The 2012 ASHS Annual Conference

Crumbly fruit in red raspberry has been observed wherever the crop is grown worldwide.  In most cases, crumbly fruit has been attributed to virus infection, in most cases Raspberry bushy dwarf virus (RBDV) infection.  Since the turn of the century, crumbly fruit in northern Washington (nWA) and British Columbia, Canada (BC) has become more severe and spreads more rapidly in new plantings.  The same cultivars grown in Oregon that are infected with RBDV do not have the severe crumbly fruit and RBDV spreads more slowly in Oregon. In addition, it was observed that populations of the large raspberry aphid (Amphorophora agathonica) were much higher in nWA/BC than in Oregon.  As a result of the difference in the spread rate of RBDV and severity of crumbly fruit between nWA/BC and Oregon we investigated the possibility that severe crumbly fruit may be caused by a virus complex.  This led to the identification of two new viruses, Raspberry leaf mottle virus (RLMV) and Raspberry latent virus (RpLV) from symptomatic plants in nWA.   As part of the SCRI project ‘Management of Rubus complexes in Rubus’, RpLV was characterized and determined to be a novel reovirus.  At the time all known plant infecting reoviruses were transmitted by hoppers.  Leafhopper species from Rubus in nWA failed to transmit RpLV in greenhouse experiments, thus, aphids were tested as vectors.  It was found that the large raspberry aphid could transmit RpLV, albeit inefficiently, and that RpLV replicated in the aphid.  The same aphid was able to transmit RLMV quite efficiently.  In field surveys in nWA/BC, RLMV was found to spread quickly in fields with incidence of infection approaching 100% in 4-year-old fields.  In the same fields, the incidence of RpLV was less than 40%.  In sWA and Oregon, the incidence of both viruses was much lower, usually less than 30% and 20% for RLMV and RpLV, respectively, in 8-year-old fields.  At the same time crumbly fruit was less severe in sWA/Oregon compared to nWA/BC. Field plots were established with each virus and all combinations of the RBDV, RLMV and RpLV as well as healthy plants. In these plots, RBDV plus RLMV had the greatest impact on plant growth, whereas RBDV plus RpLV had the greatest impact on fruit quality. Thus, mixed infections of these three viruses impacts plant growth, fruit yield, and fruit quality.