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1.
Pseudomonas syringae pv. actinidiae (Psa) was identified as the causal agent of severe epidemics of bacterial canker on Actinidia chinensis (yellow kiwifruit) in central Italy occurring during 2008–9. A total of 101 strains were obtained from infected leaves, twigs, branches and trunks of cvs Hort16A, Jin Tao and CK3. Outbreaks were also found on A. deliciosa cv. Hayward. A representative set of 21 strains were compared with other Psa strains isolated from previous outbreaks in Japan and Italy as well as with P. s. pv. syringae strains obtained from A. chinensis and with strains of genomospecies 8. Repetitive‐sequence PCR (rep‐PCR) typing using BOX and ERIC primer sets revealed that all Psa strains obtained during 2008–9 showed the same fingerprinting profile. This profile, however, was different from those of strains previously isolated in Japan and Italy. Multilocus sequence typing (MLST) of gapA, gltA, gyrB and rpoD revealed a higher genetic variability among the strains than rep‐PCR, with some of them showing the same sequence pattern although isolated from different areas, cultivars and years. None of the recently obtained strains possessed genes coding for phaseolotoxin or coronatine, and all had an effector protein, namely hopA1, differentiating them from the strains causing past outbreaks in Japan and Italy. All isolates were inhibited in vitro by copper‐based compounds, antibiotics, geraniol, citronellol and by a chitin‐based organic compound. The recent epidemics found in central Italy on yellow kiwifruit appear to have been caused by a different Psa population than those previously recorded in Japan, South Korea and Italy.  相似文献   

2.
Pseudomonas syringae pv. aptata is the causal agent of bacterial leaf spot disease of sugar beet (Beta vulgaris). During 2013, 250 samples were collected from leaf lesions with typical symptoms of bacterial leaf spot in commercial fields of sugar beet in Serbia, and 104 isolates of P. syringae pv. aptata were obtained. Identification and characterization was performed using biochemical, molecular and pathogenicity tests. Identification included LOPAT tests and positive reactions using primers Papt2F and Papt1R specific for P. syringae pv. aptata. Repetitive (rep) sequence‐based PCR typing with ERIC, REP and BOX primers revealed high genetic variability among isolates and distinguished 25 groups of different fingerprinting profiles. Pulse‐field gel electrophoresis (PFGE) and multilocus sequence analysis (MLSA) of representative isolates showed higher genetic variability than in rep‐PCR analysis and distinguished three and four major genetic clusters, respectively. A pathogenicity test performed with 25 representative isolates on four cultivars of sugar beet confirmed the occurrence of leaf spot disease and showed correlation between the most aggressive isolates and the genetic clusters obtained in MLSA. All these findings point to the existence of several lines of P. syringae pv. aptata infection in Serbia that are genetically and pathologically different.  相似文献   

3.
Citrus blast and black pit caused by Pseudomonas syringae pv. syringae (Pss) is the only bacterial disease reported in Tunisian Citrus orchards. The phylogenetic relationship between Pss strains was studied based on multilocus sequence analysis (MLSA), using partial sequences of housekeeping genes rpoD, rpoB, gyrB, cts, and pfk for 14 representative Pss Citrus strains, including the reference strain LMG5496. The MLSA revealed that the studied Tunisian Citrus strains are closely related to LMG5496 and cluster in phylogroup 02. Based on the cts gene, the majority of Citrus strains clustered in clades “a” and “b”. However, five strains were placed in a newly defined clade “g”. We describe the presence of six different type III secreted effectors (T3SEs). These were found with frequencies of 100% for the effector hopAN1 and the helper hrpK1, 65% for hopT1-2, and 14% for hopN1, hopR1, and hopQ1-2. Investigation of copper resistance showed that 67% of our Pss Citrus strains from Tunisia are resistant to copper sulphate in vitro, and the copper resistance genes copABCDR were detected in 23% of the strains. Our results present new data concerning the genetic diversity and phylogeny, presence of T3SEs, and copper resistance within the Pss populations that affect Citrus in Tunisia.  相似文献   

