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1.
Tapesia yallundae was observed in early July on wheat straws, which had been inoculated with isolates of Pseudocercosporella herpotrichoides (W-type) 9 months previously and placed in plots of winter wheat, to act as inoculum in a resistance screen. A perfect state was not observed on straws inoculated with R-type isolates in the same experiment. One hundred and thirty-four single-ascospore isolates were obtained and observations on morphology in culture, pathogenicity to wheat and rye seedlings, resistance to benomyl and the pattern of restriction fragment length polymorphisms demonstrated that all isolates were W-type, although some grew at half the expected rate on agar, and at least two isolates were involved in the production of apothecia. Apothecia were produced in vitro on straws inoculated with single isolates of P. herpotrichoides only when they were incubated in contact with other straws similarly inoculated with certain other isolates. No apothecia were produced on straws with only isolate present, suggesting the need for at least two strains, possibly representing different mating types, for apothecium formation. Apothecia of T. yallundae were produced in vitro on straw pieces which had been inoculated individually with W-type isolates, 14-16 weeks after straws of different isolates were mixed. Evidence for genetic recombination between isolates was obtained when single-ascopore colonies were analysed for resistance to benomyl in culture and for restriction-length polymorphisms (RFLPs).  相似文献   

2.
Field plots in three consecutive crops of winter wheat were sampled at approximately 2-week intervals from April to July in 1989, 1990 and 1991. Culm and stem bases were examined for symptoms of eyespot, sharp eyespot and brown foot rot. The W-type and R-type of Pseudocercosporella herpotrichoides, P. anguioides, Fusarium culmorum, F. avenaceum and Microdochium nivale grown from this plant material on agar were identified. Eyespot was most severe in 1991, when plant development was least rapid following cool weather in late winter and the summer was relatively cool and wet. Sharp eyespot was most severe in 1990, which had a warm summer with moderate rainfall. The other warm summer, 1989, was drier and these conditions favoured late development of brown foot rot, associated mainly with F. culmorum which was scarce at other times. Sharp eyespot sometimes increased where prochloraz, which decreased eyespot, was applied. Distinct symptoms of more than one disease occurred less frequently on the same stem than expected from the individual total occurrences, but co-occurrences of different fungi were often more frequent than expected. In July 1990, Fusarium spp. co-occurred with R-type, but not W-type, P. herpotrichoides more frequently than expected, and in July 1990 and 1991 M. nivale and both W-type and R-type co-occurred more frequently than expected. Fusarium spp. and M. nivale were more frequent, especially in the earlier samples, on nodes than on internodes, whilst P. herpotrichoides normally infected at the internodes. The results suggest that stems weakened or altered by a primary colonizer are often a suitable substrate for a secondary colonizer, often a Fusarium sp., which may begin infection at a distance from the original lesion and often not cause distinct symptoms itself.  相似文献   

3.
In a survey carried out in 1984, isolates of the eyespot fungus, Pseudocercosporella herpotrichoides , from cereals in the UK, Denmark and West Germany were tested in vitro for sensitivity to the fungicide prochloraz. Of 194 isolates tested, 191 showed no growth on agar amended with prochloraz at 2 μg/ml or more. The mean concentration of prochloraz calculated to inhibit colony growth by 50% (IG50) was 0 44+0−010 μg/ml. The three isolates that grew at 2 μg/ml displayed weak colony development and were clearly disrupted by the presence of the fungicide. R-type isolates appeared more sensitive to prochloraz than W-type isolates. Comparisons with similar data for isolates obtained from other years revealed no consistent change with time in sensitivity to prochloraz.  相似文献   

4.
Isolates of Pseudocercosporella herpotrichoides were classified by a variety of established techniques including colony morphology, colour, pathogenicity on seedlings and spore morphology. In all cases, certain isolates could not be clearly classified and correlation between the systems was incomplete. In particular, the typing system of Nirenberg in which two varieties of P. herpotrichoides (var. herpotrichoides and var. acuformis ) are recognized did not correlate with the widely used UK system based on colony morphology on PDA: fast, even (F E) and slow, feathery (S/F). Restriction fragment length polymorphisms in total DNA and rDNA indicated groupings related to morphology (and pathogenicity) with considerable polymorphisms in rDNA of F/E isolates. Generally, good correlation was found between RFLP markers and other tests.  相似文献   

