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Zindović J, Čizmović M, Vučurović A, Margaria P, Škorić D. Increased Diversity of Citrus Tristeza Virus in Europe. PLANT DISEASE 2024; 108:1344-1352. [PMID: 37990525 DOI: 10.1094/pdis-09-23-1718-re] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2023]
Abstract
This study investigated the genetic diversity of Citrus tristeza virus (CTV) isolates from Montenegro and Croatia, European countries with the northernmost citrus-growing regions situated on the Eastern Adriatic coast. Fifteen complete or nearly complete CTV genomes were reconstructed by high-throughput sequencing of samples collected in distinct municipalities in Montenegro and Opuzen municipality in Croatia. Phylogenetic analyses assigned some of the sequences to VT and T30 strains, previously recorded in Europe, while remarkably other isolates were placed in S1 and RB groups, which have not been reported in Europe so far. In addition, a new phylogenetic lineage comprising only isolates from Montenegro was delineated and tentatively proposed as the MNE cluster. Recombination analysis revealed evidence of 11 recombination events in the sequences obtained in this study, between isolates of related strains, within isolates of the same strain, and between distant strains. These findings show that CTV diversity in Europe is higher than reported before and calls for the reevaluation of management strategies.[Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
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Affiliation(s)
- Jelena Zindović
- Department for Plant Protection, Biotechnical Faculty, University of Montenegro, 81000 Podgorica, Montenegro
| | - Miroslav Čizmović
- Department for Plant Protection, Biotechnical Faculty, University of Montenegro, 81000 Podgorica, Montenegro
| | - Ana Vučurović
- Department of Biotechnology and Systems Biology, National Institute of Biology, 1000 Ljubljana, Slovenia
| | - Paolo Margaria
- Plant Virus Department, Leibniz-Institute DSMZ, 38124 Braunschweig, Germany
| | - Dijana Škorić
- Department of Biology, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
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2
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Biswas KK, Keremane ML, Marais LJ, Ramadugu C, Lee RF. Population dynamics of Citrus tristeza virus (CTV) in single aphid-transmitted sub-isolates of the South African GFMS12 isolate. FRONTIERS IN PLANT SCIENCE 2022; 13:1024556. [PMID: 36388600 PMCID: PMC9650399 DOI: 10.3389/fpls.2022.1024556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Accepted: 10/05/2022] [Indexed: 06/16/2023]
Abstract
Grapefruit trees in South Africa have been cross protected against severe stem pitting genotypes of Citrus tristeza virus (CTV) since the 1920s using a mild strain initially called 'Nartia' but later referred to as grapefruit mild strain 12 (GFMS12). In the current study, the GFMS12 isolate was used as the source for single aphid transmissions (SAT) using Toxoptera citricida, commonly called the brown citrus aphid (BrCA). The BrCA-transmitted CTV sub-isolates were analyzed by the heteroduplex mobility assay (HMA), serological assays, genetic marker analysis (GMA), and selected sub-isolates were biologically indexed. Reverse transcription PCR of genomic regions was conducted using universal primers followed by cloning the PCR products, HMA and sequence analysis; nine genotypes of CTV were identified in the complex of GFMS12, including both severe and mild genotypes. A single BrCA transmitted up to six CTV genotypes simultaneously in one sub-isolate. The HMA was found to be a rapid, reliable tool for the identification of genotypes and can be useful in the development of CTV management strategies and budwood certification programs.
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Affiliation(s)
- K. K. Biswas
- Citrus Research and Education Center (CREC), University of Florida, Lake Alfred, FL, United States
- Plant Protection, Indian Council of Agricultural Research (ICAR)-Indian Agricultural Research Institute, New Delhi, India
| | - M. L. Keremane
- Citrus Research and Education Center (CREC), University of Florida, Lake Alfred, FL, United States
- Agricultural Research Service, United States Department of Agriculture (USDA), Riverside, CA, United States
| | - L. J. Marais
- Citrus Research and Education Center (CREC), University of Florida, Lake Alfred, FL, United States
| | - C. Ramadugu
- Botany & Plant Sciences, University of California, Riverside, Riverside, CA, United States
| | - R. F. Lee
- Citrus Research and Education Center (CREC), University of Florida, Lake Alfred, FL, United States
- Agricultural Research Service, United States Department of Agriculture (USDA), Riverside, CA, United States
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3
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Kubina J, Hily JM, Mustin P, Komar V, Garcia S, Martin IR, Poulicard N, Velt A, Bonnet V, Mercier L, Lemaire O, Vigne E. Characterization of Grapevine Fanleaf Virus Isolates in ‘Chardonnay’ Vines Exhibiting Severe and Mild Symptoms in Two Vineyards. Viruses 2022; 14:v14102303. [PMID: 36298857 PMCID: PMC9609649 DOI: 10.3390/v14102303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 10/14/2022] [Accepted: 10/18/2022] [Indexed: 12/03/2022] Open
Abstract
Fanleaf degeneration is a complex viral disease of Vitis spp. that detrimentally impacts fruit yield and reduces the productive lifespan of most vineyards worldwide. In France, its main causal agent is grapevine fanleaf virus (GFLV). In the past, field experiments were conducted to explore cross-protection as a management strategy of fanleaf degeneration, but results were unsatisfactory because the mild virus strain negatively impacted fruit yield. In order to select new mild GFLV isolates, we examined two old ‘Chardonnay’ parcels harbouring vines with distinct phenotypes. Symptoms and agronomic performances were monitored over the four-year study on 21 individual vines that were classified into three categories: asymptomatic GFLV-free vines, GFLV-infected vines severely diseased and GFLV-infected vines displaying mild symptoms. The complete coding genomic sequences of GFLV isolates in infected vines was determined by high-throughput sequencing. Most grapevines were infected with multiple genetically divergent variants. While no specific molecular features were apparent for GFLV isolates from vines displaying mild symptoms, a genetic differentiation of GFLV populations depending on the vineyard parcel was observed. The mild symptomatic grapevines identified during this study were established in a greenhouse to recover GFLV variants of potential interest for cross-protection studies.
