Control and monitoring: monitoring and eradication of sharka in south-east Italy over 15 years

When the first foci of sharka were discovered in Puglia region (south-east Italy) in the late 1980s, the regional agricultural authorities launched a programme for Plum pox virus (PPV) monitoring and disease eradication. The infecting virus strain was identified as PPV-D. From 1989 to 1993, a strong eradication campaign was successfully carried out involving 13 plum and 2 apricot orchards with different levels of infection. During 1994–2000, besides plum, apricot and peach, monitoring was extended to sweet cherry. At that time, surveys and testing did not reveal any new PPV focus, but the eradication of infected trees continued in a couple of orchards. In 2001–05, particular attention was paid to peach, as devastating PPV-M outbreaks had developed in other areas of the country. A new PPV focus was found in apricot, caused by PPV-Rec, which was promptly eradicated. In the following two years, surveys in the once infected orchard and surrounding peach plantings did not detect any virus spread. The endeavour has taken 15 years making this PPV monitoring and eradication programme the longest in Italy. Its overall results indicate that the fruit tree industry in Puglia region can now be regarded as essentially PPV-free.     

Current status of sharka disease in Puglia (Italy) and implementation of an eradication programme1

Plum pox potyvirus (PPV) was introduced into Puglia (IT) a few years ago with infected propagative material coming from nurseries outside the region. Infections were detected in commercial plum and apricot orchards, but not in local nurseries. Extensive surveys were carried out in young apricot, plum and peach orchards to assess the distribution, incidence and spread of PPV infections, with a view to possibly enforcing an eradication programme. Surveys were based on visual inspections of about 300 commercial orchards and nurseries (covering an area of more than 550 ha) in the whole of Puglia, by ELISA and IBM tests, and by biological testing on GF305 of field samples. A total of 23,000 plants were individually checked by ELISA and IEM. The eradication involved 13 plum (35 ha) and 2 apricot (5 ha) orchards showing different levels of PPV infection. Six of the plum plantings showed infection exceeding 30% and were completely uprooted; in the remaining orchards, infection did not exceed 10% and uprooting was limited to infected trees. PPV was never detected in peach. The high incidence of PPV in some plum orchards was due to the heavy initial contamination of propagating material. Secondary virus spread was monitored in apricot orchards and found to occur at a low rate.     

Epidemiology of sharka disease in North America

The history of North American (USA and Canada) epidemics of Plum pox virus (PPV), as well as hypotheses about the general North American epidemiology of PPV, are summarized. The hierarchical sampling method, combined with reliable DASI-ELISA detection/confirmation procedures, were successfully used for extensive PPV surveys of stonefruit-producing areas in both countries. The influence of epidemiological analyses on eradication policy is described.     

Hosts and symptoms of Plum pox virus: ornamental and wild Prunus species

Several ornamental and wild Prunus species have been identified as natural and/or experimental hosts for Plum pox virus (PPV). The significance of natural vs. experimental hosts, graft or bud-transmitted infections vs. aphid-transmitted infections in ornamental or wild Prunus hosts, and their relevance in the field situation, are not clearly understood. However, since PPV is aphid-transmitted, any host in the field or nursery serves as a potential reservoir and source of inoculum and must be monitored and controlled in any PPV eradication or management programme.     

Results of the systematic survey and control of Plum pox potyvirus in Slovenia

Sharka, caused by Plum pox potyvirus (PPV), was first observed in Slovenia in 1987. In the following years, the presence of PPV was confirmed by DAS-ELISA in samples originating from orchards, individual trees and propagation material of stone fruits. In 1998, a systematic survey was initiated to prevent and control the spread of sharka and to establish pest-free production sites. In the first 3 years of the systematic survey, the presence of PPV was also monitored outside production sites for propagating material and their buffer zones, in order to establish the current incidence of sharka in Slovenia. The results showed an overall presence of PPV infection in Slovenia. Since 2000, the survey has focused mainly on nurseries, mother trees and stool-beds. In spite of strict official supervision and eradication measures, the incidence of sharka in propagating material production sites increased until 2002. A significant decrease in the number of PPV-infected mother trees, stool-beds, nurseries and buffer zones was finally obtained in 2002, as a consequence of the vast effort dedicated to containment of sharka in Slovenia.     

Control and monitoring: control of Plum pox virus in the United Kingdom

Plum pox virus (PPV) was first identified in the United Kingdom in 1965. Despite a rigorous eradication policy, the disease spread quickly and established itself in all the main plum-growing areas in England. In 1975, the policy was changed from a blanket eradication campaign to one of containment; retaining statutory control of PPV on propagation material but allowing the industry to control the disease in orchards. As part of the current containment campaign, annual surveys are carried out on propagation material. These surveys show that the incidence of PPV in this material is very low and that only the D-strain is present. The precise situation regarding PPV incidence in commercial orchards is unknown. Given the low incidence in propagation material, it is likely that PPV is uncommon in actively managed orchards. However, some infected orchards probably do still exist, especially older, unmanaged or abandoned ones. Overall, the history of PPV control in the UK is one of unsuccessful eradication but successful containment. The UK experience demonstrates that given the right combination of strain and host, alongside a regular testing regime, it is possible to control PPV through the establishment of a regulated certification scheme and the supply of virus-free planting material.     

