Molecular Evaluation of Aphid-resistant Black Raspberry Germplasm for Improved Durability in Black and Red Raspberry

Over the last century, the black raspberry (Rubus occidentalis L.) industry in the United States has undergone a slow but steady contraction because of a lack of adapted and disease resistant cultivars. The Pacific Northwest (PNW) is the major black raspberry production region in North America, with the value of utilized production in Oregon in 2014 valued at $9.6 million over 1650 acres. Continuing research on health benefits of a diet rich in phytonutrients, and black raspberries in particular, has led to a resurgence of interest in this fruit and a renewal of breeding efforts. While the crop faces numerous challenges in the PNW that are being addressed with breeding and genomics, one of the major problems is the severe impact Black raspberry necrosis virus (BRNV) has on plant health and the industry’s viability. BRNV is an aphid (Amphorophora agathonica Hottes)-borne virus that, in the industry standard cultivar (Munger), causes a rapid decline in vigor leading to plant death. In addition to black raspberry, aphid resistance is important to the red raspberry processing industry in Washington and Oregon, where aphid-vectored viruses are a major component of a crumbly fruit disease complex. Three sources of aphid resistance were identified in wild black raspberry germplasm collected from Ontario, Canada (ON), Maine (ME), and Michigan (MI). The evaluation of the aphid resistance sources are being studied on three full-sib black raspberry populations designated ORUS 4304 (ME), ORUS 4305 (ON), and ORUS 4812 (MI). A major focus of this study is to better characterize and develop DNA-based markers that can be used in breeding programs to enable pyramiding of different sources of resistance in new breeding material to ultimately provide resistance that will not easily be overcome by the aphids. At present, the ability to combine these sources effectively is limited by a lack of knowledge regarding their mechanisms and linkage. To date, 17 black raspberry populations with single and combinations of sources of aphid resistance have been phenotyped. Preliminary molecular evaluation for aphid susceptibility of the 17 populations suggest two unique genes in those with sources of resistance from MI and ON.