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Affiliation(s)
- Julie Kubina
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
| | - Jean-Michel Hily
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
- IFV, 30240 Le Grau-Du-Roi, France
| | - Pierre Mustin
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
| | - Véronique Komar
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
| | - Shahinez Garcia
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
| | | | - Nils Poulicard
- PHIM, Université Montpellier, IRD, INRAE, Cirad, SupAgro, 34000 Montpellier, France
| | - Amandine Velt
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
| | - Véronique Bonnet
- Maison Moët & Chandon, 20 Avenue de Champagne, 51200 Épernay, France
| | - Laurence Mercier
- Maison Moët & Chandon, 20 Avenue de Champagne, 51200 Épernay, France
| | - Olivier Lemaire
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
| | - Emmanuelle Vigne
- INRAE, SVQV UMR-A 1131, Université de Strasbourg, 68000 Colmar, France
- Correspondence:
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Walking Together: Cross-Protection, Genome Conservation, and the Replication Machinery of Citrus tristeza virus. Viruses 2020; 12:v12121353. [PMID: 33256049 PMCID: PMC7760907 DOI: 10.3390/v12121353] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 11/25/2020] [Indexed: 01/23/2023] Open
Abstract
"Cross-protection", a nearly 100 years-old virological term, is suggested to be changed to "close protection". Evidence for the need of such change has accumulated over the past six decades from the laboratory experiments and field tests conducted by plant pathologists and plant virologists working with different plant viruses, and, in particular, from research on Citrus tristeza virus (CTV). A direct confirmation of such close protection came with the finding that "pre-immunization" of citrus plants with the variants of the T36 strain of CTV but not with variants of other virus strains was providing protection against a fluorescent protein-tagged T36-based recombinant virus variant. Under natural conditions close protection is functional and is closely associated both with the conservation of the CTV genome sequence and prevention of superinfection by closely similar isolates. It is suggested that the mechanism is primarily directed to prevent the danger of virus population collapse that could be expected to result through quasispecies divergence of large RNA genomes of the CTV variants continuously replicating within long-living and highly voluminous fruit trees. This review article provides an overview of the CTV cross-protection research, along with a discussion of the phenomenon in the context of the CTV biology and genetics.
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Selvaraj V, Maheshwari Y, Hajeri S, Yokomi R. A rapid detection tool for VT isolates of Citrus tristeza virus by immunocapture-reverse transcriptase loop-mediated isothermal amplification assay. PLoS One 2019; 14:e0222170. [PMID: 31487325 PMCID: PMC6728045 DOI: 10.1371/journal.pone.0222170] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2019] [Accepted: 08/21/2019] [Indexed: 11/18/2022] Open
Abstract
Severe strains of Citrus tristeza virus (CTV) cause quick decline and stem pitting resulting in significant economic losses in citrus production. A immunocapture reverse-transcriptase loop-mediated amplification (IC-RT-LAMP) assay was developed in this study to detect the severe VT strains that are typically associated with severe CTV symptoms. The sensitivity of RT-LAMP assay was determined by ten-fold serial dilutions of CA-VT-AT39 RNA, in comparison to one-step RT-droplet digital (dd) PCR. RT-LAMP detected up to 0.002 ng RNA with an amplification time of 10:35 (min:sec.), equivalent to 11.3 copies as determined by one step RT-ddPCR. The RT-LAMP assay specifically detected CA-VT-AT39 RNA and did not cross react with other CTV genotypes tested (T36, T30, RB, S1 and T68). To facilitate rapid on-site detection, the RT-LAMP assay was improved by first capturing the CTV virions from citrus crude leaf sap using CTV-IgG (IC-RT-LAMP), thereby eliminating nucleic acid extraction steps. IC-RT-LAMP assay was optimized with two-fold dilutions of CTV-IgG ranging from 1:500 to 1:16,000. The IC-RT-LAMP assay detected the CA-VT-AT39 virions in all dilutions tested. The minimum amplification time was 6:45 (min:sec) with 1:500 and 1:1000 of CTV-IgG dilutions. The limit of detection of IC-RT-LAMP assay with crude leaf sap of CA-VT-AT39 was 1:320 with a maximum amplification time of 9:08 (min:sec). The IC-RT-LAMP assay was validated for VT genotype by comparing to IC-RT-qPCR using the CTV from 40 field tree samples. A 100% agreement was observed between tests, regardless of single or mixed infections of CTV VT with other genotypes. Therefore, the IC-RT-LAMP assay can serve as a useful tool in the management of potentially severe strains of CTV.
