Commercial blackberry production is increasing in the southern and eastern United States (Strik et al., 2007). The majority of the production in this region is based on the use of floricane-fruiting cultivars, where fruiting occurs on second-year canes and the harvest season commences in June and ends in mid-August. In 1995, the University of Arkansas and North Carolina State University jointly released NC 194, a primocane-fruiting blackberry selection that was intended for use as parental germplasm (Ballington and Moore, 1995). Ten years later, the University of Arkansas released the first primocane-fruiting cultivars Prime-Jim® and Prime-Jan® (Clark et al., 2005). Although small in scope, the North Carolina State University blackberry breeding program continued to devote a portion of their resources to the breeding of primocane-fruiting blackberries since the release of NC 194 and have had several lines in observational trials in multiple locations in the state.
In North Carolina, we have observed low productivity when primocane-fruiting experimental cultivars from both breeding programs were grown in observational plots at research stations in the Piedmont region (elevation 300–400 ft). However, when primocane-fruiting experimental blackberry cultivars were grown in Mills River, NC (elevation 2000 ft), fruit production was much higher; both fruit size and number of fruit were greater than those observed in the Piedmont region. Although fruit production potential was much greater in the higher elevation, fall frosts often damaged fruit and ended the harvest season before the crop could reach its full potential (J.R. Ballington, personal communication). In Clarksville, AR, primocane-blackberries produce only a small amount of fruit in the late summer, likely as a result of lack of heat tolerance of the flowers (Clark, 2008; Stanton et al., 2007). However, when these same experimental cultivars were grown in Aurora, OR, harvest commenced in August and extended into October (Strik et al., 2008).
Season extension techniques are used to advance or delay the fruiting season of many small fruit crops including raspberry (Rubus idaeus) and blackberry (Pritts, 2008; Pritts et al., 1992; Strik and Thompson, 2009; Strik et al., 2008). When rowcovers were applied over the rows of primocane-fruiting raspberries in the early spring before primocane emergence, fruit production occurred up to 3 weeks earlier than in rows without rowcovers. Strik et al. (2008) were able to advance bloom by 14 d when rowcovers were placed over dormant plots of primocane-fruiting experimental blackberry cultivars in Oregon. No studies have been conducted to evaluate the efficacy of rowcover use in promoting earlier fruiting in primocane-fruiting blackberries in the high elevations of the southern Appalachian region.
The objectives of this research were 2-fold. First, we wanted to document yield of primocane-fruiting experimental blackberry cultivars from the North Carolina State University and University of Arkansas breeding programs in the southern Appalachian Mountains. Second, we wanted to examine the efficacy of rowcover use in promoting earlier fruiting and higher yields in nine primocane-fruiting experimental blackberry cultivars.
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