4.
Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from healthy and diseased stone fruits tissues sampled from 38 stone fruits orchard sites in Iran in 2010 and 2011. These strains were tested for pathogenicity and the presence of the syrB gene and were genetically characterized by using ERIC (enterobacterial repetitive intergenic consensus), REP (repetitive extragenic palindromes), and BOXAIR and IS50 (insertion sequences) primers and PCR. All 78 strains of Pss tested were moderately to highly pathogenic on Loring peach seedlings. A total of 78 isolates of the Pss amplified a 752-bp fragment with the syrB primers. To assess genetic diversity among the strains, genomic DNA was extracted from strains and used in rep-PCR and IS50-PCR analysis. Cluster analysis was performed using UPGMA. The strains of Pss were separated into nine distinguishable genotypic groups by the combination data set of both rep-PCR and IS50-PCR at 73 % similarity level. There was no significant correlation between genetic diversity and geographical origin of the isolates. These results indicate that a combination of rep-PCR and IS50-PCR fingerprinting can be used as a high resolution genomic fingerprinting method for elucidating intrapathovar diversity among strains of Pss. The results of this study demonstrated the existence of a considerable genetic diversity among Pss strains causing canker of stone fruit trees in Iran. In this study, genetic variability in Iranian strains of Pss were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.  相似文献   

5.
Bacterial isolates from tomato plants with symptoms revealing pith necrosis collected over a 20‐year period were screened and characterized using biochemical and pathogenicity tests, as well as molecular approaches. The examined isolates were categorized into two main Pseudomonas species: P. corrugata and P. mediterranea. The diversity of these isolates was characterized through a variety of biochemical, serological, pathogenicity, DNA fingerprinting and multi‐locus sequence analysis features. Of the total Pseudomonas isolates causing pith necrosis, the biochemical profile of the selected non‐fluorescent pseudomonads consisting of P. corrugata and P. mediterranea revealed differentiation in only three characters among 43 examined. Serological analysis managed to identify the P. corrugata isolates using the laboratory prepared antiserum anti‐PC14. Genomic analyses using rep‐PCR fingerprinting and multilocus sequence analysis (MLSA) revealed considerable inter‐ and intraspecies genetic diversity. However, artificial inoculations of several plant species revealed similar pathogenicity patterns for both P. corrugata and P. mediterranea isolates. These results provide the basis for a more comprehensive understanding of the biology, sources and shift in genetic diversity and evolution of both P. corrugata and P. mediterranea populations and could support the development of molecular identification tools and epidemiological studies in diseases caused by these species. Moreover, this is the first report of P. mediterranea in Greece on tomato as well as on pepper plants.  相似文献   

6.
Bacterial speck caused byPseudomonas syringae pv.tomato is an emerging disease of tomato in Tanzania. Following reports of outbreaks of the disease in many locations in Tanzania, 56 isolates ofP. syringae pv.tomato were collected from four tomato- producing areas and characterized using pathogenicity assays on tomato, carbon source utilization by the Biolog Microplate system, polymerase chain reaction and restriction fragment length polymorphism (RFLP) analysis. All theP. syringae pv.tomato isolates produced bacterial speck symptoms on susceptible tomato (cv. ‘Tanya’) seedlings. Metabolic fingerprinting profiles revealed diversity among the isolates, forming several clusters. Some geographic differentiation was observed in principal component analysis, with isolates from Arusha region being more diverse than those from Iringa and Morogoro regions. The Biolog system was efficient in the identification of the isolates to the species level, as 53 of the 56 (94.6%) isolates ofP. syringae pv.tomato were identified asPseudomonas syringae. However, only 23 isolates out of the 56 (41.1%) were identified asPseudomonas syringae pv.tomato. The results of this work indicate the existence ofP. syringae pv.tomato isolates in Tanzania that differ significantly from those used to create the Biolog database. RFLP analysis showed that the isolates were highly conserved in theirhrpZ gene. The low level of genomic diversity within the pathogen in Tanzania shows that there is a possibility to use resistant tomato varieties as part of an effective integrated bacterial speck management plan. http://www.phytoparasitica.org posting August 8, 2008.  相似文献   

7.
Leaves and fruits of walnut trees exhibiting symptoms of bacterial blight were collected from six locations in Poland. Isolations on agar media resulted in 18 bacterial isolates with colony morphology resembling that of the Xanthomonas genus. PCR using X1 and X2 primers specific for Xanthomonas confirmed that all isolates belonged to this genus. In pathogenicity tests on unripe walnut fruits, all isolates caused typical black necrotic lesions covering almost the entire pericarp. Results of selected phenotypic tests indicated that characteristics of all isolates were the same as described for the type strain of Xanthomonas arboricola pv. juglandis. Genetic analyses (PCR MP, ERIC‐, BOX‐PCR and MLSA) showed similarities between the studied isolates and the reference strain of X. arboricola pv. juglandis CFBP 7179 originating from France. However, reference strains I‐391 from Portugal and LMG 746 from the UK were different. MLSA analysis of partial sequences of the fyuA, gyrB and rpoD genes of studied isolates and respective sequences from GenBank of pathotype strains of other pathovars of X. arboricola showed that the X. arboricola pv. juglandis isolates consisted of different phylogenetic lineages. An incongruence among MLSA gene phylogenies and traces of intergenic recombination events were proved. These data suggest that the sequence analysis of several housekeeping genes is necessary for proper identification of X. arboricola pathovars.  相似文献   

