Stepped‐up surveillance for early detection of Anoplophora chinensis in a nursery district

The Plant Protection Service of Lombardy Region (Italy) has been working to control Anoplophora chinensis for many years. A specific plan was developed by the Plant Protection Service in 2011 to implement stepped‐up surveillance for early detection of this pest in the most important nursery area in the region. The Canneto sull'Oglio district area hosts the highest concentration of commercial nurseries in Lombardy. The nurseries specialize in the cultivation of full‐size deciduous ornamental trees. The reinforced surveillance plan includes the following steps: planning, inspection of the urban green spaces, surveillance in rural areas and surveillance of identified sources of risk. A new procedure was defined for the enhanced territorial surveillance, as there were no established guidelines to follow. Two buffer zones were delineated, with a 2 km radius and a 500 m radius around all the areas dedicated to nursery cultivation, and a grid of 500 × 500 m was superimposed on it. Between one and four inspection points were defined for each cell, depending on the risk to plant health, and more than 3450 inspection points were identified, corresponding to 11 233 potential host plants that were to be inspected. In addition, the fields of 16 nurseries classified as high risk sources were inspected as well as the potential hosts in the buffer zone of 100 m radius around them. The annual cost of the surveillance is 30 000 EUR, which corresponds to about 0.025% of the annual production value of the nurseries in this district.     

Fireblight situation in Bulgaria and measures undertaken by the NPPO1

Fireblight disease, caused by Erwinia amylovora was first detected in Bulgaria on quince in the region of Plovdiv in 1989. The disease was initially localized in that area but, during 1995/1997, due to favourable climate conditions, it became epidemic. Infected trees were grubbed out and destroyed. The main hosts are quince and pear (over 40% of affected trees), then apple, medlar and Cotoneaster. Containment measures undertaken by the Bulgarian NPPO are laid down in the Plant Protection Law, in Phytosanitary Regulation no. 1 for phytosanitary control, and in Phytosanitary Regulation no. 5 of 1996 (amended 1997) for containment of fireblight. Phytosanitary control is mainly focused on fruit‐tree nurseries and on the distribution of healthy plants for planting. In 2003, 41 protected zones and 29 protected sectors within infested areas have been established.     

Regulatory measures against Erwinia amylovora in Switzerland*

Switzerland joined the list of fireblight‐affected European countries in 1989. Vigorous and systematic steps were taken to limit the impact of the disease on fruit production and amenity plants. These efforts are codified in a Swiss law detailing prevention, eradication, control measures and issues of compensation. As with many Swiss legal directives, there is a defined coordination of federal and cantonal responsibilities and, in the case of fireblight, there is also an emphasis at all levels on personal responsibility of owners of susceptible objects (e.g. nurseries, orchards, host plants). Extension activities have been a key component in achieving compliance with disease management regulations and in obtained public support for control efforts. Agroscope FAW Wädenswil has taken a leading role in this respect through its website http://www.feuerbrand.ch .     

Fireblight in the Po valley (Italy): the monitoring programmes of Emilia‐Romagna and Veneto regions1

Erwinia amylovora, causing fireblight, is a very important quarantine pest for Italy. Since the beginning of the 1980s, import of host plants from countries where the disease occurs has been limited and subjected to laboratory analyses. Fireblight was found for the first time in Puglia (southern Italy) in 1990. Following this finding, a national monitoring network was set up in order to find new cases as rapidly as possible. In 1994, the first outbreaks of fireblight were found in Emilia‐Romagna. In 1997, a severe epidemic spread throughout this region and the first cases were reported in the bordering regions Veneto and Lombardia. To face this new situation, additional specific local monitoring was set up. This article describes the operational and legislative measures taken in Emilia‐Romagna and Veneto to contain the disease in orchards, to allow marketing of healthy plants for planting and to regulate the movement of beehives.     

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.     

Plant protection problems caused by phytonematodes in Greece1

The major nematode pests of cultivated plants in Greece include root-knot nematodes Meloidogyne spp. (in almost all plants except citrus), cyst-forming nematodes Globodera rostochiensis, G. pallida (in potato), Heterodera avenae (in cereals), Ditylenchus dipsaci (in vegetables and ornamental plants) and Tylenchulus semipenetrans (in citrus). Based on observations made on samples examined at Benaki Phytopathological Institute, it was confirmed that serious infestation of new kiwi orchards with Meloidogyne spp. originated from seedlings infested at the nursery. Also the wide distribution of the nematode Tylenchulus semipenetrans in citrus orchards was mainly attributed to infested seedlings. The above observations led us, in 1985, to the decision to study the nematological fauna of nurseries in Greece.     

