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.     

Epidemiology of sharka disease in Spain

PPV was first detected in Spain in 1984 in Japanese plum ( Prunus salicina Lindl) cv. Red Beaut and spread very quickly to other Japanese and European plums and apricot cultivars but left peach cultivars unaffected. In the years following the detection of PPV, the predominant aphid species visiting Prunus orchards in Mediterranean areas were Aphis gossypii followed by Aphis spiraecola , the latter being the main aphid species found at present. Both species are considered to be the main vectors of PPV in Spanish early Prunus growing areas. Spatial analysis of the spread of PPV-D in Japanese plum and apricot trees confirmed the lack of significant association between immediately adjacent trees. The observed spatial pattern of sharka suggests a lack of movement of PPV-viruliferous aphid vectors to immediately adjacent trees and indicates their preferential movement to trees several tree spaces away. PPV-D is the only type currently present in Spain, with the exception of a PPV-M outbreak that was detected in and successfully eradicated from Aragón in 2002. The short-distance spread of PPV-M infection occurred as far as 12 m along the rows of peach trees. However, PPV-D has not been observed to spread through peach cultivars, despite being grown in the vicinity of heavily infected plots of apricot or Japanese plum trees.     

A preliminary account of the sanitary status of stone-fruit trees in Morocco

Field surveys were carried out in the main stone-fruit growing areas of Morocco to evaluate the sanitary status of commercial orchards, varietal collections and nurseries. The presence of virus and virus-like diseases was checked by ELISA, sap transmission to herbaceous hosts, testing on woody indicators and molecular hybridization (dot-blot and tissue-printing). 1211 samples (382 almond, 339 peach, 291 plum, 150 apricot and 49 cherry) were tested by ELISA for the presence of Prunus necrotic ring spot virus (PNRSV), Prune dwarf virus (PDV), Apple chlorotic leaf spot virus (ACLSV), Apple mosaic virus (ApMV) and Plum pox virus (PPV). The overall average of virus infection rate was 16.4%, whereas that of single species was: 22.6% for almond, 17.8% for plum, 15% for peach, 10.2% for cherry, and 2.7% for apricot. The following viruses were detected: PNRSV, PDV, ACLSV and ApMV. 565 samples were tested by dot-blot and tissue-printing hybridization for the presence of Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd). 48 samples were infected, 41 by PLMVd and 7 by HSVd. In addition, nested-PCR tests identified Plum bark necrosis and stem-pitting associated virus (PBNSPaV) in a few almond trees affected by stem pitting.     

Viruses and viroids of stone fruits in Syria

Field surveys were carried out in the main stone fruit-growing areas of Syria to evaluate the sanitary status of mother blocks, varietal collections and commercial orchards. The presence of virus and virus-like diseases was checked by enzyme-linked immunosorbent assay (ELISA), sap transmission to herbaceous hosts, testing on the woody indicators Prunus persica cv. GF 305 and Prunus serrulata cv. Kwanzan and dot-blot hybridization tests. A total of 1337 samples was tested by ELISA (444 apricot, 283 peach, 246 cherry, 222 almond and 142 plum). The overall mean infection rate was 13%, and the percentage infection level of single species was: peach 24%, cherry 16%, almond 13.5%, apricot 6%, plum 5%. The following viruses and viroids were detected: PNRSV, PDV, ACLSV, PPV, ApMV, PLMVd and HSVd ¹ .     

Viruses of stone fruits in Albania

Surveys were carried out in the main stone-fruit growing areas of Albania to assess the phytosanitary status of Prunus in conimercial orchards and varietal collections. The presence of virus and virus-like diseases and their identification was ascertained through field observations, sap transmission to herbaceous hosts, graft transmission to woody indicators, ELISA and IEM tests. The mean infection level was 42%. In particular, infections in apricot and almond were 12 and 16%, respectively, i.e. lower than in plum and cherry (47 and 56%, respectively). The following viruses were identified: plum pox potyvirus (PPV). apple chlorotic leaf spot trichovirus (ACLSV). prunus necrotic ringspot (PNRSV) and prune dwarf (PDV) ilarviruses. PPV infection was very severe in plum, and limited in apricot and peach. Apple mosaic ilarvirus (ApMV), and six nepoviruses tested for (SLRV, TBRV, RRV, CLRV, ArMV and ToRSV) were not encountered in Primus.     