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Affiliation(s)
- Vijayanandraj Selvaraj
- USDA-ARS, San Joaquin Valley Agricultural Sciences Center, Parlier, CA, United States of America
| | - Yogita Maheshwari
- USDA-ARS, San Joaquin Valley Agricultural Sciences Center, Parlier, CA, United States of America
| | - Subhas Hajeri
- Citrus Pest Detection Program, Central California Tristeza Eradication Agency, Tulare, CA, United States of America
| | - Raymond Yokomi
- USDA-ARS, San Joaquin Valley Agricultural Sciences Center, Parlier, CA, United States of America
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Pechinger K, Chooi KM, MacDiarmid RM, Harper SJ, Ziebell H. A New Era for Mild Strain Cross-Protection. Viruses 2019; 11:E670. [PMID: 31340444 PMCID: PMC6669575 DOI: 10.3390/v11070670] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 07/12/2019] [Accepted: 07/14/2019] [Indexed: 11/18/2022] Open
Abstract
Societal and environmental pressures demand high-quality and resilient cropping plants and plant-based foods grown with the use of low or no synthetic chemical inputs. Mild strain cross-protection (MSCP), the pre-immunization of a plant using a mild strain of a virus to protect against subsequent infection by a severe strain of the virus, fits with future-proofing of production systems. New examples of MSCP use have occurred recently. New technologies are converging to support the discovery and mechanism(s) of action of MSCP strains thereby accelerating the popularity of their use.
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Affiliation(s)
- Katrin Pechinger
- The New Zealand Institute for Plant and Food Research Limited, Auckland 1142, New Zealand
| | - Kar Mun Chooi
- The New Zealand Institute for Plant and Food Research Limited, Auckland 1142, New Zealand
| | - Robin M MacDiarmid
- The New Zealand Institute for Plant and Food Research Limited, Auckland 1142, New Zealand
- School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand
| | - Scott J Harper
- Department of Plant Pathology, Washington, State University, Prosser, WA 99350, USA
| | - Heiko Ziebell
- Julius Kühn Institute, Institute for Epidemiology and Pathogen Diagnostics, Messeweg 11-12, 38104 Braunschweig, Germany.
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7
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Read DA, Pietersen G. Analysis of Genotype Composition of Citrus tristeza virus Populations Using Illumina Miseq Technology. Methods Mol Biol 2019; 2015:179-194. [PMID: 31222704 DOI: 10.1007/978-1-4939-9558-5_13] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Recent research describing the strain-specific mechanisms underlying experimental CTV superinfection exclusion has far-reaching implications for the manner in which cross-protecting sources should be selected for. The strain composition of both cross-protecting sources and field populations needs to be sufficiently characterized to improve control of severe stem-pitting and decline isolates. Many of the biological, serological, and molecular techniques used in previous studies yield very limited information about the strain composition of populations and the relative titer of their components. In this chapter we describe a protocol for the characterization of CTV populations, based on the use of the next-generation sequencing Illumina MiSeq platform of p33 gene amplicons.
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Affiliation(s)
- David A Read
- Biotechnology Platform, Agricultural Research Council, Onderstepoort, South Africa
| | - Gerhard Pietersen
- Department of Genetics, Stellenbosch University, Stellenbosch, South Africa.
