共查询到20条相似文献，搜索用时 546 毫秒
1.
ABSTRACT Southern wilt of geraniums (Pelargonium hortorum), caused by the soilborne bacterium Ralstonia solanacearum race 3 biovar 2 (R3bv2), has inflicted significant economic losses when geranium cuttings latently infected with this quarantine pest were imported into the United States. Little is known about the interaction between R. solanacearum and this ornamental host. Using UW551, a virulent R3bv2 geranium isolate from a Kenyan geranium, we characterized development of Southern wilt disease and R3bv2 latent infection on geranium plants. Following soil inoculation, between 12 and 26% of plants became latently infected, carrying average bacterial populations of 4.8 x 10(8) CFU/g of crown tissue in the absence of visible symptoms. Such latently infected plants shed an average of 1.3 x 105 CFU/ml in soil run-off water, suggesting a non-destructive means of testing pools of asymptomatic plants. Similarly, symptomatic plants shed 2 x 10(6) CFU/ml of run-off water. A few hundred R. solanacearum cells introduced directly into geranium stems resulted in death of almost all inoculated plants. However, no disease transmission was detected after contact between wounded leaves. Increasing temperatures to 28 degrees C for 2 weeks did not convert all latently infected plants to active disease, although disease development was temperature dependent. Holding plants at 4 degrees C for 48 h, a routine practice during geranium cutting shipment, did not increase frequency of latent infections. R. solanacearum cells were distributed unevenly in the stems and leaves of both symptomatic and latently infected plants, meaning that random leaf sampling is an unreliable testing method. UW551 also caused potato brown rot and bacterial wilt of tomato, surpassing race 1 strain K60 in virulence on tomato at the relatively cool temperature of 24 degrees C. 相似文献
2.
ABSTRACT Investigations were conducted to determine whether the effects of tillage practices on the prevalence of brown stem rot of soybean (caused by Phialophora gregata), Heterodera glycines, and Phytophthora sojae were confounded by soil texture in samples collected in the fall of 1995 and 1996. Soil and soybean stem samples, along with tillage information, were collected from 1,462 randomly selected fields in Illinois, Iowa, Minnesota, Missouri, and Ohio in collaboration with the National Agricultural Statistics Service. The incidence of brown stem rot was determined from 20 soybean stem pieces collected from each field in a zigzag pattern. The detection frequency of P. sojae (expressed as percent leaf disks colonized) and population densities of H. glycines were determined from soil cores also collected in a zigzag pattern. The soil samples were grouped into various textural classes, and the effect of soil texture and tillage relations on the activities of each pathogen were determined. Both tillage and soil texture affected the incidence of brown stem rot; however, there was no interaction between tillage and soil texture. Conservation tillage had a greater (P < 0.05) incidence of brown stem rot in clay loam and silty clay loam than did conventional tillage. The detection frequency of P. sojae was not affected by tillage, but a tillage x texture interaction (P = 0.013) indicated that the effect of tillage depended on soil texture. There was a greater (P < 0.05) detection frequency of P. sojae in conservation tillage than in conventional tillage in silt loam and loam soils. However, in sandy loam, the detection frequency of P. sojae was greater (P = 0.0099) in conventional tillage than in conservation tillage. Population densities of H. glycines were significantly affected by both tillage and soil texture, but overall, there was no tillage x texture interaction. There was an inverse relationship between population densities of H. glycines and percent clay (r = -0.81, P = 0.01) in no-till fields, but little or no change in nematode densities was observed with increasing clay content in tilled fields. Population densities of H. glycines were less (P < 0.05) in no-till fields than in tilled fields in silty clay loam and clay soils. There was no difference in H. glycines densities between the tillage categories in soils sandier than silty clay loam or clay. The findings emphasize the need for cautious interpretation of the effects of tillage practices on diseases and pathogens in the absence of information on soil texture. 相似文献
3.
