首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 0 毫秒
1.
Prohexadione‐Ca is primarily used for the control of shoot growth in pome and other fruit trees. During its development, treated apple and pear trees were found to be significantly less affected by fireblight (Erwinia amylovora) and other pathogens, although prohexadione‐Ca is inactive as a bactericide or fungicide. Prohexadione is a structural mimic of 2‐oxoglutaric acid, and the distinct dioxygenases involved in gibberellin biosynthesis that require this compound as a cosubstrate are blocked. As a result, less growth‐active gibberellins are formed and treated plants remain compact. 2‐Oxoglutaric acid‐dependent dioxygenases are also involved in flavonoid metabolism. In shoots of apples and pears, prohexadione‐Ca causes considerable changes in the formation of flavonoids and their phenolic precursors by inhibiting flavanone 3‐hydroxylase. Convincing evidence is available that prohexadione‐Ca triggers pathogen resistance primarily by inducing the formation of 3‐deoxyflavonoids, in particular luteoforol, with phytoalexin‐like properties. Morphoregulatory effects caused by prohexadione‐Ca are only of secondary relevance. 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.  相似文献   

2.
M. Keck 《EPPO Bulletin》2004,34(3):347-349
In 1993, fireblight (Erwinia amylovora) was detected for the first time in Austria, in the most westerly part of the country (Vorarlberg). During the following years, especially since 1998, a stepwise migration from west to east was observed. For control, mechanical measures are mostly used. As these measures require early recognition of symptoms, broad information campaigns for the public and extensive surveys of host plants have been set up. Suspicious plant samples are sent to the central laboratory for diagnosis. Regional plant protection services are assisted by trained volunteers. Eradication and pruning measures are performed by trained working teams. Infected plant material is burned. In all pome‐fruit production areas, the disease forecasting system Maryblyt has been established. Regulations concerning the movement of beehives have been adopted, together with prohibition of the planting of certain ornamental host plants (Crataegus, Cotoneaster). Chemical treatments are limited to one copper oxychloride product. In 2003, temporary application of Prohexadione‐Ca for the prevention of shoot infections was authorized. In some areas, the rigorous application of control measures has reduced the incidence of fireblight and possibly slowed down its progress. However these measures are not sufficient to protect against new, unexpected outbreaks.  相似文献   

3.
M. Zsolt 《EPPO Bulletin》2004,34(3):391-394
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.  相似文献   

4.
Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other diseases in pome fruit trees and other crop plants. In addition to acting as a growth regulator, prohexadione-calcium interferes with flavonoid metabolism and induces the accumulation of the 3-deoxycatechin luteoliflavan in shoots of pome fruit trees. Luteoliflavan does not possess any remarkable antimicrobial activity. Therefore luteoforol, its unstable and highly reactive precursor, has been tested in vitro for its bactericidal and fungicidal activities. Luteoforol was found to be highly active against different strains of Erwinia amylovora, the causal agent of fire blight, and all other bacterial and fungal organisms tested. Phytotoxic effects were also observed in pear plantlets. The results obtained indicate that prohexadione-calcium induces luteoforol as an active principle with non-specific biocidal properties. It is proposed that luteoforol is released upon pathogen attack from its cellular compartment and inhibits further disease development by destroying pathogen cells as well as by inducing a hypersensitive-like reaction in the host plant tissue. This mechanism would be closely analogous to the one known for structurally related phytoalexins in sorghum.  相似文献   

5.
The Gram‐negative bacterium Erwinia amylovora, causal agent of fire blight disease in pome fruit trees, encodes a type three secretion system (T3SS) that translocates effector proteins into plant cells that collectively function to suppress host defences and enable pathogenesis. Until now, there has only been limited knowledge about the interaction of effector proteins and host resistance presented in several wild Malus species. This study tested disease responses in several Malus wild species with a set of effector deletion mutant strains and several highly virulent E. amylovora strains, which are assumed to influence the host resistance response of fire blight‐resistant Malus species. The findings confirm earlier studies that deletion of the T3SS abolished virulence of the pathogen. Furthermore, a new gene‐for‐gene relationship was established between the effector protein Eop1 and the fire blight resistant ornamental apple cultivar Evereste and the wild species Malus floribunda 821. The results presented here provide new insights into the host–pathogen interactions between Malus sp. and E. amylovora.  相似文献   

