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1.
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2.
To clarify the mechanism of seed transmission of Pepper mild mottle virus (PMMoV), the virus was immunolocalized in Capsicum annuum seeds using fluorescence microscopy. Two distinct patterns were observed: In the first, PMMoV was present in the epidermis and parenchyma but not in the endosperm or embryo; in the second, the virus was restricted to the surface of the epidermis and parenchyma. These findings shed light on the fundamental mechanisms of seed transmission of tobamoviruses and may aid in the design of new methods to prevent the spread of seedborne virus diseases.  相似文献   

3.
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4.
The location of Pepper mild mottle virus (PMMoV) within seeds as they developed on inoculated seedlings of pepper (Capsicum annuum) was followed over time by detecting the viral coat protein using immunofluorescence microscopy. Seedlings were inoculated with PMMoV when the flower buds on the first and second branching nodes were in bloom. Fluorescence indicating the presence of PMMoV was first observed around immature seeds and placentas in the ovaries on the fourth branching node at 20 days post-anthesis (20 DPA), which corresponded to 39 days post-inoculation (39 DPI). The area with fluorescence gradually expanded from the placenta into the integument and the parenchyma, and finally reached the tip of the immature seeds by 34 DPA (53 DPI). The embryo or endosperm beyond the endothelium never fluoresced during the experiment [i.e., ending at 81 DPA (102 DPI)]. For visualizing viral routes of invasion from seeds into new seedlings, PMMoV-infected C. annuum seeds that were heterozygous for the L 3 tobamovirus-resistance gene were sown in soil at 30°C. After ~2 weeks, the cotyledon developed virally induced necrosis. These findings shed light on the infection cycle of PMMoV through vertical transmission in C. annuum.  相似文献   

5.
Late blight, caused by the oomycete Phytophthora infestans, is a threat to potato‐cropping systems worldwide. In the Ecuadorian Andes, despite a high late blight incidence in foliage, tuber blight is rare. In this work, the hypothesis that Ecuadorian Andean soils are naturally suppressive to P. infestans tuber infection was evaluated. Soils from four potato‐growing regions were assessed for disease suppressiveness by determining the effects of soil heat treatment on P. infestans sporangia and their ability to infect potato slices after 1, 8, 15 and 30 days of exposure to soils. Tuber infection after inoculation with P. infestans‐infested soils was consistently lower during the evaluation period compared with heat‐treated soils. Fresh, untreated soils affected germination and viability of P. infestans sporangia in a site‐dependent manner. In addition, the effect of heat treatment on soil bacterial communities was assessed through terminal restriction fragment length polymorphism analysis of the 16S rDNA gene region. Heat treatment disrupted bacterial community composition, and a subset of terminal restriction fragments (TRF) was either positively or negatively correlated with tuber infection. Bacterial TRF negatively correlated with tuber infection corresponded in fragment size to taxa with known ability to inhibit pathogens and promote plant growth. Finally, bacterial isolates obtained from untreated soils, which inhibited P. infestans growth in vitro, represented 22–47% of isolates recovered, and matched classes predicted by the TRFs. This work represents a first step in understanding the mechanisms behind the low incidence of tuber blight in Andean potato‐cropping systems.  相似文献   

6.
Ustilaginoidea virens is the causal agent of false smut disease of rice. In this study, we developed a real-time polymerase chain reaction (PCR) assay to clarify the relationship between false smut occurrence on rice and quantification of U. virens from soil in Japan. The method here described is sensitive, detecting less than 50 fg of pathogen DNA, and specific to the nuclear ribosomal DNA for U. virens when tested across 27 rice-pathogenic fungi and bacteria, 26 other fungi and bacteria and four plant species. As few as eight chlamydospores of U. virens per gram soil were detected when added to sterilized Gley and Ando soils. The real-time PCR assay for the soil samples was at least 100-fold more sensitive than the conventional and nested-PCR assays tested. By quantification of U. virens with real-time PCR using DNA extracted from naturally contaminated Gley soils and visual assessment of the disease in agricultural fields, a linear correlation between cycle threshold (CT) values and the number of false smut balls was revealed. Therefore, this specific quantitative assay could be a useful tool for optimization of disease control strategies, and for studying the ecology of U. virens.  相似文献   