Effect of a Soil Amendment on the Survival of Ralstonia solanacearum in Different Soils 总被引：1，自引：0，他引：1
ABSTRACT The effect of a soil amendment (SA) composed of urea (200 kg of N per ha) and CaO (5,000 kg/ha) on the survival of Ralstonia solanacearum in four Philippine soils was investigated in a series of laboratory experiments. Within 3 weeks after application, the SA either caused an initial decrease, a final decline, or no change in the pathogen population, depending on the particular soil type. An initial decrease occurred in a soil with a basic pH and resulted in a significantly (P < 0.001) lower pathogen population immediately and at 1 week after amending the soil. This decrease was probably due to the high pH in the soil during urea hydrolysis. A final decline in the R. solanacearum population after 3 weeks occurred in two soils in which nitrite accumulated after 1 week. In these soils, no decline in bacterial levels occurred when nitrite formation was inhibited by 2-chloro-6-trichloromethylpyridine. In the soil with low pH, no nitrite accumulated and the R. solanacearum population did not decline. The suppressive effects of pH and nitrite on R. solanacearum growth were confirmed by in vitro experiments. Ammonium reduced the growth of R. solanacearum, but was not suppressive. Interactions of pH with ammonium and nitrite also occurred, whereby ammonium reduced growth of R. solanacearum only at pH 9 and nitrite was suppressive only at pH 5. Nitrate had no effect on R. solanacearum growth in vitro. 相似文献
4.
ABSTRACT Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot. 相似文献
5.
为明确不同土壤质地对禾谷孢囊线虫Heterodera avenae发生危害的影响,分别测试了6种土壤质地中禾谷孢囊线虫的侵染、发育及其种群动态。结果显示：在整个小麦生长季,不同土质中禾谷孢囊线虫2龄幼虫（J2）的种群变化趋势一致。冬前土壤中少量线虫孵化,11月下旬各种土质中J2种群密度达到10.8~14.2条/100 mL土壤;4月初为J2发生高峰期,其种群密度为54.6~77.1条/100 mL土壤,且土壤中含壤土比例越高J2数量越大;J2在壤土与砂土比为6：1和1：0土壤中侵入根系的数量最多,单株根系J2数量为672.7~685.0条,且土壤中砂土比例越大J2侵入数量越少,相应地根系内3龄幼虫和形成的孢囊数量也越少;不同土质中不同时期孢囊内虫口减退率不同,但在生长季末不同土质中孢囊内虫口总减退率无显著差异。研究表明,土质对孢囊内虫口减退率无影响,土质沙性越大越不利于禾谷孢囊线虫的发生危害。 相似文献
6.
A reliable, sensitive, low-cost and easy-to-use technique is described for the detection of Ralstonia solanacearum (the causal organism of bacterial wilt, BW) in soil. A total of 273 potato isolates belonging to five different biovars (Bv), originating from 33 countries worldwide, were tested and successfully detected by antibodies produced at the International Potato Center (CIP). Isolates of R. solanacearum belonging to Bv1 and Bv2A were successfully detected by double antibody sandwich–enzyme-linked immunosorbent assay (DAS–ELISA) at low population levels after incubation of soil suspensions for 48 h at 30°C in a new semiselective broth containing a potato tuber infusion. Detection thresholds of 20 and 200 CFU g−1 inoculated soil were obtained for Bv1 and Bv2A, respectively. Sensitivity of detection of Bv2A was similar or even higher in five different inoculated soil types. No cross-reactions were obtained in DAS–ELISA after enrichment of soil suspensions (i) prepared from 23 different soils sampled in BW-free areas in six departments of Peru; and (ii) inoculated with 10 identified bacteria and 136 unknown isolates of soil microbiota isolated from eight different locations. Only the blood disease bacterium gave a low-level reaction after enrichment. In naturally infested soils, average sensitivities of 97·6 (SE 14·8) and 100·9 (SE 22·6) CFU g−1 were obtained for biovars 1 and 2A, respectively. By making serial dilutions of the soil suspension before enrichment, densities of R. solanacearum could be determined in a semiquantitative way. Results also showed that composite samples of five soils could be analysed to assess field soil populations without reducing detection sensitivity. 相似文献
7.
Mixtures of wet vegetable wastes (Brassica, carrot or onion) and dry onion waste were composted at 50 °C for 7 days. The incorporation of the raw or composted vegetable waste mixtures into sandy loam, silt and peat soils reduced the viability of sclerotia of S. cepivorum in glasshouse pot bioassays. The reduction in viability was dependent on waste type, rate of incorporation, duration of exposure and soil type. Onion waste was the most effective waste type in reducing sclerotia viability in all three soils. The Brassica and carrot wastes were as effective as the onion waste in silt soil but less effective in sandy loam and peat soil. A 50% w/w incorporation rate of the wastes gave the largest reduction in viability, with an increase in reduction over time. Composted onion waste reduced sclerotia viability under glasshouse and field conditions although the effect was smaller in the field. Composted onion waste incorporated into soil at 50% w/w reduced the incidence of Allium white rot on onion seedlings in glasshouse pot tests. Incidence and control of the disease differed with soil type. The most consistent control was achieved in peat soil whereas no control was observed in silt soil. Incorporation of the waste 2 months prior to sowing or transplanting reduced seedling emergence in sandy loam soil and growth in all three soil types. The potential for field application of composted vegetable wastes as a sustainable method for control of Allium white rot and waste disposal is discussed. 相似文献
8.
