Bacterium Erwinia Amylovora Research Articles

Molecular Mechanisms of Pathogenesis and Resistance to the Bacterial Pathogen Erwinia amylovora, Causal Agent of Fire Blight Disease in Rosaceae

Fire blight, caused by the necrogenic Gram-negative bacterium Erwinia amylovora, is one of the most destructive bacterial diseases of apple (Malus × domestica) and pear (Pyrus communis), among other members of the Rosaceae family. This disease poses a major economic threat to pome production as there are no available effective control measures. Genetic enhancement of fire blight resistance in apples is the best alternative for averting disease damage, loss of crop, and loss of whole trees. In this review, current knowledge of the molecular mechanisms of E. amylovora pathogenesis will be presented, especially those of effector proteins during bacterial–host interactions, as well as assessment of current understanding of the molecular controls of plant host resistance. Recent studies are elucidating how type III effectors modulate plant susceptibility and promote growth and dissemination of the pathogen. The large multidomain protein DspE is essential for E. amylovora pathogenesis and plays an additional role(s) in inhibiting salicylic acid-mediated innate immunity. On the other hand, the apple host defends itself against E. amylovora invasion by relying on quantitative resistance genes that likely respond to and/or complex with E. amylovora effectors. Thus far, a total of 27 quantitative trait loci (QTL) linked to fire blight resistance have been identified in different apple genetic backgrounds and in response to different E. amylovora strains. In addition to quantitative genetic approaches, microarray analysis of E. amylovora-challenged apple genotypes identified differential transcriptional expression in susceptible and resistant apples. Mechanisms of bacterial pathogenicity and plant host resistance offer intriguing scenarios as to how effector proteins in E. amylovora interact with groups of genes for resistance in the apple host, particularly when considering that these quantitative genes have small effects in plant defense against the invading bacterial pathogen. This collective knowledge will provide insights into bacterial pathogenesis and plant host resistance, as well as highlight implications and opportunities for developing fire blight-resistant apple cultivars.

Evaluation of Susceptibility of Different Pear Hybrid Populations to Fire Blight (Erwinia amylovora)

Fire blight disease caused by pathogenic bacterium Erwinia amylovora, is the serious disease of pear, and there is not a certain chemical management against this disease except antibiotic-type compounds such as streptomycin. It is very important to improve new fire blight resistant cultivars in case of integrated disease management. With this purpose, different crosses have been made between Pyrus communis varieties that have good fruit characteristics and resistant cultigens. Besides, self and open pollination treatments have been carried out in maternal plants. The disease resistance level of the hybrids obtained from these combinations was determined by artificial inoculations by Erwinia amylovora in greenhouse conditions. A total of 3284 hybrids were inoculated, and 2631 of them survived and were distributed to different susceptibility classes. 19.88% of the inoculated hybrids was killed by Erwinia amylovora. Total distribution of the hybrids to susceptibility classes was as 6.18% in class “A- slightly susceptible”, 3.11% in class “B- less susceptible”, 8.89% in class “C- mid-susceptible”, 20.28% in class “D- susceptible”, and 61.54% in class “E- very susceptible”. Majority of class “A- slightly susceptible” hybrids were obtained from ‘Magness’ x ‘Ankara’ combination. ‘Kieffer’ x ‘Santa Maria’, ‘Kieffer’ open pollination, ‘Magness’ x ‘Akça’, ‘Magness’ x ‘Kieffer’, ‘Magness’ x ‘Santa Maria’, ‘Mustafa Bey’ x ‘Moonglow’ treatments displayed good results with respect to “A- slightly susceptible” character. It is very important to evaluate these hybrid pear populations through different fruit and tree characteristics in the future.

Fireblight (Erwinia amylovora) affects Mal d 1-related allergenicity in apple

Fireblight infection of apple and pear trees is a bacterial disease of serious economic concern. In this study, apple fruits (cultivar “Elstar”, “Topaz”) from healthy trees and trees naturally infected by the fireblight-causing bacterium Erwinia amylovora, as well as leaves from infected seedlings (cultivar “Golden Delicious”), were analysed for their Mal d 1 allergen concentrations. In addition, trees were treated with the two Aureobasidium pullulans biocontrol strains CF10 and CF40, active ingredients of Blossom Protect FB. Mal d 1, an 18 kDa intracellular protein is the major apple allergen in Northern and Central Europe and is a member of the family 10 of pathogenesis-related proteins, which is upregulated upon stress and pathogen attack. In young symptomless leaves from infected seedlings Mal d 1.01 transcript levels were significantly increased when compared to controls from healthy plantlets. Quantitative Mal d 1 transcript expression in field grown apple fruits did not show significant differences between samples from infected trees and controls. However, Mal d 1 protein content in apple fruits increased in fruits from infected trees. In fruits from trees with fireblight but treated with A. pullulans, Mal d 1 transcript and protein levels were reduced. These data show that an increase of Mal d 1-related allergenicity in fruits may result from fireblight infection. Thus, successful strategies against fireblight are needed to protect the orchards and simultaneously control the allergen content in fruits.

