scholarly journals Incidence, Transmissibility, and Genotype Analysis of Citrus tristeza virus (CTV) Isolates from CTV Eradicative and Noneradicative Districts in Central California

Plant Disease ◽  
2005 ◽  
Vol 89 (8) ◽  
pp. 859-866 ◽  
Author(s):  
R. K. Yokomi ◽  
R. L. DeBorde
Keyword(s):  
Citrus Tristeza Virus ◽  
Transmission Rate ◽  
Aphis Gossypii ◽  
Cotton Aphid ◽  
Central California ◽  
Virus Incidence ◽  
The Impact ◽  
Tristeza Virus ◽  
Tulare County ◽  
Citrus Tristeza

Growers in 45% (44,100 ha) of the citrus acreage in California stopped eradicating Citrus tristeza virus (CTV)-infected trees from their fields in 1995-96. The impact of leaving infected trees on the rate of CTV spread was determined by comparing temporal incidence of CTV in plots in Strathmore, Tulare County without eradication with incidence in a plot in McFarland, Kern County with eradication. From 1997 to 2003, CTV incidence in the Strathmore plots ranged from 6 to 42%, with annual spread rates from 1.6 to 3.6%. CTV incidence in the McFarland plot increased from 0 to 5% between 2001 and 2003 before infected trees were removed. Using a subplot hierarchical bulk sampling method, virus incidence over a 3-year period in a 6.5 km2 area near McFarland was estimated to range from 0.09 to 0.69%, which indicated that CTV suppression was still being achieved in this area. Vector tests using the cotton aphid, Aphis gossypii, identified highly transmissible isolates (30 to 61% transmission rate) and a larger proportion of highly transmissible isolates were found in the McFarland plots. Thirty-six CTV isolates from recently infected plot trees were obtained and analyzed. None of these isolates reacted with monoclonal antibody MCA13 that detects presumptive CTV severe strains. Molecular analysis using polymerase chain reaction and sequence-specific primers showed that all isolates had a genotype identical to the T30 mild isolate from Florida.

scholarly journals Survey Methods for Assessment of Citrus Tristeza Virus Incidence

1998 ◽  
Vol 88 (7) ◽  
pp. 715-723 ◽  
Author(s):  
G. Hughes ◽  
T. R. Gottwald
Keyword(s):  
Field Data ◽  
Citrus Tristeza Virus ◽  
Survey Methods ◽  
Enzyme Linked Immunosorbent Assay ◽  
Central California ◽  
Accuracy And Precision ◽  
Virus Incidence ◽  
Field Data Collection ◽  
Tristeza Virus ◽  
Citrus Tristeza

The assessment of citrus tristeza virus incidence by sampling involves laboratory testing by enzyme-linked immunosorbent assay of leaf material collected in the field. Using field data and computer simulation, methods of field data collection were compared. One method was similar to that used by the Central California Tristeza Eradication Agency, in which 4 to 6% of the trees in a planting block are sampled and material from each tree sampled is assayed separately. This method was compared with an alternative method in which about 25% of the trees in a block are sampled, and material from groups of four trees is bulked and assayed together. Our comparative study indicated that the latter method results in increased accuracy and precision of estimates of citrus tristeza virus incidence without increasing unduly the number of laboratory assays required.

scholarly journals Spread of Citrus Tristeza Virus in Citrus Orchards in Central California

Plant Disease ◽  
2020 ◽  
Vol 104 (7) ◽  
pp. 1925-1931
Author(s):  
Raymond K. Yokomi ◽  
Mark S. Sisterson ◽  
Subhas Hajeri
Keyword(s):  
Citrus Tristeza Virus ◽  
Virus Spread ◽  
Central California ◽  
Aphid Control ◽  
Citrus Orchards ◽  
Individual Trees ◽  
Extension Center ◽  
Tristeza Virus ◽  
Tulare County ◽  
Citrus Tristeza

In California, citrus tristeza virus (CTV) is regulated by a State Interior Quarantine. In CTV abatement districts in central California, trees with CTV that react to MCA13 (MCA13-positive [MCA13+]), a strain-discriminating monoclonal antibody, are rogued to prevent virus spread. The Tulare County Pest Control District, however, does not participate in this abatement program except for a 1.6-km2 zone around the Lindcove Research and Extension Center, Exeter, CA. To quantify CTV spread under these two disparate management programs, CTV surveys were conducted in abatement plots with mandatory aphid control and nonabatement plots. Abatement plot surveys used hierarchical sampling of 25% of trees with samples pooled from four adjacent trees. Detection of MCA13+ CTV in a sample prompted resampling and testing of individual trees. From 2008 to 2018, incidence of CTV increased by an average of 3.9%, with only two MCA13+ samples detected. In contrast, in nonabatement plots, incidence of CTV increased by an average of 4.6% between 2015 and 2018. Increase in MCA13-negative (MCA−) isolates was 11 times greater than that of MCA13+ isolates, with the number of MCA13+ trees increasing by 19 trees between 2015 and 2018. MCA13− isolates were more randomly distributed, suggesting primary spread, whereas MCA13+ CTV isolates were more aggregated, suggesting some secondary spread. These results suggest that spread of MCA13+ isolates was limited by a combination of tree removal and aphid vector suppression. MCA13+ samples were VT isolates with some mixtures with T30 isolates. Despite the presence of VT isolates, all CTV-infected trees were asymptomatic.