5.
Isolates of Pseudocercosporella herpotrichoides , causal agent of the eyespot disease of cereals, are usually classified as W-type or R-type on the basis of differential pathogenicity towards wheat and rye hosts, a distinction often correlated with cultural morphology. Polyacrylamide gel electrophoresis (PAGE) of soluble proteins was used to compare 101 isolates of Pseudocercosporella spp. including both W-types and R-types, and the related species P. anguioides and P. aestiva . Of 16 enzyme activities detected, seven were differential for the pathotypes. Isozyme polymorphisms for five enzymes clearly differentiated W-type from R-type isolates, a result confirmed by pathogenicity tests. Within each pathotype, isozyme patterns were similar for isolates of diverse geographical origins, including Europe, North America, South Africa and New Zealand. Isolates of P. anguioides and P. aestiva could also be distinguished on the basis of isozyme patterns. The mechanisms maintaining these polymorphisms, and the value of PAGE for population studies of this pathogen, are discussed.  相似文献   

6.
A site with no known history of cereal growing or carbendazim fungicide use was inoculated in 1983 with an equal mixture of spores of R-type and W-type isolates of Pseudocercosporella herpotrichoides. all sensitive to carbendazim. Following three consecutive years of carbendazim sprays, more than 90% of isolates recovered were carbendazim-resistant. A majority of R-type isolates was recovered after 3 years and resistance was found to be more frequent in R-type than in W-type isolates. A mixture of carbendazim with prochloraz initially delayed the development of carbendazim resistance, but after 3 years the incidence of resistance was similar to that where carbendazim alone was applied. The best control of eyespot was given by the mixture and by a split application of prochloraz in the first year, by the mixture in the second year, and by the split prochloraz application in the final year. A greater proportion of R-type isolates was recovered from prochloraz-treated plots than from unsprayed plots; the proportion of these that were resistant to carbendazim was lower than that from carbendazim treatments. Throughout this study isolates resistant to prochloraz were not detected.  相似文献   

7.
Alternaria dauci (Kühn) Groves and Skolko, the cause of leaf blight of carrot, was observed to produce chlamydospores and microsclerotia in vitro. Four different isolates produced chlamydospores on potato dextrose agar, V8 agar and Czapek-Dox agar at 10, 18 and 28°C, from neighbouring cells of hyphae of the submerged mycelium, forming long chains. Formation of chlamydospores was completed in a multiple stage process, including swelling of cells, development of secondary septa, rounding up of cells and cell wall thickening. Mature chlamydospores were released from the mycelium mostly in clusters and in short or long chains, and sometimes in pairs. They were globose to ellipsoid, smooth or verrucose, pale brown in colour, and averaged 13.87?×?11.37 μm, (length × width). Microsclerotia were formed on PDA, by only one isolate, at 28°C first at the edges of the colony, by close contact of hyphae that exhibited extensive branching and intermingling. In their final form microsclerotia were multi-celled, closely attached masses of short and broad dark grey cells, less compact woven at the edges of the microsclerotium. This is the first illustration of chlamydospore and microsclerotia formation in Alternaria dauci.  相似文献   

8.
In order to determine whether a given isolate of Pseudocercosporella herpotrichoides. the cause of eyespot disease of cereals, belongs to the W-type or the R-type, we have developed a test based on the polymerase chain reaction (PCR). Sequences of the internal transcribed spacer (ITS) region of the ribosomal genes were determined for three different isolates of each pathotype. Primers complementary to variable sequences were specifically chosen to amplify differentially DNA from W- and R-types. Specific reaction conditions of the PCR assay were experimentally determined by testing four isolates of each type that exhibit a wide range of sensitivity to fungicides.  相似文献   