Control and monitoring: eradication of Plum pox virus in Switzerland

In 1967, sharka disease ( Plum pox virus ; PPV) was detected for the first time in Switzerland. By the end of the 1970s, the disease was considered as eradicated after a rigorous campaign of survey and eradication. Since then, periodical inspections and random testing of imported plants and young orchards have been performed by Swiss plant protection services. This permitted the detection of outbreaks of PPV in 2004. Consequently, a new survey and eradication campaign began.     

Plum pox virus: diagnosis and spread inhibition by weed control

Journal of Plant Diseases and Protection - Plum pox virus (PPV) is a plant virus (genus Potyvirus, family Potyviridae) infecting stone fruit trees. Since the first report from Bulgaria in 1917, PPV...     

Plum pox virus detection in dormant plum trees by PCR and ELISA

An immunocapture polymerase chain reaction (IC-PCR) protocol and ELISA were compared for their effectiveness in detecting plum pox virus (PPV) in dormant plum material. Although the IC-PCR was about one thousand times more sensitive than ELISA, PPV was detected by ELISA in 71–80% of bark samples collected in December, January and March 1996/97 from pot-grown rootstock trees inoculated with PPV the previous March, compared with 85–86% detection in the same samples by IC-PCR. In similar samples from one-year-old shoots taken from infected branches of orchard trees, 66–81% were positive by ELISA compared with 81–87% by IC-PCR. With bulked samples taken from the fibrous roots of the pot-grown trees, PPV was detected in 92–100% of samples by IC-PCR in winter compared with only 38–65% by ELISA. These results were confirmed in samples from the roots and shoots of the same trees in 1997/98. Three samples per shoot would have been sufficient to detect PPV by ELISA in 87 of the 88 infected shoots tested during the two winters. However, infected shoots are irregularly distributed in diseased trees and PCR assays of root samples offer the potential for improving the reliability of identifying trees infected with PPV.     

Breeding for resistance: breeding for Plum pox virus resistant plums (Prunus domestica L.) in Germany

In German plum breeding programmes new varieties tolerant to Plum pox virus (PPV) were initially obtained by selecting hybrids originating from crossings between tolerant old varieties while, later on, sharka tolerant varieties bred in Čačak, Serbia were used as crossing partners. Varieties released from these programmes replaced the sensitive ones in all sharka infected regions in Germany. While all the new tolerant varieties can be infected by the virus, PPV symptoms on the fruits are acceptable. However, environmental factors can weaken the plant, causing them to suffer more from PPV infections and to display worse symptoms on fruits, as did occur during some recent very dry and warm years. A breeding programme at the University of Hohenheim is tackling this problem with genotypes that show a hypersensitive response after infection. These genotypes are completely field resistant to PPV, remaining virus free in the field since they cannot be infected via aphid transmission. They are able to isolate the virus after infection. The first hypersensitive variety was 'Jojo'. Many seedlings originating from crossings with at least one hypersensitive parent are under evaluation. Since the inheritance of the trait 'hypersensitivity against PPV' is very good, combining hypersensitivity with excellent fruit quality and good cropping capacity will be possible soon. In 2005, a breeding programme for hypersensitive Prunus genotypes began at the Technical University of Munich.     

Rapid detection of plum pox virus by reverse transcription recombinase polymerase amplification

Journal of Plant Diseases and Protection - Plum pox virus (PPV) is one of the most destructive viral pathogens infecting stone fruit trees worldwide. As PPV causes a viral disease that requires...     

Control and monitoring: Plum pox virus quarantine situation in France

Sharka disease caused by Plum pox virus (PPV) is present in several areas in France, and its total eradication from the territory is not considered feasible. Although sharka falls under mandatory control measures, the objective is, in the infected areas, to contain the disease in the orchards at sufficiently low levels so that the production remains economically viable. In parallel, official controls are carried out to guarantee that plants for planting, including seedlings, which are moved in trade are free from PPV.     

Control and monitoring: quarantine situation of Plum pox virus in New Zealand

Biosecurity New Zealand recognizes that Plum pox virus (PPV) is one of the most destructive diseases of stone fruit and aims to keep New Zealand free from it. PPV has never been detected in New Zealand orchards during national surveys. but it has been detected in post-entry quarantine. Biosecurity New Zealand has analysed the potential pathways for PPV to enter the country, and developed phytosanitary regulations and prevention control measures to reduce the risks. A contingency plan, a response programme, and diagnostic protocols have been developed and simulation exercises based on a hypothetical PPV incursion have been carried out.     

Comparison of four techniques for plum pox virus detection

Journal of Plant Diseases and Protection - Twenty-four stone fruit trees showing typical symptoms of plum pox virus (PPV) were tested for PPV using ELISA, RT-PCR, real-time RT-PCR and RT-LAMP. The...     