Spread of verticillium wilt by nursery plants in olive groves in the Halkidiki area (Greece)1

Olive groves have been established during the last decade in the coastal area of Halkidiki and in the northern part of the Kassandra peninsula (GR). Visual symptoms of verticillium wilt were observed recently all over this area, particularly in young trees of cv. Hondrolia Halkidikis but not in the occasional old trees already in the orchards. The symptoms appeared regardless of the previous crop (cotton or not), so the nurseries supplying the farmers with young trees were assumed to be the primary source of infection. A survey of olive nurseries in the area was conducted during 1991. Eleven out of the total 18 nurseries in the area were located in the Verticillium dahliae-infested zone and 9 of these were sampled. Three-year-old olive seedlings were selected and isolations were made from the xylem onto PDA acidified with 0.25% lactic acid. V. dahliae-infected seedlings were detected in 4 out of the 9 nurseries examined. The presence of infected young trees in nurseries covering 15.6% of the total nursery area provided strong evidence that nurseries may be responsible for the recent expansion of verticillium wilt in the area.     

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.     

Experiences with the control of fireblight in Norway during 1986/20031

Fireblight was detected for the first time in Norway in 1986, in a limited outbreak on ornamentals, in particular Cotoneaster. An organization for the eradication and containment of the disease was rapidly established, and given comprehensive statutory powers and resources to do surveys and to remove diseased plants and highly susceptible plants from infested areas. The activities have so far been successful. The disease has remained within a restricted area on the West Coast, and has not moved into important fruit‐growing areas or nurseries. Since 2000, fireblight has spread to some adjoining areas, mainly due to uncontrolled movement of beehives. New statutory powers prohibit movement of beehives out of infested areas from May to October.     

Fireblight Inoculum: Sources and Dissemination1

Understanding the disease cycle of fireblight requires knowledge of the sources of inoculum and means of dissemination. In regions where the disease is endemic, hold–over cankers are the most important source of primary inoculum. Dissemination of primary inoculum occurs by rain or by crawling or flying insects. Often, blossoms infested with Erwinia atnylovora (Burrill) Winslow et al. provide secondary inoculum that is disseminated by pollinating insects or by rain. Later in the growing season, secondary inoculum produced in infected tissues may be disseminated by rain or by sucking and biting insects. Relatively rare sources of inoculum and inefficient means of dissemination may be responsible for introducing the pathogen to areas where fireblight has not been found previously. E. amylovora may be carried to new locations in intimate association with host tissues (infected nursery stock), in association with vectors (insects, birds or man), or by wind as “strands” or in airborne water drops. Every effort should be made to prevent introduction of E. amylovora into areas now thought to be free of fireblight. Attempts to eradicate the disease from several new areas in northern Europe have been unsuccessful. Because weather conditions and the host plants present in southern Europe are especially conducive to severe damage from fireblight, plant protection personnel are advised to prepare now for the possible introduction of disease. Personnel should be trained to recognize the disease and plans should be drawn to contain it or to manage host plants to minimize disease losses.     

Traditional and commercial apple and pear cultivars as sources of resistance to fireblight1

In Hungary, fireblight research programmes were initiated on pear in 1999 and on apple in 2000, with the aim of evaluating the susceptibility or resistance of commercial cultivars. Sources of resistance for future breeding were also sought among traditional apple cultivars collected from Ukraine and pear cultivars in the Hungarian gene bank (Szigetcsép). Experiments were done under secure conditions. Inocula were mixtures of characteristic Erwinia amylovora isolates from pear and apple in Hungary. Host responses (symptom development, disease severity and multiplication rate of bacterial cells in host tissues) were assessed on shoots, flowers and fruits. About 30 pear and 30 apple cultivars, and 35 apple hybrids, were tested and grouped into four categories for pear and three for apple. Of the pear cultivars tested, 50% were susceptible, 30% moderately susceptible and only 10% of low susceptibility. Different plant organs occasionally displayed different responses. Members of the last two groups might serve as useful candidates for growing under IPM conditions. Among the traditional Hungarian varieties tested, we found high resistance in ‘Sikulai’ and ‘Szemes alma’, which could be used as sources of fireblight resistance in breeding programmes and also grown in organic orchards. Furthermore, among the offspring of the apple ‘Prima’ (scab‐resistant), we have found highly resistant lines.     