7.
Tobamoviruses induce crop diseases that are responsible for significant economic losses around the world. Like other tobamoviruses, Cucumber green mottle mosaic virus (CGMMV) forms highly stable particles that can persist for long periods on plant debris, in soil and on seed surfaces. These particles serve as a primary source of infection, infecting seedlings from which the virus can then be mechanically transmitted to other neighbouring plants. Contaminated seeds also provide a route for the movement of the virus between countries and its introduction into new areas. Effective seed disinfection treatments and the use of uncontaminated seed may reduce the global prevalence of this virus. Several treatments based on the use of heat or chemicals have been reported to effectively eliminate CGMMV and other tobamoviruses from seeds. An evaluation of these treatments on highly contaminated seed lots revealed inconsistent results, which encouraged the construction of a more accurate detection method that combines morphological, serological, molecular and biological analyses in one protocol. The detection of viable (infectious) viral particles in seed treated with heat, trisodium phosphate or a combined treatment, indicates that these treatments are insufficient. The serological detection of CGMMV in the inner parts of infected seeds provides a possible explanation for the inconsistent efficacy of these treatments.  相似文献   

8.
Footrot disease due to Nectria haematococca (anamorph Fusarium solani f.sp. pisi) is an economically important disease of peas globally. However, our ability to predict accurately the likelihood of footrot infections is limited because there is no method to determine inoculum density prior to planting. In this research, a PCR-based assay was developed to quantify the pea pathogenicity gene (PEP3), exclusive to highly pathogenic forms of N. haematococca, from DNA extracted from agricultural field soils. The applicability of using quantitative PCR (qPCR) to measure this gene in soil was validated, and the relationship between PEP3 gene numbers and footrot disease was also studied. Results showed that the quantitative assay is both efficient and specific; amplification efficiency of the Q-PCR assay for the PEP3 gene was 92%. Gene copy numbers were shown to vary significantly (P = 0.01) between fields, and were positively correlated to the number of spores of pathogenic N. haematococca, and to footrot disease. PEP3 numbers of up to 100 g−1 soil constituted a threshold number for infection—potentially capable of causing economically significant pea footrot disease. The density of virulent N. haematococca in soil fields capable of causing footrot disease could be determined with a high degree of accuracy, with this assay. It offers the opportunity for prediction of pea footrot infections in agricultural soils prior to cultivation.  相似文献   

9.
Isoxaflutole is a new pre-emergence corn herbicide which controls both grass and broadleaf weeds. Experiments were performed in the laboratory to study the sorption of isoxaflutole in five different soils (Moorhead, MN; East Monroe, CO; Ellendale, MN; South Deerfield, MA; and Chelsea, MI) using the batch equilibration technique. Total initial isoxaflutole solution concentrations for each soil were 0.05, 0.15, 0.3. 0.8, 1.5, 2.0 and 4.0 mg litre−1. Analysis of [ring-14C] isoxaflutole was performed using liquid scintillation counting, and sorption data were fitted with the Freundlich model. Isotherms of isoxaflutole in all the soils were non-linear as depicted by the exponent (n < 1.0), indicating differential distribution of sorption site energies in various soils. Since the isotherms were non-linear the data fit Freundlich's isotherm well, as was indicated by high values of the regression coefficient (r2). The Freundlich sorption coefficient ranged from 0.555 to 50.0 (litre nmg l−nkg−1). Multiple regression of the sorption constant, KF against selected soil properties indicated that organic matter content was the best single predictor of isoxaflutole sorption (r2 = 0.999) followed by soil pH (r2 = 0.954). Clay content of the soils did not have a high correlation with KF values (r2 = 0.453), while the sorption of isoxaflutole was not influenced by the Ca2+ concentration in the soil solution. Isoxaflutole sorption increased with an increase in organic matter content of soils. Sorption of isoxaflutole decreased as the soil pH increased from 4.5 to 8.5, which was depicted by the reduction of KF values. Sorption of isoxaflutole to the soils varied with differences in binding energies. At a particular net energy value (E*), the corresponding site energy distribution [F(E*)] values followed the order, Chelsea, MI > Moorhead, MN > East Monroe, CO > South Deerfield, MA > Ellendale, MN. The negative magnitude of Gibbs free energy of sorption (ΔG x) indicates the spontaneity of the given sorption process in the soils from Moorhead, MN; East Monroe, CO and Chelsea, MI. © 1999 Society of Chemical Industry  相似文献   

