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1.
The inoculum potential of Polymyxa betae and BNYVV was studied from 52 random samples of Belgian soils and 10 samples from other European countries, by culture of bait plants in tubes under controlled conditions on serial dilutions of the soils in sterile sand. P. betae was detected in all samples within the range of 0.01 to 27.1 infection units per g of soil. BNYVV was detected by ELISA on root extracts of bait plants grown on three Belgian soil samples. All the tested samples from rhizomania-infested areas in France, FRG, the Netherlands, Switzerland and Austria, were found to be infested by BNYVV by this technique. For BNYVV survey, the plant bait technique appears more reliable than the analysis of rootlets collected in the field and observation of external symptoms in case of low BNYVV infestations or non-expression because of unfavourable environmental conditions. P. betae isolates from various origins heavily infected Beta spp. but only moderately spinach. Chenopodium album was slightly infected by 2 of the 7 isolates, C. murale by 4 of them.  相似文献   

2.
The host range of Polymyxa graminis isolates originating from peanut clump-infested areas in India (Andhra Pradesh and Rajasthan), Pakistan and Senegal was studied on monocotyledonous and dicotyledonous cultivated species, using known quantities of sporosori as inoculum. Profuse multiplication occurred only on some graminaceous species, but the various isolates showed different host specificity. All the isolates produced high infection on sorghum and pearl millet, and all but one isolate from Rajasthan infected maize. Wheat, rye and barley were susceptible to some of the tested isolates. The isolates from Rajasthan and Pakistan produced moderate to severe infection on at least one of these species. On rice, groundnut and sugar beet, only traces of infection by some isolates were detected, whereas no infection was observed on mustard and sunflower. Differences of susceptibility in Pennisetum spp. and Sorghum spp. were demonstrated. The variations in host specificity among isolates from peanut clump-infested areas may result from an adaptation of P. graminis populations to various biotopes. The implications of these results for the management of peanut clump disease are discussed. A comparison of the host ranges of isolates of P. graminis and P. betae from temperate areas demonstrated that distinct types of Polymyxa might be identified based on their relative ability to multiply on susceptible species. Nevertheless, overlapping in the host ranges among the different Polymyxa types, characterised by distinct ecological and genomic features, raises doubts about the host range as a classification criterion for the Polymyxa genus.  相似文献   

3.
Since 2001, several isolates of Blumeria graminis, the causal agent of cereal powdery mildew, maintained on detached leaves at the John Innes Centre, Norwich, UK, have spontaneously become infected with an unknown filamentous fungus whose mycelia have quickly overgrown the powdery mildew colonies and destroyed them completely. A total of five isolates of the contaminant were obtained and identified as Paecilomyces farinosus based on morphological characteristics and rDNA ITS sequence data. To determine whether these P. farinosus isolates can be considered as biocontrol agents (BCAs) of powdery mildews, we studied the interactions between P. farinosus and the following four powdery mildew species: B. graminis f.sp. hordei infecting barley, Oidium neolycopersici infecting tomato, Golovinomyces orontii infecting tobacco and Podosphaera fusca infecting cucumber. The powdery mildew colonies of all these four powdery mildew species were quickly destroyed by P. farinosus in leaf cultures but neither conidial suspensions nor cell-free culture filtrates of P. farinosus isolates could suppress the spread of powdery mildew infections on diseased barley, tomato, tobacco or cucumber plants in the greenhouse. It is concluded that P. farinosus cannot be considered as a promising BCA of powdery mildew infections although it can destroy powdery mildew colonies in detached leaf cultures and can be a menace during the maintenance of such cultures of cereal, apple, cucurbit and tomato powdery mildew isolates.  相似文献   

