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United States Department of Agriculture

Agricultural Research Service

Research Project: Physiology and Genetic Improvement of Small Fruit Crops

Location: Horticultural Crops Research

2011 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
In 2010, we released a new blackberry cultivar called ‘Onyx’ and a new strawberry cultivar called ‘Sweet Bliss’. ‘Onyx’ blackberry is a late-season cultivar with outstanding fresh fruit quality. ‘Sweet Bliss’ is suitable for fresh market production and has excellent flavor. We are also seeking approval to patent a new cultivar of red raspberry called ‘Vintage’. We identified four sources of genetic resistance to aphids in black raspberry and began to use the information to develop new cultivars resistant to black raspberry necrosis virus. The virus kills thousands of plants each year and is transferred from plant to plant by aphids. To improve strawberry production and quality in the United States, we propagated 700 new strawberry clones and began to evaluate their performance in California, Florida, Michigan, New Hampshire, and Oregon. The clones are also being evaluated in France, United Kingdom, and The Netherlands. To develop new cultivars of raspberry with high resistance to root rot, we examined existing cultivars for traits that reduce infection by Phytophthora, a fungal-like organism associated with the disease. We discovered that resistant cultivars produced a waxy layer of chemicals in their outer layer of root cells. The layer reduces penetration by the pathogen. Next, plants will be selected with this trait to develop the new cultivars with high root rot resistance. We initiated a study to determine threshold for freeze tolerance in cranberry. Sprinkler irrigation is used for frost protection of cranberry, but growers struggle with the question of when to turn their system on during frost events. We designed a chamber to control temperature in the field and are evaluating plant response to frost over the growing the season. Results of the study will be used to develop a sprinkler irrigation guide for frost protection in cranberry. No such guide currently exists. We developed a new technique to reduce soil pH for better production of blueberry. Blueberries require low pH soil for good growth and production. Growers often mix tons of sulfur fertilizer in a field to reduce pH prior to planting blueberry. The new method reduces soil pH quickly (weeks vs. months) using only a fraction of the sulfur required by traditional application of granular sulfur. The practice will help farmers to grow blueberries in nontraditional production regions such as California with high pH soils. We are also testing the potential benefits of the practice in other crops.

4. Accomplishments
1. Release of 'Onyx' trailing blackberry. Trailing blackberries have historically been highly regarded for their fruit quality, especially flavor, as a processed product but the fruit were typically too soft to be shipped in the fresh market and were available in a very limited season. Through a traditional breeding program, ORUS 1523-4 was identified as superior genotype in a population of seedlings from a controlled cross, through further testing it was determined that this selection should be released as the cultivar ‘Onyx’. ‘Onyx' produces good yields of very high quality fruit in the late season. The cultivar is gaining acceptance among distributors and is well suited to the wholesale fresh market. ‘Onyx’ is being enthusiastically planted by commercial growers interested in fresh market blackberries for shipping in the late trailing blackberry season and will fill a critical need in this season.

2. A mechanism of resistance to root rot in raspberry. Root rot is caused by a fungal-like pathogen that often kills the infected raspberry plant, and hundreds of acres of raspberry are affected each year. Fields are often treated with fungicides to slow but not eliminate root rot development. We discovered that raspberry resistance to root rot is associated with a waxy layer of chemicals produced in the root cells. The information will be used to develop new raspberry cultivars resistant to root rot.

3. Major discoveries in black raspberry chemistry and insect resistance. Populations of black raspberry were assembled with the help of colleagues throughout the Eastern United States, a collection trip funded by the USDA-ARS Plant Exchange office, and accessions from the USDA-ARS National Clonal Germplasm Repository. These populations were screened for aphid resistance, the vector of the debilitating black raspberry necrosis virus. Four sources of resistance were identified which, when incorporated into advanced breeding lines, will have a major impact on the long-term economic viability of the crop. We also identified an anthocyanin mutant associated with black raspberry color that will help us understand anthocyanin biosynthetic pathways in raspberries.

4. A new technique to reduce soil pH for growing blueberries. Blueberry plants require low soil pH for good growth and production. To reduce soil pH, many growers mix tons of sulfur fertilizer in the field prior to planting. In cooperation with a researcher from the University of Evora in Portugal, a new method was developed to reduce soil pH. The method reduces soil pH quickly (weeks vs. months) using only a fraction of the fertilizer required by conventional sulfur application. The practice will help farmers expand production to regions of the country, such as western Oregon and California, where soil pH is considered too high for blueberry.

5. Release of 'Sweet Bliss' strawberry. New strawberry cultivars that have better fruit quality than current standards, especially for fresh market production, are needed in order for growers to be able to profitably produce strawberries. Through a traditional breeding program, ORUS 2180-1 was selected from a population of seedlings generated from a controlled cross. Through further testing in cooperation with Washington State University and Agriculture and Agri-Foods Canada, it was determined that this selection should be released as a cultivar. ‘Sweet Bliss' is intended primarily for commercial, fresh market producers as it has outstanding flavor, good handling properties and excellent yields. Thousands of plants have been planted of ‘Sweet Bliss’ Pacific Northwest. ‘Sweet Bliss' is expected to become a major cultivar in the region and help growers increase their competitiveness.

Review Publications
Bryla, D.R., Trout, T.J., Ayars, J.E. 2010. Weighing lysimeters for developing crop coefficients and efficient irrigation practices for vegetable crops. HortScience. 45(11):1597-1604.

Bryla, D.R., Gartung, J.L., Strik, B. 2011. Evaluation of irrigation methods for highbush blueberry. I. Growth and water requirements of young plants. HortScience. 46(1):95-101.

Hancock, J.F., Finn, C.E., Dale, A., Luby, J.J., Callow, P.W., Serce, S. 2010. Reconstruction of the strawberry, Fragaria × ananassa, using native genotypes of F. virginiana and F. chiloensis. HortScience. 45:1006-1013.

Dossett, M., Finn, C.E. 2010. Identification of resistance to the large raspberry aphid in black raspberry. Journal of the American Society for Horticultural Science. 135(5):438-444.

Finn, C.E., Strik, B.C., Yorgey, B.M., Martin, R.R. 2011. 'Onyx' trailing blackberry. HortScience. 46:657-659.

Last Modified: 06/22/2017
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