10.
Adsorption, incubation and soil-column experiments with bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were carried out in ten different soils from the marches surrounding the Doñana National Park (Huelva, SW Spain). Adsorption isotherms for the different soils showed a good fit with the Freundlich equation. Bentazone was poorly adsorbed in all the soils studied, with no significant relationship between theKf values and soil characteristics. A significant correlation was obtained between the soil organic matter content and the distribution constant values (Kd) calculated at an equilibrium concentration of 200 μg cm−3. The low adsorption and non-degradation of bentazone on these soils suggest that the herbicide readily percolates through soils to reach the surface and ground waters. The mobility of bentazone through three soil columns was also studied. The mass balances carried out showed that bentazone was totally eluted from the soil columns. The theoretical model applied to explain bentazone leaching under our experimental conditions seems to be suitable for soil columns with a uniform water-flow rate.  相似文献   

11.
Sorption of different classes of weak organic acids was measured using soils with a range of pH values, taken from long-term field experiments that had received different amounts of lime. Non-ionisable compounds were used to demonstrate that the soils of different pH used in the experiments have similar sorptive properties. Values of the sorption coefficients for chloride ion were negative at all pHs except one. Sorption of moderately polar, monobasic, weak acids was weak in acidic soils and very weak in neutral and alkaline soils where they were predominantly dissociated. A lipophilic weak acid was strongly sorbed even at high pH. A model is presented which estimates soil/water distribution coefficients, at any soil pH, from lipophilicity and pKa of the acid and organic matter content of the soil. The model was derived using sorption measured for substituted phenoxyacetic acids. Sorption values calculated using the model were compared with values measured for chlorsulfur on and showed useful agreement. Dibasic acids were strongly sorbed, probably by the mechanism of ligand exchange, if they were chelating agents with potential to form 5- or 6-membered rings with an acceptor atom. Phenylphosphonic acid was strongly sorbed, being a strong monodentate ligand.  相似文献   

12.
为评价氯胺嘧草醚的环境安全性,采用批量平衡法测定了氯胺嘧草醚在5种土壤中的吸附-解吸行为,并运用数学模型对其吸附-解吸特性及移动性能进行了分析。结果表明:氯胺嘧草醚在5种土壤中的等温吸附-解吸曲线符合Freundlich模型,吸附常数（Kf值）范围在6.991~18.49之间;不同土壤对其的吸附作用强弱依次为:黑土 > 水稻土 > 褐土 > 潮土 > 红土。氯胺嘧草醚在5种土壤中的有机碳吸附常数（KOC）范围在704.4~1 579之间,推测其在土壤中具有低移动性;薄层层析试验也表明,氯胺嘧草醚在土壤中的移动性较弱。氯胺嘧草醚在5种土壤中的吸附自由能绝对值均小于40 kJ/mol,表明其吸附机理主要是物理吸附。其Kf值与土壤有机质含量、黏粒含量呈正相关,而与土壤pH值呈负相关。解吸试验表明,氯胺醚在其中3种土壤中的解吸过程存在滞后现象。研究表明,在正常使用情况下,氯胺嘧草醚不易对地表水或地下水造成污染风险。  相似文献   

13.
ABSTRACT The Capsicum spp. L genes (L(1) to L(4)) confer resistance to tobamoviruses. Currently, the L(4) gene from Capsicum chacoense is the most effective resistance gene and has been used widely in breeding programs in Japan which have developed new resistant cultivars against Pepper mild mottle virus (PMMoV). However, in 2004, mild mosaic symptoms began appearing on the leaves of commercial pepper plants in the field which possessed the L(4) resistance gene. Serological and biological assays on Capsicum spp. identified the causal virus strain as a previously unreported pathotype, P(1,2,3,4). PMMoV sequence analysis of the virus and site-directed mutagenesis using a PMMoV-J of the P(1,2) pathotype revealed that two amino acid substitutions in the coat protein, Gln to Arg at position 46 and Gly to Lys at position 85, were responsible for overcoming the L(4) resistance gene.  相似文献   

