tendencies, and external bud appearance. However, verification of these claims and cultivar comparisons with respect to these characteristics are lacking. The objectives of this project were to 1) evaluate flower initiation, bud development, and potential return bloom across several cultivars of cranberry, including recent introductions; and 2) determine the relationship between external appearance of buds and the presence/absence of flower initials. Samples of upright shoots representing the cultivars Searles, Stevens, HyRed, and Crimson Queen were collected from a commercial cranberry marsh located in central Wisconsin during the 2011 and 2012 growing seasons. Collected uprights were separated based on reproductive status (i.e., reproductive or vegetative). Buds were then dissected and analyzed for presence/absence of flower initials using light and scanning electron microscopy. Growing degree days (GDD) were calculated and related to the progression of bud development. Flower initials were first observed on 29 July 2011 and 10 July 2012, or 290 and 322 GDD, respectively. Excluding 'Searles', dates of initiation were the same across all cultivars and did not differ based on reproductive status. Descriptive bud data demonstrated that wider buds are more likely to contain flower initials and overall bud width tended to be greater among recent cultivar releases. Biennial bearing tendencies were also lower among recently released cultivars, as exhibited by greater occurrences of potential return bloom. Results from the study provide evidence that recently released cultivars differ in bud development, have an increased potential for return bloom, and overall wider buds. These findings suggest newer cultivars may have different mechanisms regulating mixed bud development and other yield-contributing factors.