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.     

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: 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.     

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.     

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.     

Factors Affecting the Spread of Plum pox virus Strain M in Peach Orchards Subjected to Roguing in France

ABSTRACT We evaluated the impact of roguing on the spread and persistence of the aggressive Plum pox virus strain M (PPV-M) in 19 peach orchard blocks in Southern France. During a 7- to 10-year period, orchards were visually inspected for PPV symptoms, and symptomatic trees were removed every year. Disease incidence was low in all orchards at disease discovery and was <1% in 16 of the 19 orchard blocks. The spread of Sharka disease was limited in all 19 blocks, with an annual disease incidence between 2 and 6%. However, new symptomatic trees were continuously detected, even after 7 to 10 years of uninterrupted control measures. An extended Cox model was developed to evaluate to what extent tree location, orchard characteristics, environment, and disease status within the vicinity influenced the risk of infection through time. Eleven variables with potential effect on tree survival (i.e., maintenance of a tree in a disease- free status through time) were selected from survey data and databases created using a geographical information system. Area of the orchard, density of planting, distance of a tree from the edge of the orchard block sharing a boundary with another diseased orchard, and distance to the nearest previously detected symptomatic tree had a significant effect on the risk for a tree to become infected through time. The combined results of this study suggest that new PPV-M infections within orchards subjected to roguing resulted from exogenous sources of inoculum, disease development of latent infected trees, as well as infected trees overlooked within the orchards during visual surveys. A revision of the survey and the roguing procedures used for more effective removal of potential sources of inoculum within the orchards and in the vicinity of the orchards would improve disease control suppression of 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.     

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.     

Control and monitoring: control strategies for Plum pox virus in Canada

In 2000, Plum pox virus (PPV) was discovered in Canada in the provinces of Ontario and Nova Scotia. Delimitation surveys were used to define quarantine areas. An eradication strategy was developed based on a threshold value for virus incidence which triggered removal of the entire orchard block. Each year the threshold value is being lowered until reaching a zero tolerance level. Growers are compensated financially for their losses. A two-tiered certification programme was designed to provide clean replacement trees. Initially, growers planted PPV-tested trees as an interim measure until fully virus-tested stock became available. It is hoped that this eradication programme will eliminate PPV from Canada by 2010.     

Prevention and Control of Fireblight1

A review is given of the possible measures against fireblight in countries which so far do not have the disease (the “have–nots”) and in countries which do (the “haves”). In the “have–nots”, precautions can be taken by putting into practice our knowledge of susceptibility and sensitivity of host plants in non–commercial as well as in commercial plantations. Some guidelines are given. Planting of the most susceptible non–commercial host plants should be avoided whilst testing and breeding programs for resistance should be stimulated. In the “haves”, an attempt should first be made to eradicate the disease. Some remarks are made about this point. When eradication has proved to be impossible, special attention should be given to the health of the source material for nurseries. This point is worked out in some detail. Also in the “haves”, preventive measures can and should be taken, inside and outside nurseries and orchards. These measures are specified. In cases where infection is found, the foci should be destroyed as soon as possible, without exception in nurseries and orchards, and preferably also outside these holdings. A number of remarks about this point are made. Only by practising an integrated policy by a combination of the measures mentioned can one achieve a maximum of control and a minimum of damage by this disease.     

Epidemiology of sharka disease in France

Plum pox virus was first detected in France in the 1960s. Both PPV-D and PPV-M strains are present but epidemics related to the PPV-M strain detected in the late 1980s are the most problematic. The two PPV strains have unequal distributions in peach and apricot orchards and different prevalences. More than 20 different aphid species have been identified as vectors of PPV but most of them do not colonize Prunus species. Thus, aphids involved in the spread of PPV in orchards are essentially visiting aphids. The main sources of inoculum for the vectors are leaves and fruits of infected stone-fruit trees. Spontaneous, wild and ornamental Prunus species such as Prunus dulcis , P. spinosa or P. pissardii are susceptible to PPV isolates found in France but their role as a reservoir in sharka epidemics is probably negligible. The disease spreads rapidly in orchards but the rate of progression may vary according to the identity of the PPV strain and the Prunus species. Analysis of spatial patterns of disease has shown that secondary spread by aphids frequently occurs over short distances in the orchards (aggregated patterns) but also that dissemination at longer distances (of several hundred metres) is a common event.     

A model for the invasion and spread of rhizomania in the United kingdom: implications for disease control strategies

ABSTRACT Rhizomania disease of sugar beet represents a major economic threat to the sugar industry in the United Kingdom. Here we use the UK rhizomania epidemic as an exemplar of a range of highly infectious spatially heterogeneous diseases. Using a spatially explicit stochastic model, we investigated the efficacy of a spectrum of possible control strategies, both locally reactive and national in character. These include the use of novel cultivars of beet with different responses to infection, changes in cultivation practice, and reactive containment policies at the farm scale. We show that strictly local responses, including a containment policy similar to that initially implemented in the United Kingdom in response to the disease, are largely ineffective in slowing the spread because they fail to match the natural scale of the epidemic. Larger spatial-scale processes are considerably more successful. We conclude that epidemics have intrinsic temporal and spatial scales that must be matched by any control strategy if it is to be both effective and efficient. We have generated probability distributions for the proportion of farms symptomatic. Over the course of the epidemic, such distributions develop a bimodality that we hypothesize to correspond to the matching of spatial heterogeneity in the susceptible population to the intrinsic scales of the epidemic.     