Resistance to plum pox potyvirus in apricots1

The susceptibility of 115 apricot cultivars to plum pox potyvirus (PPV) has been examined, since 1981, in the experimental plots of the Pomology Institute at Naoussa and Skydra, Makedonia (GR). Inoculation was assured by aphids, transmitting strain PPV-M (Marcus) from naturally infected trees in adjacent peach orchards. For each cultivar, four to six trees were examined for at least 4 years. Observations on symptoms were made on leaves early in May and on fruits at maturity. Most cultivars expressed severe disease symptoms. Those without symptoms were inoculated by grafting onto heavily infected old apricot trees. The grafted shoots were tested for PPV in the following year by ELISA and on the woody indicator GF305. The cultivars which were rated as resistant after artificial inoculation and ELISA came from North America: Early Orange, Stella, NJA2, Sunglo, Veecot, Harlayne, Goldrich and Henderson. Most of these have been crossed with quality cultivars for the creation of resistant hybrids. The PPV resistance of large numbers of these apricot hybrids is now under investigation.     

Viruses and viroids of stone fruits in Jordan

Field surveys were carried out in the main stonefruit-growing areas of Jordan to assess the sanitary status of varietal collections, mother plant blocks and commercial orchards. The presence of virus and virus-like diseases was determined by ELISA, sap transmission to herbaceous hosts, graft transmission to Prunus persica cv. GF 305 and P. serrulata cv. Kwanzan, and molecular hybridization tests. A total of 1312 samples was tested by ELISA (531 peach, 361 plum, 218 apricot, 135 almond and 67 cherry trees). The overall mean level of infection was about 14%, indicating an acceptable sanitary status as a whole, considering that no sanitary selection has ever been carried out in Jordan. The infection level of different species was: peach (18%), cherry (15%), almond (14%), apricot (11%) and plum (10%). The following viruses and viroids were identified: Plum pox potyvirus (PPV), Prunus necrotic ringspot ilarvirus (PNRSV), Prune dwarf ilarvirus (PDV), Apple mosaic ilarvirus (ApMV), Apple chlorotic leaf spot trichovirus (ACLSV), Hop stunt viroid (HSVd) and Peach latent mosaic viroid (PLMVd). Most of these agents (ApMV, ACLSV, PLMVd and HSVd) are reported for the first time from Jordan.     

Serological characterization of Italian isolates of plum pox potyvirus1

An Italian isolate of plum pox potyvirus (PPV) from apricot, Ispave 17, was used as antigen for production of monoclonal antibodies. Six clones secreting specific antibodies to PPV were obtained. All these monoclonal antibodies were used to test a collection of different Italian PPV isolates, collected from plum, apricot and peach orchards, and other European isolates (including PPV-D and PPV-M serotypes), using DAS-ELISA, SDS-PAGE, western blot and GIEM. In western blot analysis, the PPV-M and PPV-D coat protein, detected directly from crude peach GF305 extracts, showed different electrophoretic mobility, the coat protein of PPV-M being slightly larger than that of PPV-D. ELISA tests, performed with fixed dilutions of antibodies and limiting dilutions of clarified samples, showed with some monoclonal antibodies a marked difference between PPV-M and PPV-D strains, at ratios greater than 1:40 (w/v). Also in GIEM some monoclonal antibodies gave a good labelling reaction only with PPV-D serotype. With the help of this differentiation, it was found that all Italian isolates tested were of the D serotype and none of the severe M strain of PPV, which has not been reported in Italy.     

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.     

Evaluation of peach and nectarine cultivars in Bulgaria for their resistance to plum pox potyvirus

In spring and summer 1989, it was established that plum pox potyvirus (PPV) was present in certain peach cultivars in Bulgaria. At the same time, we started to investigate the distribution of PPV in naturally infected 4–5 year-old peach and nectarine cultivars and hybrids in order to optimize PPV detection. Over 160 peach and nectarine cultivars and hybrids were evaluated. In about 40% of the genotypes, typical plum pox symptoms were observed. The latter were estimated and divided into groups depending on their susceptibility to PPV. Observations were made on the population density of seven aphid species established in the peach orchards. Five proved to be vectors of the virus. Myzus persicae was the vector that played the main role in spreading the virus on peach.     

Breeding for resistance to plum pox potyvirus in the Czech Republic1

Breeding for plum cultivars resistant to plum pox potyvirus (PPV) is in progress in the Czech Republic, while projects for apricot and peach have started in 1991. The aim is to create an assortment of apricot and peach cultivars for northern regions of Europe in which PPV is widely distributed.     