Relative significance of nursery infections and orchard inoculum in the development and spread of apple canker (Nectria galligena) in young orchards

Three nurseries produced apple rootstocks (M9) and budwood (cv. Royal Gala), which they exchanged at the end of the first year. Each nursery then budded its own budwood onto the rootstocks it had produced and that from the other two nurseries. Budded trees were grown on for a further year before being planted at HRI, East Malling in southern England; NIHPBS, Loughgall in Northern Ireland; and ADAS, Rosemaund in the West Midlands of England. Canker development was monitored twice a year. The position of the infected trees within the orchard was recorded, as was the position of the canker on each tree (main-stem or peripheral). Nectria galligena was isolated from representative cankers and analysed using molecular techniques. At the sites in Northern Ireland and HRI there was a strong positional effect, especially of peripheral cankers, indicating that most of the inoculum was external and had been spread from neighbouring orchards. There was little or no positional effect on main-stem cankers at any of the three sites. The proportions of different isolates taken from peripheral cankers was different in Northern Ireland from that in England, suggesting different populations associated with the geographic areas. In contrast, the populations of N. galligena obtained from main-stem cankers were very similar in England and Northern Ireland. It was concluded that a small proportion of trees developing canker were infected during propagation, with no symptom development until after planting. In a second trial it was demonstrated that trees infected during the propagation phase, and particularly at budding and heading back, could develop canker up to 3 years later. While it is clear that some canker developing in the orchard can be associated with the nursery of production, in climatic conditions conducive to the formation and dissemination of conidia, inoculum from surrounding infected orchards is the primary source of the pathogen. Aerial spread is therefore an essential element of the epidemiology of N. galligena, and its control is a crucial part of any canker-control programme.     

Fireblight in Békés County (Hungary) in 1996/20021

Fireblight (Erwinia amylovora) appeared in Hungary in 1996. Most damage occurred on apple, pear, quince and medlar, and also on the ornamentals Pyracantha, Sorbus, Cotoneaster and Crataegus. In 1996–2006, an official programme for elimination of infected parts of plants started in Békés county. This mainly concerned trees in towns and villages, since there are few pome‐fruit orchards in the county. Work teams under official direction pruned back or cut down trees. In total, some 13 000 trees were pruned back and nearly 11 000 were cut down. In addition, 21 villages were subjected to special phytosanitary measures. Infection decreased considerably between 1996 and 2002, but over 90% of the inhabited areas in the county remained subject to special measures, because of the very dispersed occurrence of fireblight.     

Inoculum sources of Botryosphaeriaceae species in New Zealand grapevine nurseries

This study investigated the sources of inoculum of Botyosphaeriaceae species in three commercial grapevine nurseries in New Zealand. Botryosphaeriaceae propagules were detected on the surfaces of 33 to 100?% of canes and 33?% of dead grapevine materials using microscopy, plating assays and PCR with Botryosphaeriaceae multi-species primers (Bot100F/Bot472R). Isolations also showed that 15 to 68?% of the canes were internally infected by Botryosphaeriaceae species, with Neofusicoccum luteum and N. parvum being the most predominant species. Incidence varied between nurseries, with Nursery 5 having highest N. luteum incidence (53?%) and Nursery 3 having highest N. parvum incidence (88?%). Botryosphaeriaceae DNA was detected in rain-water run-off from the mother-vine canopy, but not in soil samples collected around infected mother-vines. However, samples from the nursery propagation stages had no visible or viable Botryosphaeriaceae propagules although PCR using multi-species primers detected Botryosphaeriaceae DNA from wash and hydration tanks, on grafting tools and in callusing media from the different nurseries. The single-stranded conformational polymorphism (SSCP) was able to identify N. parvum, N. luteum and Diplodia mutila as the most common species present in the nursery system. Overall results indicated that the canes grown in mother-vine blocks were the most likely source of inoculum for infection of young grafted plants by Botryosphaeriaceae species.     

Effectiveness of preventing flowering of hawthorn in protecting pear orchards from fire blight infection

Since 1984 when a new Ministerial Regulation on fire blight came into force, there have been 20 protected regions in the Netherlands, where nurseries of rosaceous plants, and pear and apple orchards are extra protected against fire blight. This policy is also necessary to meet the requirements of the European Community (EC) on fire blight. Two of the measures in the protected regions are the prohibition of flowering of the native hawthorn (Crataegus monogyna andC. laevigata), and destruction of blighted plants. In the unprotected regions, flowering is allowed, and destruction of blighted plants is limited to a zone of 500 metres around orchards.For three years, the effectiveness of preventing flowering of hawthorn in protecting pear orchards against fire blight infection was studied in the field. Five test areas of about 3 km × 3 km were chosen with hawthorns and pear orchards. Two of these areas were in protected regions and three in unprotected regions. The more than 50 000 hawthorns in the areas were grouped into 1125 sites of hawthorn. The 126 orchards larger than 0.2 ha contained about 180 000 trees.During the three years light to moderate epidemics of fire blight were observed in the regions. Fire blight occurred in 2.3% of the non-flowering sites and 19.8% of the flowering (or fruiting) sites at least once in 1987, 1988 or 1989. The prohibition of flowering for hawthorn in protected areas was rather well implemented, so that in protected areas a smaller proportion of sites of hawthorns had fire blight (4.1%) than in unprotected areas (14%). Moreover, there were fewer sites per square kilometre in the protected areas (13) than in the unprotected areas (26).In protected areas, 53% and in unprotected areas 59% of the pear orchards had fire blight during 1987, 1988 or 1989. The difference was not significant. The first reason for the ineffectiveness of the preventing of flowering prevention in hawthorn to control fire blight in pear orchards was the inadequate hygiene of the pear orchards in both types of region. If it be assumed that a new focus is most probably initiated by the nearest existing focus, the second reason was that fire blight hardly spread from hawthorn to pear in the period of this study. Spread of fire blight within pear orchards and between pear orchards occurred frequently.     