8.
Since 2008, Pseudomonas syringae pv. actinidiae virulent strains (Psa‐V) have quickly spread across the main areas of kiwifruit (Actinidia deliciosa and A. chinensis) cultivation causing sudden and re‐emerging outbreaks of bacterial canker to both species. The disease caused by Psa‐V strains is considered worldwide as pandemic. Recently, P. syringae strains (ex Psa‐LV, now called PsD) phylogenetically related to Psa‐V have been isolated from kiwifruit, but cause only minor damage (i.e. leaf spot) to the host. The different biological significance of these bacterial populations affecting kiwifruit highlights the importance of having a diagnostic method able to detect Psa‐V, which is currently solely responsible for the severe damage to the kiwifruit industry. In order to improve the specific molecular detection of Psa‐V, a real‐time PCR assay has been developed based on EvaGreen chemistry, together with a novel qualitative PCR (PCR‐C). Both methods are based on specific primer sets for the hrpW gene of Psa. The real‐time PCR and PCR‐C were highly specific, detecting down to 50 and 200 fg, respectively, and were applied to a range of organs/tissues of kiwifruit with and without symptoms. These methods are important tools for both sanitary and certification programmes, and will help to avoid the spread of Psa‐V and to check possible inoculum sources. In addition to being used as routine tests, they will also enable the study of the biology of Psa‐V and the disease that it causes, whilst avoiding the detection of other populations of related P. syringae present in kiwifruit.  相似文献   

9.
Bacterial canker is one of the most important diseases of cherry (Prunus avium). This disease can be caused by two pathovars of Pseudomonas syringae: pv. morsprunorum and pv. syringae. Repetitive DNA polymerase chain reaction-based fingerprinting (rep-PCR) was investigated as a method to distinguish pathovars, races and isolates of P. syringae from sweet and wild cherry. After amplification of total genomic DNA from 87 isolates using the REP (repetitive extragenic palindromic), ERIC (enterobacterial repetitive intergenic consensus) and BOX primers, followed by agarose gel electrophoresis, groups of isolates showed specific patterns of PCR products. Pseudomonas syringae pv. syringae isolates were highly variable. The differences amongst the fingerprints of P. syringae pv. morsprunorum race 1 isolates were small. The patterns of P. syringae pv. morsprunorum race 2 isolates were also very uniform, with one exception, and distinct from the race 1 isolates. rep-PCR is a rapid and simple method to identify isolates of the two races of P. syringae pv. morsprunorum; this method can also assist in the identification of P. syringae pv. syringae isolates, although it cannot replace inoculation on susceptible hosts such as cherry and lilac.  相似文献   

10.
Pseudomonas syringae is described as a species complex, containing P. syringae-related species classified into 13 phylogroups and 23 clades. Pseudomonas syringae is one of the main pathogens of fruit trees, affecting nut trees, hazelnut and kiwi, pome and stone fruits. Bacterial canker of apricots is an important disease in regions of production with cold winters and conducive soils. This work characterizes the bacteria able to induce canker in apricots isolated in different French orchards. Bacteria from four phylogroups were able to induce canker. The pathogenicity to apricot was not linked to the pathogenicity to the three herbaceous species and cherry fruits tested, and was not always related to hypersensitive reaction on tobacco and ice nucleation activity. Bacteria pathogenic to apricot belong to phylogroups 01, 02, 03 and 07. The bacteria of phylogroups 01a and 07a (Pseudomonas viridiflava) characterized in this work have not previously been described as pathogenic to apricot.  相似文献   

