Location: Horticultural Crops Research2011 Annual Report
1a. Objectives (from AD-416)
1. Develop and validate diagnostic tests for the viruses involved in these complexes and transfer these validated tests to interested parties; 2. Identify candidate virus vectors based on virus genomics with greenhouse transmission testing; 3. Identify virus combinations capable of causing severe disease outbreaks, and; 4. Evaluate virus and vector resistance in Rubus germplasm; conduct field transmission tests to determine when viruses are being spread in the field and implement targeted control based on vector biology for management of the diseases. 5. Communicate the results: Outreach, Education and Implementation for growers, extension agents, and agricultural consultants.
1b. Approach (from AD-416)
This project aims to minimize or eliminate the impact of virus complexes in production fields through minimal pest management targeting the virus/vector combinations easiest to control, this includes the improvement of virus testing in certification programs.
3. Progress Report
Raspberry plants with single infections of Raspberry bushy dwarf virus (RBDV), Raspberry leaf mottle virus (RLMV) and Raspberry latent virus (RpLV) were identified. Starting with these single infections, ‘Meeker’ raspberry plants were grafted to develop single and mixed infections for field studies. The virus combinations created are: RBDV, RLMV, RpLV, RBDV + RLMV, RBDV + RpLV, RLMV + RpLV, RBDV + RLMV + RpLV, as well as plants that tested free of known viruses. Once the desired infections in ‘Meeker’ were developed, each plant was propagated vegetatively for replicated field trials. Replicated field trials were established at the Northern Washington Research and Extension Center (NWREC) at Mt. Vernon, WA and at the USDA-ARS research farm on Peoria Rd, near Corvallis, OR. Initial studies on the titers of the three viruses in mixed infections as well as single infections is being monitored by real-time RT-PCR using Taqman probes. Initially, it appears that the titer of RBDV in the presence of RLMV is as much as 500 fold higher than in plants singly infected with RBDV. This is being repeated this summer and autumn to look at the role of temperature on virus interactions. Virus infection is the leading cause of decline in black raspberry production in the Pacific Northwest. In a project led by an ARS Research Geneticist at Corvallis, OR, four clones of black raspberry with aphid resistance have been identified and are being used to develop aphid resistant commercial cultivars of black raspberry. Black raspberry with aphid resistance have been planted plots at Mt. Vernon and Lynden Washington, where there is a very high aphid pressure to determine if the aphid resistance will reduce virus infections in the field. All field plots are part of a multi-year study. Real time PCR assays were developed for several viruses of small fruit crops (RLMV, RBDV, RpLV, Grapevine leafroll virus 3 and Blueberry shock virus to improve detection efficiency and for studies on virus interactions. This effort is continuing for other viruses of the berry crops. With the large number of new viruses identified in berry crops the past 10 years, we are exploring the possibility of using Deep or High Throughput sequencing to make the characterization of viruses of these crops more efficient. We have obtained sequences for blueberry, raspberry, blackberry, elderberry, sugarberry, rose and redbud using this technology. We are now expanding this to use it as a means to identify possible threats to the berry crops by looking at viruses in native relatives of the important berry crops, and also to look at new diseases that are observed in these crops. Several of these viruses have been found in blackberry cultivars from the Arkansas breeding program that are being grown in the Pacific Northwest. There is no evidence of these viruses spreading to the Pacific Northwest since the viruses have not been found in raspberry or blackberry cultivars from the breeding programs in this region. These virus tests have been incorporated into the testing for the National Clean Plant programs to ensure material free of the viruses is being developed for commercial growers.