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1.
ABSTRACT The effect of solar irradiance (SI) on the viability of sporangia of isolates belonging to two clonal lineages, US-1 and US-8, of Phytophthora infestans was assessed. Exposure during a 3-h period on sunny days (SI > 600 W/m(2)) drastically reduced germination regardless of the time of day of the exposure. After 1 h of exposure on sunny days, the viability of sporangia decreased by approximately 95%, and the effective time necessary to inactivate 95% of the sporangia was 1.1 h. The effective dose to inactivate 95% of the sporangia on sunny days was 2.6 MJ/m(2). On overcast (SI < 300 W/m(2)) days, survival after 3 h was reduced only slightly. Thus, other variables being equal, sporangia will survive hours longer in the atmosphere on cloudy days than on sunny days. 相似文献
2.
采用常规微生物分离和植物生物量测定等方法,将木霉菌REMI变异菌株的孢子进行种子接菌、土壤接菌、水中接菌,研究木霉菌REMI变异菌株对农作物甜瓜和玉米及杂草等生长性状、甜瓜根际土壤微生物和鱼苗生长以及在水中存活等的影响,检测其生物安全性。结果表明,除Ttrm53外,其余木霉菌变异株和出发菌株T21对甜瓜和玉米种子安全,并且能够显著提高种子的出苗率、增加须根数和促进幼苗生长;部分变异菌株对杂草具有抑制作用;供试木霉菌变异株对甜瓜根际土壤真菌有抑制作用,对细菌和放线菌群体数量无显著影响;木霉菌孢子在河水及自来水中均不能萌发,分生孢子在水中存活约12～18天,厚垣孢子约18～27天,菌体自行消解;对鱼苗生长没有不良影响。 相似文献
3.
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
4.
棉铃疫菌的越冬存活 总被引：9，自引：0，他引：9
用MTT活体染色法,对棉铃疫苗(Phytophthora boehmeriae Sawada)的存活越冬进行了研究,结果表明:孢子囊和卵孢子均可在棉田土中的病残体(烂钤壳,棉籽)上存活。其中孢子囊可存活3~4个月,且其存活率可高达58.0%,认为孢子囊在棉铃疫病的再侵染过程中起重要作用。但孢子囊在1月份温度达零度时就全部死亡,不能越冬。而卵孢子在历经1990年至1991年冬季零度以下76天(其中最低温度达-2.8℃)后仍可以存活,在存活300天以后其存活率达48.8%,证明卵孢子是毫无疑问的越冬菌态。生物测定,越冬后卵孢子形态观察,卵孢子萌动变化与温度的关系表明,越冬存活的卵孢子可以成为棉铃疫病的初侵染来源。 相似文献
5.
P Mirovsky 《Folia parasitologica》1989,36(2):107-112
The growth of six strains of Plasmodium falciparum in 5% CO2, 5% O2, 90% N2 and normal air atmosphere was determined daily by microscopical examination of blood films. All strains were able to grow in flasks without additional gas mixture but significantly lower parasitaemia was observed within the first five days of cultivation. Attempt at cultivating in petri dishes without candle jar technique failed but parasites survived in plasticine sealed dishes. The cultivation in air cannot be recommended for cultures initiated from cryopreserved material or low parasitaemia (0.1-0.3%) cultures. 相似文献
6.
Phytophthora infestans in a subtropical region: survival on tomato debris, temporal dynamics of airborne sporangia and alternative hosts 总被引：2，自引：0，他引：2
Little is known about inoculum dynamics of late blight caused by Phytophthora infestans in tropical/subtropical areas, particularly in Brazil. The objectives of the present study were to assess (i) the survival of the pathogen on stems, leaflets and tomato fruits, either buried or not in soil; (ii) the pathogenicity of P . infestans to mostly solanaceous plant species commonly found in Brazil that could act as inoculum reservoir; and (iii) the temporal dynamics of airborne sporangia. Phytophthora infestans survived in tomato plant parts for less than 36 days under greenhouse and field conditions. In greenhouse tests, pathogen structures were detected earlier on crop debris kept in dry than in wet soil conditions. Isolates of two clonal lineages of P. infestans , US-1 from tomato, and BR-1 from potato, were inoculated on 43 plant species. In addition to potato and tomato, Petunia × hybrida and Nicotiana benthamiana were susceptible to the pathogen. Airborne inoculum was monitored with Rotorod and Burkard spore traps as well as with tomato and potato trap plants. Sporangia were sampled in most weeks throughout 2004 and in the first two weeks of 2005. Under tropical/subtropical conditions, airborne inoculum is abundant and is more important to late blight epidemics than inoculum from crop debris or alternative hosts. 相似文献
7.
