Fresh-market blackberries (Rubus subgenus Rubus Watson) have a growing market worldwide, with the continued release of new blackberry cultivars to meet demand. Like other dark-pigmented fruits, blackberries are a rich source of bioactive components that can significantly affect human health (Clark et al., 2002; Conner et al., 2005; Seeram, 2008; Siriwoharn et al., 2004). Many factors affect the production and quality of fresh-market blackberries including the genetic background, soil type, weather conditions, and plant management.
Fresh-market blackberries need to have attributes that appeal to consumers, but also withstand the market chain from harvest to commercialization. Key attributes for quality fresh-market blackberries include firm berries with a good balance between acidity and sugar content. Achieving sugar and acid balance and maintaining fruit quality during storage are major goals of fresh-market blackberry breeders. Based on consumer sensory studies, a desired fresh-market blackberry should have a berry weight of 8–10 g, soluble solids of 9% to 10%, and titratable acidity between 0.9% and 1.0% (Threlfall et al., 2016a). In addition to sugars and acids, phytochemicals play an important role in consumer perception of flavors. Soares et al. (2013) reported that phenolic compounds, such as anthocyanins and hydrolysable tannins, affect bitterness in fruits and derived products. Other important fresh-market blackberry quality attributes include firmness, seediness, red drupelet incidence, and decay resistance.
More recently, primocane fruiting has become a major focus in blackberry breeding (Clark and Finn, 2008; Strik et al., 2007). In the last years, the University of Arkansas has released primocane-fruiting cultivars such as ‘Prime-Jim®’, ‘Prime-Jan®’, ‘Prime-Ark 45®’, and ‘Prime-Ark® Traveler’ (Clark and Perkins-Veazie, 2011; Clark and Salgado, 2016; Clark et al., 2005). Blackberries typically produce fruit on the second-year canes (floricanes), requiring canes to be overwintered to produce a crop. However, primocane-fruiting blackberry plants can bear fruit on current-season canes (primocanes). Thus, primocane-fruiting blackberry genotypes (selections and cultivars) can produce two cropping seasons, one during the summer on floricanes and the other during midsummer to fall on primocanes. Primocane fruiting has contributed to the expansion of blackberry production similar to the expansion achieved with primocane-fruiting red raspberries (Rubus idaeus L.) (Clark and Perkins-Veazie, 2011). Primocane-fruiting blackberries show great promise for improving the availability of fresh-market blackberries worldwide using off-season production systems (Strik et al., 2007).
In 2004, the University of Arkansas released ‘Prime-Jim®’ and ‘Prime-Jan®’, the first commercial primocane-fruiting cultivars (Clark et al., 2005). The first shipping-quality, primocane-fruiting blackberry was released, as ‘Prime-Ark® 45’ (Clark and Perkins-Veazie, 2011) in 2009. ‘Prime-Ark® Traveler’ is the world’s first commercially released, thornless primocane-fruiting blackberry with shipping-quality fruit (Clark and Salgado, 2016).
In Arkansas, primocane-fruiting blackberry genotypes typically flower and fruit during mid to late summer, when average daily high temperatures range from 32 to 40 °C. Primocane-fruiting cultivars such as ‘Prime-Jim®’ and ‘Prime-Jan®’ exhibited poor summer heat tolerance in field trials (Clark et al., 2005) in Arkansas, resulting in low berry weight, crumbly berries, and poor flavor. Double and otherwise misshapen fruit have been seen on primocane-fruiting genotypes and are associated with high heat during bud, flower, and fruit development (Clark, 2008).
Primocane cultivars have better fruit production in areas with daily high temperatures of 25 to 30 °C during flowering and fruit development. According to Thompson et al. (2009), the yield of primocanes from ‘Prime-Jan®’ grown in Oregon was 0.3–3.6 kg/plant with berry weights 4.0–8.1 g. Although ‘Prime-Jan®’ does not produce primocane fruit well in Arkansas, subsequent releases such as ‘Prime-Ark® Traveler’ produced 4306–10,287 kg·ha−1 (0.95–2.3 kg/plant) with berry weights from 4.7 to 7.3 g, and ‘Prime-Ark® 45’ produced 4978–10,540 kg·ha−1 (1.1–2.3 kg/plant) with berry weights from 5.1 to 7.3 g (Clark and Salgado, 2016).
In recent sensory studies on fresh-market blackberries grown in Arkansas, floricane berries from primocane cultivars have had positive consumer attributes. ‘Prime-Ark® Traveler’ had the highest liking values for overall impression and overall flavor; consumers liked the shape and firmness of this cultivar. ‘Prime-Ark® Traveler’ and ‘Prime-Ark® 45’ had the highest liking values for appearance and size (Threlfall et al., 2016b). Consumer and physiochemical studies on fresh-market blackberries can provide positive findings to guide the growth of the blackberry industry.
The physiochemical attributes that affect quality of fresh-market blackberries from floricanes have been researched, but there is little information on these attributes of blackberries from primocanes of the same genotypes to describe any differences in berries harvested from the different cane types. The objective of this study was to investigate physiochemical attributes of fresh-market blackberries harvested from two cane types (floricane and primocane) of four primocane genotypes (APF-238, APF-268, ‘Prime-Ark® 45’, and ‘Prime-Ark® Traveler’) grown at the University of Arkansas Fruit Research Station, Clarksville in 2015 and 2016.
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