Optimization of PCR in application of hot start Taq DNA polymerase for detection of Erwinia amylovora with primers FER1-F and FER1-R1

There are two approaches in detection of bacterium Erwinia amylovora by PCR. One is based on detection of plasmid pEA29 and the other is based on detection of a chromosomal DNA sequence, specific for E. amylovora, in a sample. Since pathogenic strains without pEA29 have been isolated from the environment, methods based on this plasmid have been compromised and PCR methods based on chromosomal DNA species specific sequences became only reliable methods. PCR method with chromosomal primers FER1-F and FER1-R is currently the most reliable method due to its high sensitivity and specificity. The goal of this research is to make a significant improvement of the method by optimization of PCR in application of hot start DNA Taq polymerase, instead of wax, to obtain a hot start reaction. This enzyme, which is currently widely applied, can provide simpler achievement of hot start, saving labor and time and decreasing possibility of cross contamination of samples. Experiments showed that simple replacement of a regular recombinant Taq DNA polymerase by a hot start Taq DNA polymerase leads to complete failure of the reaction. Many optimization experiments had to be carried out to obtain an operational and reliable PCR which simultaneously has high sensitivity and specificity. Content of the reaction mixture, as well as temperature and time parameters of PCR, were significantly changed to achieve proper optimization.

Inland and foreign Erwinia amylovora isolates by carbohydrate utilization

Fire blight, a plant disease caused by the bacterium Erwinia amylovora, produces serious losses in apple and pear orchards all over the world. Since the appearance of fire blight in Hungary (Hevesi, 1996) Erwinia amylovora isolates were collected in different years, from different hosts and areas in order to establish gene bank for future epidemiological studies. We had isolates from foreign countries as well. The aim of our research was to compare all of the Hungarian and foreign isolates by carbohydrate utilization. In our experiments effect of carbohydrates on E. amylovora multiplication was determined using API 50 CH strip (bioMérieux, France). By the API 50 CH strip method we checked a number of unstudied carbohydrates. The results of the tests shows colour changes. Based on utilization of 49 carbohydrates of API 50 CH kit by E. amylovora isolates, two groups of carbohydrates can be defined: “Utilized” - and “Not utilized” carbohydrates. All isolates utilized 20 different carbohydrates after 164 hour incubation. Conversely, isolates also could be divided into four groups (1, 2, 3, 4) by arbutin and raffinose utilization. In group 1.-isolates utilize arbutin; 2.- utilize raffinose; 3.- utilize both arbutin and raffinose; 4. -utilize neither arbutin nor raffinose. Presumably carbohydrate content of nectar could play an important role on invasion of the (E. amylovora) bacterium via flower.It could be concluded that the carbohydrate utilization – completed with genetic analysis – can be used for characterization of Erwinia amylovora isolates.

Development and evaluation of a real-time PCR assay targeting chromosomal DNA of Erwinia amylovora

To develop and evaluate a new and reliable real-time PCR detection protocol on chromosomal DNA of the contagious plant pathogenic bacterium Erwinia amylovora, the causal agent of fire blight. A Taqman minor-groove-binder real-time PCR assay targeting a hypothetical protein coding gene of Erw. amylovora has been developed. Colony PCR of 113 bacterial strains from different taxa was performed to prove specificity. Serial decimal dilutions of Erw. amylovora showed a consistent detection sensitivity of 2 bacterial units per microl. All strains of Erw. amylovora could be identified, and there were no cross-reactions with matrices or other bacteria also testing naturally contaminated samples. Rapid, reliable and sensitive detection of Erw. amylovora is important to avoid the spread of the disease within orchards, and the distribution by contaminated plant material or vectors carrying the pathogen. The selected conserved target gene allows relative quantitative detection of Erw. amylovora from different sources and host taxa. The newly developed protocol also enables the detection of recently found natural strains that lack the species-specific plasmid pEA29, which was so far widely used as target for detection and identification of this plant pathogen by PCR. This study demonstrates that the newly developed and evaluated real-time assay can specifically be used for identifying all known strains of the EU quarantine plant pathogen Erw. amylovora. Low concentrations of the bacteria can be detected and relatively quantified using a different target area than other real-time PCRs designed so far.

