Characteristics of Elderberry Fruit In Response to Genotype, Environment, and Pruning Management

American elderberry (Sambucus canadensis L.) is an emerging horticultural crop in North America.  The native shrub produces fruit that is used to make jams, jellies, beverages, dietary supplements, food coloring, and wines.  Elderberry produces fruit on both new (primary) and old (secondary) stems.  Little is known about the characteristics of fruit produced on these two different types of plant growth, or how genetic and environmental factors affect fruit quality.  Replicated elderberry orchards were planted at two locations in Missouri, USA (Mt. Vernon and Mountain Grove) in 2000 for a long-term pruning study.  Randomized plots were assigned one of three cultivars (‘Adams II’, ‘Bob Gordon’, or ‘Netzer’), and one of two pruning regimens (annual removal of all shoots, and selective horticultural pruning) so that fruit were produced almost exclusively on either primary or secondary stems.  In 2006, ripe fruit were harvested from each plot and frozen.  For analysis, 250 mL of fruit were thawed, macerated, strained through cheese cloth, and the resulting juice centrifuged at 3,500 rpm for 10 min.  Supernatant juice was analyzed for pH, total soluble solids [TSS (^oBrix)], and titratable acidity [TA (g 100mL^-1).  Fruit harvested from Mountain Grove had significantly higher TSS (11.82), lower pH (4.71), and higher TA (0.64), compared with fruit from Mt. Vernon (TSS 11.16, pH 4.98, and TA 0.56).  Among fruit from the three cultivars, no differences were detected for TSS, however pH and TA varied significantly, with pH ranging from 4.97 for ‘Adams II’ to 4.73 for ‘Bob Gordon’, and TA ranging from 0.65 for ‘Bob Gordon’ to 0.54 for ‘Netzer’.  When comparing fruit produced on primary or secondary stems, no differences in TSS were detected, however fruit from primary stems had significantly lower pH (4.76) and higher TA (0.62) compared with fruit from secondary stems (pH 4.91 and TA 0.58).  Among experimental factors, fruit with more desirable enological characteristics (lower pH, higher TA, and higher TSS) was generally produced at Mountain Grove, by ‘Bob Gordon’, and on primary stems.  Plants at Mountain Grove were more vigorous and yielded higher than plants at Mt. Vernon, and ‘Bob Gordon’ out-performed the other cultivars in terms of vigor and yield.  Fruit from primary stems is generally borne on single, very large cymes, whereas secondary stems produce more numerous, smaller cymes.  As we better understand how genetic, environmental, and horticultural factors interact to determine elderberry fruit quality, important production decisions can be made.