Evaluation of vigor and winter hardiness of black raspberry breeding populations (Rubus occidentalis) grown in the southeastern US

Demand for fresh berry products continues to grow in the United States; however, commercial raspberry production in the southeastern US is difficult because cultivars are not well adapted to the warm climate and fluctuating winter temperatures, where heat degrades plant vigor and fruit quality, and warm spells in mid to late winter can cause low chilling plants to break bud too early. Recent research about the health benefits of a polyphenolic-rich diet has led to a resurgence of interest and breeding efforts in black raspberry, and is the driving factor for this particular research. Two half-sib populations, ORUS 4304 and ORUS 4305 (307 progeny total) were planted in Jackson Springs, North Carolina in 2012. From fall 2012-spring 2015, a number of traits were measured on each plant, among them vigor, winter hardiness, and heat damage, analyzed in several different ways. Plant vigor increased or decreased over harvest seasons based on individual differences in the segregating plant population, but also showed correlations with temperature, i.e., less vigorous plants were more susceptible to damage by heat or cold. Overall, ORUS 4305 was less vigorous than ORSU 4304. As is the case with most raspberries grown in the southeast, vigor in general is expected to decrease over time; however, certain individuals show transgressive segregation for the trait. Linkage mapping for both populations is underway to identify and validate QTL for vigor, winter hardiness, heat tolerance, and other traits within black raspberry. Ultimately, we hope to gain a more complete understanding of black raspberry physiology and genetics to make breeding commercial quality cultivars a possibility in the southeast.