11.
Bacterial apical necrosis (BAN), caused by the bacterium Pseudomonas syringae pv. syringae (Pss), is currently the most limiting disease affecting the mango crop in the Mediterranean area. The copper‐based compound Bordeaux mixture (BM) is considered to be the conventional treatment against BAN, but it does not act as a bactericide. Alternative experimental treatments to BM that are compatible with organic farming were tested for their ability to control BAN disease. Field trials were conducted over six seasons in different mango orchards with natural infestation of Pss. The experimental treatments included applications of Silicon gel (a commercial formulation of aqueous potassium silicate), dicalcium phosphate, Kaolinite, and Ulmasud B® (bentonite, powder); BM was applied as the conventional treatment. During the first two seasons (small‐scale trial, 2002–2004), all these experimental compounds were applied in order to select those treatments providing the greatest reduction of BAN symptoms. In the next three seasons (2005–2008), a semi‐commercial scale trial was carried out with the best‐performing treatments, resulting in the selection of Silicon gel. Finally, Silicon gel was tested in a commercial scale trial during the last season (2008–2009). Trees treated with Silicon gel showed significantly fewer necrotic buds and leaves, reaching disease levels very similar to those using the conventional treatment with BM. However, minor differences in P. syringae‐like population levels were observed, as has been described in previous studies. The possible mode of action of the Silicon gel is discussed. Currently, the Silicon gel compound is undergoing the registration process for its commercial use in mango management in Spain.  相似文献   

12.
Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) is a disease of crucifer crops. The objective of this study was to characterize races of Xcc, their distribution and genetic diversity in India. Two hundred and seventeen isolates of bacteria were obtained from 12 different black rot‐infected crucifer crops from 19 states of India; these were identified as Xcc based on morphology, hrpF gene and 16S rRNA gene based molecular markers and pathogenicity tests. Characterization of races was performed by using a set of seven differential crucifer hosts, comprising two cultivars of turnip (Brassica rapa var. rapa) and cultivars of Indian mustard (B. juncea), Ethiopian mustard (B. carinata), rapeseed mustard (B. napus), cauliflower (B. oleracea) and Savoy cabbage (B. oleracea var. sabauda). Races 1, 4 and 6 of Xcc were identified and, among these races, race 1 followed by race 4 dominated most of the states of India. Genetic diversity of the Indian isolates of Xcc was analysed using repetitive sequence‐based PCR (rep‐PCR) including primers for REP (repetitive extragenic palindromic), ERIC (enterobacterial repetitive intergenic consensus) and BOX (amplifying with BOX A1 R primer) repetitive elements. This method of fingerprinting grouped the isolates into 56 different DNA types (clusters) with a 75% similarity coefficient. Among these clusters, DNA types 22 and 53 contained two different races 1 and 4, whereas DNA type 12 contained races 1, 4 and 6. However, no clear relationship was observed between fingerprints and races, hosts or geographical origin.  相似文献   

13.
A collection of Pseudomonas syringae and viridiflava isolates was established between 1993 and 2002 from diseased organs sampled from 36 pear, plum and cherry orchards in Belgium. Among the 356 isolates investigated in this study, phytotoxin, siderophore and classical microbiology tests, as well as the genetical methods REP-, ERIC- and BOX- (collectively, rep-) and IS50-PCR, enabled identification to be made of 280 isolates as P. syringae pv. syringae (Pss), 41 isolates as P. syringae pv. morsprunorum (Psm) race 1, 12 isolates as Psm race 2, three isolates as P. viridiflava and 20 isolates as unclassified P. syringae. The rep-PCR methods, particularly BOX-PCR, proved to be useful for identifying the Psm race 1 and Psm race 2 isolates. The latter race was frequent on sour cherry in Belgium. Combined genetic results confirmed homogeneities in the pvs avii, and morsprunorum race 1 and race 2 and high diversity in the pv. syringae. In the pv. syringae, homogeneous genetic groups consistently found on the same hosts (pear, cherry or plum) were observed. Pathogenicity on lilac was sometimes variable among Pss isolates from the same genetic group; also, some Psm race 2 and unclassified P. syringae isolates were pathogenic to lilac. In the BOX analyses, four patterns included 100% of the toxic lipodepsipeptide (TLP)-producing Pss isolates pathogenic to lilac. Many TLP-producing Pss isolates non-pathogenic to lilac and the TLP-non-producing Pss isolates were classified differently. Pseudomonas syringae isolates that differed from known fruit pathogens were observed in pear, sour cherry and plum orchards in Belgium.  相似文献   