Sensitivity of the detection of plum pox potyvirus by molecular assays1

Recently, plum pox potyvirus (PPV) has been found in Basilicata, southern Italy, on plum, apricot and peach. In 1992-09, we started a large-scale survey to verify the effectiveness of diagnostic methods used during seasons when it is difficult to reveal any presence of the virus. The assays were carried out by dot-blot hybridization on stone-fruit cultivars normally planted in this area. The virus was found, by dot-blot hybridization, to be present in seven cultivars of peach, four of apricot and one of plum. All plants were 8–10 years old and, except for two apricot cultivars, were not displaying any apparent symptoms in spring 1992. Five peach cultivars, intended for use as primary sources of propagation material, were then selected for further study, and assayed in 1992–11 by ELISA and RT-PCR. ELISA tests on these selected peach cultivars were consistently negative, while PCR tests were consistently positive. However ELISA tests gave positive results when repeated in 1993–05. These results not only suggest that primary propagation material should be tested by techniques more sensitive than ELISA, but also question the usefulness of carrying out tests during any phenological phases of the plant.     

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.     

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.     

Sanitary status of stone-fruit trees in East Anatolia (Turkey) with particular reference to apricot

Field surveys were carried out in the main stone-fruit-growing areas of East Anatolia (Turkey) to assess the sanitary status of varietal collections, mother blocks and commercial orchards. The presence of virus and virus-like diseases was ascertained by enzyme-linked immunosorbent assay (ELISA), sap transmission to herbaceous hosts, graft transmission to peach cv. GF305 and molecular hybridization tests. A total of 1019 samples was tested by ELISA (859 apricot, 120 cherry, 21 almond and 19 peach). The sanitary status of apricot was extremely satisfactory, as the infection level was less than 0.3%. Cherry and almond, however, showed 21% and 33% infection respectively. The viruses identified were apple chlorotic leaf spot trichovirus (ACLSV), prune dwarf ilarvirus (PDV) and prunus necrotic ringspot ilarvirus (PNRSV). The commonest virus was PDV. Plum pox potyvirus (PPV), apple mosaic ilarvirus (ApMV) and the nepoviruses tomato black ring (TBRV), raspberry ringspot (RpRSV), strawberry latent ringspot (SLRV), cherry leaf roll (CLRV), arabis mosaic (ArMV) and tomato ringspot (ToRSV) were not encountered. Peach latent mosaic viroid (PLMVd) and hop stunt viroid (HSVd) were not detected either.     

Epidemiology of Plum pox virus strain M in Greece

Plum pox virus has been endemic in Greece since 1967 causing important losses in apricot and to a lesser extent in peach crops. A survey undertaken in 1992 in public and private mother-tree plantations to estimate its incidence revealed that the virus was absent in isolated areas far from commercial stone-fruit crops. Virus titers decrease significantly during the hot months in the infected trees but re-increase in October–November permitting reliable detection. It is virulent M-type isolates which are effectively transmitted by aphids that are mostly recovered. Aphis gossypii and Hyalopterus pruni were the most abundant virus vectors captured during the small scale monitoring undertaken in apricot orchards in 1999 and 2000. Virus spread was monitored in two apricot orchards from 1996 to 2000 and analysed. Initial infections followed a completely random spatial pattern, while loose clusters appeared in succeeding years, to finally reach a uniform distribution representing high infection levels. The nearby ecological conditions greatly affected the rate of disease development.     

History and importance of plum pox in stone-fruit production1

Plum pox potyvirus (PPV), which first appeared in Bulgaria in 1915, has spread to nearly every European country, and can today also be found in various eastern Mediterranean countries. The pest is of great economic importance especially in some southern and central European countries, causing considerable losses in production of primarily plum, apricot and peach. The extent of losses varies between countries of different climates, depending on cultivars and virus strains. In joint infections with other viruses, PPV provokes synergistic effects, enhancing the economic importance of the pest. Since PPV is transmitted by insects, spread of the virus can be reduced only by eradicating sources of infection and use of virusfree propagating material. Thus introduction of more reliable detection techniques is essential, facilitating mass testing of trees. Close collaboration in studying strain-related problems of PPV and in searching for resistant and tolerant cultivars is similarly important.     

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.     

桃李间作对桃树上节肢动物群落的影响

2006年和2007年,对桃李间作果园和单作桃园害虫和天敌进行了调查。通过对主要害虫山楂叶螨（Tetranychus viennensis Zacher）和梨小食心虫［Grapholitha molesta (Busck)］种群动态的比较分析,发现桃李间作可以增加桃树上山楂叶螨的种群数量;从空间分布的角度发现,当梨小食心虫密度高时桃李间作可以降低梨小食心虫的空间分布聚集程度。天敌功能团的典范对应分析表明桃李间作对天敌群落的影响是不稳定的。