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1.
A sensitive real-time polymerase chain reaction (PCR) assay was developed for the quantification of Spongospora subterranea, the cause of powdery scab and root galling in potato, and the vector of Potato mop top virus. A specific primer pair and a fluorogenic TaqMan® probe were designed to perform a quantitative assay for the detection of S. subterranea in soil, water and plant tissue samples. The assay was tested using DNA from cystosori, zoospores, plasmodia and zoosporangia of the pathogen. DNA was extracted directly from cystosori suspended in water and from clay soil with varying levels of added cystosori. DNA obtained from zoospores released into nutrient solution by cystosori in the presence of tomato bait plants was also tested, as was DNA from plasmodia and zoosporangia in infected tomato roots. In many cases, detection was successful even at low inoculum levels. This specific quantitative assay could therefore be a useful tool for studying the biology of S. subterranea, and for the optimisation of disease avoidance and control measures.  相似文献   

2.
Infectivity of resting spores ofPolymyxa betae in soil stored air-dry or moist was determined by assessing infection of bait plants that were exposed to the soil. Storage of soil under air-dry conditions at room temperature resulted in a delayed onset of germination of resting spores compared to germination in soil stored under moist and cool conditions, as inferred from the infection of the bait plants. Bait plants had to be exposed for more than 12 h to flooded infested soil before germination and infection had occurred. However, when soil was prewetted for 24 h before exposing bait plants, germination, infection and transmission of beet necrotic yellow vein virus (BNYVV) were accomplished within 12 h, but only with the moistly stored soil. When resting spores isolated from roots were stored for 4 and 8 weeks under dry conditions at 22°C, germination of viruliferous spores, as measured by detection of BNYVV in bait plants exposed for 48 h to the spores, was less than that of spores stored in moist soil at 22°C. Approximately 100% of bait plants were infected after exposure to resting spores that were frozen in demineralized water or stored cool (5°C) in water or moist soil for 42 weeks. Air-dry cool storage for 42 weeks resulted in a low percentage of infection. Storage conditions of soil influence the results of bioassays for detection of rhizomania when short baiting periods are applied, whereas differences in infectivity were not detected using a bioassay with long duration.  相似文献   

3.
A system to culture viruliferousPolymyxa betae and to produce zoospores is described. The zoo spores were used for inoculation of beet seedlings, grown in nutrient solution, in tests for resistance to beet necrotic yellow vein virus (BNYVV). On most occasions in a time course experiment, and with various zoospore cultures, the partially resistant cultivar Rima and the accession Holly-1–4 had virus concentrations similar to the susceptible cultivar Regina, but the virus concentration inBeta vulgaris ssp.maritima accession WB42 was significantly lower (P<0.05). ‘Regina’ could be distinguished from various resistant accessions by a significantly higher virus concentration (P<0.05) shortly after inoculation, or after transplanting the seedlings from the nutrient solution into sand. Results of screening for resistance to BNYVV, using zoospores for inoculation, did not correspond with results of a test in which infested soil was used.Tests in which seedlings are grown in nutrient solution and inoculated with zoospores are suitable for the detection of accessions with a high level of resistance to BNYVV. To obtain virus infection in all plants, the optimal density of the zoospore suspension should first be determined and plants should be assayed shortly after inoculation.  相似文献   

4.
Spread of Phytophthora root and crown rot in three pot plant species was studied on ebb-and-flow benches where the nutrient solution was recirculated. The plant species and their respective pathogens were: Saintpaulia ionantha – P. nicotianae, Gerbera jamesonii – P. cryptogea, and Spathiphyllum wallissii – Phytophthora spp. Ebb-and-flow benches were infested with the pathogen using different methods: 18–25% of the plants on a bench were inoculated or potted in soil infested with the pathogen or the nutrient solution was infested by either zoospores or mycelium fragments. More than 80% of the inoculated Saintpaulia plants and 22% of plants potted in infested soil developed disease but no spread of the disease was observed. Infestation of the nutrient solution did not result in any diseased Saintpaulia plant. More than 70% of the Gerbera plants developed disease as a result of spread of the pathogen irrespective of the infestation method used. No significant spread of the disease was observed with inoculated Spathiphyllum plants nor from plants potted in infested soil. A few Spathiphyllum plants developed disease symptoms after infestation of the nutrient solution with zoospores. In one experiment, nearly all Spathiphyllum plants were diseased after infestation of the nutrient solution with mycelium fragments. The presence of an irrigation mat significantly reduced the spread of the Phytophthora disease in Gerbera and Spathiphyllum. The possibility of an irrigation mat acting as a filter for zoospores is discussed.  相似文献   