14.
A survey of bleeding canker disease, caused by Pseudomonas syringae pv. aesculi, was undertaken across Ireland. Incidence has become severe and can be considered epidemic, as 61% of the 1587 horse chestnut trees surveyed showed symptoms of the disease. Bacteria were isolated from a sample of trees and characterized using gyrBDNA sequencing. DNA was also extracted directly from wound tissue. The Irish P. syringae pv. aesculi genotype was identical to genotypes previously sequenced with gyrB from the UK and some other locations in Europe. Real‐time PCR, using existing primers and a newly designed, more pathovar‐specific primer set, was assessed for use in disease screening. With molecular screening, a total of 11 trees from a sample of 55 tested positive for P. syringae pv. aesculi in Ireland. It was more efficient to extract DNA directly from wound tissue, especially fresh bark, for disease detection than to undertake bacterial isolation with subsequent molecular analysis. A further set of sequencing primers was developed for the amplification of the gyrB gene from P. syringae pv. aesculi and their specificity was shown using a diverse sample of bacterial isolate DNAs. The study also isolated and identified other bacterial species from diseased material; some of these are known pathogens (Brenneria nigrifluens, P. marginalis and P. syringae) or have previously been identified as potentially beneficial endophytes of host trees (Erwinia billingiae, E. tolentana, P. fluorescens, P. putida and Raoultella).  相似文献   

15.
Of thirty fluorescent Pseudomonas isolates originating from symptomatic tissues of sweet (Prunus avium) and sour cherry (Prunus cerasus), plum (Prunus domestica), peach (Prunus persica) and apricot (Prunus armeniaca), 23 were identified as P. syringae using LOPAT tests. Further characterization of those isolates by GATTa and L-lactate utilization tests showed that 10 of them belonged to race 1, six to race 2 of P. syringae pv. morsprunorum (Psm) and six other isolates were identified as pathovar syringae (Pss). One isolate (791) was determined as atypical. Phenotypic determination and genetic analysis of studied isolates for toxin production revealed that isolates of Pss produced syringomycin, 3 Psm race 1 produced coronatine and 6 Psm race 2 produced yersiniabactin. Genetic diversity of all isolates was evaluated with the PCR melting profile (PCR MP) method. A dendrogram constructed with PCR MP patterns showed positive correlation with phenotypically distinguished pathovars. Isolates of Psm races 1 and 2 formed distinct, tight clusters, whereas Pss isolates were more heterogeneous. Isolate 791 was placed within Pss isolates. Bacteria identified as Pss caused more severe symptoms on immature cherry fruits compared to Psm, which corresponded to determined pathovars and races.  相似文献   

16.
In order to characterize the pathogen(s) responsible for the outbreak of fusarium diseases in Algeria, 48 Fusarium spp. isolates were collected from diseased tomato in Algeria and compared with 58 isolates of Fusarium oxysporum originating from seven other Mediterranean countries and 24 reference strains. Partial sequences of the translation elongation factor EF‐1α gene enabled identification of 27 isolates as F. oxysporum, 18 as F. commune and three as F. redolens among the Algerian isolates. Pathogenicity tests confirmed that all isolates were pathogenic on tomato, with disease incidence greater at 28°C than at 24°C. All isolates were characterized using intergenic spacer (IGS) DNA typing, vegetative compatibility group (VCG) and PCR detection of the SIX1 (secreted in xylem 1) gene specific to F. oxysporum f. sp. lycopersici (FOL). No DNA polymorphisms were detected in the isolates of F. redolens or F. commune. In contrast, the 27 Algerian isolates of F. oxysporum were shown to comprise nine IGS types and 13 VCGs, including several potentially new VCGs. As none of the isolates was scored as SIX1+, the 27 isolates could be assigned to F. oxysporum f. sp. radicis‐lycopersici (FORL). Isolates from Tunisia were also highly diverse but genetically distinct from the Algerian isolates. Several Tunisian isolates were identified as FOL by a PCR that detected the presence of SIX1. The results show that isolates from European countries were less diverse than those from Tunisia. Given the difference between Algerian populations and populations in other Mediterranean countries, newly emergent pathogenic forms could have evolved from local non‐pathogenic populations in Algeria.  相似文献   