Virulence Characteristics Accounting for Fire Blight Disease Severity in Apple Trees and Seedlings

The gram-negative bacterium Erwinia amylovora is the causal agent of fire blight, the most destructive bacterial disease of rosaceous plants, including apple and pear. Here, we compared the virulence levels of six E. amylovora strains (Ea273, CFBP1367, Ea581a, E2002a, E4001a, and HKN06P1) on apple trees and seedlings. The strains produced a range of disease severity, with HKN06P1 producing the greatest disease severity in every assay. We then compared virulence characteristic expression among the six strains, including growth rates in immature apple fruit, amylovoran production, levansucrase activity, biofilm formation, carbohydrate utilization, hypersensitive cell death elicitation in tobacco leaves, and protein secretion profiles. Multiple regression analysis indicated that three of the virulence characteristics (amylovoran production, biofilm formation, and growth in immature apple fruit) accounted for >70% of the variation in disease severity on apple seedlings. Furthermore, in greenhouse-grown 'Gala' trees, >75% of the variation in disease severity was accounted for by five of the virulence characteristics: amylovoran production, biofilm formation, growth in immature apple fruit, hypersensitive cell death elicitation, and sorbitol utilization. This study demonstrates that virulence factor expression levels account for differences in disease severity caused by wild isolates of E. amylovora on apple trees.

Erwinia amylovora-induced defense mechanisms of two apple species that differ in susceptibility to fire blight

The bacteria Erwinia amylovora, the causal agent of fire blight, infects most members of the Maloideae including pear and apple. In this work the defense responses against this pathogen were monitored in two apple species grown in vitro, in the susceptible Malus domestica Borkh. cv. ‘Idared’ (later on ‘Idared’) and the resistant Malus x robusta (Carrière) Rehder var. persicifolia Rehder ( Mrp). Our results indicate that the resistant plants might represent a less favorable environment for bacterial growth. At the same time, in these plants higher basic levels for some defense-related compounds such as salicylic acid or their activities such as the PAL enzyme activity can be found. In fire blight infected plants both the known pathways for SA synthesis as well as most of the phenylpropanoid genes examined were repressed due to disease, but apparently could be compensated by complex regulatory mechanisms. Not only the nature but also the quantity of defense-related compounds is likely to influence the outcome of plant–pathogen interactions.

Synthesis of amino acid conjugates to 2-imino-3-methylene-5-carboxypyrrolidine and 2-imino-3-methylene-6-carboxypiperidine

The four stereomers of 2-imino-3-methylene-5- l(carboxy- l-valyl)pyrrolidine, a bacterial metabolite that is inhibitory to the fire blight bacterium Erwinia amylovora, were synthesised and compared for antibacterial activity. Several alternative amino acid conjugates with l, l-stereochemistry were also prepared, and the synthesis was extended to 3-methylenepiperidine-6- l-carboxylic acid and a selection of 2-imino-3-methylenepiperidine-6- l-carboxy- l-amino acid conjugates. All synthetic amino acid conjugates ( l, l-stereomers) were inhibitory to the growth of E. amylovora. The likely participation of the conjugated iminomethylene moiety as a Michael acceptor is implicated.

Determination of application time for chemical control of fire blight disease in pear varieties

Fire blight, caused by the bacterium Erwinia amylovora, is a serious disease of pear, apple, and other plants of the Rosaceae family. In this study, from the point of view of continuousness of protection of fire blight disease and shoot growth in growing season, application times and effectiveness of host resistance inducers, harpin protein, benzothiadiazole, prohexadione-Ca as alternatives to conventional products, streptomycin, copper and maneb+copper were evaluated on susceptible pear varieties in greenhouse and field conditions. Type 1 and Type 2 applications for prevention of the disease and Type 3 and Type 4 applications for evaluation of shoot growth were performed. Type 2 application of harpin protein gave remarkable effectiveness on prevention of the disease about 49% and 65% in greenhouse and field, respectively. After Type 1 and 2 applications by prohexadione-Ca and benzothiadiazole, disease severity significantly decreased comparing to applications of copper and maneb+copper and, controls. Only prohexadione-Ca applications significantly reduced shoot lengths and plants were highly affected by the application Type 4 of this chemical. According to findings, applications of Type 2 provided better results than Type 1 on all of pear varieties in greenhouse and field conditions and use of resistance inducing substances during the production season is proposed in managing of shoot blight phase of fire blight disease.