With the scheduled phasing out of methyl bromide, there is an urgent need for alternatives. We evaluated the efficacy of propargyl bromide as a potential replacement for methyl bromide for the control of barnyardgrass (Echinochloa crus-galli) and Fusarium oxysporum in an Arlington sandy loam, a Carsitas loamy sand and a Florida muck soil. Soil was mixed with barnyardgrass seeds or F oxysporum colonized on millet seeds, and treated with propargyl bromide at a range of concentrations. The mortality of the fungi and weed seeds was determined after 24 h of exposure at 30 degrees C. The concentrations required to inhibit 50% barnyard seed germination (LC50) were 2.8, 2.4 and 48.5 micrograms g-1 in the sandy loam, loamy sand and muck soil, respectively. In contrast, the LC50 values for F oxysporum were 11.2, 10.8 and 182.1 micrograms g-1 in the sandy loam, loamy sand and muck soil, respectively. The low efficacy of propargyl bromide in the muck soil was a result of the rapid degradation and high adsorption of the compound in the soil. The degradation half-life (t1/2) was only 7 h in the muck soil at an initial concentration of 6.8 micrograms g-1, compared to 60 and 67 h in the sandy loam and loamy sand, respectively. The adsorption coefficients (Kd) were 0.96, 0.87 and 5.6 cm3 g-1 in the sandy loam, loamy sand and muck soil, respectively. These results suggest that registration agencies should consider site-specific properties in recommending application rates for propargyl bromide. 相似文献
9.
The behaviour of the morpholine fungicide fenpropimorph applied to soil was investigated in a laboratory chamber. The volatility and metabolism of a 14C-labelled fenpropimorph formulation (Corbel®) was studied after application to three soils (sandy loam, loamy clay and loamy sand), simulating a four-day weather scenario in the volatilization chamber. Additional experiments were conducted under standard climatic conditions over a period of 24 h using sandy soils with different pH values. The results of the first experiments showed that most of the radioactivity applied remained in the soils as unchanged fenpropimorph four days after application. In the experiments with the sandy loam and loamy clay, less than 5% of the applied radioactivity was removed by volatilization whereas 11·4% volatilized from the surface of the loamy sand. The comparatively higher volatilization of the fungicide from the loamy sand was confirmed by the later experiments indicating that higher soil pH favoured volatilization of [14C]fenpropimorph from sandy soils. Thus 5·6% (pH 5·0), 18·9% (pH 5·8) and 28·3% (pH 6·6) of the radioactivity applied volatilized within one day after application. The overall recoveries were between 93·8% and 111·3% in these experiments. © 1998 SCI 相似文献
10.
Nevain A. S. Messiha Ariena H. C. van Bruggen Anne D. van Diepeningen Oscar J. de Vos Aad J. Termorshuizen N. N. A. Tjou-Tam-Sin J. D. Janse 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(4):367-381
Ralstonia solanacearum race 3 biovar 2, the causative agent of potato brown rot (bacterial wilt), is an economically important disease in tropical,
subtropical and temperate regions of the world. In view of previous reports on suppression of the disease by organic amendments,
and the expansion of organic agriculture, it was timely to compare the effects of organic and conventional management and
various amendments on brown rot development in different soils (type: sand or clay; origin: Egypt or the Netherlands). Brown
rot infection was only slightly reduced in organically compared to conventionally managed sandy soils from Egypt, but organic
management significantly increased disease incidence and pathogen survival in Dutch sandy and clay soils, which correlated
with high DOC contents in the organic Dutch soils. There was no correlation between disease incidence or severity and bacterial
diversity in the potato rhizosphere in differently managed soils (as determined by 16S DGGE). NPK fertilization reduced bacterial
wilt in conventional Egyptian soils but not in Dutch soils. Cow manure amendment significantly reduced disease incidence in
organic Dutch sandy soils, but did not affect the bacterial population. However, cow manure did reduce densities of R. solanacearum in Egyptian sandy soils, most probably by microbial competition as a clear shift in populations was detected with DGGE in
these and Dutch sandy soils after manure amendment. Amendment with compost did not have a suppressive effect in any soil type.