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8
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Yokomi R, Selvaraj V, Maheshwari Y, Chiumenti M, Saponari M, Giampetruzzi A, Weng Z, Xiong Z, Hajeri S. Molecular and biological characterization of a novel mild strain of citrus tristeza virus in California. Arch Virol 2018; 163:1795-1804. [PMID: 29550931 DOI: 10.1007/s00705-018-3799-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Accepted: 02/28/2018] [Indexed: 10/17/2022]
Abstract
Strain differentiating marker profiles of citrus tristeza virus (CTV) isolates from California have shown the presence of multiple genotypes. To better define the genetic diversity involved, full-length genome sequences from four California CTV isolates were determined by small-interfering RNA sequencing. Phylogenetic analysis and nucleotide sequence comparisons differentiated these isolates into the genotypes VT (CA-VT-AT39), T30 (CA-T30-AT4), and a new strain called S1 (CA-S1-L and CA-S1-L65). S1 isolates had three common recombination events within portions of genes from VT, T36 and RB strains and were transmissible by Aphis gossypii. Virus indexing showed that CA-VT-AT39 could be classified as a severe strain, whereas CA-T30-AT4, CA-S1-L and CA-S1-L65 were mild. CA-VT-AT39, CA-S1-L, and CA-S1-L65 reacted with monoclonal antibody MCA13, whereas CA-T30-AT4 did not. RT-PCR and RT-qPCR detection assays for the S1 strain were developed and used to screen MCA13-reactive isolates in a CTV collection from central California collected from 1968 to 2011. Forty-two isolates were found to contain the S1 strain, alone or in combinations with other genotypes. BLAST and phylogenetic analysis of the S1 p25 gene region with other extant CTV sequences from the NCBI database suggested that putative S1-like isolates might occur elsewhere (e.g., China, South Korea, Turkey, Bosnia and Croatia). This information is important for CTV evolution, detection of specific strains, and cross-protection.
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Affiliation(s)
- Raymond Yokomi
- United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA, 93648-9757, USA.
| | - Vijayanandraj Selvaraj
- United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA, 93648-9757, USA
| | - Yogita Maheshwari
- United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA, 93648-9757, USA
| | - Michela Chiumenti
- Institute for Sustainable Plant Protection, Italian National Research Council, Sezione di Bari, Via Amendola 122/D, 70126, Bari, Italy
| | - Maria Saponari
- Institute for Sustainable Plant Protection, Italian National Research Council, Sezione di Bari, Via Amendola 122/D, 70126, Bari, Italy
| | - Annalisa Giampetruzzi
- Department of Soil Plant and Food Science, University of Bari Aldo Moro, Via Amendola 165/A, 70126, Bari, Italy
| | - Ziming Weng
- School of Plant Sciences and BIO5 Institute, University of Arizona, Tucson, AZ, 85721-7186, USA
| | - Zhongguo Xiong
- School of Plant Sciences and BIO5 Institute, University of Arizona, Tucson, AZ, 85721-7186, USA
| | - Subhas Hajeri
- Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA, 93274-9367, USA
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Harper SJ, Cowell SJ, Dawson WO. Isolate fitness and tissue-tropism determine superinfection success. Virology 2017; 511:222-228. [PMID: 28888112 DOI: 10.1016/j.virol.2017.08.033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 08/24/2017] [Accepted: 08/26/2017] [Indexed: 01/07/2023]
Abstract
The mechanism of cross-protection, the deliberate infection of plants with a "mild" virus isolate to protect against "severe" isolates, has long been a topic of debate. In our model system, Citrus tristeza virus (CTV), this appears to be genotype-specific superinfection-exclusion, suggesting a simple recipe for cross-protection. However, this concept failed in field trials, which led us to examine the process of superinfection-exclusion more closely. We found that exclusion relies on the relative fitness of the primary versus the challenge isolates, and the host infected, and that significant differences in superinfection success could occur between isolates that differ by as few as 3 nucleotides. Furthermore, we found that exclusion was not uniform throughout the plant, but was tissue-specific. These data suggest that cross-protection is not a simple like-for-like process but a complex interaction between the primary and challenge isolates and the host.
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Affiliation(s)
- S J Harper
- Department of Plant Pathology, Washington State University, Prosser, WA 99350, USA.
| | - S J Cowell
- Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
| | - W O Dawson
- Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
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Yokomi RK, Selvaraj V, Maheshwari Y, Saponari M, Giampetruzzi A, Chiumenti M, Hajeri S. Identification and Characterization of Citrus tristeza virus Isolates Breaking Resistance in Trifoliate Orange in California. PHYTOPATHOLOGY 2017; 107:901-908. [PMID: 28453412 DOI: 10.1094/phyto-01-17-0007-r] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Most Citrus tristeza virus (CTV) isolates in California are biologically mild and symptomless in commercial cultivars on CTV tolerant rootstocks. However, to better define California CTV isolates showing divergent serological and genetic profiles, selected isolates were subjected to deep sequencing of small RNAs. Full-length sequences were assembled, annotated and trifoliate orange resistance-breaking (RB) isolates of CTV were identified. Phylogenetic relationships based on their full genomes placed three isolates in the RB clade: CA-RB-115, CA-RB-AT25, and CA-RB-AT35. The latter two isolates were obtained by aphid transmission from Murcott and Dekopon trees, respectively, containing CTV mixtures. The California RB isolates were further distinguished into two subclades. Group I included CA-RB-115 and CA-RB-AT25 with 99% nucleotide sequence identity with RB type strain NZRB-G90; and group II included CA-RB-AT35 with 99 and 96% sequence identity with Taiwan Pumelo/SP/T1 and HA18-9, respectively. The RB phenotype was confirmed by detecting CTV replication in graft-inoculated Poncirus trifoliata and transmission from P. trifoliata to sweet orange. The California RB isolates induced mild symptoms compared with severe isolates in greenhouse indexing tests. Further examination of 570 CTV accessions, acquired from approximately 1960 and maintained in planta at the Central California Tristeza Eradication Agency, revealed 16 RB positive isolates based on partial p65 sequences. Six isolates collected from 1992 to 2011 from Tulare and Kern counties were CA-RB-115-like; and 10 isolates collected from 1968 to 2010 from Riverside, Fresno, and Kern counties were CA-RB-AT35-like. The presence of the RB genotype is relevant because P. trifoliata and its hybrids are the most popular rootstocks in California.