5.
U. MERZ 《EPPO Bulletin》1989,19(3):585-592
Spongospora subterranea, causal agent of powdery scab of potatoes and vector of potato mop-top furovirus, survives in the soil as balls of resting spores (cystosori). So far, the factors affecting longevity, germination and infectivity of cystosori have not been investigated. A rapid and versatile bioassay with tomatoes as bait plants has been developed to quantify the infectivity of cystosorus inoculum or infested soil. The intensity of root infection, as a measure of infectivity, was determined by evaluating the quantity of zoosporangia present in epidermal cells and root hairs of the whole, stained root system. A correlation was obtained between the intensity of root infection and the cystosorus inoculum density in nutrient solution. Sterile soil suppressed the inoculum potential of pure cystosori. Infectivity of untreated soil decreased with increasing time of storage. Root infection was not influenced by the pH level of the nutrient solution.  相似文献   

6.
Inoculation of plants by spraying with a suspension of zoospores (released from sporangia of Sclerospora graminicola ) induced immediate encystment of the zoospores and drastically reduced their ability to cause disease. The incidence of infection in spray-inoculated pearl millet seedlings was reduced from 90% when sporangia were sprayed, to less than 30% when zoospores were sprayed. Rapid encystment was observed when zoospores were sprayed from both a hand-pumped sprayer and a compressed-gas sprayer and was probably caused by shearing forces. Chilling suspensions of sporangia prior to spraying delayed zoospore release and was an effective method for maintaining infection potential. Disease incidence was higher when sporangia were chilled to 0·2°C rather than to 4°C. Chilling resulted in some abnormal zoospore structures being released from sporangia when suspensions were returned to 20°C. The frequency of these structures increased with increasing chilling time. For seedlings sprayed with sporangia before zoospore release, a small reduction in disease incidence was observed when chilled inoculum was used, probably due to cold disruption of zoosporogenesis. For large-scale disease resistance screening, this reduction is outweighed by the benefit of a uniform and adequately high disease pressure that can be obtained over many hours using chilled spore suspensions.  相似文献   

7.
Alfalfa, maize, sorghum and sugarbeet plants were inoculated with zoospores ofPhytophthora andPythium species in order to assess the effects of inoculum density, plant age and temperature on disease severity. Seedlings were grown axenically in test tubes and inoculated with zoospore suspensions. Disease severity was assessed by measuring the root growth and discoloration of treated and control seedlings. The incremental root length of all plants decreased and root discoloration increased as inoculum concentration of the pathogen increased. Changes were more intensive among low levels of zoospore concentrations and no significant differences in disease severity were found for inoculum densities higher than 104 zoospores ml-1. Disease severity was negatively related to plant age. Disease development on sugarbeet seedlings infected withPythium andPhytophthora species was affected by temperature, but the pattern of response was determined by the pathogen’s temperature preferences. The incremental root length decreased as temperature increased up to 25°C. The effect ofPythium dissimile andPhytophthora cactorum on root length was significantly lower at 35°C than at 25°C, whereasPythium aphanidermatum andPhytophthora nicotianae caused significant damage to roots even at 35°C. http://www.phytoparasitica.org posting Dec. 3, 2001.  相似文献   

8.
Pepino mosaic virus (PepMV) was shown to be efficiently transmitted between tomato plants grown in a closed recirculating hydroponic system. PepMV was detected in all plant parts after transmission via contaminated nutrient solution using ELISA, immunocapture RT‐PCR, RT‐PCR, electron microscopy, and by inoculation to indicator plants. Detection of PepMV in nutrient solution was only possible after concentration by ultracentrifugation followed by RT‐PCR. Roots tested positive for PepMV 1–3 weeks after inoculation, and subsequently a rapid spread from the roots into the young leaves and developing fruits was found within 1 week. PepMV was only occasionally detected in the older leaves. None of the infected plants showed any symptoms on fruits, leaves or other organs. Pre‐infection of roots of tomato cv. Hildares with Pythium aphanidermatum significantly delayed PepMV root infections. When mechanically inoculated with PepMV at the 2–4 leaf stage, yield loss was observed in all plants. However, only plants of cv. Castle Rock recorded significant yield losses when infected via contaminated nutrient solution. Yield losses induced by infection with PepMV and/or P. aphanidermatum ranged from 0·4 up to 40% depending on experimental conditions.  相似文献   

