Evaluation location: Oregon, United States
Abstract
Because of its intense anthocyanin pigments, black raspberry (Rubus occidentalis L.) has a long history of use as a natural colorant and dye. Recent studies showing black raspberries to be a rich source of anthocyanins and other dietary phytochemicals have led to renewed interest in breeding better adapted cultivars that meet the demands of these markets. Anthocyanin content is a critical indicator of fruit quality for fresh and processed markets. Previous studies characterizing black raspberry anthocyanins have focused on existing cultivars comprising a narrow genetic base; however, progress in breeding new cultivars with better adaptability and disease resistance will rely on the use of new germplasm sources. Using high performance liquid chromatography/diode array detector/ion trap mass spectrometer, we examined anthocyanin content and profiles in the juice of fruit from black raspberry seedlings representing 78 wild populations from across the species’ native range over a two year period. Anthocyanin profiles were similar to those previously reported, however total anthocyanin content varied widely. Total anthocyanins in individual clones ranged from 39 to 996 mg/100 ml (expressed as cyanidin-3-glucoside) and averaged slightly higher in 2010 than in 2009. Black raspberry cultivars fell in the middle of this range, with individual wild clones ranging from less than one fourth to nearly three times the anthocyanin concentration of the industry standard, ‘Munger’. Genetic diversity for anthocyanin content is present in recently collected wild black raspberry germplasm and should be carefully evaluated when using this material for breeding improved cultivars.
Materials and Methods
During the summer of 2006, friends and colleagues living in eastern North America, within the native distribution of R. occidentalis, were solicited to send seed or fruit from wild plants in their area. Through this effort, seeds were obtained from more than 110 locations across the range, including 18 US states and two Canadian provinces. Upon arrival in the lab, seeds were extracted from the fruit, dried, and stored in a cool dry place until being treated to promote germination as described by Dossett and Finn (2010).
In September of 2007, seedlings were planted in the field in a randomized complete block design with four replications representing 78 wild populations at the USDA-ARS North Farm (Corvallis, OR, USA). Wild populations were represented by four plants per replication as were plants of ‘Jewel’, ‘Mac Black’, and ‘Munger’ for comparison. Plants were spaced 0.9 m apart and trained to a three-wire trellis system with a lower wire at 0.5 m and two parallel wires hung 0.15 m apart at 0.9 m. In early June, primocane tips were pruned at 1 m to induce branching. In late winter, floricanes from the previous fruiting season were removed and branches on new floricanes were pruned to approximately 30 cm in length.
In 2009, two seedlings from each plot were randomly selected and approximately 100 g of fruit from each were harvested for further evaluation. Initial analysis of this data (not shown) indicated that variation between plots was generally greater than variation from within a plot. This, combined with disease pressure limiting the availability of fruit in many plots, led to the decision to harvest a bulk sample of approximately 100 g of fruit from each plot for analysis in 2010.
Collection, handling, and extraction of fruit samples was otherwise performed as described by Dossett et al. (2008). Anthocyanin profiles were determined by HPLC/diode array detector/ion trap XCT mass spectrometer (HPLC/DAD/ESI-MS/MS) on an Agilent 1100 series system (Agilent Technologies, Santa Clara, CA, USA). The guard and analytical columns, mobile phase composition, and the gradient program used for HPLC analysis are described by Lee and Finn (2007), and the protocol for identifying and quantifying anthocyanins was described by Dossett et al. (2008, 2010, 2011). Total anthocyanins were determined by summing the amounts of the individual anthocyanins detected.