Prevalence and distribution of Botryosphaeriaceae species in New Zealand grapevine nurseries

To determine presence of infection by botryosphaeriaceous fungi in plant materials from different grapevine nurseries, different types of grafted plants and cuttings were requested from nine grapevine nurseries around New Zealand. Of the 311 propagation materials and plants collected, 23?% were infected by botryosphaeriaceous fungi. The highest incidence was in failed grafted plants (33?%), followed by Grade 1 plants (28?%), rootstock cuttings (19?%), scion cuttings (17?%) and Grade 2 plants (7?%). For grafted plants, most isolates (80?%) were from near the graft unions while infections on rootstocks and scion cuttings were mostly from the middle (39?%) and basal parts (46?%). Identification of isolates by morphological and molecular methods showed that seven species were present in nurseries, being Neofusicoccum luteum (57?%), N. parvum (18?%), N. australe (8?%), Diplodia mutila (8?%), Botryosphaeria dothidea (5?%) and D. seriata (3?%), with one novel isolate of N. macroclavatum. These results show that Botryosphaeriaceae species were present in propagation materials and in the grafted plants supplied by nurseries, indicating that some of the current vineyard infections may have originated in the propagation nurseries.     

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.     

Molecular detection and quantification of Colletotrichum abscissum in sweet orange propagative material

Postbloom fruit drop disease (PFD) has caused serious impacts on citrus production in the Americas, occurring sporadically and suddenly during rain in the flowering period. In São Paulo State, Brazil, Colletotrichum abscissum is the causal agent responsible for over 80% of the disease incidence. Pathogen dispersal over long distances and the origin of primary inoculum are still unclear for PFD epidemics. We tested the hypothesis that citrus propagation material can harbour C. abscissum DNA by quantifying it in leaves of budwood increase block trees (BIB) and young citrus plants (YP) using multiplex quantitative PCR (qPCR). C. abscissum DNA was detected in all citrus nurseries, regardless of the type of propagative material, the sweet orange variety, or the nursery location. Overall, 73.4% of all samples from citrus nurseries have DNA from the pathogen, with a detection limit of 10 conidia. The average of 155 conidia found in YP was higher than the conidia observed on leaf samples from BIB (p = 0.03), although leaf samples from cultivars Valencia and Pera did not differ significantly, with means around 127 and 118 conidia, respectively (p = 0.75). This is the first molecular detection of C. abscissum in citrus propagative material. The multiplex qPCR assay may be used as a protocol for an accurate diagnosis of C. abscissum in citrus propagative material, may assist a better understanding of the pathogen dispersal over long distances, and may be used for further studies involving the quantification of C. abscissum in citrus orchards.     

Effectiveness of the resistance inducer prohexadione‐Ca against fireblight in shoots of apple trees inoculated with Erwinia amylovora1

Due to the lack of effective, non‐phytotoxic and publicly acceptable materials for controlling fireblight in pome fruit trees, novel strategies against Erwinia amylovora are being sought. Resistance‐inducing compounds, such as prohexadione‐Ca, represent promising alternatives. Prohexadione‐Ca is the active substance of the bioregulator Regalis, currently being introduced in several European countries and overseas. Prohexadione‐Ca reduces shoot elongation due to inhibition of gibberellin biosynthesis. Furthermore, it leads to significant changes in the spectrum of flavonoids and their phenolic precursors in pome fruits, which causes reduced susceptibility to fireblight and other pathogens. In 2002 and 2003, container‐grown apple trees of the cultivars ‘Idared’ and ‘Freedom’ were treated with different dosages of prohexadione‐Ca two weeks before inoculation with E. amylovora. The effect of prohexadione‐Ca against shoot blight was determined by measuring the lengths of necrotic lesions and symptoms on vascular bundles caused by the pathogen. Treatments with prohexadione‐Ca turned out to be much superior to the ones with streptomycin, kasugamycin and a bacterial antagonist, which were used for comparison. Acibenzolar‐S‐methyl (Bion), another resistance‐inducing compound, was included in some of the experiments and gave intermediate results. The simultaneous control of excessive shoot growth and shoot infections by fireblight is seen as a major advantage of using prohexadione‐Ca in pome fruit trees.