9.
BACKGROUND: Phytophthora nicotianae Breda de Haan is a common pathogen of ornamental plants in recycled irrigation systems. In a previous study, annual vinca (Catharanthus roseus Don) inoculated with zoospore suspensions using a CO2‐pressurized sprayer had less foliage blight than plants inoculated using a hand sprayer. Here, the impact of hydrostatic pressure, agitation and aeration with CO2 on the survival of P. nicotianae zoospores was examined. RESULTS: Exposure of zoospores to 840 kPa hydrostatic pressure for 8 min or agitation at a mixing intensity (G) of 6483 s?1 for 4 min at 22–23 °C did not kill zoospores, but resulted in viable cysts. Motile and forcefully encysted zoospores of P. nicotianae were equally infectious on vinca or lupine (Lupinus polyphylus Lindl.). Bubbling CO2 into zoospore‐infested water at 110.4 mL (0.2 g) min?1 for 5 min caused 81% reduction in the number of germinated zoospores. Pressure at 630 kPa (16.3 g CO2) or 70 kPa (3.85 g CO2) facilitated CO2 injection and shortened the zoospore inactivation time to 30 s. When air was bubbled through the suspension, germination was similar to the control. CONCLUSIONS: Exposure to CO2 killed P. nicotianae zoospores in water. Neither pressure nor agitation had an effect on zoospore viability or infectivity. Based on results of this study, the authors designed a recycling CO2 water treatment system that is currently under evaluation. Copyright © 2010 Society of Chemical Industry  相似文献   

10.
Hoagland's solution (HS), a defined nutrient supplement for plants, has been previously reported to stimulate zoospore release from resting spores of the potato pathogen Spongospora subterranea f. sp. subterranea. This study obtained direct empirical evidence for an increase in zoospore release with HS treatment, and identified Fe‐EDTA as the stimulant component of HS. Stimulation of resting spores by HS and Fe‐EDTA resulted in greater and earlier zoospore release compared to a distilled water control, and in the presence of a susceptible tomato host plant resulted in enhanced root infection. Given the labile nature of S. subterranea zoospores, it was postulated that stimulation of premature release of zoospores from the dormant resting spores in absence of susceptible hosts could reduce soil inoculum levels. In two glasshouse trials in the absence of host plants, both Fe‐EDTA and HS soil treatments reduced S. subterranea soil inoculum levels, providing proof of concept for the ‘germinate to exterminate’ approach to inoculum management.  相似文献   

11.
Alfalfa (Medicago sativa) is one of several legumes that is affected by Aphanomyces root rot (ARR) caused by Aphanomyces euteiches. Symptoms of ARR on alfalfa seedlings include a yellow-grey discolouration of roots, rotting and loss of lateral roots, stunted growth, chlorotic foliage and reduction of nitrogen-producing nodules on roots. Infection can also occur on adult plants leading to loss of lateral roots and nodules. At the seedling stage, ARR decreases alfalfa stand establishment, and field longevity is reduced when adult plants are infected. A. euteiches is an oomycete pathogen that has motile zoospores and thick-walled oospores that can survive for many years in soil. Two races are currently recognized by pathogenicity on differential alfalfa check cultivars. Most alfalfa cultivars contain race 1 resistance, but there is an increasing development of cultivars with resistance to race 2. Management strategies include planting resistant cultivars, avoiding planting in fields with poor drainage and rotating crops with nonhost plants.  相似文献   

