1a.Objectives (from AD-416)
The objective of this cooperative research project is to conduct collaborative small fruit research of mutual benefit to ARS and Washington State University and to coordinate grower field trials complementary to the small fruits research programs at USDA-ARS Horticultural Crops Research Unit.
1b.Approach (from AD-416)
Studies will involve insect collections using sticky cards and water pan traps which will be used throughout the season to establish the phenology of insect development and dispersal. There will be trap plants for virus transmission studies placed in field trials throughout the growing season to determine when viruses are being moved in the field. Plots of raspberry with mixed virus infections will be established at the Mt. Vernon research station. There will also be nematode sampling over the season to study nematode populations after cover crop trials and chemical control trials.
A virus induced crumbly fruit disease in ‘Meeker’ and other red raspberry cultivars has been observed in northern Washington, USA and British Columbia, Canada. Raspberry bushy dwarf virus (RBDV), Raspberry leaf mottle virus (RLMV) and Raspberry latent virus (RpLV) were detected in raspberries with severe crumbly fruit. In efforts to determine the role of each virus in the crumbly fruit disease complex, ‘Meeker’ plants with defined virus combinations were developed. These plants were propagated and used to establish field trials. There were significant differences in plant growth during the first growing season; plants with all 4 viruses exhibited severe stunting compared to plants with single infections. The titer of RBDV was increased at least 500-fold when it occurred in mixed infections with RLMV compared to RBDV in single infections while the titer of RLMV was similar in single infections and in mixed infections with RBDV (using quantitative PCR tests). These findings along with the lack of severe crumbly fruit symptoms in ‘Meeker’ red raspberry singly infected with RBDV in Oregon, where the incidence of the aphid-borne viruses is much lower, suggest the existence of a novel virus complex associated with severe crumbly fruit in red raspberries. The complex may involve RBDV, RLMV and/or RpLV. Field studies are underway to determine the effect of each of these viruses singly and in all combinations on crumbly fruit symptom development in ‘Meeker’ red raspberry. The first harvest of fruit from the plots in Oregon has just been completed, and there are significant differences between the plants with mixed infections compared to healthy plants or plants with single infections. Since this is the first year of harvest and the plots in Washington have not yet been harvested, it is too early to determine the impact of mixed virus infections on fruit quantity and quality. The study will be carried out through the second year of harvest before any final conclusions can be drawn from the work. The preliminary results suggest that mixed infections result in more severe stunting, reduce fruit yields and more crumbly fruit. Since the 3 viruses in this complex are all transmitted by the large raspberry aphid (Amphorphora agathonica), studies are also underway to develop a degree day model for the development of this aphid that will allow growers to time treatments of the aphid to reduce virus transmission. Since, growers already use some type of 'clean up' spray to minimize the insect contaminants in harvested raspberries, it is anticipated that timing of this 'clean up' spray to coincide with the major aphid flight might give aphid control with the same treatment that is currently used to minimize fruit contaminants with insects. Sticky cards and water pan traps are being placed in and around raspberry fields with different approaches to the use of 'clean up' sprays to manage insect contamination in their fruit. Aphid eggs are also being monitored for hatch, then number of degree days between hatch and first flight. This data will be incorporated into the degree day model. The project was monitored with meetings, e-mail, and phone calls.