4.
Studies were made of isolates of Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici J. Walker from different length crop sequences of wheat and barley following permanent grassland. Studies were done on the influence of cropping intensity of soils, natural and steam disinfested, on disease expression from added inoculum. Efforts were also made to detect interactions between isolates and soils from the same and different cropping sequences. Investigation of variability in the pathogen related to virulence and specificity as well as to saprophytic traits. In general, mean virulence of isolates increased up to the point where approximately peak disease levels occurred in the field, and diminished subsequently. Host specificity of isolates from a monospecies system was also pronounced at this point whereas it was not evident in the first 2 crops; it did not increase further after the 5th or 6th cereal of a single species. There was evidence of loss of competitive saprophytic ability in isolates from long sequences as against those from 1st, 2nd and 3rd crops after permanent pasture. A differential sensitivity response from Gliomastix murorum (Cda.) Hughes var. felina (Marsh) Hughes was observed with isolates from 1 to a 3 year sequence compared with isolates from sequences of 4 to 8 years. Isolates from a 1st to a 3rd crop restricted colony growth of G. murorum in culture whereas those from 4th to the 8th cereal were overgrown by this fungus. Isolates from the 1st cereal after grass darkened considerably with age, those from a 2nd less so and those from a 3rd successive crop remained almost totally hyaline; those from longer sequences darkened considerably but were very variable for this trait. The influence of soil from more intensively cropped cereal sequences, which was destroyed by steam disinfestation, was to depress disease levels from applied inoculum. This soil inhibitory effect set in between the first and 3rd cereal.  相似文献   

5.
Both airborne spores of Rhynchosporium secalis and seed infection have been implied as major sources of primary inoculum for barley leaf blotch (scald) epidemics in fields without previous history of barley cropping. However, little is known about their relative importance in the onset of disease. Results from both quantitative real‐time PCR and visual assessments indicated that seed infection was the main source of inoculum in the field trial conducted in this study. Glasshouse studies established that the pathogen can be transmitted from infected seeds into roots, shoots and leaves without causing symptoms. Plants in the field trial remained symptomless for approximately four months before symptoms were observed in the crop. Covering the crop during part of the growing season was shown to prevent pathogen growth, despite the use of infected seed, indicating that changes in the physiological condition of the plant and/or environmental conditions may trigger disease development. However, once the disease appeared in the field it quickly became uniform throughout the cropping area. Only small amounts of R. secalis DNA were measured in 24 h spore‐trap tape samples using PCR. Inoculum levels equivalent to spore concentrations between 30 and 60 spores per m3 of air were only detected on three occasions during the growing season. The temporal pattern and level of detection of R. secalis DNA in spore tape samples indicated that airborne inoculum was limited and most likely represented rain‐splashed conidia rather than putative ascospores.  相似文献   

6.
Polymyxa graminis is the vector of several important viruses, including Soilborne cereal mosaic virus, Wheat spindle streak mosaic virus, Barley yellow mosaic virus and Barley mild mosaic virus, of winter cereals worldwide. Surveys were carried out to detect these viruses and their vector P. graminis in 300 soil samples from the main wheat and barley production areas of the Anatolian part of Turkey collected in May 2002, June 2004 and May 2005. For these surveys, various susceptible wheat and barley cultivars were pot grown in the collected soil samples in a greenhouse and then analysed using ELISA and RT-PCR to detect the presence of different virus species. In addition, a combination of light microscopy following roots staining with acid fuchsin and PCR was used for detection of P. graminis. All soil samples analysed were found to be free of these soilborne viruses and their vector.  相似文献   

7.
J.W. Deacon 《EPPO Bulletin》1976,6(4):297-308
Biological control of take-all by Phialophora radicicola Cain and similar fungi is reviewed, and new evidence is presented on the possible role of hyper-parasites, like Pythium oligandrum Drechsler, to augment this. Phialophora radicicola var. graminicola Deacon is abundant in British grasslands. Its role in biological control of take-all has been demonstrated in the glasshouse with natural soils and natural population levels of this control agent. Also there is much circumstantial evidence for its beneficial role in agriculture, especially in cereal monoculture following grass crops, and in natural and amenity grasslands. Some other similar fungi control take-all in the glasshouse, but their roles in current agricultural practice are not known. The take-all fungus, itself, can reduce infection of roots by P. radicicola, so there is a dynamic interaction between these fungi. This is affected by host type, relative inoculum potentials of the fungi, and possibly by environmental conditions. By careful manipulation, therefore, it might be possible to control take-all under a wide range of field conditions. The chief role of P. radicicola and similar fungi is to delay establishment of severe take-all early in cereal monoculture, rather than to combat an existing high disease level. It may therefore be desirable to combine different biocontrols, and hyperparasites like Pythium oligandrum may be important in this respect. This fungus was tested against varieties of Gaeumannomyces graminis Arx & Olivier and Phialophora radicicola in the laboratory; the host responses differed greatly, from marked susceptibility (P. radicicola var. radicicola) to almost complete resistance (G. graminis var. graminis). Hence, P. oligandrum might be used to alter relative population levels of these fungi in the field, but first its behaviour in natural soils must be studied.  相似文献   