Transgenic apple plants overexpressing the Lc gene of maize show an altered growth habit and increased resistance to apple scab and fire blight

Transgenic apple plants (Malus x domestica cv. 'Holsteiner Cox') overexpressing the Leaf Colour (Lc) gene from maize (Zea mays) exhibit strongly increased production of anthocyanins and flavan-3-ols (catechins, proanthocyanidins). Greenhouse plants investigated in this study exhibit altered phenotypes with regard to growth habit and resistance traits. Lc-transgenic plants show reduced size, transversal gravitropism of lateral shoots, reduced trichome development, and frequently reduced shoot diameter and abnormal leaf development with fused leaves. Such phenotypes seem to be in accordance with a direct or an indirect effect on polar-auxin-transport in the transgenic plants. Furthermore, leaves often develop necrotic lesions resembling hypersensitive response lesions. In tests, higher resistance against fire blight (caused by the bacterium Erwinia amylovora) and against scab (caused by the fungus Venturia inaequalis) is observed. These phenotypes are discussed with respect to the underlying altered physiology of the Lc-transgenic plants. The results are expected to be considered in apple breeding strategies.

An assessment of the relative resistance of three hawthorn species to three strains of Erwinia amylovora using three different inoculation methods

Fire blight is an important disease of hawthorn plants. In this study, the level of susceptibility of three hawthorn species (Crataegus monogyna, Crataegus laevigata, Crataegus persimilis) to the bacterium Erwinia amylovora was investigated. The results showed that all species were highly susceptible to this pathogen. In addition, the relative virulence of three different E. amylovora strains on the above species was examined. Variability among the strains was found, with strain 3 being the most virulent and strain 1 the least.

Evaluation of a Cider Apple Germplasm Collection of Local Cultivars from Spain for Resistance to Fire Blight (Erwinia amylovora) Using a Combination of Inoculation Assays on Leaves and Shoots

Fire blight, caused by the bacterium Erwinia amylovora, is among the three most important diseases of apple. A major effective method for its integrated management is the reduction of the susceptibility of the host. Cider apple production in Spain is based on local apple cultivars with minimum crop management and phytosanitary control. After the entry of fire blight in Spain, the selection and planting of cultivars with low susceptibility to this disease has thus become of paramount importance. In consequence, and as part of a wider characterization effort, we undertook the evaluation of an apple germplasm collection of local apple cultivars from Spain for susceptibility to fire blight. Because of the quarantine status of E. amylovora in Europe, we evaluated the use of a detached leaf inoculation assay in combination with a traditional shoot inoculation assay to reduce the amount of plant material to evaluate and to minimize pathogen manipulation. Comparison of the susceptibility values for 78 apple cultivars indicated a low but significant correlation (r = 0.56; α = 0.01) between the leaf and shoot inoculation methods. Although the detached leaf assay was not reliable for the direct selection of cultivars with low susceptibility, it was useful to optimize resources and limit the potential dispersal of the pathogen by allowing the exclusion of medium and highly susceptible cultivars from further evaluation. Shoot inoculation of 103 apple cultivars allowed the identification of 48 cultivars with high levels of resistance to fire blight, which could serve as starting material both for apple production and for breeding programs.

CHARACTERIZATION OF TRANSGENIC APPLES EXPRESSING THE HrpN GENE

Fire blight is the major bacterial disease of Maloideae caused by the necrogenic bacterium Erwinia amylovora, which pathogenicity requires a functional type III protein secretion system (TTSS). The protein harpin N Ea is secreted through the TTSS and targeted to the intercellular spaces of plant tissues where it acts as an elicitor of plant defense reactions. In order to create novel mechanisms for fire blight resistance in apple, we have generated transgenic apples expressing the hrpN gene from E. amylovora under the control of the constitutive CaMV35S or the pathogen-inducible tobacco Str246C promoters, with or without the tobacco PRI gene secretion signal peptide. The characterization of these harpin N Ea transgenic apples was carried out by: (1) quantification of the constitutive and induced expression of the transgene (by Q-RT-PCR); (2) in planta localization of the harpin N Ea protein; (3) evaluation of fire blight resistance after greenhouse inoculation; (4) targeted transcriptomic analysis to identify defenses induced by the presence of the transgene.