ABSTRACT Experiments to identify the factors affecting survival of Bremia lactucae sporangia after deposition on lettuce leaves were conducted in growth chambers and outdoors under ambient conditions. Lettuce seedlings at the four-leaf stage were inoculated with B. lactucae sporangia under dry conditions. Sporangia deposited on lettuce seedlings were incubated at different temperature and relative humidity (RH) combinations, exposed to 100, 50, 25, and 0% sunlight in the second experiment, and exposed to different artificial lights in wavelength ranges of UVA (315 to 400 nm), UVB (280 to 315 nm), or fluorescent light in the third experiment. After exposure for 0 to 48 h in the first experiment and 0 to 12 h in the second and third experiments, seedlings in two pots were sampled for each treatment, and sporangia were washed from 15 leaves excised from the sampled seedlings. Germination of sporangia was determined in water after incubation in the dark at 15 degrees C for 24 h. The sampled seedlings with remaining leaves were first transferred to optimal conditions for infection (24 h), for the development of downy mildew, and then assessed for disease after 9 days. Sporangia survived much longer at 23 degrees C (>12 h) than at 31 degrees C (2 to 5 h), regardless of RH (33 to 76%). Germination percentage was significantly reduced after exposure to 50 and 100% sunlight. UVB significantly reduced sporangium viability, while fluorescent light and UVA had no effect relative to incubation in the dark. Infection of seedlings followed a pattern similar to germination of sporangia. Solar radiation is the dominant factor determining survival of B. lactucae sporangia, while temperature and RH have small, insignificant effects in coastal areas of California. This suggests that infections by sporangia that survived a day are probable only on cloudy days or on leaves that are highly shaded. 相似文献
8.
9.
Wang H Li W Chen Q Huang Y Li K Xia H Wang M Cai L Shang S Shi J 《Phytopathology》2012,102(3):267-271
A simple, rapid, small-scale microbioassay for infection of tobacco seedlings by Phytophthora parasitica var. nicotianae was developed here. This assay uses tobacco seedlings cultivated in petri dishes for a standardized method for quantitation of initial zoospore inocula and high-throughput screening of antagonistic bacteria. Zoospore inocula between 10(2) to 10(5) spores per petri dish were inoculated on 14-day-old tobacco seedlings for the susceptibility test. The optimum inocula was established to be ten thousand zoospores. One hundred and fifty pure culture bacteria with different pigments, growth rates, and morphologies were isolated from rhizosphere soil of tobacco and screened for protective ability against tobacco black shank. Fifteen bacteria presented high activity against P. parasitica on tobacco seedlings. They were identified by Biolog GEN III MicroPlate and distributed as Bacillus amyloliquefaciens, B. licheniformis, Paenibacillus pabuli, B. atrophaeus, B. subtilis, B. pumilus, and B. endophyticus, respectively. Four antagonists chosen randomly from the 15 bacteria all exhibited the same 100% protective activity in planta as that in the petri dishes. This microassay proved to be a rapid, reproducible, and efficient method for screening of potential biological agents or microorganisms and may be useful for studying mechanisms of infection and control of Phytophthora spp. under hydroponic conditions. 相似文献
10.
Summary. Fluroxypyr-MHE (methylheptyl ester) was hydrolysed to fluroxypyr in soil/water suspensions at rates several thousand times that in distilled, deionized water at similar pH and temperature: the pH 7, 25°C half-life in water was 454days, compared to 2, 5, and 5·5 hours in 1 : 100 soil/water suspensions of a Barnes loam, Catlin silt loam, and Mhoon clay. The catalysed hydrolysis did not occur in decanted, aqueous supernatants of centrifuged Barnes soil suspensions, nor in Barnes soil/water suspensions which had been autoclaved. In soils incubated (26·1°C) at field moist conditions, only 1 to 2% of the fluroxypyr-MHE had not hydrolysed after three days. An extracellular enzyme was suggested as the catalyst. 相似文献
11.