8.
The disease development and population structure of Puccinia graminis f. sp. avenae, which causes stem rust on oats, were studied to investigate if sexual reproduction plays an important role in the epidemiology of the disease. The genetic population structure of P. graminis f. sp. avenae in Sweden was investigated by sampling 10 oat fields in July and August 2008 and seven fields during the same period in 2009. Nine single‐pustule isolates were first used to test simple sequence repeat (SSR) markers developed for P. graminis f. sp. tritici. Eleven of the 68 tested SSR markers were useful for genotyping P. graminis f. sp. avenae. For the main study, DNA from single uredinia was extracted and the SSR markers were used to genotype 472 samples. Both allelic and genotypic diversity were high in all fields, indicating that P. graminis f. sp. avenae undergoes regular sexual reproduction in Sweden. No significant relationship between genetic and geographic distances was found. Disease development was studied on two farms during 2008 and 2009. The apparent infection rates ranged between 0·17 and 0·55, indicating the potential for rapid disease development within fields. The incidence of oat stem rust has increased recently in Sweden. One possible explanation is a resurgence of its alternate host, barberry (Berberis spp.), after the repeal of the barberry eradication law in 1994. Barberry is present in several grain‐producing areas in Sweden, which supports the conclusion that P. graminis f. sp. avenae undergoes regular sexual reproduction there.  相似文献   

9.
This study showed how barley plants can be shifted in their response to isolates of the mildew pathogen Blumeria graminis with different host adaptation by overexpression of the barley phytoglobin gene HvHb1. At early infection stages, plants overexpressing phytoglobin (GPHb1) showed less papilla formation and more hypersensitive response against both virulent and avirulent pathogen isolates compared to the wildtype (WT) plants. The shift was most pronounced in a wheat-adapted isolate (B. graminis f. sp. tritici). At later infection stages, GPHb1 plants infected with a virulent pathogen isolate (A6) showed less leaf chlorosis compared to the WT plants, indicating delayed senescence. The chlorophyll level was significantly higher in A6-infected GPHb1 plants 9 days after inoculation (dai) and the senescence indicators sphingosine-1-phosphate:ceramide ratio and phytol content confirmed delayed senescence. At 14 dai the percentage of fungal DNA was significantly higher on the GPHb1 plants than on WT plants, probably as a result of the delayed senescence. The results show that overexpression of phytoglobin (previously known as plant haemoglobin) can be an important tool to understand disease-related stress effects in plants of agronomic importance and for understanding basic resistance mechanisms. Studying this process in more detail may provide insights into how to alleviate stress-related senescence in plants.  相似文献   

10.
Stripe rust of wheat caused by Puccinia striiformis f. sp. tritici is one of the most important diseases on wheat worldwide, especially in temperate regions with cool moist weather conditions. A rapid and reliable detection of the pathogen in latent infected wheat leaves during overwintering of the fungus in the dormant stage will contribute to determine the initial inoculum potential and thus to predict early outbreak and to improve effective management of the disease. To achieve this aim, a PCR-based method was developed for specific and sensitive detection of P. striiformis. Specific primers were designed according to a genome-specific sequence of P. striiformis. To evaluate the specificity of the primers, seven different isolates and races of P. striiformis as well as six other pathogens of wheat were tested. All isolates of P. striiformis yielded a distinct band of a fragment of 470 bp, while using DNA of the other wheat pathogens as a template no amplification product was detected. The sensitivity of the primers was tested using serial dilutions of total DNA from P. striiformis; the limit of detection was 10 pg of DNA. Using extracts from P. striiformis-infected wheat leaves, the fungus could be determined in the leaves before symptoms appeared. The stripe rust could also be detected in the dormant stage by the PCR assay in samples of wheat leaves taken during the winter season. The application of the PCR assay may be useful for rapid and reliable detection of P. striiformis in latent infected leaves of overwintering wheat plants.  相似文献   