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Affiliation(s)
- Raymond K Yokomi
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
| | - Vijayanandraj Selvaraj
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
| | - Yogita Maheshwari
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
| | - Maria Saponari
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
| | - Annalisa Giampetruzzi
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
| | - Michela Chiumenti
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
| | - Subhas Hajeri
- First, second, and third authors: U.S. Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757; fourth and sixth authors: Institute for Sustainable Plant Protection, National Research Council, Sezione di Bari, Via Amendola 165/A, 70126 Bari, Italy; fifth author: Department of Soil Plant and Food Science, University of Bari, Via Amendola 165/A, 70126 Bari, Italy; and seventh author: Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367
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11
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Understanding superinfection exclusion by complex populations of Citrus tristeza virus. Virology 2016; 499:331-339. [DOI: 10.1016/j.virol.2016.10.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 09/28/2016] [Accepted: 10/01/2016] [Indexed: 12/20/2022]
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12
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Xiao C, Yao RX, Li F, Dai SM, Licciardello G, Catara A, Gentile A, Deng ZN. Population structure and diversity of citrus tristeza virus (CTV) isolates in Hunan province, China. Arch Virol 2016; 162:409-423. [PMID: 27771790 DOI: 10.1007/s00705-016-3089-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 09/22/2016] [Indexed: 12/01/2022]
Abstract
Stem-pitting (SP) is the main type of citrus tristeza virus (CTV) that causes severe damage to citrus trees, especially those of sweet orange, in Hunan province, China. Understanding the local CTV population structure should provide clues for effective mild strain cross-protection (MSCP) of the SP strain of CTV. In this study, markers for the p23 gene, multiple molecular markers (MMMs), and sequence analysis of the three silencing suppressor genes (p20, p23 and p25) were employed to analyze the genetic diversity and genotype composition of the CTV population based on 51 CTV-positive samples collected from 14 citrus orchards scattered around six major citrus-growing areas of Hunan. The results indicated that the CTV population structure was extremely complex and that infection was highly mixed. In total, p23 gene markers resulted in six profiles, and MMMs demonstrated 25 profiles. The severe VT and T3 types appeared to be predominantly associated with SP, while the mild T30 and RB types were related to asymptomatic samples. Based on phylogenetic analysis of the amino acid sequences of p20, p23 and p25, 19 representative CTV samples were classified into seven recently established CTV groups and a potentially novel one. A high level of genetic diversity, as well as potential recombination, was revealed among different CTV isolates. Five pure SP severe and two pure mild strains were identified by genotype composition analysis. Taken together, the results update the genetic diversity of CTV in Hunan with the detection of one possible novel strain, and this information might be applicable for the selection of appropriate mild CTV strains for controlling citrus SP disease through cross-protection.
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Affiliation(s)
- Cui Xiao
- Horticulture and Landscape College, Hunan Agricultural University, Changsha, 410128, China
| | - Run-Xian Yao
- Horticulture and Landscape College, Hunan Agricultural University, Changsha, 410128, China
| | - Fang Li
- Horticulture and Landscape College, Hunan Agricultural University, Changsha, 410128, China
| | - Su-Ming Dai
- Horticulture and Landscape College, Hunan Agricultural University, Changsha, 410128, China.,Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization, Hunan Agricultural University, Changsha, 410128, China
| | - Grazia Licciardello
- Parco Scientifico e Tecnologico della Sicilia, z.i., Stradale Lancia 57, 95121, Catania, Italy
| | - Antonino Catara
- Parco Scientifico e Tecnologico della Sicilia, z.i., Stradale Lancia 57, 95121, Catania, Italy
| | - Alessandra Gentile
- Dipartimento di Agricoltura, Alimentazione e Ambiente, Università degli Studi di Catania, Piazza Università 2, 95131, Catania, Italy.
| | - Zi-Niu Deng
- Horticulture and Landscape College, Hunan Agricultural University, Changsha, 410128, China. .,Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization, Hunan Agricultural University, Changsha, 410128, China.
