Grapevine leafroll-associated virus 3.

Grapevine leafroll disease (GLD) is one of the most important grapevine viral diseases affecting grapevines worldwide. The impact on vine health, crop yield, and quality is difficult to assess due to a high number of variables, but significant economic losses are consistently reported over the lifespan of a vineyard if intervention strategies are not implemented. Several viruses from the family Closteroviridae are associated with GLD. However, Grapevine leafroll-associated virus 3 (GLRaV-3), the type species for the genus Ampelovirus, is regarded as the most important causative agent. Here we provide a general overview on various aspects of GLRaV-3, with an emphasis on the latest advances in the characterization of the genome. The full genome of several isolates have recently been sequenced and annotated, revealing the existence of several genetic variants. The classification of these variants, based on their genome sequence, will be discussed and a guideline is presented to facilitate future comparative studies. The characterization of sgRNAs produced during the infection cycle of GLRaV-3 has given some insight into the replication strategy and the putative functionality of the ORFs. The latest nucleotide sequence based molecular diagnostic techniques were shown to be more sensitive than conventional serological assays and although ELISA is not as sensitive it remains valuable for high-throughput screening and complementary to molecular diagnostics. The application of next-generation sequencing is proving to be a valuable tool to study the complexity of viral infection as well as plant pathogen interaction. Next-generation sequencing data can provide information regarding disease complexes, variants of viral species, and abundance of particular viruses. This information can be used to develop more accurate diagnostic assays. Reliable virus screening in support of robust grapevine certification programs remains the cornerstone of GLD management

Grapevine Leafroll: A Complex Viral Disease Affecting a High-Value Fruit Crop

Grapevine (Vitis spp.) is one of the most widely grown fruit crops in the world. It is a deciduous woody perennial vine for which the cultivation of domesticated species began approximately 6,000 to 8,000 years ago in the Near East. Grapevines are broadly classified into red- and white-berried cultivars based on their fruit skin color, although yellow, pink, crimson, dark blue, and black-berried cultivars also exist. Grapevines can be subject to attacks by many different pests and pathogens, including graft-transmissible agents such as viruses, viroids, and phytoplasmas. Among the virus and virus-like diseases, grapevine leafroll disease (GLD) is by far the most widespread and economically damaging viral disease of grapevines in many regions around the world. The global expansion of the grape and wine industry has seen a parallel increase in the incidence and economic impact of GLD. Despite the fact that GLD was recognized as a potential threat to grape production for several decades, our knowledge of the nature of the disease is still quite limited due to a variety of challenges related to the complexity of this virus disease, the association of several distinct GLD-associated viruses, and contrasting symptoms in red- and white-berried cultivars. In view of the growing significance of GLD to wine grape production worldwide, this feature article provides an overview of the state of knowledge on the biology and epidemiology of the disease and describes management strategies currently deployed in vineyards

Leafroll disease is spreading rapidly in a Napa Valley vineyard

In the 1930s and 1940s, little was known about viruses, and information on plant diseases caused by viruses was just beginning to appear in the scientific literature. Problems with grapevines in California, first referred to as “red leaf,” were initially attributed to inexperience in viticultural techniques and poor growing conditions. However, the problem was later identified as leafroll disease, which causes red leaves, and poor yields and fruit quality. We evaluated its rate of spread for 5 years in a Napa Valley vineyard, and found an average rate of more than 10% per year. Leafroll disease can be vectored by low-level populations of grape mealybugs, and is now spreading rapidly in at least one Napa Valley vineyard for unknown reasons. Using stock for planting vines that is certified as virus-free is a key strategy in preventing the spread of grapevine leafroll disease

The Benefits from Certified Virus-Free Nursery Stock: A Case Study of Grapevine Leafroll-3 in the North Coast Region of California

Viruses and related pathogens have no cure and impose large costs on plant production. These diseases are typically spread through infected planting stock and plant propagation material. However, virus spread can be minimized if clean stock is used. We examine the costs and benefits of a virus testing and certification program for Grapevine Leafroll-3 in the North Coast region of California. We compare grower costs and benefits from using certified stock, and we extrapolate to the industry as a whole to estimate costs and benefits to consumers and producers of winegrapes, for the North Coast region. We find that the benefits from certification are large—in excess of $50 million per year for the region—and that they substantially outweigh the costs. We also find large potential benefits from roguing and replacing diseased vines rather than leaving them in the vineyard where they can spread disease. Additionally, we find large costs associated with disease entering from neighboring properties—nearly$300 per acre annually, using our baseline parameterization

Plant health: How diagnostic networks and interagency partnerships protect plant systems from pests and pathogens

Early detection and rapid response are crucial in any effort to reduce the risk of new and emerging biological threats to crops and other plant resources. This underscores the importance of having the necessary diagnostic expertise, infrastructure and resources in place. Three programs — the National Plant Diagnostic Network, the National Clean Plant Network and the Citrus Clonal Protection Program — illustrate how accurate and rapid diagnosis plays a critical role in providing healthy plants for growers and in securing production systems for food and fiber. These three programs depend on statewide, regional and national networking among university, state and federal scientists, regulatory officials and industry members to help mitigate the impacts of plant pests and diseases

Virus surveys of commercial vineyards show value of planting certified vines

Viruses are of great concern in vineyards. They cost the California wine grape industry as much as $91,661 per acre over the life of a vineyard, according to a 2015 economic study of the North Coast wine-growing region. As a first step toward managing viruses, growers are encouraged to plant certified material regulated by the California Grapevine Registration and Certification program. There are risks in sourcing plant material from stocks that are not subject to the same level of regulation. We surveyed vineyards of varying ages for eight common viruses to demonstrate the value of selecting certified material for new plantings