Performance and phenology of wild black raspberry (Rubus occidentalis L.) germplasm in a common garden

A lack of genetic diversity in cultivated black raspberry (Rubus occidentalis L.) germplasm has been widely recognized as a major factor limiting progress towards breeding improved cultivars. Despite this, little effort has been made since the early twentieth century to systematically collect and evaluate wild black raspberry for germplasm improvement. In recent years, there has been renewed interest in black raspberry breeding to replace existing cultivars that lack durability and disease resistance. We planted seedlings from 109 wild black raspberry populations, representing 24 US states and two Canadian provinces, in the field in replicated trial plots in Corvallis, Oregon (USA), to evaluate their performance. These populations showed wide variation in morphology, architecture, fruiting season, vigor, and apparent field tolerance to Verticillium wilt. For nearly every trait examined, wild black raspberry germplasm exhibited a range of variation beyond existing cultivars, and showed great potential for use in future breeding. While most populations were fairly uniform phenotypically, segregation for fruit gloss and possible tolerance to Verticillium wilt was noted in a few, indicating the possibility of simple inheritance of these traits. A few populations with unusual morphology, such as spinelessness or flower abnormalities, were identified, as were populations that flowered on first year canes and produced fall fruit. Populations from the southern edge of the range appear to be particularly well adapted to western Oregon, with vigorous upright growth, strong canes, and some with a low incidence of Verticillium wilt. This germplasm will be of great value to breeders interested in developing improved black raspberry cultivars.