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13
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Some like it hot: citrus tristeza virus strains react differently to elevated temperature. Arch Virol 2016; 161:3567-3570. [DOI: 10.1007/s00705-016-3083-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 09/19/2016] [Indexed: 12/21/2022]
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14
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Read DA, Pietersen G. PCR bias associated with conserved primer binding sites, used to determine genotype diversity within Citrus tristeza virus populations. J Virol Methods 2016; 237:107-113. [PMID: 27599411 DOI: 10.1016/j.jviromet.2016.09.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Revised: 09/02/2016] [Accepted: 09/02/2016] [Indexed: 01/07/2023]
Abstract
Citrus tristeza virus (CTV) is present in almost all of the major citrus production areas where it continues to reduce the profitability of citriculture. The accurate characterisation of CTV populations, which are usually made up of a number of disparate strains, requires the use of robust PCR protocols. Mismatches between primers and their corresponding binding sites may introduce primer-associated bias during amplification. The primer-associated bias of four sets of CTV specific primers, targeting the A and F regions and the p33 and p23 genes, were evaluated. This was done through the amplification of defined templates followed by their characterisation using the sequencing of multiple clones, as well as Illumina next generation sequencing. High levels of bias were found to be associated with the primer pairs targeting the A and F regions. The p33 gene primers were found to be biased against two genotypes and suggestions for preventing this apparent bias are discussed. The primer pair targeting the conserved p23 gene was found to have very little associated bias. Primers should undergo rigorous screening before being used to characterize virus populations that are known to exhibit high levels of variation, especially within primer binding sites.
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Affiliation(s)
- David Alan Read
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0002, South Africa.
| | - Gerhard Pietersen
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0002, South Africa; Agricultural Research Council-Plant Protection Research Institute, Pretoria 0002, South Africa.
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15
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Bergua M, Phelan DM, Bak A, Bloom DC, Folimonova SY. Simultaneous visualization of two Citrus tristeza virus genotypes provides new insights into the structure of multi-component virus populations in a host. Virology 2016; 491:10-9. [PMID: 26874013 DOI: 10.1016/j.virol.2016.01.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 01/21/2016] [Accepted: 01/22/2016] [Indexed: 11/20/2022]
Abstract
Complex Citrus tristeza virus (CTV) populations composed of mixtures of different strains of the virus are commonly found in citrus trees in the field. At present, little is known about how these populations are formed, maintained, and how they are structured within a host. Here we used a novel in situ hybridization approach allowing simultaneous visualization of two different RNA targets with high sensitivity and specificity to examine the distribution of two isolates, T36 and T68-1, representing phylogenetically distinct strains of CTV, in a citrus host in single and mixed infections. Remarkably, in doubly inoculated plants the two virus variants appeared to be well mixed within the infected tissue and showed no spatial segregation. In addition, both CTV variants were often found occupying the same cells. Possible mechanisms involved in shaping CTV populations and the biological significance of the observed lack of structural separation of the individual components are discussed.
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Affiliation(s)
- María Bergua
- University of Florida, Department of Plant Pathology, Gainesville, FL 32611, USA
| | - Dane M Phelan
- University of Florida, Department of Molecular Genetics and Microbiology, FL 32603, USA
| | - Aurélie Bak
- University of Florida, Department of Plant Pathology, Gainesville, FL 32611, USA
| | - David C Bloom
- University of Florida, Department of Molecular Genetics and Microbiology, FL 32603, USA
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16
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Finding balance: Virus populations reach equilibrium during the infection process. Virology 2015; 485:205-12. [PMID: 26291064 DOI: 10.1016/j.virol.2015.07.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Revised: 07/15/2015] [Accepted: 07/21/2015] [Indexed: 12/18/2022]
Abstract
Virus populations, mixtures of viral strains or species, are a common feature of viral infection, and influence many viral processes including infection, transmission, and the induction of disease. Yet, little is known of the rules that define the composition and structure of these populations. In this study, we used three distinct strains of Citrus tristeza virus (CTV) to examine the effect of inoculum composition, titer, and order, on the virus population. We found that CTV populations stabilized at the same equilibrium irrespective of how that population was introduced into a host. In addition, both field and experimental observations showed that these equilibria were relatively uniform between individual hosts of the same species and under the same conditions. We observed that the structure of the equilibria reached is determined primarily by the host, with the same inoculum reaching different equilibria in different species, and by the fitness of individual virus variants.
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17
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Harper SJ, Cowell SJ, Dawson WO. With a little help from my friends: complementation as a survival strategy for viruses in a long-lived host system. Virology 2015; 478:123-8. [PMID: 25666523 DOI: 10.1016/j.virol.2014.12.041] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 12/07/2014] [Accepted: 12/20/2014] [Indexed: 11/16/2022]
Abstract
In selective host species, the extent of Citrus tristeza virus (CTV) infection is limited through the prevention of long-distance movement. As CTV infections often contain a population of multiple strains, we investigated whether the members of a population were capable of interaction, and what effect this would have on the infection process. We found that the tissue-tropism limitations of strain T36 in selective hosts could be overcome through interaction with a second strain, VT, increasing titer of, and number of cells infected by, T36. This interaction was strain-specific: other strains, T30 and T68, did not complement T36, indicating a requirement for compatibility between gene-products of the strains involved. This interaction was also host-specific, suggesting a second requirement of compatibility between the provided gene-product and host. These findings provide insight into the 'rules' that govern interaction between strains, and suggest an important mechanism by which viruses survive in a changing environment.