6.
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.  相似文献   

7.
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.  相似文献   

8.
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.  相似文献   

9.
Fire blight is the most damaging bacterial disease in apple production worldwide. Cankers and symptomless infected shoots are known as sites for the overwintering of Erwinia amylovora, subsequently providing primary inoculum for infection in the spring. In the present work, further potential sources of inoculum were investigated. Real‐time PCR assays covering a 3‐year‐period classified 19·9% of samples taken from fruit mummies as positive. Bacterial abundance in fruit mummies during autumn, winter and spring was up to 109 cells per gram of tissue and correlated well with later infection rates of blossoms. Blossoms of non‐host plants growing close to infected trees were also shown to be colonized by E. amylovora and to enable epiphytic survival and propagation of bacteria. The results indicate a potential role of fruit mummies and buds in overwintering and as a source of primary inoculum for dissemination of the pathogen early in the growing season. Non‐host blossoms may also serve as an inoculum source in the build‐up of the pathogen population. Both aspects may contribute significantly to the epidemiology of E. amylovora. The significance of infected rootstocks as an inoculum source is also discussed. Fruit mummies might be used to determine pathogen pressure in an orchard before the beginning of the blooming period.  相似文献   

10.
Symptoms of shoot proliferation characteristic of phytoplasma diseases were observed on nectarine (Prunus persica var. nucipersica) and peach (P. persica) trees in the Sarada plain, south of Lebanon. The presence of phytoplasmas in the two orchards visited was confirmed by nested polymerase chain reaction using universal primers. The amplified DNA fragments were cloned and sequenced. Blast analysis of over 1000 nucleotides demonstrated the presence of ‘Candidatus Phytoplasma phoenicium’ which is considered to be the causal agent of Almond witches’ broom. This phytoplasma which belongs to the pigeon pea witches’ broom group (16SrIX) can be devastating since Almond witches’ broom has killed thousands of almond trees in Lebanon and Iran. Previous reports indicated that Almond witches’ broom may be transmitted by grafting to peach and nectarine under experimental conditions. This is the first report of a natural and epidemic spread of ‘Ca. Phytoplasma phoenicium’ in peach and nectarine. Farmers in the region were advised to eradicate the infected trees immediately. Further studies on the epidemiology of ‘Ca. Phytoplasma phoenicium’ and its vector(s) are recommended in order to develop successful eradication or disease management programmes.  相似文献   

11.
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.  相似文献   

12.
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.  相似文献   

13.
O. Vahala 《EPPO Bulletin》2004,34(3):339-341
Inspectors of the Czech NPPO surveyed the occurrence of fireblight Erwinia amylovora in an area of Jihomoravsky region (South Moravia) proposed as an EU protected zone, including 16 designated buffer zones around nurseries. The disease was not detected in communes where fireblight hosts are grown (nurseries, variety testing stations, orchards) or in buffer zones around nurseries. In 902 communes where fireblight hosts are grown only in orchards or not at all, wild host plants were inspected at 2.629 observation points (2137 located by GARMIN GPS). In Vy?kov district, suspected fireblight was confirmed at one observation point on Crataegus, growing by a railway in Rousínov commune and, in the course of a delimiting survey outside observation points, in four other communes (Drnovice, Habrovany, Komo?any and Vy?kov).  相似文献   