ABSTRACT Rain splash dispersal of Gibberella zeae, causal agent of Fusarium head blight of wheat, was investigated in field studies in Ohio between 2001 and 2003. Samplers placed at 0, 30, and 100 cm above the soil surface were used to collect rain splash in wheat fields with maize residue on the surface and fields with G. zeae-infested maize kernels. Rain splash was collected during separate rain episodes throughout the wheat-growing seasons. Aliquots of splashed rain were transferred to petri dishes containing Komada's selective medium, and G. zeae was identified based on colony and spore morphology. Dispersed spores were measured in CFU/ml. Intensity of splashed rain was highest at 100 cm and ranged from 0.2 to 10.2 mm h(-1), depending on incident rain intensity and sampler height. Spores were recovered from splash samples at all heights in both locations for all sampled rain events. Both macroconidia and ascospores were found based on microscopic examination of random samples of splashed rain. Spore density and spore flux density per rain episode ranged from 0.4 to 40.9 CFU cm(-2) and 0.4 to 84.8 CFU cm(-2) h(-1), respectively. Spore flux density was higher in fields with G. zeae-infested maize kernels than in fields with maize debris, and generally was higher at 0 and 30 cm than at 100 cm at both locations. However, on average, spore flux density was only 30% lower at 100 cm (height of wheat spikes) than at the other heights. The log of spore flux density was linearly related to the log of splashed rain intensity and the log of incident rain intensity. The regression slopes were not significantly affected by year, location, height, and their interactions, but the intercepts were significantly affected by both sampler height and location. Thus, our results show that spores of G. zeae were consistently splash dispersed to spike heights within wheat canopies, and splashed rain intensity and spore flux density could be predicted based on incident rain intensity in order to estimate inoculum dispersal within the wheat canopy. 相似文献
12.
Downy mildew of hop, caused by Pseudoperonospora humuli , is an important disease in most regions of hop production and is managed largely with regular fungicide applications. A PCR assay specific to P . humuli and the related organism P . cubensis was developed and used to monitor airborne inoculum in hop yards to initiate fungicide applications. The PCR amplified as little as 1 fg of genomic DNA of P . humuli , and yielded an amplicon in 70% of reactions when DNA was extracted from single sporangia. In the presence of 25 mg of soil, an amplicon was amplified in 90% of reactions when DNA was extracted from 10 or more sporangia. During nine location-years of validation, PCR detection of the pathogen in air samples occurred no later than 8 days after the appearance of trace levels of disease signs and/or detection of airborne spores in a volumetric spore sampler. Inoculum was detected on average 4·5 days before (range −8 to 14 days) the first appearance of basal spikes in six commercial yards, or 1·3 days after (range −5 to 1 days) sporangia were detected in a volumetric spore sampler in experimental plots. In commercial yards, use of PCR to initiate the first fungicide application led to enhanced disease control or a reduction in fungicide use in four of six yards compared to growers' standard practices. These results indicate that the efficiency and efficacy of hop downy mildew management can be improved when control measures are timed according to first detection of inoculum. 相似文献
13.
A. J. van der Plaats-Niterink 《European journal of plant pathology / European Foundation for Plant Pathology》1975,81(1-2):22-37
A review is given on observations ofPythium spp. so far published. In personal investigations about 4000 isolates ofPythium species were obtained from soil, water, Daphnias and plants during 1966–1972. Special attention was paid to the progressive colonization of the newly reclaimed polder Zuidelijk Flevoland: the numbers of species per sample increased from 0 in 1966 to 13 in 1972. The percentage of samples which did not contain anyPythium decreased from 54 in 1968 to 0 in 1972. From Zuidelijk Flevoland altogether 21 species were isolated, from Oostelijk Flevoland 22, of which 19 occurred in both the polders. The soil depth down to 10 cm had little influence on the occurrence ofPythium species. From soils near Rhenen and Zutphen 12 and 19 species respectively were isolated, from flax and flaxfields 11, from forests 8, from roots of different plants 17 and from water 11. Besides species already previously recorded, 15 new records ofPythium species for the Netherlands are documented. Species with filamentous non-swollen sporangia preferentially occurred in water and wet soils while species with spherical sporangia or hyphal swellings dominated in cultivated soils, forests and in the roots of phanerogams. In 1968 species with filamentous non-swollen sporangia comprised 89% of the isolations from Zuidelijk Flevoland; this percentage decreased to 9 in 1972. The percentage of isolates with spherical sporangia or hyphal swellings from cultivated soils, forest soils or plant material was mostly over 90.P. rostratum Butler, though found in all kinds of soils, was often the only species which could be isolated from dry sandy soil samples.P. sylvaticum Campbell & Hendrix was the most common species in cultivated soils in the Netherlands (37% of the isolates in 1968–1972), followed byP. oligandrum Drechsler (22%) andP. paroecandrum Drechsler (11.5%). 相似文献
14.