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Affiliation(s)
- S J Harper
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA.
| | - S J Cowell
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
| | - W O Dawson
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
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18
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Dawson WO, Bar-Joseph M, Garnsey SM, Moreno P. Citrus tristeza virus: making an ally from an enemy. ANNUAL REVIEW OF PHYTOPATHOLOGY 2015; 53:137-55. [PMID: 25973695 DOI: 10.1146/annurev-phyto-080614-120012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Virus diseases of perennial trees and vines have characteristics not amenable to study using small model annual plants. Unique disease symptoms such as graft incompatibilities and stem pitting cause considerable crop losses. Also, viruses in these long-living plants tend to accumulate complex populations of viruses and strains. Considerable progress has been made in understanding the biology and genetics of Citrus tristeza virus (CTV) and in developing it into a tool for crop protection and improvement. The diseases in tree and vine crops have commonalities for which CTV can be used to develop a baseline. The purpose of this review is to provide a necessary background of systems and reagents developed for CTV that can be used for continued progress in this area and to point out the value of the CTV-citrus system in answering important questions on plant-virus interactions and developing new methods for controlling plant diseases.
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Affiliation(s)
- William O Dawson
- Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, Florida 33850; ,
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19
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Varanda CMR, Machado M, Martel P, Nolasco G, Clara MIE, Félix MR. Genetic diversity of the coat protein of Olive mild mosaic virus (OMMV) and Tobacco necrosis virus D (TNV-D) isolates and its structural implications. PLoS One 2014; 9:e110941. [PMID: 25350108 PMCID: PMC4211703 DOI: 10.1371/journal.pone.0110941] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2014] [Accepted: 09/25/2014] [Indexed: 01/08/2023] Open
Abstract
The genetic variability among 13 isolates of Olive mild mosaic virus (OMMV) and of 11 isolates of Tobacco necrosis virus D (TNV-D) recovered from Olea europaea L. samples from various sites in Portugal, was assessed through the analysis of the coat protein (CP) gene sequences. This gene was amplified through reverse transcriptase polymerase chain reaction (RT-PCR), cloned, and 5 clone sequences of each virus isolate, were analysed and compared, including sequences from OMMV and TNV-D isolates originally recovered from different hosts and countries and available in the GenBank, totalling 131 sequences. The encoded CP sequences consisted of 269 amino acids (aa) in OMMV and 268 in TNV-D. Comparison of the CP genomic and amino acid sequences of the isolates showed a very low variability among OMMV isolates, 0.005 and 0.007, respectively, as well as among TNV-D isolates, 0.006 and 0.008. The maximum nucleotide distances of OMMV and TNV-D sequences within isolates were also low, 0.013 and 0.031, respectively, and close to that found between isolates, 0.018 and 0.034, respectively. In some cases, less variability was found in clone sequences between isolates than in clone sequences within isolates, as also shown through phylogenetic analysis. CP aa sequence identities among OMMV and TNV-D isolates ranged from 84.3% to 85.8%. Comparison between the CP genomic sequences of the two viruses, showed a relatively low variability, 0.199, and a maximum nucleotide distance between isolates of 0.411. Analysis of comparative models of OMMV and TNV-D CPs, showed that naturally occurring substitutions in their respective sequences do not seem to cause significant alterations in the virion structure. This is consistent with a high selective pressure to preserve the structure of viral capsid proteins.