First outbreaks of fireblight in Slovenia1

Slovenia was recognized as free from Erwinia amylovora until 2001. A low incidence of the disease was reported in 2001 and 2002 in the north‐west uplands of the Gorenjska region. In 2001, only 3 trees in extensive orchards were found positive at one location out of 791 monitoring locations all over the country. In 2002, the same location in Naklo and a second one in a 1‐km radius were found positive, whilst 875 other monitoring locations were fireblight‐free. Despite strict phytosanitary measures implemented after discovery of the first focus, the bacterium spread in 2003 to the entire Gorenjska region, with further spread towards eastern and southern Slovenia. The NPPO registered 184 new foci by the end of the season in Gorenjska. Twenty‐three foci are scattered in other regions. Phytosanitary measures were applied in every focus. Spread of the bacterium was probably enabled by favourable weather conditions, the presence of the inoculum and intensive bee‐hive movement, resulting in flower infections. Since eradication has not been successful, it is concluded that E. amylovora is now present at low prevalence in Slovenia.     

枣疯病传病途径的研究

 枣疯病是我国枣树上一种严重的传染性病害。多年试验表明:土壤、花粉、种子均不传病,病叶汁液接种以及病健树根系在地下的自然接触也不传病;人工嫁接虽可传病,但枣树繁殖一般不通过嫁接,因而不是自然传病的途径。经过对在枣树上活动害虫的系统调查,1980年于河北玉田选常见的11种叶蝉进行了传病实验,证明橙带拟菱纹叶蝉(Hishimonides aurifacialis Kuoh)、凹缘菱纹叶蝉(Hishimonus sellatus Ulhler)和红闪小叶蝉(Typhlocyba sp.)均能传播枣疯病。从接种发病的实生枣苗维管束和媒介叶蝉的唾液腺的超薄切片中,都检查到枣疯病原类菌原体。鉴于这三种叶蝉普遍存在于北方枣区。因此,认为是枣疯病在北方枣区自然传病的主要媒介。     

Plum pox virus and the estimated costs associated with sharka disease

Since first being recorded in 1917–18 in Bulgaria, sharka (plum pox) disease has progressively spread via infected plant material to be present in most Prunus -growing nations today. The disease has serious agronomic and political consequences because it causes enormous economic losses. In countries in which sharka is endemic, a high percentage of apricot and European plum production is unmarketable because of the disease. To these figures should be added the costs of sanitary controls, surveys and eradication programmes against sharka virus. Estimated costs associated with sharka management worldwide in the last 30 years exceed 10 000 million euros. However, improvements in knowledge of the disease and in techniques used to identify the disease are significantly aiding disease control and management.     

戊唑·多菌灵·乙膦铝乳胶液对苹果枝干轮纹病的防治效果

近年,在矮砧密植苹果园发现苗木栽植后幼树主干上的枝干轮纹病发生严重,急需有效的防治方法。针对生产中的需求,本研究对幼树枝干轮纹病的防治方法进行了探索,结果显示:用乳胶液配制的戊唑·多菌灵·乙膦铝混合剂对枝干轮纹病防治效果显著高于同种药剂的水溶液,对剪锯口枝干轮纹病防治效果可达63.7%~100%,是药剂水溶液防效的2~3倍;生长季施用2次,对枝干轮纹病病斑的铲除率为45.2%,是药剂水溶液防效的9.6倍以上。结果表明,戊唑·多菌灵·乙膦铝乳胶液对枝干轮纹病防治效果显著,可以用于苗木剪锯口的防护,以及新建果园中幼树枝干轮纹病的治疗。研究结果为生产中幼树枝干轮纹病的防治提供了有效的方法。     

Cost/Benefit Analysis as Used in the United Kingdom for Eradication Campaigns against Alien Pests and Diseases1

The reasons for using, and the methods used for cost benefit analysis of eradication campaigns against alien pests and diseases in the UK are discussed. Details of the costanalysis for a current campaign against white rust of chrysanthemums ( Puccinia horiana ) are given.     

Sugarbeet rhizomania in England1

Concern about the introduction of rhizomania to UK heightened when the disease was confirmed in The Netherlands in 1983. A series of precautionary measures supported by legislation was quickly enacted to reduce this risk. Extensive surveys of harvested beet and of growing crops failed to reveal any infection until 1987 when a single isolated outbreak was found near Bury St Edmunds in Suffolk. Plants in the affected field showed typical rhizomania symptoms and laboratory tests confirmed the presence of beet necrotic yellow vein furovirus (BNYVV). Further investigation of isolates from the outbreak field revealed the presence of beet soil-borne furovirus in addition to BNYVV and sometimes both were present in mixed infections. Intensive surveys in the immediate area of the outbreak, both by field inspections of growing crops and by soil bait testing, confirmed infection only in the one field and the margin of the adjacent field. Immediate containment measures were followed by soil sterilization with methyl bromide to minimize the movement of infection from the area. Surveys of beet will continue, but results to date suggest that the distribution of the disease is limited in extent.     

Genetic variability of <Emphasis Type="Italic">Plum pox virus</Emphasis> isolates in the Czech Republic

Plum pox virus (PPV), the causal agent of Sharka disease, is an important pathogen of stone fruit trees. In this study, 24 new Czech PPV isolates from five different orchards were collected and characterized, molecularly. PPV-D isolates were identified in all orchards studied; whereas PPV-Rec isolates were identified in only two of them. A phylogenetic analysis on (Cter) NIb-(Nter) CP was performed. Three Czech PPV-D isolates BOH11CZ, BOH12CZ, and BOH13CZ diverged into a significantly separated cluster. PPV-Rec isolates formed a fairly homogenous group. However, the Bohutice and the Lipov PPV-Rec isolates clustered in two significantly separated branches.