9.
Mycelial isolates (115) of Pseudocercosporella herpotrichoides were obtained from five field sites in England. Carbendazim-resistant isolates were detected by their mycelial growth on agar containing 1 μg/ml carbendazim. Resistant isolates were found at two of the five sites examined and one of these had never been treated with benzimidazole fungicides. Amongst the carbendazim- resistant isolates there was a predominance of isolates with pale mycelium, an irregular colony margin and a relatively slow growth rate; however, this association was not absolute. Large differences in the effects of carbendazim on mycelial growth of sensitive and resistant isolates were demonstrated; growth of sensitive isolates was completely inhibited at 0.5 μg /ml carbendazim whilst five of the six resistant isolates examined grew on agar containing 1000 μg/ml fungicide. The carbendazim-resistant isolates were cross-resistant to benomyl, thiophanate-methyl and to a Icsser degree thiabendazole, but not to prochloraz. Conidia of carbendazim-resistant isolates were as resistant. Carbendazim-resistant isolates were just as pathogenic to wheat as sensitive isolates. The implications of these results and other reports of benzimidazole resistance in P. herpotrichoides are discussed in relation to disease control.  相似文献   

10.
Field occurrence of vinclozolin resistance in Monilinia fructicola   总被引：1，自引：1，他引：0  
Strains of Monilinia fructicola resistant to vinclozolin were isolated from fruit affected by brown rot from an orchard where the fungicide had been used over four seasons. Resistant isolates were pathogenic to peach fruit, and resistance of one isolate was confirmed following dipping of inoculated fruit in fungicide suspensions. In culture, one of four resistant isolates was identical in colony morphology and sporulation to sensitive isolates from different geographic areas. The other resistant isolates produced dark mycelium on PDA and were slower growing. Vinclozolin-resistant isolates were resistant in vitro to two other dicarboximide fungicides, iprodione and procymidone.  相似文献   

11.
Surveys of 528 randomly selected commercial fields in England and Wales in 1983 showed that isolates of Pseudocercosporella herpotrichoides resistant to benomyl were common and widespread on winter wheat and winter barley. During June and July resistant strains were recovered from 16 to 66% of fields and the proportion of resistant isolates was 37–52%. The frequency of occurrence of resistant isolates was positively correlated with the number of applications of carbendazimgenerating (MBC) fungicides during the previous 8 years. Benomyl resistance was found in 21–48% of fields where it was claimed that MBC had never been used, and 7–28% of isolates from those fields, were resistant. Resistance was more frequent in R-type than in W-type isolates of the pathogen. The proportion of R-type isolates decreased as the number of previous winter wheat crops rose and increased with the number of winter barley crops grown and with the number of MBC sprays applied to crops in previous years. The implications of these findings for the control of eyespot in England and Wales are discussed.  相似文献   

12.
新疆首次报道轮枝镰孢菌引起骏枣果实黑点病   总被引：1，自引：0，他引：1  
Black spot disease was found on fruits of Jun jujube in Hetian area, Xinjiang, in June,2010. The typical spots on fruits were round or suborbicular, concave slightly,dark brown and the diameter was about 4 mm. The colony grew fast with irregular edge on PSA medium, while relatively slow with smooth edge on PDA medium. The colonies were white at the early stage, slightly pink finally and flocculent on the both culture medium. The conidia arranged chain shape and the spore chain was basipetal. The rDNA ITS sequence,cyt b gene sequence and EF-1α gene sequence were amplified and analyzed. The result showed that the homology was above 99% between the isolate and Fusarium verticillioides strains based on the three DNA sequences. By morphology combining with molecular biology techniques,the pathogen of Jun jujube black spot disease was identified as F. verticillioides. It is the first report on jujube disease caused by F. verticillioides in the world.  相似文献   