ABSTRACT A wide range of commercially formulated fungicides cause in vitro effects on mating behavior in specific isolates of Phytophthora infestans, the causal agent of late blight of potato and tomato. Four isolates of P. infestans representing each of the four common US genotypes, US-1, US-6, US-7, and US-8 and varying in their sensitivity to metalaxyl, were exposed to a variety of fungicides used to control late blight in petri dish assays at concentrations ranging from 1 to 100 mug a.i./ml. Exposure of each of these normally heterothallic single mating type isolates of P. infestans to 9 of the 11 commercial fungicide formulations tested resulted in the formation of oospores after 2 to 4 weeks. The highest numbers of oospores were formed on media amended with Ridomil 2E (metalaxyl) and Ridomil Gold EC (mefenoxam) at 0.1 to 10 mug a.i./ml, averaging as many as 471 and 450 oospores per petri dish, respectively. Several other fungicides including Maneb, Manzate (Mancozeb), Curzate (cymoxanil + mancozeb), and Acrobat MZ (dimethomorph + mancozeb) also induced oospore formation, producing from 0 to 200 oospores per plate at fungicide concentrations from 0.1 to 10 mug a.i./ml. The metalaxyl resistant isolates formed oospores in response to the fungicides more often than the metalaxyl sensitive isolates. No oospores were formed on media amended with Bravo (chlorothalonil) or Tattoo C (chlorothalonil + propamocarb HCl) and these compounds completely suppressed growth of the isolates at 0.1 and 1 mug a.i./ml. Three metalaxyl resistant A2 isolates mated with both A1 and A2 isolates after exposure to the fungicides Ridomil 2E and Ridomil Gold EC. Alterations in mating type expression were also observed in a metalaxyl sensitive A1 isolate after exposure to Benlate (benomyl). Copious amounts of chemicals are applied annually to potato and tomato production areas to control late blight. Our results indicate that a wide range of chemically diverse fungicides can induce normally heterothallic metalaxyl resistant isolates of P. infestans to form oospores in vitro after short exposures to the fungicides. 相似文献
15.
This study investigated survival of the pathogens Phytophthora ramorum, P. alni and P. kernoviae as zoospores or sporangia in response to an important water quality parameter, electrical conductivity (EC), at its range in irrigation water reservoirs and irrigated cropping systems. Experiments with different strengths of Hoagland’s solution showed that all three pathogens survived at a broad range of EC levels for at least 3 days and were stimulated to grow and sporulate at ECs > 1·89 dS m?1. Recovery of initial populations after a 14‐day exposure was over 20% for P. alni subsp. alni and P. kernoviae, and 61·3% and 130% for zoospores and sporangia of P. ramorum, respectively. Zoospore survival of these pathogens at ECs < 0·41 dS m?1 was poor, barely beyond 3 days in pure water; only 0·3% (P. alni), 2·9% (P. kernoviae) and 15·1% (P. ramorum) of the initial population survived after 14 days at EC = 0·21 dS m?1. The variation in rates of survival at different EC levels suggests that these pathogens survive better in cropping systems than in irrigation water. Containment of run‐off and reduction in EC levels may therefore be non‐chemical control options to reduce the risk of pathogen spread through natural waterways and irrigation systems. 相似文献
16.
ABSTRACT Isolates of Phytophthora infestans, collected from bittersweet, hairy nightshade, petunia, potato, potato vine, and tomato in western Washington, 1998 to 1999, were evaluated for virulence complexity as well as mating type, metalaxyl insensitivity, allozymes of glucose-6-phosphate isomerase and peptidase, and DNA fingerprint with the RG57 probe. Results were compared with those from similar collections made in the same region during the 1990s. Generally, virulence complexity was high for most of the isolates regardless of year, genotype, or host. No marked shift in virulence complexity was evident for the populations studied, and unnecessary virulences were maintained. During 1998 and 1999, isolates of the US-8 and US-11 genotypes had 4 or more virulence factors. US-8 isolates averaged 8.2 and 9.3, whereas US-11 isolates averaged 5.4 and 6.3 virulence factors. The frequency of US-8 isolates that were sensitive to metalaxyl ranged from 5% in 1998 to 72% in 1999. All of the US-11 isolates tested in 1998 and 1999 were insensitive to metalaxyl. From 1996 to 1999 on potato, the recovery of US-8 increased, whereas the recovery of US-11 decreased. No evidence of new genotypes or sexual recombination was found. Western Washington was a desirable location for screening germ plasm for durable resistance to late blight due to the high frequency and persistence of complex virulences. 相似文献
17.