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Affiliation(s)
- Carla M. R. Varanda
- Laboratório de Virologia Vegetal, Instituto de Ciências Agrárias e Ambientais Mediterrânicas Universidade de Évora, Évora, Portugal
| | - Marco Machado
- Laboratório de Virologia Vegetal, Instituto de Ciências Agrárias e Ambientais Mediterrânicas Universidade de Évora, Évora, Portugal
| | - Paulo Martel
- Departamento de Ciências Biológicas e Bioengenharia, Faculdade de Ciências e Tecnologia da Universidade do Algarve, Faro, Portugal
| | - Gustavo Nolasco
- Laboratório de Virologia Vegetal, Universidade do Algarve, Faro, Portugal
| | - Maria I. E. Clara
- Laboratório de Virologia Vegetal, Instituto de Ciências Agrárias e Ambientais Mediterrânicas Universidade de Évora, Évora, Portugal
| | - Maria R. Félix
- Laboratório de Virologia Vegetal, Instituto de Ciências Agrárias e Ambientais Mediterrânicas Universidade de Évora, Évora, Portugal
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20
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Zablocki O, Pietersen G. Characterization of a novel citrus tristeza virus genotype within three cross-protecting source GFMS12 sub-isolates in South Africa by means of Illumina sequencing. Arch Virol 2014; 159:2133-9. [DOI: 10.1007/s00705-014-2041-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 02/28/2014] [Indexed: 10/25/2022]
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21
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Rubio L, Guerri J, Moreno P. Genetic variability and evolutionary dynamics of viruses of the family Closteroviridae. Front Microbiol 2013; 4:151. [PMID: 23805130 PMCID: PMC3693128 DOI: 10.3389/fmicb.2013.00151] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 05/29/2013] [Indexed: 11/15/2022] Open
Abstract
RNA viruses have a great potential for genetic variation, rapid evolution and adaptation. Characterization of the genetic variation of viral populations provides relevant information on the processes involved in virus evolution and epidemiology and it is crucial for designing reliable diagnostic tools and developing efficient and durable disease control strategies. Here we performed an updated analysis of sequences available in Genbank and reviewed present knowledge on the genetic variability and evolutionary processes of viruses of the family Closteroviridae. Several factors have shaped the genetic structure and diversity of closteroviruses. (I) A strong negative selection seems to be responsible for the high genetic stability in space and time for some viruses. (2) Long distance migration, probably by human transport of infected propagative plant material, have caused that genetically similar virus isolates are found in distant geographical regions. (3) Recombination between divergent sequence variants have generated new genotypes and plays an important role for the evolution of some viruses of the family Closteroviridae. (4) Interaction between virus strains or between different viruses in mixed infections may alter accumulation of certain strains. (5) Host change or virus transmission by insect vectors induced changes in the viral population structure due to positive selection of sequence variants with higher fitness for host-virus or vector-virus interaction (adaptation) or by genetic drift due to random selection of sequence variants during the population bottleneck associated to the transmission process.
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Affiliation(s)
- Luis Rubio
- Instituto Valenciano de Investigaciones AgrariasMoncada, Valencia, Spain
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22
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Harper SJ. Citrus tristeza virus: Evolution of Complex and Varied Genotypic Groups. Front Microbiol 2013; 4:93. [PMID: 23630519 PMCID: PMC3632782 DOI: 10.3389/fmicb.2013.00093] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 04/03/2013] [Indexed: 12/22/2022] Open
Abstract
Amongst the Closteroviridae, Citrus tristeza virus (CTV) is almost unique in possessing a number of distinct and characterized strains, isolates of which produce a wide range of phenotype combinations among its different hosts. There is little understanding to connect genotypes to phenotypes, and to complicate matters more, these genotypes are found throughout the world as members of mixed populations within a single host plant. There is essentially no understanding of how combinations of genotypes affect symptom expression and disease severity. We know little about the evolution of the genotypes that have been characterized to date, little about the biological role of their diversity and particularly, about the effects of recombination. Additionally, genotype grouping has not been standardized. In this study we utilized an extensive array of CTV genomic information to classify the major genotypes, and to determine the major evolutionary processes that led to their formation and subsequent retention. Our analyses suggest that three major processes act on these genotypes: (1) ancestral diversification of the major CTV lineages, followed by (2) conservation and co-evolution of the major functional domains within, though not between CTV genotypes, and (3) extensive recombination between lineages that have given rise to new genotypes that have subsequently been retained within the global population. The effects of genotype diversity and host-interaction are discussed, as is a proposal for standardizing the classification of existing and novel CTV genotypes.
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Affiliation(s)
- S J Harper
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida Lake Alfred, FL, USA
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23
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Folimonova SY. Developing an understanding of cross-protection by Citrus tristeza virus. Front Microbiol 2013; 4:76. [PMID: 23577008 PMCID: PMC3616238 DOI: 10.3389/fmicb.2013.00076] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Accepted: 03/15/2013] [Indexed: 11/29/2022] Open
Abstract
Citrus tristeza virus (CTV) causes two citrus diseases that have caused devastating losses in global citrus production. The first disease is quick decline of trees propagated on the sour orange rootstock. The second disease is stem pitting, which severely affects a number of economically important citrus varieties regardless of the rootstock used and results in reduced tree growth and vigor as well as in reduced fruit size and quality. Both diseases continue to invade new areas. While quick decline could be effectively managed by the use of resistant and/or tolerant rootstocks, the only means to protect commercial citrus against endemic stem pitting isolates of CTV has been cross-protection with mild isolates of the virus. In some citrus areas cross-protection has been successful and allowed production of certain citrus cultivars despite the presence of severe stem pitting isolates in those regions. However, many other attempts to find isolates that would provide sustained protection against aggressive isolates of the virus had failed. In general, there has been no understanding why some mild isolates were effective and others failed to protect. We have been working on the mechanism of cross-protection by CTV. Recent considerable progress has significantly advanced our understanding of how cross-protection may work in the citrus/CTV pathosystem. As we demonstrated, only isolates that belong to the same strain of the virus cross protect against each other, while isolates from different strains do not. We believe that the results of our research could now make finding protecting isolates relatively straightforward. This review discusses some of the history of CTV cross-protection along with the recent findings and our "recipe" for selection of protecting isolates.
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