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.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Frontiers Research Foundation. The published article can be found at: http://www.frontiersin.org/Microbiology.Keywords: Ampelovirus, GLRaV-3, Grapevine leafroll disease, Closteroviridae, Genetic variantsKeywords: Ampelovirus, GLRaV-3, Grapevine leafroll disease, Closteroviridae, Genetic variant

Characterization of potato leafroll virus

Potato leafroll virus (PLRV) was purified from infected potato (Splanum tuberosum L.) by using a mixture of chloroform and butanol for clarification and polyethylene glycol for concentration. The virus sedimented as a single band in a sucrose density gradient. Yield of purified virus varied from 0.4-0.6 mg/kg fresh weight of potato foliage. Virus yield was higher from tissue immediately processed after harvest than from tissue stored at 4 C or -20 C for a day or longer. The A 260/A 280 varied from 1.74-1.82. Antiserum prepared against purified virus had a maximum titre of 1024 in agar gel double diffusion tests. PLRV in unconcentrated potato sap could not be detected by agar gel tests, but could be detected by enzyme-linked immunosorbent assay. A pure line of the mild strain of PLRV was isolated, and an antiserum with a maximum titre of 2560 by agar gel tests was produced. PLRV had a sedimentation coefficient of 127 S by linear log sucrose density gradient centrifugation and 117 S by analytical ultracentrifugai-tion. A buoyant density of 1.38-1.39 g/cm³ was obtained from isopycnic centrifugation in cesium chloride and analytical ultracentrifugation in cesium sulphate. The nucleic acid content of PLRV was estimated from the particle densities to be 26-28%.The PLRV nucleic acid had:, a moi wt of 2.0 x 10⁶; was degraded by RNase but not by DNase; reacted with orcinol but not with diphenylamine; and had a broad range of melting temperatures from 35 to 85 C in 1 x SSC buffer with hyper-chromicity of 20-21%. These properties indicated that PLRV nucleic acid is a single-stranded RNA. The sedimentation coefficient of the RNA molecule before and after treatment with formaldehyde was 34.5 S and 20.7 S, respectively. Dissociated coat protein migrated as a single band in polyacrylamide gel electrophoresis and the average subunit molwt was 26 300. PLRV should be considered a member of the luteovirus group.Land and Food Systems, Faculty ofGraduat

Graft-transmissible agent causes bark necrosis and stem pitting in plum trees

In two Central Valley plum orchards, nearly all the trees started exhibiting copious amounts of dark gumballs on scaffold branches and main trunks. Exposed bark showed extensive tissue necrosis and necrotic stem-pitting on the surface of the woody cylinders. Eventually, both orchards had to be removed and replanted. The symptoms were highly suggestive of a viral or viruslike disease agent. We began studies to characterize the pathogen associated with the failure of these orchards and were successful in associating the disease with a new virus that proved to have an extensive host range in many cultivated Prunus. Characterization of this virus is under way

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

New closterovirus in ‘Redglobe’ grape causes decline of grafted plants

In California, first-generation table grape vineyards were planted on their own roots. But in recent years growers have been replanting onto acreage previously in grapes more often. Grafted plants are being sought to overcome nematodes and other site-related problems. We investigated the etiology of the decline and death of ‘Redglobe’ table grape scions propagated on different rootstocks, using a series of greenhouse and field experiments, and reverse transcriptase-polymerase chain reaction (RT-PCR) assays. We determined that a specific graft-transmissible agent was closely associated with declining young grapevines. The ‘Redglobe’ closterovirus that we identified was given the trivial name Grapevine rootstock stem lesion associated virus (GRSLaV)

California mealybugs can spread grapevine leafroll disease

UC Davis's Foundation Plant Materials Service (FPMS) maintains the disease-tested, professionally identified collection of grape scion and rootstock varieties, which is the core of the California Grapevine Registration and Certification Program. In 1992; newly developed serological testing techniques revealed the presence of grapevine leafroll-associated viruses (GLRaVs) in previously healthy vines in an older foundation propagating block, indicating active and recent virus spread. FPMS responded by increasing isolation distances and implementing a comprehensive virus screening program using the new methodology. The critical problem was the lack of information on leafroll virus epidemiology. When the distribution of infected plants in the old vineyard was mapped, new infections were frequently adjacent to known diseased grapevines. This study examined the ability of mealybugs, a putative leafroll vector, to transmit this group of viruses. We were able to confirm that four species found in California — obscure, longtailed, citrus and grape mealybug — can transmit GLRaV-3 isolates. This is the first experimental evidence of grapevine leafroll virus transmission by obscure and grape mealybug. In addition, we report for the first time that GLRaV-5 can be transmitted by longtailed mealybug

New closterovirus in ‘Redglobe’ grape causes decline of grafted plants

In California, first-generation table grape vineyards were planted on their own roots. But in recent years growers have been replanting onto acreage previously in grapes more often. Grafted plants are being sought to overcome nematodes and other site-related problems. We investigated the etiology of the decline and death of ‘Redglobe’ table grape scions propagated on different rootstocks, using a series of greenhouse and field experiments, and reverse transcriptase-polymerase chain reaction (RT-PCR) assays. We determined that a specific graft-transmissible agent was closely associated with declining young grapevines. The ‘Redglobe’ closterovirus that we identified was given the trivial name Grapevine rootstock stem lesion associated virus (GRSLaV)