11.
When fungal germlings, after forming haustoria of Blumeria graminis f. sp. hordei (B. graminis), were removed from the surfaces of barley coleoptiles by cellulose acetate, followed by challenge inoculation with the non-pathogen Erysiphe pisi, they infected the nonhost barley coleoptile cells. This phenomenon was not observed on the coleoptile surface when the fungal germlings of B. graminis were removed before the formation of haustoria. Also, when the surface was inoculated with the pathogen of barley B. graminis as a challenger, after removing the fungal germlings of inducer post haustorial formation, the penetration efficiency of the fungi increased significantly compared with that of the control. Furthermore, when we extracted the crude-susceptibility inducing factor (suppressor) from coleoptiles before and after the formation of haustoria of B. graminis, suppressor activity against infection with E. pisi was observed only in the extract of barley coleoptiles that included haustoria of B. graminis about 18 h or later after inoculation. Surprisingly, however, the extract did not increase the penetration efficiency of B. graminis significantly. Thus, we hypothesize that the suppressor extracted from barley coleoptiles in which B. graminis had formed haustoria has no effect on increasing the penetration efficiency of the primary infection from the appressorium of B. graminis but has an effect on the infection with non-pathogen E. pisi.  相似文献   

12.
The new powdery mildew fungicide quinoxyfen belongs to the novel quinoline class of chemistry. Although its biochemical mode of action is unknown, quinoxyfen does not act in the same way as other cereal fungicides. It is a systemic protectant which inhibits the early stages of mildew infection on a wide range of crops, and provides season-long protection from a single early-season spray applied around GS 31. The base-line sensitivity profile of quinoxyfen was defined for barley powdery mildew (Erysiphe graminis f.sp. hordei) from over 340 field isolates collected from different parts of the UK from 1991 onwards. Sensitivities ranged from <0·0001→0·16 mg litre-1 with a mean of 0·003 mg litre-1. Current work is extending the base-line sensitivity studies to wheat powdery mildew (E. graminis f.sp. tritici), and includes isolates from European trials, but so far this new data set has shown no differences from barley powdery mildew. Quinoxyfen-resistant mutants were generated in the laboratory, and some similar resistant strains were obtained from treated field crops. These laboratory and field strains were always defective, in some way, for sporulation and, curiously, all required the presence of quinoxyfen for survival in culture. Attempts to generate resistant mutants that sporulated normally were unsuccessful. These studies suggested that the resistance risk for quinoxyfen is low. The recommended anti-resistance strategy accompanying introduction of quinoxyfen avoids seed treatments and late-season applications. Instead, a single early (GS 31) treatment using either pre-formulated mixtures or alternating with a fungicide with different mode of action is recommended. This strategy will be supported by continued monitoring of wheat and barley powdery mildew. ©1997 SCI  相似文献   

13.
Beet necrotic yellow vein virus (BNYVV) is transmitted by Polymyxa betae to sugar beet, causing rhizomania disease. Resistance-breaking strains of BNYVV, overcoming single (Rz1) or double (e.g. Rz1  +  Rz2) major resistance genes in sugar beet have been observed in France and recently in the USA and Spain. To demonstrate if resistance-breaking is dependent on inoculum density, the inoculum concentration of BNYVV and P. betae in soil samples where resistance-breaking had been observed was estimated using the most probable number (MPN) method. The MPN-values obtained displayed highly significant differences with respect to the virus concentration in various soils and did not correlate with the ability to overcome resistance. Virus quantification in susceptible plants demonstrated that soils containing resistance-breaking isolates of BNYVV did not produce higher virus concentrations. The MPN assay was repeated with Rz1  +  Rz2 partially-resistant sugar beets to see if the resistance-breaking is concentration-dependent. There was no correlation between soil dilution and increased virus concentration in Rz1  +  Rz2 plants produced by BNYVV resistance-breaking strains. Determination of the absolute P. betae concentration by ELISA demonstrated that all resistance-breaking soil samples contained elevated concentrations. However, the calculation of the proportion of viruliferous P. betae did not show a positive correlation with the resistance-breaking ability. Finally resistance-breaking was studied with susceptible, Rz1 and Rz1  + Rz2 genotypes and standardised rhizomania inoculum added to sterilised soil. Results from these experiments supported the conclusion that resistance-breaking did not correlate with virus concentration or level of viruliferous P. betae in the soil.  相似文献   