The absence of a disease suppressive effect of mineral and organic fertilization in Dutch clay soils may be related to the
already high availability of inorganic and organic nutrients in these soils. This study shows that the mechanism of disease
suppression of soil-borne plant pathogens may vary strongly according to the soil type, especially if quite different types
of soil are used. 相似文献
11.
ABSTRACT The physiology and virulence of Ralstonia solanacearum biovar 2 strain 1609, kept in water at 4 and 20 degrees C, were studied. At 20 degrees C, total cell and plate count (colony forming units; CFU) numbers were similar, between log 5.03 and log 5.55 CFU, and log 5.03 and log 5.51 cells per ml, at days 0 and 132, respectively. However, CFU in the cultures kept at 4 degrees C dropped from log 6.78 CFU/ml at day 0 to below detection after 84 days. The presence of catalase in the agar resulted in higher CFU, and at day 84, log 1.95 CFU/ml still was detectable. No colonies were observed at day 125. The presence of viable-but-nonculturable (VBNC) cells in the 4 degrees C cultures was confirmed using SYTO9 viability staining. Viable cell numbers were log 1.77 higher than CFU on plates with catalase. At day 84 and after 125 days, log 3.70 viable cells per ml still were present. Shifts in subpopulations differing in viability were found by flow cytometric sorting of 4 degrees C-treated cells stained with SYTO9 (healthy) and propidium iodide (PI; compromised). The SYTO9-stained cell fractions dropped from 99 to 39%, and the PI-stained fractions increased from 0.7 to 33.3% between days 0 and 125. At 20 degrees C, the SYTO9-stained fraction remained stable at 99% until day 132. SYTO9-stained cells sorted from 4 degrees C cultures at day 100 were injected into tomato plants. Upon incubation for 30 days, these plants did not show wilting. However, more than log 4.19 CFU and log 8.17 cells were recovered from these plants. Cells from colonies isolated from the nonwilted plants did not regain their virulence as demonstrated by subsequent injection into several new sets of tomato plants. Cells from 4 degrees C cultures injected at day 125 were not able to cause wilting of, or proliferate in, tomato plants. The threat posed by VBNC R. solanacearum cells upon incubation at 4 degrees C was thus ephemeral because cells lost their capacity to cause disease after 125 days. 相似文献
12.
Sulcotrione soil persistence in spring maize ( Zea mays L.) crops grown on a sandy loam soil was greater at pH 5·5 and 6·0 (soil half-life T 1/2 ≈58 days) than at pH 7·1 ( T 1/2 = 44 days). Sulcotrione was also applied as recommended on a summer maize crop at the five- to six-leaf growth stage, grown on a sandy loam soil. Sulcotrione soil half-life was 44 days, and the herbicide remained mainly in the 0- to 5-cm surface soil layer during the cropping period, in spite of the high water solubility and the heavy rains at the end of August; lower sulcotrione concentrations (10–18% of the total during the 2-month period after sulcotrione application) were detected in the 5- to 10-cm surface soil layer. The herbicide was applied pre-emergence to winter wheat ( Triticum aestivum L.) at four sites that differed in their soil texture and composition: loamy sand, sandy loam, loam and clay loam. Persistence was greater in the soils containing more organic matter. In soils having similar organic matter contents, persistence was lower in the soil containing more sand relative to loam and clay. During the winter crops, sulcotrione moved down to the 10- to 15-cm soil layer, in spite of the fact that the rains were lower in winter than in summer. Sulcotrione most generally was not detected in the 15–20 cm soil layer of the maize and winter wheat crops. 相似文献
13.
The diversity of 40 strains of Ralstonia solanacearum causing bacterial wilt of potato in the major potato-growing areas of Iran was assessed. Based on rep-PCR genomic fingerprinting, strains fell into two distinct groups. The first group contained 37 of the 40 strains and the second consisted of three strains from a narrow tropical region in Iran. The three strains from the narrow tropical region were found to be phenotypically and genotypically most similar to R. solanacearum biovar 2T strains, whereas all other strains were phenotypically and genotypically identified as being R. solanacearum biovar 2/race 3. Phylogenetic analysis of endoglucanase gene sequence information of two of the strains from the tropical region revealed that they belonged to phylotype II of the R. solanacearum species complex and had 100% sequence similarity to a biovar 2T strain from potato in Peru. This is the first report of the presence of R. solanacearum phylotype II/biovar 2T in Iran and the first report of the existence of this group of R. solanacearum outside South America. 相似文献
14.