In laboratory tests, mycelium and sporangia of Phytophthora meadii survived in soil for about 3 weeks, whereas chlamydospores survived for 12 weeks. When petioles of rubber (Hevea brasiliensis) colonized by P. meadii were buried in soil, chlamydospores formed in the tissues after about 2 weeks and P. meadii could be reisolated up to 22 weeks after burial. Colonized petioles buried in soil in a rubber plantation decayed more rapidly than those in laboratory tests, and attempts to reisolate P. meadii after 18 weeks were unsuccessful, although chlamydospores were still visible. P. meadii was isolated most readily from soil in a rubber plantation during epidemics of pod and leaf disease, suggesting that sporangia from these sources maintained soil inoculum at a high level. Inoculum detected in soil before pod and leaf infection may have arisen from subclinical infections or from chlamydospores surviving in petioles from the previous season. 相似文献
18.
ABSTRACT The dispersal of spores of Fusarium culmorum, a biological control agent for the aquatic weed Hydrilla verticillata, was investigated in aquatic systems. Macroconidia and chlamydospores that were applied to the surface of the liquid settled rapidly in deionized water, tap water, 5% Hoagland's solution, natural spring water, or river water held in glass containers. The rate of fall, as measured for 50% of the spores, was determined to be 9 cm h(-1). Rapid lateral dispersal of spores from a point source occurred in still water. This initial spore movement occurred at a rate of >9 m h(-1) (15 cm min(-1)), approximately 100 times faster than the rate of settlement. The spores attained an even lateral distribution in a still, closed system. Spores dispersed rapidly in moving water and were transported with the water current. Spores were determined to carry positive electrostatic charges as they migrated towards the negative pole during electrophoresis. The physical components of dispersal of F. culmorum spores were defined in a still aquatic system to consist of rapid lateral dispersal and sinking due to gravity. In moving water, the dynamics of water movement was superimposed over the other two factors. 相似文献
19.
When beet seedlings exposed as bait plants in infested soil were placed in a nutrient solution, they released Polymyxa betae zoospores, infected with beet necrotic yellow vein furovirus. The roots produced the first zoospores 5 days after the start of soil baiting. When seedlings were inoculated with zoospore suspensions, infection occurred within 5 min and reached a maximum in 30 min. The suspensions remained infectious for at least 2 h after removal of the bait plants from which the zoospores were released. So many spores were released into the suspension that disease transmission could be obtained within half an hour from an infected plant to a healthy plant, placed together into fresh medium. Suspensions could be diluted 1/16 with nutrient solution without any loss of infectivity, whereas 1/4 dilution with tap water resulted in a complete loss of infectivity. 相似文献
20.
Cotton was grown in containers of soil with sclerotia of Phymatotrichum omnivorum. Plants were grown for 3 weeks in the greenhouse and then transferred to field plots. Foliar and stem symptoms of Phymatotrichum root rot occurred 15–50 days after field placement. Mean incubation periods (defined as time from field placement to symptoms) were about 24 days for placements made in June and July and about 35 days for placements made in August and September 1984. Colonization of roots was more advanced in the top 24 cm of soil. The time taken for symptoms to appear was not related to the amount of root colonization at the time plants were transferred to the field. In the later two planting dates a drop in soil water potential to approximately −25 bars after 20–24 days was associated with the delay in symptom expression. There were significant linear relationships between the length of the incubation period (days), or its inverse (day−1 ), and the independent variables: mean maximum daily temperature (°C) in the top 12 cm layer of soil, soil water potential in the 31–60 cm layer of soil and their product (representing the interaction of these two variables). In general, symptom expression was faster at higher temperatures and with wetter conditions. Newly-formed sclerotia were found most frequently in containers some 5–6 weeks after plant death when soil temperatures had decreased and soils were close to saturation (September and October). 相似文献