14.
发生在我国的小麦黄花叶病毒病   总被引：6，自引：0，他引：6  
本文对山东荣成流行的一种小麦病毒病进行了鉴定。提纯的病毒颗粒为长线状,13×100—300nm及13×350—650nm。汁液接种感染小麦,但不感染烟草、苋色藜等植物。病土、病根以及含有禾谷类多粘菌(POlymyxa graminis)游动孢子的浸液可以传毒于小麦、大麦及黑麦。此病毒与大麦黄花叶病毒(BYMV)、小麦梭条花叶病毒(WSSMV)有血清学关系,与小麦土传花叶病毒(WSBMV)无血清学关系。病叶表皮细胞中有无定形内含体。超薄切片可见风轮状内含体。实验结果表明,荣城地区发生的这种小麦病毒病是小麦黄花叶病毒所致。  相似文献   

15.
Organic management of soils is generally considered to reduce the incidence and severity of plant diseases caused by soil-borne pathogens. In this study, take-all severity on roots of barley and wheat, caused by Gaeumannomyces graminis var. tritici, was significantly lower in organically-managed than in conventionally-managed soils. This effect was more pronounced on roots of barley and wheat plants grown in a sandy soil compared to a loamy organically-managed soil. Fluorescent Pseudomonas spp. and in particular phlD+ pseudomonads, key factors in the take-all decline phenomenon, were represented at lower population densities in organically-managed soils compared to conventionally-managed soils. Furthermore, organic management adversely affected the initial establishment of introduced phlD+ P. fluorescens strain Pf32-gfp, but not its survival. In spite of its equal survival rate in organically- and conventionally-managed soils, the efficacy of biocontrol of take-all disease by introduced strain Pf32-gfp was significantly stronger in conventionally-managed soils than in organically-managed soils. Collectively, these results suggest that phlD+ Pseudomonas spp. do not play a critical role in the take-all suppressiveness of the soils included in this study. Consequently, the role of more general mechanisms involved in take-all suppressiveness in the organically-managed soils was investigated. The higher microbial activity found in the organically-managed sandy soil combined with the significantly lower take-all severity suggest that microbial activity plays, at least in part, a role in the take-all suppressiveness in the organically-managed sandy soil. The significantly different bacterial composition, determined by DGGE analysis, in organically-managed sandy soils compared to the conventionally-managed sandy soils, point to a possible additional role of specific bacterial genera that limit the growth or activity of the take-all pathogen.  相似文献   

16.
Late blight caused by the oomycete Phytophthora infestans is a disease of potato and tomato of worldwide relevance and is widespread throughout Europe and the Mediterranean region. While pathogen populations in northern Europe have been sampled and characterized for many years, the genetic structure of populations from southern Europe, including Italy, has been less studied. Between 2018 and 2019, we collected 91 samples of P. infestans from potato and tomato crops in Italy, Algeria, and Tunisia on FTA cards and genotyped them using 12-plex microsatellites. These samples were compared to genotypes of P. infestans previously collected within the framework of the EuroBlight network and from published sources. Four clonal lineages were identified: 13_A2 (Blue 13), 2_A1, 23_A1, and 36_A2. Two other isolates collected could not be matched to any currently known clonal lineage. The 13_A2 and 36_A2 lineages were found exclusively in southern Italy and Algeria, while 2_A1 was only found in Algeria. This is the first report of the 36_A2 lineage in Italy. Two isolates from Solanum nigrum were 13_A2, suggesting this weed host could be a reservoir of inoculum. The 23_A1 lineage was found widely on infected tomato crops in Italy and is the same as the lineage US-23 that is widespread in North America. Differences in genotypes across the country suggests that there may be different sources of introduction into Italy, possibly via infected seed tubers from other countries in Europe, tubers for consumption from North Africa, or tomatoes.  相似文献   

