Biotypic Diversity and Resistance to the Raspberry Aphid Amphorophora agathonica in Pacific Northwestern North America

Resistance to colonization by the raspberry aphid (Amphorophora agathonica Hottes) has been an important objective in North American red raspberry (Rubus idaeus L.) breeding programs since the 1930s because of its effectiveness in controlling the spread of aphid-transmitted viruses in red raspberry. The most widely used source of resistance in North America has been the gene Ag1 from ‘Lloyd George’. The widespread use of Ag1 to control aphids led to the appearance of a resistance-breaking biotype in British Columbia, Canada, in 1990. Our objective was to identify biotypes of A. agathonica present in the commercial red raspberry production region of southwestern British Columbia and northwestern Washington and determine what sources of resistance may still be effective against this pest. We collected 12 aphid isolates and screened them against 15 raspberry cultivars and four selections. Although it has been widely believed that only two biotypes (regular and Ag1-breaking) of A. agathonica were present in the region, we identified six distinct biotypes and characterized them by their ability or inability to colonize a differential set of raspberry cultivars. This has confirmed the loss of previously recognized and unrecognized sources of resistance in some cultivars. The data also support the presence of a seventh biotype that has not yet been observed. In addition, we confirmed resistance from three sources of wild North American red raspberries that hold up to each of these biotypes. Our results will serve as a guide for future efforts to characterize the prevalence of different aphid biotypes in the region and the identification of new sources of resistance for breeding.

Identification of Resistance to the Large Raspberry Aphid in Black Raspberry

The large raspberry aphid (Amphorophora agathonica Hottes) is an important vector of viruses in Rubus L. across North America. Although breeding for aphid resistance has long been recognized as an important tool for protecting red raspberries (Rubus idaeus L.) from viral infection, this is the first report of resistance to A. agathonica in black raspberry (Rubus occidentalis L.). Seedlings from 132 wild populations of black raspberries, representing the species' native range, were screened for resistance to A. agathonica. Strong resistance was found in three of these populations, one from Ontario (ORUS 3778), one from Maine (ORUS 3817), and one from Michigan (ORUS 4109). Resistance to the large raspberry aphid in ORUS 3778 and ORUS 3817 is dominant and appears to be conferred by different genes. We propose that the genes for resistance in ORUS 3778 and ORUS 3817 be designated Ag4 and Ag5, respectively. Resistance to A. agathonica in ORUS 4109 also appears to be controlled by a dominant allele at a single locus, but cannot be differentiated from Ag4 at this time.

First Report of Rubus yellow net virus on Rubus idaeus in Alberta, Canada

In North America, Rubus yellow net virus (RYNV), a member of the genus Badnavirus, family Caulimoviridae, is vectored in a semipersistent manner by the large raspberry aphid (Amphorophora agathonica Hottes) and is responsible for producing net-like chlorosis of tissue along the leaf veins (2). Red raspberry (Rubus idaeus L.) is commonly grown in Canada and after the dry, hot summer of 2006 in southern Alberta, a group of garden raspberry plants located near Lethbridge, Alberta exhibited interveinal chlorosis resembling viral symptoms. Nonenveloped, 140 × 30 nm, bacilliform particles typical of badnaviruses were observed in infected leaves by transmission electron microscopy. The presence of RYNV was confirmed by immunocapture of virions from extracts of symptomatic leaves using Sugarcane bacilliform virus polycolonal antiserum (Agdia Incorporated, Elkhart, IN) followed by PCR amplification of a 451-bp fragment with RYNV-specific primers based on the highly conserved region of the reverse transcriptase and ribonuclease H genes (5′-ATCCTCAAAGGGTTACGTAGCTGGTT-3′ and 5′-TTCAAGCCACCTTACCCTCGAAGGTTT-3′). Sequence of clones from the PCR product (GenBank Accession No. EU327346) showed 87% identity to a previously sequenced isolate of RYNV (GenBank Accession No. AF468454) (1). To our knowledge, this is the first report of RYNV in Alberta, Canada, and as an important component of raspberry veinbanding disease, it poses a new threat to the Alberta raspberry industry. References: (1) A. T. Jones et al. Ann. Appl. Biol. 141:1, 2002. (2) R. Stace-Smith. Can. J. Bot. 33:269, 1955.

012 EXPLOITATION OF RUBUS STRIGOSUS IN RASPBERRY BREEDING

The indigenous North American red raspberry, Rubis strigosus has been neglected in breeding programs. Only four cultivars, `Cuthbert', `Latham', `Herbert' and `Ranere' provide most of the germplasm contained in present-day cultivars; no more than six individual wild genotypes of the species are represented by the four cultivars. In recent years, the B.C. breeding program has screened seedling populations of hitherto unexploited genotypes of the species from various locations in North America. Useful traits identified in selections from the populations include levels of resistance to 1) the North American aphid vector, Amphorophora agathonica, of the raspberry mosaic virus complex, 2) to several cane diseases and 3) to root rot caused by Phytophthora fragariae var rubi, as well as desirable fruit traits, such as bright, non-darkening red color and easy release. Selections with cultivar potential have now been identified in the second and third backcross generations from the species.