Issue link: http://read.dmtmag.com/i/123973
roadblocks that make it challenging or even impossible to prove a virus found in grapevines causes a particular disease. First, most grapevine viruses can only infect grapevines. Virus transmission in woody plants, such as grapevines, is much more difficult to accomplish in the lab as compared to in herbaceous plants, which are much easier to manipulate and infect. Second, grapevine viruses are found as mixed infec- AT A GLANCE + Whether long-known or newly discovered, the most important virus is the one affecting your own vineyard. + Certain viruses can have seri- ous effects on vine health and resulting wine quality. + Two different DNA viruses were recently discovered: Grapevine vein clearing and Grapevine red blotch-associated viruses. + Effective disease control requires clean planting stock, plus frequent disease and insect monitoring. tions and it is difficult to isolate one from another. Third, virus transmission in vines occurs only by grafting or mediated by specific insects (mealybugs, soft scale insects) or nematodes known as virus vectors. Consequently, many of the grapevine-infecting viruses are known as "grapevine associated" with different diseases (e.g. leafroll, rugose wood, red blotch, etc.). When mixed virus infections occur, it is difficult to determine which one of the many present might be causing the problem. Regardless, the recurrent association of viruses can be correlated over the years with symptoms in the vineyard. DECLINE-CAUSING VIRUSES The most important group of viruses relative to vineyard disease management is the Nepoviruses. Nepoviruses are spread by nematodes and cause severe vine decline, leaf deformations and uneven fruit set and maturation in the vineyard. The most common decline-causing viruses are Arabis mosaic (ArMV), Grapevine fanleaf (GFLV), tobacco (TRSV) and tomato ringspot (ToRSV). Infected vineyards rapidly decline and die within three or four years after detection. There is a high degree of specificity between the viruses and the species of nematode able to transmit them: ArMV is transmitted by Xiphinema diversicaudatum, GFLV is transmitted by the dagger nematode Xiphinema index, and ToRSV and TRSV are transmitted by Xiphinema americanum. In infected vineyards (even after removal) remaining nematodes are able to transmit the viruses for many years. GRAPEVINE LEAFROLL AND RUGOSE WOOD ASSOCIATED VIRUSES Another important group of grapevine-associated viruses cause leafroll and rugose wood diseases. The virus species that cause leafroll disease are named Grapevine leafroll associated virus (GLRaV) followed by a number (e.g., GLRaV1 to -9) grouped in one family (Closteroviridae) and placed into three taxonomic sub-groups or genera, Ampelovirus, Closterovirus and Velarivirus. The Ampeloviruses – GLRaV-1 and GLRaV-3 being the most common in the vineyard – are transmitted non-specifically by mealybugs and soft-scale insects. GLRaV-2 is a Closterovirus transmitted primarily by grafting. Finally, GLRaV-7 has been proposed to be a member of the Velarivirus because it induces mild leafroll symptoms in grapevines. No insect transmis- ZYMAFLORE FX10®: The elegance of heritage Yeast for Bordeaux-style red wines, tested and approved by many US winemakers! • Silky structure (tannin intensity but low astringency). • Masks the perception of green character. • Terroir expression. • High alcohol tolerance. • Fermentation security. LAFFORT U.S.A. - 1460 Cader Lane, Suite C Petaluma, CA 94954 - laffortusa@laffort.com - (707) 775-4530 – www.laffortusa.com w w w. v w m media.com M a y - J u n e 2 0 13 | V I N E YA R D & W I N E RY M A N A G E M E N T 71