scholarly journals Citrus tristeza virus P33 Protein Is Required for Efficient Transmission by the Aphid Aphis (Toxoptera) citricidus (Kirkaldy)

Viruses ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 1131
Author(s):  
Turksen Shilts ◽  
Choaa El-Mohtar ◽  
William O. Dawson ◽  
Nabil Killiny
Keyword(s):  
Citrus Tristeza Virus ◽  
Transmission Rate ◽  
Control Strategies ◽  
Virus Transmission ◽  
Plant Viruses ◽  
Transmission Mechanisms ◽  
Infectious Clones ◽  
Underlying Mechanisms ◽  
Tristeza Virus ◽  
Citrus Tristeza

Plant viruses are threatening many valuable crops, and Citrus tristeza virus (CTV) is considered one of the most economically important plant viruses. CTV has destroyed millions of citrus trees in many regions of the world. Consequently, understanding of the transmission mechanism of CTV by its main vector, the brown citrus aphid, Aphis (Toxoptera) citricidus (Kirkaldy), may lead to better control strategies for CTV. The objective of this study was to understand the CTV–vector relationship by exploring the influence of viral genetic diversity on virus transmission. We built several infectious clones with different 5′-proximal ends from different CTV strains and assessed their transmission by the brown citrus aphid. Replacement of the 5′- end of the T36 isolate with that of the T30 strain (poorly transmitted) did not increase the transmission rate of T36, whereas replacement with that of the T68-1 isolate (highly transmitted) increased the transmission rate of T36 from 1.5 to 23%. Finally, substitution of p33 gene of the T36 strain with that of T68 increased the transmission rate from 1.5% to 17.8%. Although the underlying mechanisms that regulate the CTV transmission process by aphids have been explored in many ways, the roles of specific viral proteins are still not explicit. Our findings will improve our understanding of the transmission mechanisms of CTV by its aphid vector and may lead to the development of control strategies that interfere with its transmission by vector.

scholarly journals Survey Methods for Assessment of Citrus tristeza virus Incidence in Urban Citrus Populations

Plant Disease ◽  
2002 ◽  
Vol 86 (4) ◽  
pp. 367-372 ◽  
Author(s):  
G. Hughes ◽  
T. R. Gottwald ◽  
K. Yamamura
Keyword(s):  
Survey Methodology ◽  
Citrus Tristeza Virus ◽  
Survey Methods ◽  
Acceptance Sampling ◽  
Large Area ◽  
Two Stage ◽  
Commercial Cultivation ◽  
Virus Incidence ◽  
Tristeza Virus ◽  
Citrus Tristeza

This article concerns survey methodology for pathogens in urban citrus populations, motivated in particular by the need for assessments of Citrus tristeza virus (CTV) incidence. We envisage a large area R not devoted primarily to the commercial cultivation of citrus, that nevertheless has a substantial population of citrus trees. It is desired to sample the citrus population of area R in order to be able to make a statement about the level of infection of the population with CTV, or with particular isolates thereof. We describe a two-stage acceptance sampling scheme in which area R is divided into N sampling units, of which n are inspected. The size of the sampling units, while much smaller than R, is still large, so subsampling is carried out, introducing the possibility of misclassification of sampling units. To account for misclassification of sampling units, a larger number must be inspected than if it were assumed that there were no misclassifications. We describe the calculation of sample sizes required for subsampling within sampling units and for the total number of sampling units to be inspected, using parameters that can be adjusted to meet different specified regulatory scenarios.

scholarly journals Serological Detection of Citrus tristeza virus with Antibodies Developed to the Recombinant Coat Protein

Plant Disease ◽  
2009 ◽  
Vol 93 (1) ◽  
pp. 11-16 ◽  
Author(s):  
M. M. Iracheta-Cárdenas ◽  
P. Metheney ◽  
M. L. Polek ◽  
K. L. Manjunath ◽  
R. F. Lee ◽  
...  
Keyword(s):  
Coat Protein ◽  
Large Scale ◽  
Citrus Tristeza Virus ◽  
Monitoring Program ◽  
Enzyme Linked Immunosorbent Assay ◽  
Serological Detection ◽  
Central California ◽  
Tristeza Virus ◽  
Recombinant Coat Protein ◽  
Citrus Tristeza