Isolation and activity ofXenorhabdusantimicrobial compounds against the plant pathogensErwinia amylovoraandPhytophthora nicotianae

Broad-spectrum antibiotics produced by symbiotic bacteria [entomopathogenic bacterium (EPB)] of entomopathogenic nematodes keep monoxenic conditions in insect cadavers in soil. This study evaluated antibiotics produced by EPB for their potential to control plant pathogenic bacteria and oomycetes. Entomopathogenic bacterium produce antibiotics effective against the fire blight bacterium Erwinia amylovora, including streptomycin resistant strains, and were as effective in phytotron experiments as kasugamycin or streptomycin. Xenorhabdus budapestensis and X. szentirmaii antibiotics inhibited colony formation and mycelial growth of Phytophthora nicotianae. From X. budapestensis, an arginine-rich fraction (bicornutin) was adsorbed by Amberlite((R)) XAD 1180, and eluted with methanol : 1 n HCI (99 : 1). Bicornutin inactivated zoospores, and inhibited germination and colony formation of cystospores at <<25 ppm. An UV-active molecule (bicornutin-A, MW = 826), separated by HPLC and thin-layer chromatography, was identified as a novel hexa-peptide : RLRRRX. Xenorhabdus budapestensis produces metabolites with strong antibacterial and cytotoxic activity. Individual compounds can be isolated, identified and patented, but their full antimicrobial potential may be multiplied by synergic interactions. Active compounds of two new Xenorhabdus species might control plant diseases caused by pathogens of great importance to agriculture such as Erw. amylovora and P. nicotianae.

Two distinct major QTL for resistance to fire blight co-localize on linkage group 12 in apple genotypes ‘Evereste’ andMalus floribundaclone 821

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most destructive diseases of apple (Malus xdomestica) worldwide. No major, qualitative gene for resistance to this disease has been identified so far in apple. A quantitative trait locus (QTL) analysis was performed in two F1 progenies derived from two controled crosses: one between the susceptible rootstock cultivar 'MM106' and the resistant ornamental cultivar 'Evereste' and the other one between the moderately susceptible cultivar 'Golden Delicious' and the wild apple Malus floribunda clone 821, with unknown level of fire blight resistance. Both progenies were inoculated in the greenhouse with the same reference strain of E. amylovora. The length of stem necrosis was scored 7 and 14 days after inoculation. A strong QTL effect was identified in both 'Evereste' and M. floribunda 821 at a similar position on the distal region of linkage group 12 of the apple genome. From 50% to 70% of the phenotypic variation was explained by the QTL in 'Evereste' progeny according to the scored trait. More than 40% of the phenotypic variation was explained by the M. floribunda QTL in the second progeny. It was shown that 'Evereste' and M. floribunda 821 carried distinct QTL alleles at that genomic position. A small additional QTL was identified in 'Evereste' on linkage group 15, which explained about 6% of the phenotypic variation. Although it was not possible to confirm whether or not 'Evereste' and M. floribunda QTL belonged to the same locus or two distinct closely related loci, these QTL can be valuable targets in marker-assisted selection to obtain fire blight resistant apple cultivars and form a starting point for discovering the function of the genes controlling apple fire blight resistance.

Hypersensitive response and acyl-homoserine lactone production of the fire blight antagonists Erwinia tasmaniensis and Erwinia billingiae.

SummaryFire blight caused by the Gram‐negative bacterium Erwinia amylovora can be controlled by antagonistic microorganisms. We characterized epiphytic bacteria isolated from healthy apple and pear trees in Australia, named Erwinia tasmaniensis, and the epiphytic bacterium Erwinia billingiae from England for physiological properties, interaction with plants and interference with growth of E. amylovora. They reduced symptom formation by the fire blight pathogen on immature pears and the colonization of apple flowers. In contrast to E. billingiae, E. tasmaniensis strains induced a hypersensitive response in tobacco leaves and synthesized levan in the presence of sucrose. With consensus primers deduced from lsc as well as hrpL, hrcC and hrcR of the hrp region of E. amylovora and of related bacteria, these genes were successfully amplified from E. tasmaniensis DNA and alignment of the encoded proteins to other Erwinia species supported a role for environmental fitness of the epiphytic bacterium. Unlike E. tasmaniensis, the epiphytic bacterium E. billingiae produced an acyl‐homoserine lactone for bacterial cell‐to‐cell communication. Their competition with the growth of E. amylovora may be involved in controlling fire blight.

