The 2012 ASHS Annual Conference

Raspberry crumbly fruit is a widespread disease most commonly caused by  virus infections. In the last decade, crumbly fruit symptoms have become more severe in ‘Meeker’ red raspberry in the Pacific Northwest (PNW) of the United States and British Columbia (BC), Canada. The cause of crumbly fruit in raspberry has long been attributed to Raspberry bushy dwarf virus (RBDV), a pollen-borne virus. However, the identification of two new viruses, Raspberry leaf mottle virus (RLMV) and Raspberry latent virus (RpLV), both present at high incidence in northern Washington and BC, suggested the existence of a new virus complex responsible for the increased severity of the disease. A field experiment was established, consisting of ‘Meeker’ plants infected by single or mixed infections of RBDV, RLMV, and RpLV in all combinations along with healthy plants. During establishment in 2010, plants co-infected with RBDV-RpLV-RLMV and RBDV-RLMV had a 71% and 76% reduction, respectively, in primocane growth. Also in the first fruiting year, plants co-infected with RBDV-RpLV-RLMV and RBDV-RpLV had the lowest berry weights, firmness and number of drupelets. Comparisons of virus titers across treatments revealed that the titer of RBDV was increased approximately 400-fold in plants co-infected with RLMV or RLMV-RpLV relative to the titer in plants infected with RBDV alone or with RBDV and RpLV. The significant increase in titer of RBDV in presence of RLMV in the field was also found in greenhouse grown plants, suggesting that environmental conditions do not have an impact on this dramatic virus interaction. Neither RBDV nor RpLV had an impact on titers of co-infecting viruses. Taken together, these findings suggest that growth reduction and severe crumbly fruit disease in ‘Meeker’ are caused by a co-infection of RBDV and RLMV or RpLV. RLMV and RpLV are transmitted by the large raspberry aphid, Amphorophora agathonica. RLMV spreads rapidly in norhtern Washington and BC with the incidence approaching 100% four years after planting.  Studies are underway to determine whether the enhanced titer of RBDV in the presence of RLMV also occurs in the pollen. If it does, then rate of pollen transmission will be examined in plants with single or mixed infections of these two viruses.