Molecular Characterization of Aphid Resistance in Black Raspberry Germplasm

Black raspberry is a minor but lucrative crop with most of the acreage in the U.S. grown in Oregon. One of the challenges for black raspberry growers is the rapid decline of plantings resulting from aphid-borne virus infection. The North American large raspberry aphid is a vector of Black raspberry necrosis virus (BRNV) and other viruses in the Raspberry mosaic virus complex, to which all available cultivars are susceptible. BRNV spreads rapidly in the field resulting in plantings that decline in as few as two or three growing seasons. Aphid resistance was discovered in each of three separate wild black raspberry populations collected from Simcoe, Ontario, Canada (ON), Gardiner, Maine, USA (ME), and Bath, Michigan, USA (MI). Three full-sib black raspberry populations, designated ORUS 4305 (ON), ORUS 4304 (ME), and ORUS 4812 (MI), were used to study the inheritance of the aphid resistance from the three sources. We have successfully mapped the locus for the ON source of resistance, designated Ag₄, on Rubus Linkage Group 6. Association analysis suggests that black raspberry genome sequence Scaffolds 99, 525 and 684 are important for determining aphid resistance in population ORUS 4305. We have identified simple sequence repeat (SSR) loci throughout these three scaffolds and have screened the loci in a subset of each population. To date, ten SSR loci on Scaffold 99 (S99) that segregate with aphid resistance have been identified, while screening of the loci for Scaffolds 525 and 684 is in progress. Preliminary results suggest that all three resistance loci are linked and strongly associated with S99 and that each represents a unique locus. All markers will be validated in populations with mixed sources of resistance.