13.
Zhou T  Boland GJ 《Phytopathology》1997,87(2):147-153
ABSTRACT One hundred and thirty-two isolates of Sclerotinia homoeocarpa, the causal agent of dollar spot of turfgrass, were evaluated for virulence on swards and detached leaves of creeping bentgrass and for the presence of double-stranded RNA (dsRNA). In at least four isolates, the hypovirulent phenotype was associated with the presence of specific segments of dsRNA. In addition, these hypovirulent isolates often grew slowly on potato dextrose agar (PDA), formed thin colonies with atypical colony margins, and failed to produce typical black stroma. The hypovirulent phenotype and dsRNA were transmitted from hypovirulent isolate Sh12B to virulent isolate Sh48B, and the converted isolate was hypovirulent and contained dsRNA. The hypovirulent phenotype and dsRNA also were transmitted to at least four other isolates of the pathogen, including the fungicide-resistant, dsRNA isolate KY-7. Converted isolates of KY-7 developed the hypovirulent phenotype, grew on fungicide-amended medium, and contained dsRNA. Subcultures of hypovirulent isolate Sh12B that did not contain dsRNA were obtained through curative treatment using cycloheximide-containing medium and heat. Cured subcultures grew faster on PDA, had more typical colony morphologies, were more virulent on bentgrass leaves, and did not contain dsRNA. No cured subcultures were obtained from hypovirulent isolate Sh09B. Isolates regenerated from protoplasts of hypovirulent isolate Sh12B were not cured, remained hypovirulent, and contained dsRNA. Transmission of hypovirulence and dsRNA in S. homoeocarpa has potential as a novel approach to the management of dollar spot of turfgrass.  相似文献   

14.
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15.
A double-antibody-sandwich ELISA test has been developed for the detection of Pseudocercosporella herpotrichoides using a highly specific monoclonal antibody PH-10 as the capture antibody and genus-specific rabbit polyclonal antiserum as the detector antibody. The assay recognizes extracts from plants both artificially and naturally infected with P. herpotrichoides giving at least three-fold higher absorbance values with extracts from Pseudocercosporella-infected tissue than with extracts from healthy tissues or from tissues naturally infected with Microdochium nivale, Rhizoctonia cerealis or material artificially inoculated with P. anguioides. The assay tested positively against all isolates of P. herpotrichoides , including both W-type and R-type isolates. In this assay system, extraction of the antigen from the stem bases of infected plants is a one-step process not requiring any dilution procedures. The assay can be used to detect the pathogen in presymptomatic infected seedlings. The immunogen used to generate the specific monoclonal antibody and the rabbit antiserum was a mycelial extract from which the high-molecular-weight proteins and glycoproteins had been removed by ammonium sulphate precipitation. The high-molecular-weight fraction was shown to contain cross-reactive antigens; it induced antiserum in mice that cross-reacted with the other stem-base fungi even at high dilutions. The monoclonal antibody PH-10 is an IgM antibody. Heat and periodate treatment of the antigen indicate that it is a glycoprotein and that the epitope recognized by the antibody is a protein.  相似文献   

16.
Pestalotiopsis isolates obtained from the foliage, stem-base and roots of hardy ornamentals grown on commercial nurseries in the UK were identified and characterised according to pathogenicity and colony morphology. All 18 isolates were identified as Pestalotiopsis sydowiana on the basis of conidia morphology, and confirmation of identification was made by experts at CABI Bioscience. Isolates were pathogenic on the host from which originally isolated. Typical symptoms included foliar browning of foliage and stems, and the presence of black or greenish-black acervuli on diseased tissue. Isolates were not host specific and infected other species of hardy ornamentals. Three colony types on potato dextrose agar were distinguished according to colour and production of acervuli by individual isolates.Three selected isolates of P. sydowiana were characterised by examining the effects of growth media, temperature, pH, and water potential on hyphal extension. Isolates grew well on commonly used growth media, including PDA, Sabouraud dextrose agar (SDA), V8 juice agar (V8), malt extract agar (MEA) and Czapek Dox agar (CDA). The optimum temperature for growth on PDA was in the range 20–25°C, with little or no growth occurring below 5°C or above 30°C. Hyphal extension occurred over a pH range between 2.6–8.6, with optimum values occurring at pH 5.5. In general, decreases in osmotic and matric potential caused a reduction in growth. Hyphal extension on media adjusted osmotically as NaCl ceased between –9.9 and –10.5MPa. Isolates were more tolerant of osmotic than matric potential, with no growth occurring at –6.5MPa on media adjusted with polyethylene glycol.  相似文献   