14.
Erwinia amylovora has been spreading in the Czech Republic since 1986 regardless of emergency phytosanitary measures which have been taken. Its spread follows the predominant wind direction (west to east). The infested area now covers two thirds of the area of the country. Wild Crataegus spp. are the most important and widespread host plants. E. amylovora is still regulated as a quarantine pest, and areas free from fireblight are subject to special phytosanitary measures.  相似文献   

15.
Resistance in apple is evaluated by needle–inoculation of succulent shoot tips with 106–107 cells of a virulent isolate of Erwinia amylovora (Burr.) Winslow et al. (the incitant of fireblight) and measurement of the resulting cortical lesion when extension is complete. Data are now available on practically all commercial cultivars, some of which have a useful level of resistance. Some newer cultivars, particularly those with resistance to scab (Venluria inaequalis [Cooke] Wint.) derived from Malus floribunda, have good resistance to E. amylovora. A very high level of resistance is present in Asiatic Malus species, including M. x robusta, M. x sublo–bata, M. x atrosanguinea, and M. prunifolia, and in the North American species M. fusca. This type of resistance appears to be inherited polygenically, and because of its detectability in young seedlings can be used conveniently in breeding. Objectives of pear breeding programs are aimed at developing superior fruit quality combined with resistance to fireblight, psylla, and Fabraea leaf spot. Many high quality cultivars of Pyrus communis are extremely susceptible to E. amylovora and sensitivity appears to be controlled by a dominant gene Se. A high level of resistance is present in P. ussuriensis but varies considerably between clonal selections of other Pyrus species. Pear seedlings from controlled pollinations are artificially inoculated in the glasshouse with a similar bacterial suspension as used for apples, and only the most resistant ones are selected and planted in the field for future evaluation. In Beltsville, heritability studies of crosses between non–sensitive parents have indicated that selection for resistance within progenies results in a high degree of genetic gain. Interspecific hybridization has an advantage over P. communis crosses mainly when insect or fungus resistance is required.  相似文献   

16.
Invasion of apple fruit by Erwinia amylovora from fruit-bearing twigs through the abscission layer at fruit maturation was examined. Erwinia amylovora (ca. 105 cfu) tagged with bioluminescence genes from Vibrio fischeri was deposited in artificial wounds on fruit-bearing twigs of apple trees grown in a containment greenhouse on September 22, 27, or October 5, 2004. On October 22, 176 apples were harvested and cut horizontally in half. The upper halves were stamped on plates of selective medium, and the lower halves were flooded with iodine solution to assess maturity. All fruit were symptomless and fully mature. The pathogen was recovered from 19 (10.8%) apples. The result showed that if at least ca. 105 cfu of E. amylovora are present in fruit-bearing twigs at the time of fruit maturation, the bacteria can pass through the abscission layer into the fruit, even though the mature fruit lack symptoms.  相似文献   

17.
Fire blight caused by the gram-negative bacterium Erwinia amylovora is a major disease of pome fruit like apple (Malus domestica) or pear (Pyrus communis). Detection of the pathogen is hampered by low titres usually being present during initial flower infection and the brief time frame for analysis to decide upon subsequent countermeasures. Here we describe a loop-mediated isothermal amplification of DNA (LAMP) assay for genomic DNA of Erwinia amylovora, which relies on a highly specific primer design that excludes amplification from typical DNA sources of the orchard biological system and from sample handling. The assay enables the fast detection of down to approximately 20?cfu of pure Erwinia amylovora or 100?fg genomic DNA (corresponding to approximately 25 E. amyolovora equivalents) per reaction within 45?min. Fast and reliable detection of E. amylovora in orchard samples by naked eye is achieved through a visual colour change indication with hydroxynaphthol blue. The assay avoids use of complex technical devices and is thus suitable for field testing.  相似文献   

