Location: Horticultural Crops Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Enhance genetic resources for small fruit crops via germplasm acquisition, evaluation, and breeding. Objective 2: Working with plant breeders of berry crops, develop plants free of known viruses for field evaluation and release of enhanced germplasm. Objective 3: Sequence viruses associated with blueberry necrotic ringblotch and blueberry mosaic diseases for use in the development of diagnostic tools. Objective 4: Determine the utility of the recently discovered aphid resistance in black raspberry for reducing virus spread in the field.
1b. Approach (from AD-416):
Studies will be conducted to collect and evaluate germplasm from wild and domesticated small fruits and incorporate it into advanced breeding material for development of new cultivars with traits ideally adapted for commercial production. Key determinants of resistance, tolerance, and susceptibility to environmental constraints will also be ascertained and utilized for selection of new genotypes and for development of new cultural practices better suited to production of the crops. Anticipated products of the research will include: new cultivars of blackberry, blueberry, raspberry, and strawberry; new small fruit germplasm with improved and novel traits; knowledge of the availability and distribution of genetic variability in small fruit species; greater understanding of physiological mechanisms governing the response of small fruit crops to various abiotic and biotic stresses; and new cultural practices and management systems for small fruit crops that result in higher yield and fruit quality, efficient water and nutrient use, and lower environmental impact.
3. Progress Report:
We successfully conducted a breeding program in blackberry, red and black raspberry, strawberry, and blueberry, as crosses were made, selections identified, advanced selections tested, and potential cultivars were either provided to the commercial nurseries for grower trials or they were in grower trials. ‘Onyx’ blackberry and ‘Stolo’ strawberry release notices were published. 'Onyx' received a patent and patents were prepared and submitted for ‘Vintage’ red raspberry and 'Perpetua' ornamental blueberry. Our ongoing germplasm project with Rubus occidentalis that began with the collection of germplasm in the Midwestern and southern United States has led to the identification of sources of aphid resistance that should impart resistance to Black raspberry necrosis virus. Anthocyanins and phenolics were determined for this germplasm. In an SCRI blueberry project coordinated by the USDA-ARS-PSI, we phenotyped a population that will be genotyped for developing marker assisted breeding in blueberry. In our SCRI funded RosBreed project, we are working on the potential for marker assisted breeding in strawberry by merging phenotyping and genotyping information. We identified Reference Sets that includes 800+ genotypes, coordinated their propagation and distribution. This past summer, we conducted the first year of phenotyping on this germplasm at our location. We will be compiling the data from all locations (FL, CA, MI, and NH) this fall. A virus associated with Blueberry necrotic blotch disease in southern highbush blueberry in Georgia was characterized. The virus has two helicase genes, which is unique among all known viruses. Multiple sets of primers for detection of the virus were developed and evaluated each set against 55 isolates of the virus from NC, GA, FL, AR and MS. Two sets of primers detected all 55 isolates and are being used for detection of the virus in research and certification programs. Transmission experiments are being done by collaborators in FL and GA since the disease is present in those areas. We continued field trials of raspberry with mixed virus infections to determine the role of various viruses on plant growth, fruit yield and quality and to examine synergistic interactions between three viruses that commonly infect red raspberry in the Pacific Northwest. We are in the third year of the study and mid-way through harvests; the results from this year appear to be consistent with those from 2011. Raspberry bushy dwarf virus (RBDV) in combination with Raspberry leaf mottle virus (RLMV) has the greatest impact on plant growth, but the combination has fruit quality and yield comparable to single infections with RBDV. In contrast, RBDV plus Raspberry latent virus (RpLV) has a much great impact on fruit yield and quality compared to RBDV alone. There does not appear to be an interaction between RLMV and RpLV viruses in terms of plant growth or fruit quality. Also in mixed infections it was found that RLMV resulted in approximately a 400-fold increase in the concentration of RBDV. Concentrations of the other viruses were not altered in mixed infections.
1. Developed, released and patented (USPP 22358) 'Onyx' trailing blackberry for the U.S. fresh market industry. 'Onyx' has superior fruit quality in the late trailing blackberry season. This cultivar is firm enough with enough overall quality to work for wholesale fresh market sales. 'Onyx' continues the tradition of USDA-ARS releases of processing and fresh market cultivars that increase the competitiveness of berry growers.
2. Determined that wild black raspberry (Rubus occidentalis) is a relatively untapped source of genetic variability for use in breeding new and improved cultivars. Little molecular work has been done to explore genetic diversity and relationships in wild and cultivated black raspberry germplasm. The genetic diversity was determined in 148 wild and cultivated black raspberry accessions using 21 polymorphic SSR markers. Black raspberry cultivars clustered tightly and showed higher than expected heterozygosity while that of wild accessions was low. This germplasm that we have collected and characterized will be excellent parents as we work to develop higher quality black raspberry cultivars.
3. Examined virus diversity of Raspberry leaf mottle virus. Reliable virus detection depends on the identification of highly conserved regions in the viral genome that can be used to develop assays able to detect all known strains of a virus. There are multiple examples of assays that have been unwittingly developed to variable regions of a virus genome, and in these cases as few as 12% of the isolates of the virus were detected with the assay. ARS scientists in Corvallis, Oregon, together with graduate students at Oregon State University, partially sequenced the RNA of more than 40 isolates of RLMV, followed by the identification of highly conserved regions (identical sequence in all isolates, and these regions were subsequently used to prepare detection primers. These primers were able to detect all isolates of the virus tested. Use of this test gives a reliable detection assay for Raspberry leaf mottle virus, which ensures that plants provided to nurseries are free of this virus leading to higher quality planting stocks for the industry and reduced risk of introducing this virus into new areas via nursery plants.
4. Developed strawberry, raspberry and blackberry plants free of known viruses. New berry cultivars need to be tested for and freed of known viruses to improve the quality of planting stocks provided to nurseries and to minimize the risk of moving viruses to new regions of the country with the shipment of nursery stocks. ARS scientists in Corvallis, Oregon, used heat treatment combined with meristem tip-culture to eliminate known viruses from 40 Rubus (blackberry and raspberry) and 11 strawberry cultivars. These plants were tested for all known viruses by graft transmission, serological and nucleic acid based assays and will serve as the basis for plants produced by nurseries for sale to growers. Millions of plants will be produced from each of the plants provided to nurseries.Moore, P.P., Hoashi-Erhardt, W., Finn, C.E., Kempler, C. 2011. ‘Puget Crimson’ Strawberry. HortScience. 46(12):1698-1700.