17.
 大豆紫斑病是华北和东北的大豆生产中重要病害之一。华东和西南地区也有这一病害的报告[3]。虽然这是一种重要病害,可是对于它的病原菌生物学的研究尚不多。  相似文献   

18.
Surveys of 59 and 528 randomly selected winter wheat and winter barley crops in 1982 and 1983 respectively, showed that benzimidazole-resistant strains of the eyespot fungus (Pseudocercosporella herpotrichoides) were common and widespread. The frequency of occurrence of resistant isolates, both in 1982 and 1983. was positively correlated with the number of benzimidazole fungicide applications since 1975. Resistance was much more frequent in R-type than in W-type strains of P. herpotrichoides. Fungicides or fungicide mixtures, applied to winter wheat at growth stage (GS) 31, were compared for control of eyespot at six sites in 1983 and one in 1984 where benzimidazole-resistant strains were readily detected prior to spraying. Carbendazim alone gave no control of eyespot and in some trials actually increased disease levels compared with the unsprayed control. Prochloraz, either alone or in mixture with carbendazim, was the most effective fungicide giving a moderate control of eyespot (33–42% reduction) and cost-effective yield increases. DPX-II6573, tested only in the 1984 trial, was as effective as prochloraz. The practical implications of these findings are discussed.  相似文献   

19.
Sequences of the ribosomal DNA (rDNA) internal transcribed spacer (ITS) regions were examined to infer a molecular phylogeny of small-spored Phomopsis isolates, designated W-type (mainly white colony, weakly virulent, bearing both alpha and beta conidia at 25°C on PDA) and G-type (mainly gray colony, highly virulent, bearing only alpha conidia at 25°C on PDA), and P. amygdali from fruit trees. Phomopsis G-type and P. amygdali were a monophyletic group distinct from the W-type. The W-type isolates were divided into two monophyletic groups. Diaporthe citri, D. tanakae, P. asparagi, P. viticola, P. vitimegaspora and D. nomurai, which are morphologically distinguishable from W- and G-types, differed from the W- and G-types in molecular phylogenetic analyses. PCR-RFLP analysis of rDNA ITS regions was useful to distinguish each of the Phomopsis species and groups using three restriction enzymes. In mating tests, W-type isolates from fruit trees were heterothallic and inter-fertile even between isolates belonging to the different monophyletic groups. Isolates of the G-type and P. amygdali collected in Japan were cross-fertile. Some isolates from Lunaria annua, Ulmus glabra and Juglans regia belonged to one of the two monophyletic groups of the W-type and were cross-fertile with W-type isolates from Rosaceous fruit trees. Received 27 September 1999/ Accepted in revised form 27 January 2000  相似文献   

20.
Brazilian isolates of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop were examined for colony colour, mycelial growth, benomyl-resistance, pathogenicity, and genetic variability by random amplified polymorphic DNA (RAPD) analysis. All isolates were obtained from flowers and persistent calyxes from different citrus hosts from Sao Paulo, Brazil. DNA polymorphisms detected after amplification with random 10-mer primers were used to classify the isolates into two groups. Group I isolates grew rapidly on potato-dextrose agar (PDA) and were sensitive to benomyl, and group II isolates grew slowly on PDA and were benomyl-resistant. Colletotrichum acutatum was analyzed by RAPD and had high genetic similarity with group II isolates of Colletotrichum from citrus. Probably, the group I is C. gloeosporioides and group II is C. acutatum.  相似文献   

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