Rapid transcriptional response of apple to fire blight disease revealed by cDNA suppression subtractive hybridization analysis

Fire blight, caused by the bacterium Erwinia amylovora, is a destructive disease of many tree and shrub species of the Rosaceae. Suppression subtractive cDNA hybridization (SSH) was used to identify genes that are differentially up- and down-regulated in apple (Malus x domestica) in response to challenge with E. amylovora. cDNA libraries were constructed from E. amylovora- and mock-challenged apple leaf tissue at various time intervals after challenge treatment, ranging from 0.25 to 72 h post-inoculation (hpi), and utilized in SSH. Gel electrophoresis of PCR-amplified SSH cDNAs indicated a greater quantity and size diversity in the down-regulated EST population at early times after challenge (1 and 2 hpi) compared to early up-regulated sequences and to sequences down-regulated at later (24 and 48 hpi) times after challenge. A total of 468 non-redundant Malus ESTs isolated by SSH in response to E. amylovora challenge were characterized by bioinformatic analysis. Many of ESTs identified following E. amylovora challenge of apple were similar to genes previously reported to respond to bacterial challenge in Arabidopsis thaliana. The results indicate that there was a substantial early (1 and 2 hpi) transcriptional response in apple to fire blight disease involving both the down- and up-regulation of host genes. Additionally, genes identified responding to fire blight challenge early (1 and 2 hpi) differed from those identified later (25, 48, and 72 hpi) in the infection process.

Isolation of Streptomycin-Resistant Isolates of Erwinia amylovora in New York.

Streptomycin is currently the only antibiotic registered for the control of fire blight, a devastating disease of apple (Malus), pear (Pyrus), and other rosaceous plants caused by the bacterium Erwinia amylovora. Resistance of E. amylovora to streptomycin was first identified in California pear orchards in 1971 and is currently endemic in many parts of the United States. The Northeast remains the only major U.S. apple-growing region without streptomycin-resistant isolates of E. amylovora. In 2002, during a routine survey for streptomycin resistance, isolates from two neighboring orchards in Wayne County, NY were found to be highly resistant to streptomycin at a concentration of 100 μg/ml. This constitutes the first authenticated report of streptomycin resistance in New York State. Infected trees were shipped at the same time from a single nursery in Michigan. Resistance was caused by the acquisition of the strA-strB gene pair, inserted into the ubiquitous nontransmissible E. amylovora plasmid pEA29. Previously, streptomycin-resistant E. amylovora populations from Michigan were described with a similar mechanism of resistance, although the strA-strB genes are not unique to Michigan. These findings illustrate how unintentional movement of nursery material could undermine efforts to prevent the spread of antibiotic-resistant E. amylovora.

The Differences among Pear Genotypes to Fire Blight (Erwinia amylovora) Attack, Based on Observations of Natural Infection

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most damaging diseases of pear in the world. In Cluj-Napoca area, situated in central Transylvania, Romania, fire blight was observed first in 1994, very late comparative with the other countries from occidental Europe. The response of the pear cultivars and species from National Pear Collection from Cluj-Napoca to fire blight attack, assessed in natural conditions of infection, range on a large scale of variability, which denotes a strong influence of the genotype in expression of resistance or sensitivity to disease. From all genotypes, about 20.5% have not presented symptoms of attack, among them being the following: 'Blanquet precoce', 'Klementinka', 'Severianka', 'Beurre Bachelier', 'Kieffer Seedling', 'Er Shi Shinge', 'Beurre Amanlis', 'Bristol Cross', 'Beurre Liegel', 'Beurre Lucon', 'Grand Champion', 'Magness', 'Mericourt' etc. and several ancient autochthonous cultivars ('Pere malaiete', 'De zahar de Bihor', 'Cu miez rosu', 'Clopotele', 'Garoafa mare', 'Craiese', 'Para de apa'). Also, there were identified several species of Pyrus with no attack, as P. pollveria, P. common pear, P. lindlezi, P. malifolia, P. persica, P. ussuriensis, P. variolosa. The remarked genotypes could be potential sources for further breeding programmes and increase the number of genotypes available for breeding new pear cultivars resistant to Erwinia attack.