|Oliphant, James - Jim|
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2008
Publication Date: 3/20/2009
Citation: Postman, J.D., Oliphant, J.M., Hummer, K.E. 2009. Diseases Impact Management of USDA Clonal Vaccinium Genebank. Acta Horticulturae. 810:319-324.
Interpretive Summary: The USDA Agricultural Research Service maintains a collection of blueberry species and wild relatives from around the world at the National Clonal Germplasm Repository, a genebank in Corvallis, Oregon. This collection includes more than 600 blueberry, lingonberry and cranberry varieties. The primary collection was previously maintained as a field planting, but because of two plant diseases spreading in western Oregon, the collection is now grown as potted plants in a screenhouse. Conservation of a potted collection required the development of a management strategy that maintains plant vigor to provide high quality cuttings for propagation. Trials were conducted to select a potting medium with good fertility that does contain bark like most nursery potting soils. The potted blueberry plants should be able to grow for 8-10 years in the same soil, but media containing bark do not last that long. A blend of volcanic pumice (50%), peat moss (40%), and mineral loam (10%) was selected. A 3 to 5 cm deep pumice top-dress (collar) is added to the surface of each pot to create a sterile, dry, inorganic surface that prevents weed, moss and fungus gnat growth. This top-dress combined with a stable, bark-free medium creates a growing system that greatly reduces water use, nutrient leaching, salt build-up, and moisture stress. Woody plants are hard pruned in late winter to remove all flower buds, and six to eight upright shoots are selected and allowed to grow. These shoots provide cuttings that are distributed by the genebank for research or propagation requests.
Technical Abstract: The USDA Agricultural Research Service maintains a diverse collection of Vaccinium genotypes at the National Clonal Germplasm Repository (NCGR), a temperate fruit and nut genebank in Corvallis, Oregon. Vaccinium species are hosts for two diseases that occur in the U.S. Pacific Northwest and impact collection management. One is the fungus Phytophthora ramorum and the other is Blueberry shock virus (BlShV). Phytophthora ramorum is a devastating pathogen of certain oak species and has a very broad host range with varying symptoms including foliar blight in some Vaccinium species. Vaccinium germplasm must be inspected and certified to be free of this pathogen to protect the U.S. nursery industry and native flora. The pollen-borne BlShV has made it necessary to move the primary Vaccinium clonal collection from a field planting to a protected potted collection. More than 600 clonal accessions are maintained in greenhouses or screenhouses, protected from pollinators and other virus vectors. These clonal accessions represent more than 60 unique Vaccinium taxa from around the world and include 171 cranberry, 46 lingonberry, 15 lowbush blueberry and 182 highbush or rabbiteye blueberry genotypes. Migration to a protected container collection required the development of a management strategy to maintain plants in a vigorous condition, thus providing high quality vegetative growth suitable for propagation. Tree bark in growing media is a potential source of P. ramorum dissemination. Trials were conducted to select a bark-free medium with good fertility and porosity that would be stable for an expected 8-10 year lifespan of a potted blueberry plant. A blend of volcanic pumice (50%), un-milled, coarse, sphagnum peat moss (40%), and sandy loam (10%) was selected. A 3-5 cm deep pumice top-dress (collar) was added to the surface of each pot to create a sterile, dry, inorganic surface that prevents weed, moss and fungus gnat growth. This top-dress combined with a stable, bark-free potting medium creates a growing system that greatly reduces water use, nutrient leaching, salt build-up, and moisture stress. Woody Vaccinium clones are hard pruned in late winter to remove all flower buds and 6 – 8 upright shoots are selected and allowed to grow. These shoots provide cuttings that are distributed by the genebank for research or propagation.