12.
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   

13.
K. LINDSTEN 《EPPO Bulletin》1989,19(3):531-537
Some experiments with soil-borne beet viruses in cement tubes in a wire netting enclosure are described. It is confirmed that rhizomania (virus + vector) originating from German soil can survive and cause rhizomania in Sweden. Antisera produced in 1987 to one German BNYVV isolate and to one Swedish soil-borne beet virus isolate, 86-109, which is distinct from BNYVV, were used to check ELISA reactions in the tube beets. Positive ELISA was obtained not only for BNYVV but also for the 86-109 virus from tubes with German inoculum. Beets from tubes with Swedish inoculum reacted only against 86-109 antiserum. In 1988-09, ELISA of 118 sugarbeet plants from Öland and 73 from Skåne, collected in 42 different fields with spots resembling rhizomania, showed no or weak reactions against 86-109 antiserum, in contrast to plants collected in 1987. However, after transplanting the field plants into a warm glasshouse and using bait plants it was shown in ELISA and in transmission to Chenopodium quinoa that many of the bait plants became infected with the 86-109 and ‘related viruses’ but not with BNYVV. Viruses of the 86-109 type seem to be common both in Sweden and elsewhere but may escape detection, especially in mixed infections with BNYVV.  相似文献   

14.
Transmission of three strains of OMMV by an Olpidium sp. was evaluated and compared. The three strains were 1) an OMMV wild type (WT) recovered from olive trees, 2) an OMMV variant (L11) obtained after 15 serial passages of single local lesions induced in Chenopodium murale plants, and 3) a construct OMMV/OMMVL11 in which the coat protein (CP) gene replaced that of the wild type. A single-sporangial culture derived from Chinese cabbage (Brassica pekinensis) used as a bait plant grown in soil of an olive orchard, was identified as Olpidium brassicae based on the size and sequence of the generated amplicon in PCR specific tests. Each of the three virus strains was soil transmitted to cabbage roots in the absence of the fungus at similar rates of 30 to 40%. Separate plant inoculation by O. brassicae zoospores incubated with each viral strain resulted in enhanced transmission of OMMV, reaching 86% of infection whereas that of the other two strains remained practically unaffected at ca. 34%. Binding assays showed that the amount of virus bound to zoospores, estimated spectrophotometrically, was 7% in the case of OMMV, and practically nil in the case of the other two viral strains. Substitution of the coat protein (CP) gene of OMMV by that of the OMMV L11 strain, drastically reduced viral transmissibility in the presence of zoospores to the level of that observed in their absence. Our data shows that OMMV soil transmission is greatly enhanced by O. brassicae zoospores and that the viral CP plays a significant role in this process, most likely by facilitating virus binding and later entrance into the host plant roots.  相似文献   

15.
Possible Root Infection of Cercospora beticola in Sugar Beet   总被引：1，自引：0，他引：1  
A potential primary infection site of the foliar pathogen Cercospora beticola in sugar beet is described. Sugar beet seedlings of the susceptible cv. Auris were grown in a standard soil for 14 days. A monoconidial culture of a C. beticola isolate was grown to produce conidia. In experiment 1, roots were immersed in a conidial suspension of isolate code IRS 00-4, or in tap water (control), for 2 days. After incubation seedlings were potted in a peat – fine river sand mixture and placed at low relative humidity (RH) (<80%) or high RH (100%). Twelve days after infection, seedlings at high RH showed more disease incidence (90%) than seedlings grown at low RH (disease incidence = 25%), whereas no disease symptoms developed in the control seedlings. Cercospora leaf spots (CLSs) developed on the cotyledons, leaves, petioles and stems of the seedlings. In experiment 2, roots were immersed in a conidial suspension of isolate code IRS 00-2 for 5 h. Thirty-four days after infection at high RH, 100% disease incidence was observed in the treated seedlings and one CLS in the control treatment. First indications of leaf spot development were observed as reddish purple discolouration of individual parenchymatic cells. Because splash dispersal and symptoms due to infested soil were excluded, we showed that it is possible to obtain CLS symptoms in sugar beet seedlings when their roots were immersed in conidial suspensions of C. beticola, thus demonstrating that roots can be a primary infection site.  相似文献   

16.
Horizontal dispersal of beet necrotic yellow vein virus (BNYVV) by means of viruliferous zoospores ofPolymyxa betae was studied in greenhouse experiments. BNYVV was not detected in roots of sugar beet plants grown in silver sand for 4 weeks at a root-free distance of 5 cm from eitherP. betae- and BNYVV-infected plants or BNYVV-infested soil. Spread of BNYVV from inoculum sources in the field was studied in the absence and presence of tillage practices. Active dispersal in combination with root growth from and towards point sources of inoculum contributed only little to horizontal dispersal of viruliferous inoculum and spread of disease during the season, as determined for one soil type, two different years and in the absence of tillage and tread. In the second beet crop after application of inoculum to whole field plots, more BNYVV-infected plants were detected at 2 m than at 8 m distance from the infested plots in the tillage direction. In the third year, disease incidence at 8 m was high and equivalent to that at 2 m.  相似文献   

