Cranberry is a perennial vine native to northeastern continental America (Eck, 1990). Vertical stems, known as uprights, develop terminal buds that may be mixed or vegetative. Mixed buds contain flower initials that overwinter and produce fruit the next year, whereas vegetative buds lack flower initials and only contain a vegetative meristem. Alternating patterns of mixed bud formation on individual uprights leads to biennial bearing and it has been shown that fruiting uprights are less likely to develop mixed buds (Eaton, 1978; Elle, 1996; Roper et al., 1993). Competition for carbohydrates during simultaneous fruit and bud development has been provided as an explanation for biennial bearing tendencies in cranberry (Baumann and Eaton, 1986; Strik et al., 1991). However, recently released cultivars are reputed to exhibit extensive return bloom (Roper, 2006). Return bloom occurs when a fruiting upright develops a mixed bud, thereby circumventing biennial bearing.
Much of the previous research on cranberry buds is based on cultivars that are becoming less common within the industry (Goff, 1901; Lacroix, 1926; Lenhardt and Eaton, 1977; Roberts and Struckmeyer, 1943). Plantings of recently released cultivars have been increasing amidst reports that these cultivars exhibit favorable production characteristics, such as extensive return bloom. However, evaluations and comparisons of these recent introductions relative to traditional ones are lacking. Furthermore, the relationship between external bud appearance and the presence/absence of flower initials has not been systematically evaluated, particularly among recent cultivar releases (Lenhardt and Eaton, 1977; Patten and Wang, 1994). External bud appearance is an important characteristic because of its extensive use as a metric for yield prediction. This approach to prediction is qualitative and entails visual assessment of buds during the year before anticipated harvest. Large and round buds are assumed to be mixed and have the potential to contribute to the next year’s crop. Small and narrow buds, on the other hand, are assumed to be vegetative. Despite the prevalence of this approach, the margin of error between predicted and actual yield can exceed 15% (T. Dittl, personal communication). Such a large margin of error renders the reliability of this metric questionable for the cranberry industry. This metric may become increasingly problematic if external bud appearance varies dramatically, which necessitates an evaluation across cultivars.
This project sought to address the lack of information on bud initiation and development across different cultivars of cranberry, including recent introductions. Specific objectives of this project were to 1) evaluate flower initiation, bud development, and potential return bloom across cultivars; and 2) determine the relationship between external appearance of buds and the presence/absence of flower initials. Information on these characteristics will be valuable as investigators and industries explore how to optimize production and management of the different cultivars available to growers.
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