Antibodies specific for the recombinant coat protein (rCP) of the p25 gene of Citrus tristeza virus (CTV) were developed in goats and rabbits and further evaluated as a complete kit for the detection of the virus using healthy and CTV-infected tissue. The combination of goat T1 used as primary (coating) and rabbit C3 as intermediate (detecting) rCP antibodies reacted efficiently, with optical density at 405 nm (OD405) values between 0.250 and 2.000 with samples from an international collection of diverse CTV isolates. The CTV isolates tested cause a broad spectrum of disease syndromes in different citrus hosts. The OD405 values for healthy tissue were less than 0.100. Likewise, the combination of goat T1 and rabbit C3 rCP antibodies gave consistent results for CTV-positive and -negative sample discrimination when directly compared with the Central California Tristeza Eradication Agency (CCTEA) antibodies used for large-scale CTV detection and a commercially available CTV serological detection kit. The combination of goat T1 and rabbit C3 rCP antibodies showed its suitability for large-scale indexing with samples collected in commercial groves as part of the CCTEA's regular monitoring program. The evaluation included 41,195 samples from 301 commercial groves from districts 1, 2, and 3. In total, 26 trees (0.063%) were found to be CTV positive using the T1/C3 rCP antibody combination. Results of this research provide evidence that rCP antibodies can be efficiently used for both capturing and detecting CTV antigens in double-antibody sandwich indirect enzyme-linked immunosorbent assay.

scholarly journals Suitability of the MODIS-NDVI Time-Series for a Posteriori Evaluation of the Citrus Tristeza Virus Epidemic

2020 ◽  
Vol 12 (12) ◽  
pp. 1965
Author(s):  
Daniela Vanella ◽  
Simona Consoli ◽  
Juan Miguel Ramírez-Cuesta ◽  
Matilde Tessitori
Keyword(s):  
Time Series ◽  
Plant Pathogens ◽  
Management Practices ◽  
Citrus Tristeza Virus ◽  
Plant Diseases ◽  
Control Measures ◽  
Ndvi Time Series ◽  
The Impact ◽  
Tristeza Virus ◽  
Citrus Tristeza

The technological advances of remote sensing (RS) have allowed its use in a number of fields of application including plant disease depiction. In this study, an RS approach based on an 18-year (i.e., 2001–2018) time-series analysis of Normalized Difference Vegetation Index (NDVI) data, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and processed with TIMESAT free software, was applied in Sicily (insular Italy). The RS approach was carried out in four orchards infected by Citrus tristeza virus (CTV) at different temporal stages and characterized by heterogeneous conditions (e.g., elevation, location, plant age). The temporal analysis allowed the identification of specific metrics of the NDVI time-series at the selected sites during the study period. The most reliable parameter which was able to identify the temporal evolution of CTV syndrome and the impact of operational management practices was the “Base value” (i.e., average NDVI during the growing seasons, which reached R2 values up to 0.88), showing good relationships with “Peak value”, “Small integrated value” and “Amplitude”, with R2 values of 0.63, 0.70 and 0.75, respectively. The approach herein developed is valid to be transferred to regional agencies involved in and/or in charge of the management of plant diseases, especially if it is integrated with ground-based early detection methods or high-resolution RS approaches, in the case of quarantine plant pathogens requiring control measures at large-scale level.

scholarly journals Titer Variation of Citrus Tristeza Virus in Aphids at Different Acquisition Access Periods and Its Association with Transmission Efficiency

Plant Disease ◽  
2019 ◽  
Vol 103 (5) ◽  
pp. 874-879
Author(s):  
Jinxiang Liu ◽  
Lingdi Li ◽  
Hengyan Zhao ◽  
Yan Zhou ◽  
Hongsu Wang ◽  
...  
Keyword(s):  
Citrus Tristeza Virus ◽  
Transmission Rate ◽  
Virus Titer ◽  
Transmission Efficiency ◽  
Pcr Assay ◽  
Toxoptera Citricida ◽  
The Mean ◽  
Green Fluorescent ◽  
Tristeza Virus ◽  
Citrus Tristeza

Tristeza, caused by citrus tristeza virus (CTV; Closterovirus, Closteroviridae), is of significant economic importance. Tristeza epidemics have caused severe declines in productivity, and even death, of millions of citrus trees on sour orange rootstock in many regions all over the world. In the field, CTV is most efficiently vectored by the brown citrus aphid (Toxoptera citricida (Kirkaldy)) in a semipersistent manner. The transmission efficiency of the vector is influenced by its acquisition access period (AAP) for CTV. A real-time RT-PCR assay using SYBR Green fluorescent dye was used to estimate the CTV titers in groups of 15 aphids under AAPs after 0.5 to 48 h for three CTV isolates (CT11A, CT16-2, and CTLJ). Similar trends for CTV titer in viruliferous aphids were displayed for the three isolates. The maximum CTV titer was at AAP 6 h for isolates CT11A and CT16-2, and at 4 h for isolate CTLJ. During the AAPs from 0.5 to 6 h, the mean CTV titer of CT16-2 increased from 7.8 × 104 to 1.71 × 107 copies per 15 aphids, and was correlated with an increase in transmission rate from 20 to 90.9%. This suggests that the transmission efficiency is positively correlated with viral titer in the insect from 0.5 h until 6 h AAPs. While a downward trend in CTV titer was observed after a 6-h AAP, the transmission rate remained higher than 90% up to 48 h. These results indicate that factors other than the virus titer in the vector contribute to successful transmission under long acquisition conditions. This is the first detailed quantitative analysis of CTV in its main vector species following different AAPs and its association with transmission efficiency, and should enhance our understanding of T. citricida-CTV interactions.

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