Potential role of almond in sharka epidemics: susceptibility under controlled conditions to the main types of plum pox potyvirus and survey for natural infections in France 1

The changes in cropping conditions of almond and the development of efficient tools for the detection and characterization of plum pox potyvirus (PPV) populations have led us to reassess the potential susceptibility of this species to sharka disease and its role as a virus reservoir. The susceptibility of almond cv. Aï to nine isolates, representative of the known diversity among PPV populations, was assessed under controlled conditions. Most isolates were able to infect almond, by graft or aphid inoculation, causing generalized stable infections without any obvious sharka symptoms. These infected almonds were found to constitute a potential source of virus for aphid vectors, mainly in the case of M isolates. Surveys were carried out in the south of France, in foci of M and D strains of PPV, to evaluate the presence of natural infections of almond. No typical symptoms were observed and the virus was never detected. It can be assumed that the actual limited prevalence of PPV in France does not lead to a sufficiently high inoculum pressure to allow almond trees to be infected.     

Detection and characterization of Plum pox virus: serological methods

Tremendous progress has been made in the research and development of Plum pox virus (PPV) serological reagents and methods in recent years. Two facts have revolutionised the serological detection and characterization of the virus: the development of the ELISA method in 1977, and the later emergence of specific monoclonal antibody technology. The availability of commercial kits has popularised PPV diagnosis, now making diagnosis possible at large scale for quarantine purposes, eradication programmes and control of the disease in nurseries. The use of the universal monoclonal antibody 5B-IVIA, used in DASI-ELISA, is the most accurate system for routine PPV detection. Likewise, the use of typing monoclonal antibodies gives exact characterization of the main PPV types described: 4DG5 for PPV-D, AL for PPV-M, EA24 for PPV-EA, and TUV and AC for PPV-C. There is, in general, an excellent correlation between serological data obtained with PPV specific monoclonal antibodies and data obtained by molecular PCR based methods. ELISA using a single or a mixture of monoclonal antibodies will remain the preferred method for universal detection and routine screening of PPV for years to come. Today, other serological methods and reagents are also recommended in the EPPO Diagnostic Protocol, increasing the number of reliable tests available for PPV detection. These developments have helped to control sharka disease in recent years. International co-operation in this field has been crucial to the improvement and validation of serological tools for PPV detection and characterization.     

First report of plum pox virus infecting Japanese apricot (<Emphasis Type="Italic">Prunus mume</Emphasis> Sieb. et Zucc.) in Japan

For the first time, plum pox virus (PPV) has been detected in commercial Japanese apricot (Prunus mume) trees in Tokyo, Japan. These trees had ringspot or mottle on leaves, color breaking of petals and, occasionally, mild ringspots and malformation on fruits. The virus was identified based on the morphology of virus particles, serology, and RT-PCR. The amplified nucleotide fragment shared 100% identity with a partial coat protein gene of PPV-D isolates.     

Spatial Pattern Analysis of Sharka Disease (Plum pox virus Strain M) in Peach Orchards of Southern France

ABSTRACT The spatial pattern of Sharka disease, caused by Plum pox virus (PPV) strain M, was investigated in 18 peach plots located in two areas of southern France. PPV infections were monitored visually for each individual tree during one to three consecutive years. Point pattern and correlation-type approaches were undertaken using the binary data directly or after parsing them in contiguous quadrats of 4, 9, and 16 trees. Ordinary runs generally revealed a low but variable proportion of rows with adjacent symptomatic trees. Aggregation of disease incidence was indicated by the theta parameter of the beta-binomial distribution and related indices in 15 of the 18 plots tested for at least one assessment date of each. When aggregation was detected, it was indicated at all quadrat sizes and tended to be a function of disease incidence, as shown by the binary form of Taylor's power law. Spatial analysis by distance indices (SADIE) showed a nonrandom arrangement of quadrats with infected trees in 14 plots. The detection of patch clusters enclosing quadrats with above-average density of symptomatic trees, ellipsoidal in shape and generally extending from 4 to 14 trees within rows and from 4 to 10 trees perpendicular to the rows, could be interpreted as local areas of influence of PPV spread. Spatial patterns at the plot scale were often characterized by the occurrence of several clusters of infected trees located up to 90 m apart in the direction of the rows. When several time assessments were available, increasing clustering over time was generally evidenced by stronger values of the clustering index and by increasing patch cluster size. The combination of the different approaches revealed a wide range of spatial patterns of PPV-M, from no aggregation to high aggregation of symptomatic trees at all spatial scales investigated. Such patterns suggested that aphid transmission to neighboring trees occurred frequently but was not systematic. The mechanism of primary virus introduction, the age and structure of the orchards when infected, and the diversity of vector species probably had a strong influence on the secondary spread of the disease. This study provides a more complete understanding of PPV-M patterns which could help to improve targeting of removal of PPV-infected trees for more effective disease control.