17.
Inhibition of photosynthesis by metamitron in the rooting medium and its subsequent recovery after transfer of the roots to herbicide-free nutrient solution was measured in eight plant species. Fast and complete recovery within a few hours after treatment showed that metamitron, once absorbed, was rapidly and completely inactivated in the leaves of sugar beet (Beta vulgaris L.). Inactivation in perennial ryegrass (Lolium perenne L.) was slower and incomplete. It was low in Echinochloa crusgalli (L.) P.B., Amaranthus retroflexus L., Alopecurus myosuroides Huds. and bean (Phaseolus vulgaris L.), and undetectable in maize (Zea mays L.) and Portulaca oleracea L. From the transpiration rate and the concentration of metamitron in the nutrient solution that just did not cause inhibition of photosynthesis in sugar beet, uptake and inactivation rates per unit leaf area were calculated to be at least 18·5 ng/cm2/h. The same external concentration markedly depressed photosynthesis in the other more susceptible species. After leaf sprays sugar beet plants gradually resumed the normal rate of photosynthesis, but bean plants did not recover.  相似文献   

18.
Studies were carried out to test the sugar beet as a host for Clavibacter michiganensis ssp. sepedonicus (Cms), the causal agent of bacterial ring rot of potato. For that purpose field trails and greenhouse experiments were performed. At the field trails sugar beet was cultivated on plots, which were contaminated with Cms infected soil. Subsequently the plots were used for the cultivation of potatoes. Both, the harvested sugar beets and the potatoes, were tested in polymerase-chain reaction (PCR). Both, the sugar beets and the potatoes were tested negative for Cms. In the greenhouse sugar beet was treated with Cms by cultivation in Cms contaminated soil, by direct inoculation into the plant or by indirect inoculation by watering with contaminated suspensions. In most experiments Cms could not be detected in sugar beet after 18 weeks, so it did not remain viable in the plant. But in one experiment after direct inoculation Cms was detected and reisolated in sugar beet. Additionally, no infection of sugar beet was observed via contaminated soil.  相似文献   

19.
A total of 25 ornamental plant species representing 10 families were inoculated using three genotypes, each representing one of the genetic lineages NA1, NA2, and EU1 of the pathogen Phytophthora ramorum. Leaves were inoculated using suspensions with two zoospore concentrations and exposure at three temperatures, while stems were inoculated using agar plugs colonized by mycelia. Susceptibility was determined by measuring either the success of pathogen reisolation or lesion length caused by the pathogen. Infectivity was determined by counting sporangia in washes of inoculated leaves or stems. Results from all three pathogen genotypes combined were used to rank each of the 25 plant species for susceptibility and infectivity, while pooled results per genotype from all 25 hosts combined were employed for a preliminary comparison of pathogenicity and infectivity among genotypes. Statistical analyses showed that leaf results were affected by the concentration of zoospores, temperature, plant host, pathogen genotype, and by the interaction between host and pathogen genotype. Stem results were mostly affected by host and by the interaction between host and pathogen genotype. Hosts ranked differently when looking at the various parameters, and differences in rankings were also significant when comparing stem and leaf results. Differences were identified among the 25 hosts and the three pathogen genotypes for all parameters: results can be used for decision-making regarding regulations or selection of plants to be grown where infestations by P. ramorum are an issue.  相似文献   

20.
An ELISA test was developed for the quantitative detection of the obligate parasite Polymyxa betae , the vector of Beet necrotic yellow vein virus (BNYVV), in infected sugarbeet roots. The test used monoclonal and polyclonal antibodies raised to a recombinantly expressed glutathione-S-transferase (GST) from P. betae . A close correlation was found between the number of P. betae zoospores in serially diluted suspensions and absorbance values in the ELISA test. Time-course studies of plants grown in naturally infested soils in controlled environment tests demonstrated the value of the ELISA test in screening for P. betae resistance. In preliminary tests, P. betae -resistant accessions of the wild sea beet ( Beta vulgaris ssp. maritima ), which might be used to restrict the transmission of BNYVV, were identified.  相似文献   

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