18.
Two surveys (2005/2006 and 2009) were conducted in the state of São Paulo, Brazil, to investigate the incidence of ‘Candidatus Liberibacter asiaticus’ and ‘Ca. L. americanus’, two liberibacters associated with citrus huanglongbing (HLB) disease and both transmitted by Diaphorina citri, in orange jasmine (Murraya exotica), a widespread ornamental tree in cities and villages. The graft‐transmissibility of the two species, and their DNA relatedness to citrus‐associated liberibacters, were also investigated. Quantitative PCR was applied to PCR‐positive orange jasmine and HLB‐positive citrus growing in backyards and orchards to assess their inoculum source potentials. Liberibacters were detected in 91 of 786 sampled orange jasmine plants in 10 of 76 sampled locations. PCR‐positive trees exhibited yellow shoots and/or dieback symptoms indistinguishable from those on PCR‐negative trees. ‘Candidatus Liberibacter americanus’ was more common in 2005/2006 (96·6%) and ‘Ca. L. asiaticus’ in 2009 (84·8%). rplJ nucleotide sequences were identical within all populations of either species. Graft transmission succeeded only in homologous host combinations, including ‘Ca. L. americanus’ (2/10) from/to orange jasmine and ‘Ca. L. americanus’ (5/18) and ‘Ca. L. asiaticus’ (5/9) from/to citrus. Symptoms were mild and developed less rapidly in orange jasmine than in citrus, probably as a result of lower liberibacter multiplication rates. Respective titres of ‘Ca. L. americanus’ and ‘Ca. L. asiaticus’ in orange jasmine averaged 4·3 and 3·0 log cells g?1 tissue, compared with 5·5 and 7·3 in citrus. The results indicate that orange jasmine does not favour liberibacter multiplication as much as citrus. However, its importance in HLB epidemics should not be underestimated as it is a preferred host of D. citri and is not under any strict tree‐eradication programme or measures for insect control.  相似文献   

19.
The infection frequency of mature apple fruit by Erwinia amylovora and the survival of E. amylovora in the fruit stored at low temperature were investigated. The fruit stems (pedicels) of 460 mature apple fruit were inoculated with 105 or 104 cfu of bioluminescent E. amylovora, tagged with lux genes. Nine days after inoculation, 43% and 27% of the fruit inoculated with 105 and 104 cfu, respectively, were infected. All infected fruit looked healthy. After 6 months of storage at 5°C, almost all of the 142 infected fruit had viable E. amylovora. Of the fruit containing E. amylovora internally, 19.5% had latent infections and the rest had blight symptoms. E. amylovora was not uniformly distributed in the fruit flesh, and internal brown lesions were observed where E. amylovora was densely distributed. These findings showed that mature apple fruit may be infected with E. amylovora, especially as latent infections, and act as a source for long-range dissemination.  相似文献   

20.
An important issue related to the epidemiology of fire blight, a devastating disease of apples and pears, is how its causal agent, the bacterium Erwinia amylovora, survives and disseminates in the environment. Almost no information is available on the possibility of this pathogen overwintering as a necrotroph. In this study, bacterial survival in dead apple and tobacco (a non‐host) leaf tissues was addressed. In necrotized leaves collected 5, 6, 7 and 8 months following shoot inoculation of apple trees, viable E. amylovora cells were present in over 50% of samples from the midrib and in over 10% of samples from lateral veins, but were never found in parenchyma. Using a PCR‐based method, pathogen DNA was detected in more than 50% of samples that were found to be free of viable cells by conventional plating out. However, PCR analysis was insufficient to distinguish between the DNA of viable and dead bacteria. Sugars appropriate for bacterial growth were found in dead apple leaves. In spot‐inoculated attached apple and tobacco leaves, a remarkable increase in the bacterial population was observed in lesions that developed as a hypersensitive response (HR). As in other necrotrophic interactions, bacterial proliferation was associated with massive hydrogen peroxide production and progression toward plant cell death. The results indicate that E. amylovora has an ability to survive as a semi‐necrotroph or necrotroph, which allows for overwintering in dead apple leaves.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号