G. Jager H. Velvis 《European journal of plant pathology / European Foundation for Plant Pathology》1983,89(1-2):21-29
A search was made forRhizoctonia solani-suppressive soils by establishing many small experimental plots, half of which were planted withRhizoctonia-infected seed potatoes and the other half with disinfected seed stock. The sclerotium index of the harvested tubers was compared witht that of the seed potatoes. In suppressive soils, the sclerotium index of the harvest is much lower than that of the seed potatoes. None of the plots on holocene marine soils (loamy sand, sandy loam, clay loam and clay) proved to be suppressive in 1978 and 1979. Only on pleistocene, slightly acid sandy soil suppressiveness was observed. In 1978, four out of twelve plots showed suppressiveness when the plots were planted with seed potatoes produced on a sandy soil. In 1979, only two out of thirtyone plots were slightly suppressive when planted with seed potatoes produced on a young clay loam from a new polder. A higher percentage of sclerotia on tubers from sandy soils proved to be infected with antagonistic fungi (73%) than of those on tubers from marine clay or loam soils (25%). Factors that influence suppressiveness are suggested. 相似文献
15.
The soil type is a key factor influencing N(nitrogen) cycling in soil; however, gross N transformations and N_2O emission sources are still poorly understood. In this study, a laboratory ~(15)N tracing experiment was carried out at 60% WHC(water holding capacity) and 25℃ to evaluate the gross N transformation rates and N_2O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province, China. The results showed that the gross rates of N mineralization, immobilization, and nitrification were 3.60, 1.90, and 5.63 mg N/(kg·d) in silt loam soil, respectively, which were 3.62, 4.26, and 3.13 times those in sandy loam soil, respectively. The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia) in sandy loam soil and silt loam soil were all higher than 1.00, whereas the n/ia in sandy loam soil(4.36) was significantly higher than that in silt loam soil(3.08). This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil, and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_3~– leaching. Under aerobic conditions, both nitrification and denitrification made contributions to N_2O emissions. Nitrification was the dominant pathway leading to N_2O production in soils and was responsible for 82.0% of the total emitted N_2O in sandy loam soil, which was significantly higher than that in silt loam soil(71.7%). However, the average contribution of denitrification to total N_2O production in sandy loam soil was 17.9%, which was significantly lower than that in silt loam soil(28.3%). These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions. 相似文献
16.
高寒草甸不同类型草地土壤机械组成及肥力比较 总被引：3，自引：0，他引：3
研究了青藏高原高寒草甸不同类型草地土壤机械组成和土壤养分变化特征,并用相关分析探讨了土壤理化特征、土壤机械组成对不同草地类型群落物种组成、生物量变化的响应。结果表明:不同草地类型土壤机械组成分布大致是矮嵩草草甸:粉粒>细砂粒>粘粒>粗砂粒;高山嵩草草甸:细砂粒>粉粒>粘粒>粗砂粒;藏嵩草沼泽化草甸:细砂粒>粉粒>粘粒>粗砂粒;金露梅灌丛:粉粒>粘粒≥细砂粒>粗砂粒。矮嵩草草甸、高山嵩草草甸为粉砂质粘壤土,藏嵩草沼泽化草甸为壤土,金露梅灌丛为壤质粘土。矮嵩草草甸、高山嵩草草甸和金露梅灌丛土壤颗粒分布相对比较均匀(除藏嵩草沼泽化草甸外),主要集中在<0.5mm的范围内,土壤粘粒含量普遍大于20%。土壤全量养分和速效养分以及土壤物理特征均影响着高寒草甸不同草地类型土壤质量和土壤结构。土壤结构和养分状况是判断高寒草甸生态系统生态功能维持的关键指标之一。 相似文献
17.