14.
The distribution resulting from the drenching of soil with a suspension concentrate of [14C]metazoxolon was studied in the laboratory and the field. Penetration of soil columns was increased by (a) increasing the drench volume from 1 to 7.8 litres m?2, (b) changing the original soil moisture content from air-dry to field-capacity, and (c) including 1 % of ‘Renex 30’ surfactant in the drench. Penetration was greatest in soils containing large pores and was reduced when aggregates were broken down by sieving. Leaching the column with 1.56 cm of ‘rain’, 15 h after treatment, did not increase the penetration by metazoxolon. In all experiments, the maximum concentration of metazoxolon occurred in the top 2 cm of soil. Equivalent effects were found when metazoxolon was applied to a poorly-structured sandy clay loam in the field.  相似文献   

15.
Adsorption of simazine (2-chloro-4,6-bisethyl-amino-1,3,5-triazine) was 2.2–4 times greater than that of terbacil (5-chloro-6-methyl-3-t-butyl-uracil) in the same soils and adsorption of both herbicides was 2–4 times greater in the topsoils than subsoils. Adsorption was inversely correlated with herbicide movement in a thick-layer chromatography system. One year after application of 3 kg/ha to field plots, simazine residues were highest near the soil surface, whereas terbacil residues increased with soil depth in the sandy and sandy loam soils. Total residues recovered from the upper 25 cm of soils was 5% or less of the simazine originally applied, and 10% or less of the applied terbacil. In an oat seedling bio-assay, the GR50 values were generally 1.5–3 times higher for simazine than for terbacil in the same soils.  相似文献   

16.
A virus was isolated fromStreptocarpus plants that showed colour breaking of the flowers. Initial diagnostic tests indicated that this virus was a member of the Tobamovirus genus. The virus could be transmitted mechanically to several test plants. Its stability in plant sap was in line with that of other tobamoviruses, i.e. infectivity was lost after 10 min incubation at 90 °C and after dilution to 10–8. In addition, the morphology of the virus was typical for tobamoviruses. The particles had a length of about 304 nm. On test plants, the virus fromStreptocarpus could be distinguished from 7 well-defined tobamoviruses.Nicotiana glutinosa showed the most characteristic symptoms. In agar double-diffusion tests and/or double antibody sandwich enzyme-linked immunosorbent assays, no cross reactivity was observed in heterologous combinations with these 7 and 3 other tobamoviruses. Mechanical inoculation of the virus to virus-freeStreptocarpus plants resulted in the appearance of flower breaking in about 50% of the plants. On the basis of these findings, it is concluded that the virus that causes flower breaking inStreptocarpus is a distinct member of the Tobamovirus genus, and the nameStreptocarpus flower-break virus is proposed.  相似文献   

17.
The degradation of prochloraz in different soils was investigated in field and laboratory experiments. In laboratory degradation experiments in the dark, initial prochloraz concentrations decreased to 30–64% within 56 days, depending on temperature and soil pH. In neutral to basic soils, formation of up to 3.7% of the metabolite prochloraz-urea was observed. The rate of mineralization was strongly pH-dependent, not exceeding 3.2% in the acidic and 18.3% in the neutral to basic soils. Amounts of non-extractable residues ranged from 14 to 31%. Under field conditions, prochloraz disappeared much more rapidly with DT50 values of 11–43 days. The metabolites prochloraz-formylurea and prochloraz-urea were found in significant concentrations. Laboratory experiments with fresh and sterilized soils under UV irradiation confirmed the enhancing effect of light on the formation of the primary metabolite, prochloraz-formylurea. The latter is hydrolysed to prochloraz-urea predominantly by microbial degradation. © 1999 Society of Chemical Industry  相似文献   

