Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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WINTER 2012
GRAPEGROWING
Typical leafroll symptoms on
Cabernet Sauvignon
Disease distribution patterns indicate two common patterns of spread: 1) two or more infected vines directly adjacent to each other in the same row, and 2) a focus of infected vines at the edges of a vineyard with a gradient of diminishing incidence towards the middle or other side of the vineyard.
This latter pattern suggests that leafroll disease has been introduced into a vineyard from an established external source on one side of the vineyard. In most cases the number of infected vines in these gradients increases in the opposite direction of an adjacent older, infected vineyard. These vineyards probably serve as the source of the disease where mealybugs acquire the virus and then are spread to neighboring vineyards by some combination of wind, laborers, or machinery.
The introduction of leafroll disease from outside sources is particularly worrisome because it is difficult to control and has the potential to compromise the benefits of clean plant programs. Older infected vineyards are one obvious disease source; it is also possible that there are other yet unidentified outside sources.
Long-tailed mealybug adult and nymph.
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Determining if native Vitis are alternate Grapevine leafroll-associated virus (GLRaV) hosts that might serve as reservoirs important in the continued spread of grapevine leafroll disease was the objective of this research.
Vitis samples surrounding nine Napa Valley vineyards were collected and tested for GLRaV-1, -2, -3, -4, -5, and -9, Grapevine virus A (GVA), Grapevine virus B (GVB), and Grapevine virus D (GVD) using both conventional RT-PCR and realtime RT-PCR. Twenty four Vitis samples from three riparian areas not near vineyards were also included.
DNA fingerprinting indicated that the Vitis samples consisted primarily of V. californica followed by V. californica x V. vinifera hybrids. In the riparian areas not located near vineyards and areas adjacent to three of the nine vineyards, single and mixed infections of GLRaV-2, -3, GVA, and/or GVB were detected in106 of the 230 V. californica and 11 of the 19 V. californica x V. vinifera hybrids
Phylogenetic analysis of GLRaV-2 and -3 indicated the isolates from V. californica and V. californica x V. vinifera hybrids were closely related to V. vinifera isolates.
BY
Deborah Golino, Vicki A. Klaassen,
Susan T. Sim, Gerald S. Dangl,
Fatima A. Osman, Maher Al Rwahnih,
and Adib Rowhani
Foundation Plant Services and Plant Pathology Department, University of California, Davis
G
rapevine leafroll disease is one of the most economically damaging and widespread diseases of Vitis vinifera throughout the world. To date, eleven different phloem-limited viruses, identified as Grapevine leafroll- associated viruses (GLRaVs) 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, and Carnelian have been isolated from diseased grapevines and characterized. All GLRaVs can be graft-transmitted; GLRaV-1, -3, -5, and -9 are also transmitted by several species of mealybugs (Homoptera: Pseudococcidae) and soft scale insects (Hemiptera: Coccidae).
While the incidence of leafroll disease due to graft transmission has been reduced in propagative material through the use of certified clean planting stock, disease incidence associated with insect transmission still occurs in many grape growing regions.