17.
Brown rot caused by fungi belonging to the genus Monilinia is one of the major limiting factors of sour and sweet cherry production. Up to now, three species, M. fructigena, M. laxa and M. fructicola, have been identified as causal agents of brown rot on cherries worldwide. From 2010 to 2013, during the monitoring of cherry orchards in different areas of Poland, a fourth species, M. polystroma, was isolated from brown rot symptoms on sour and sweet cherry fruits. To the best of the authors’ knowledge, this is the first time M. polystroma has been reported as the causal agent of brown rot on cherries. The genetic diversity of M. polystroma isolates from cherries and other hosts was analysed using PCR MP, ISSR and RAPD techniques and showed its clear distinctness from other Monilinia spp. tested. The cluster analysis of fingerprinting data revealed a high similarity of M. polystroma isolates from Poland and their close relationship with the reference strain from Japan, indicating that this species is a recently introduced pathogen. The highest genetic distance between the examined isolates and the highest number of different genotypes was observed in an ISSR assay. Detailed genetic diversity characteristics revealed that M. polystroma isolates from cherries did not create a distinct group but were intermingled with M. polystroma isolates from other hosts. The results of the pathogenicity test conducted on different fruit species indicated a lack of host specificity for M. polystroma isolates.  相似文献   

18.
Pseudomonas syringae pv. pisi is a seedborne pathogen distributed worldwide that causes pea bacterial blight. Previous characterization of this pathogen has been carried out with relatively small and/or geographically limited samples. Here, a collection of 91 strains are examined that include strains from recent outbreaks in Spain (53 strains) and from 14 other countries, and that represent all races and the new race 8, including the type race strains. This collection was characterized on the basis of 55 nutritional tests, genetic analysis (rep‐PCR, amplification of AN3 and AN7 specific markers, and multilocus sequence typing (MLST)) and pathogenicity on the differential pea cultivars to identify races. Principal component analysis and distance dendrograms confirm the existence of two genetic lineages within this pathovar, which are clearly discriminated by the AN3/AN7 markers, rep‐PCR and MLST. Strains from races 1 and 7 amplified the AN3 marker; those from races 2, 6 and 8 amplified AN7, while strains of races 3, 4 and 5 amplified either AN3 or AN7. Nevertheless, strains were not grouped by race type by any of the genetic or biochemical tests. Likewise, there was no significant association between metabolic and/or genetic profiling and the geographical origin of the strains. The Spanish collection diversity reflects the variability found in the worldwide collection, suggesting multiple introductions of the bacteria into Spain by contaminated seed lots.  相似文献   

19.
A virulent strain of Pseudomonas syringae pv. actinidiae biovar 3 (Psa), which causes bacterial canker in kiwifruit, was first recorded in New Zealand in November 2010. This strain has severely affected Actinidia chinensis var. chinensis ‘Hort16A’ kiwifruit productivity but its effect on green Actinidia chinensis var. deliciosa ‘Hayward’ kiwifruit productivity has been variable. An observational study design was used to develop explanatory models to quantify the impacts of Psa infection on productivity (tray equivalents per hectare) of Hayward kiwifruit harvested in 2012, using data captured by industry from 2599 orchards. A total of 934 orchards were Psa positive at the end of the study period. Multivariable linear regression was used to model 2012 productivity in the presence of Psa, while controlling for regional differences, elevation, 2011 productivity, harvest dates and application of agrichemicals. The model showed productivity was initially higher in the presence of Psa, and was not reduced until after 1 year of infection. The relationship between protective spray use and productivity was also quantified. It is likely that improved disease management has offset the impact of the disease and future research should consider a reassessment of the effects of disease after longer term exposure to Psa in New Zealand. The use of an observational cohort study to assess disease impacts using multivariable analysis could have wider application in the field of plant epidemiology.  相似文献   

20.
Bacterial canker is a major disease of stone fruits and is a critical limiting factor to sweet cherry (Prunus avium) production worldwide. One important strategy for disease control is the development of resistant varieties. Partial varietal resistance in sweet cherry is discernible using shoot or whole tree inoculations; however, these quantitative differences in resistance are not evident in detached leaf assays. To identify novel sources of resistance to canker, we used a rapid leaf pathogenicity test to screen a range of wild cherry, ornamental Prunus species and sweet cherry × ornamental cherry hybrids with the canker pathogens, Pseudomonas syringae pvs syringae, morsprunorum races 1 and 2, and avii. Several Prunus accessions exhibited limited symptom development following inoculation with each of the pathogens, and this resistance extended to 16 P. syringae strains pathogenic on sweet cherry and plum. Resistance was associated with reduced bacterial multiplication after inoculation, a phenotype similar to that of commercial sweet cherry towards nonhost strains of P. syringae. Progeny resulting from a cross of a resistant ornamental species Prunus incisa with susceptible sweet cherry (P. avium) exhibited resistance indicating it is an inherited trait. Identification of accessions with resistance to the major bacterial canker pathogens is the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.  相似文献   

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