18.
Damping-off and stem rot disease-causing Sclerotium rolfsii has been reported as a destructive soil-borne pathogen of numerous crops, especially in the tropics and subtropics. Trials were conducted to test the efficacy of biocontrol agents alone or combined with Moringa oleifera leaf extracts for the control of the disease. In the laboratory, PDA was amended with Moringa leaf extract, and mycelial growth of S. rolfsii was measured. In the greenhouse and field, Trichoderma Kd 63, Trichoderma IITA 508 and Bacillus subtilis were evaluated as seed treatments, soil drench or sprinkle, separately or combined with Moringa leaf extracts. Percentage disease incidence, severity and control were recorded. In the laboratory, the higher the extract concentration the less the mycelial growth and no mycelial growth occurred on extract at 15 or 20 g leaves 10 ml−1 water. In the greenhouse, the highest disease control was observed at a Moringa extract concentration of 15 kg leaves 10 l−1 water (w/v). Seed treatments using Trichoderma Kd 63, and soil sprinkle using Trichoderma IITA 508 had a significantly (P = 0.05) higher effect on a disease incidence than Bacillus. Disease severity followed the same pattern. Moringa seed treatment combined with Trichoderma soil sprinkle resulted in significantly more than 94% and 70% disease control in the greenhouse and field, respectively, with significant yield increase in the field. This is the first report of Moringa leaf extract combined with Trichoderma as an integrated control for Sclerotium damping-off and stem rot of cowpea in the field.  相似文献   

19.
Asparagus replant-bound early decline (ARED) was characterized and its etiology was elucidated in experiments under greenhouse and field conditions. Selective soil treatments were used to differentiate between autotoxic compounds and soil-borne pathogens as causal agents. In greenhouse experiments, there were symptoms of ARED within 12—15 weeks. Asparagus plants grown in soil formerly used for asparagus (asparagus soil) showed brown lesions on primary and secondary roots, and many secondary roots had rotted. Root weights of plants grown in asparagus soil were lower than those of plants grown in fresh soil.Fusarium oxysporum f. sp.asparagi (Foa) was by far the most common species among the fungi isolated from roots with lesions. Under greenhouse and field conditions, there were similar symptoms, which indicates that the results obtained under greenhouse conditions are similar to those in the field. The vertical distribution of the ARED-causing factor(s) was studied in a greenhouse experiment in which plants were grown in soil from three layers: 0–30, 30–60, and 60–90 cm. For all four asparagus soils tested, there were ARED symptoms and similar disease severity in samples from all three depths. The causal factor persisted at least 11 years after soil was no longer used for asparagus. When asparagus soil was diluted with fresh soil to give mixtures with 100%, 80%, 50%, 20% and 0% asparagus soil, disease severity did not decrease with increasing dilution of the asparagus soil from 100% to 20%. Disease severity of all mixtures with asparagus soil was significantly higher than that for fresh soil. The results imply that ARED is caused by a pathogen colonizing the soil rather than inhibition by autotoxins released from residues of the preceding asparagus crop. This conclusion is supported by the results of greenhouse and outdoor experiments with heat and fungicide treatments of soil. ARED was nullified by heat treatments of 30 min at 55 or 60 °C but not 45 and 50 °C, eliminating autotoxins as an important cause of ARED because they are heat-stable. Foa is eliminated by a 30-min soil treatment at 55–60 °C but not 50 °C. Prochloraz, known for its toxicity toF. oxysporum, also nullified ARED. Disease severity level was related to the density of Foa in soil. The results provide conclusive evidence thatF. oxysporum f. sp.asparagi is the main cause of ARED in the Netherlands, which largely removes the need to discriminate between early decline and replant-bound early decline, because Foa is the main cause of both diseases.  相似文献   

20.
Thirty separate soil samples were taken from different locations at the Brimstone farm experimental site, Oxfordshire, UK. Incubations of isoproturon under standard conditions (15 °C; ?33 kPa soil water potential) indicated considerable variation in degradation rate in the soil, with the time to 50% loss (DT50) varying from 6 to 30 days. These differences were confirmed in a second comparative experiment in which degradation rates were assessed in 11 samples of the same soil in two separate laboratories using an identical protocol. There was a significant negative linear relationship (r2= 0.746) between the DT50 values and soil pH in this group of soils. In a third experiment, degradation rates of the related compound chlorotoluron were compared with those of isoproturon in 12 separate soil samples, six of which had been stored for several months, and six of which were freshly collected from the field. Degradation of both herbicides occurred more slowly in the stored samples than in the fresh samples but, in all of them, chlorotoluron degraded more slowly than isoproturon, and there was a highly significant linear relationship (r2=0.916) between the respective DT50 values.  相似文献   

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