17.
BACKGROUND: Proquinazid is a new quinazolinone fungicide from DuPont registered in most European countries for powdery mildew control in cereals and vines. The aim of this paper is to present baseline sensitivity data in populations of Blumeria graminis f. sp. tritici EM Marchal and Erysiphe necator (Schw) Burr as well as results from cross‐resistance studies with other fungicides. RESULTS: Proquinazid exhibited a high intrinsic activity on B. graminis f. sp. tritici isolates at rates ranging from 0.000078 to 0.02 mg L?1. Erysiphe necator isolates were comparatively less sensitive to proquinazid, with EC50 values ranging from 0.001 to 0.3 mg L?1. Proquinazid controlled equally well B. graminis f. sp. tritici isolates sensitive and resistant or less sensitive to tebuconazole, fenpropimorph, fenpropidin, cyprodinil and kresoxim‐methyl. A positive correlation (r = 0.617) between quinoxyfen and proquinazid sensitivities was found among 51 B. graminis f. sp. tritici isolates. Quinoxyfen‐resistant B. graminis f. sp. tritici isolates were slightly less sensitive to proquinazid than the quinoxyfen‐sensitive isolates; however, proquinazid remained much more active than quinoxyfen on these isolates. A stronger sensitivity relationship (r = 0.874) between proquinazid and quinoxyfen was found among 65 E. necator isolates tested in a leaf disc assay. The sensitivity values for proquinazid were significantly lower than those for quinoxyfen, confirming the higher intrinsic activity of proquinazid on both pathogens. CONCLUSION: Given the history of resistance development in powdery mildew and the observed sensitivity relationship with quinoxyfen, specifically in E. necator, we conclude that the risk of resistance developing to proquinazid might be influenced by the use of quinoxyfen. Based on these results, the authors recommend that proquinazid and quinoxyfen be managed together for resistance management. Copyright © 2009 Society of Chemical Industry  相似文献   

18.
Net form of net blotch caused by Pyrenophora teres f. teres (Ptt) is a major foliar disease of barley (Hordeum vulgare) worldwide. Knowledge of the evolution of Ptt pathogen populations is important for development of durable host-plant resistance. This study was conducted to investigate changes in genetic structure of a Ptt population within a barley field during three cropping years. The susceptible barley cultivar Henley was inoculated with Ptt isolate NB050. Leaf samples were collected during the years 2013–15 and 174 single spore Ptt isolates stored. Genotyping using Diversity Arrays Technology markers identified that 25% of isolates were clones of the inoculated isolate and 75% of isolates were multilocus genotypes (MLGs) differing from the original inoculated genotype. The novel genotypes probably originated from a combination of windborne spores from neighbouring fields, infected seed and sexual recombination in the field. The rapid change in the genotypic composition of the Ptt population in this study suggests adaptive potential of novel genotypes and demonstrates the need for barley breeders to use multiple sources of host-plant resistance to safeguard against resistance being overcome.  相似文献   

19.
Polymyxa graminis is a soil-borne obligate organism that transmits bymoviruses and furoviruses to barley and wheat. We analyzed rDNA-ITS sequences of P. graminis from roots of wheat and barley in fields in Japan and obtained five kinds of sequences; two sequences were almost the same as known ribotype Ia and IIa, respectively, and three were close to ribotype Ib. When infection of P. graminis was examined using PCR, ribotype Ia was detected only in barley, but ribotypes Ib and IIa were detected in both wheat and barley. Our analysis suggested that Japanese ribotype Ib transmits furoviruses and bymoviruses.  相似文献   

20.
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   

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