Leo van Overbeek Willemien Runia Pieter Kastelein Leendert Molendijk 《European journal of plant pathology / European Foundation for Plant Pathology》2014,138(2):323-330
Tare soil is soil attached to harvested products like potato tubers. Tare soil becomes a considerable waste stream after storage, washing and processing of harvested products. There is a high risk on contamination of tare soils with (quarantine) phytopathogens, because of import of harvested products from different regions of the world. Disinfestation is necessary to make tare soils applicable for agricultural production. Anaerobic (non-chemical) soil disinfestation (ASD) and inundation are suitable methods to disinfest tare soils. Two different soils (marine loam and glacial sand) were either treated with five (2011) or four (2012) treatments and these were: (i) no treatment (control), (ii) freshly cut grass, (iii) Herbie 7025, (iv) inundation (five cm water on top of the soil surface), and (v) combination of Herbie 7025 and inundation (2011 only). Containers with treated and untreated soils were inoculated with two quarantine phytopathogens, Ralstonia solanacearum biovar 2 and Globodera pallida. After soil inoculation, the containers were airtight closed and only opened for destructive sampling after 84 days. Then, soils were analysed for the presence of R. solanacearum biovar 2, using immunofluorescence colony staining, and for the presence of viable G. pallida eggs, determined by the number of juveniles hatched from eggs and lured to potato root exudate. Strong (> 99.4 %) declines of both pathogens in treated versus the appropriate control soils were observed. Repetition of the experiment revealed the same pattern and therefore it was concluded that ASD and inundation, as separate treatments, have promise for remediation of tare soils from contaminating quarantine pathogens. 相似文献
18.
Tomas Berglf William C Koskinen Henrik Kylin Thomas B Moorman 《Pest management science》2000,56(10):927-931
Sorption–desorption of the fungicide triadimefon in field‐moist silt loam and sandy loam soils were determined using low‐density supercritical fluid extraction (SFE). The selectivity of SFE enables extraction of triadimefon from the soil water phase only, thus allowing calculation of sorption coefficients (Kd) at field‐moist or unsaturated conditions. Triadimefon sorption was influenced by factors such as soil moisture content and temperature; sorption increased with increased moisture content up to saturation, and decreased with increased temperature. For instance, Kd values for triadimefon on the silt loam and the sandy loam soils at 40 °C and 10% water content were 1.9 and 2.5 ml g−1, respectively, and at 18% water content, 3.3 and 6.4 ml g−1, respectively. Isosteric heats of sorption (ΔHi) were −42 and −7 kJ mol−1 for the silt loam and sandy loam soils, respectively. Sorption–desorption was also determined using an automated accelerated solvent extraction system (ASE), in which triadimefon was extracted from silt loam soil by 0.01 M CaCl2. Using the ASE system, which is basically a fast alternative to the batch equilibration system, gave a similar ΔHi value (−29 kJ mol−1) for the silt loam soil (Kf = 27 µg1 − 1/n ml1/n g−1). In order to predict transport of pesticides through the soil profile more accurately on the basis of these data, information is needed on sorption as a function of soil water content. © 2000 Society of Chemical Industry 相似文献
19.
ABSTRACT Recombinant single-chain antibodies (scFvs) against the lipopolysaccharide of Ralstonia solanacearum (biovar 2, race 3) were successfully selected by phage display from a large combinatorial antibody library. Characterization with regard to cross-reaction and use in routine immunoassays showed that the selected antibodies had improved characteristics when compared with the polyclonal antiserum that is currently used for brown rot diagnosis of potato in the Netherlands. The isolated monoclonal scFvs reacted in both enzyme-linked immunosorbent assay (ELISA) and immunofluorescence cell staining with all race 3 strains tested, but with only some strains belonging to other races. Furthermore, only a few cross-reactions with saprophytic bacteria, which also cross-reacted with polyclonal antisera, were observed. Using ELISA, one of the recombinant antibodies detected as few as 5 x 10(3) bacteria in potato tuber extracts. Therefore, this antibody is potentially useful for detection of R. solanacearum race 3. 相似文献
20.
ABSTRACT Strains of Pseudomonas fluorescens producing the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) are biocontrol agents which play a key role in the suppressiveness of some soils against soilborne pathogens. We evaluated the effect of the host plant genotype on rhizosphere colonization by both indigenous and introduced 2,4-DAPG-producing P. fluorescens. First, population densities of indigenous 2,4-DAPG producers in the rhizospheres of alfalfa, barley, bean, flax, lentil, lupine, oat, pea, and wheat grown in a Fusarium wilt-suppressive Puget silt loam were determined. Population densities differed among the various crops and among pea cultivars, with lentil and oat supporting the highest and lowest densities of 2,4-DAPG producers, respectively. Second, to determine the interactions among 2,4-DAPG producers in the rhizosphere, a Shano sandy loam was inoculated individually and with all possible combinations of P. fluorescens Q8r1-96 (genotype D), F113 (genotype K), and MVP1-4 (genotype P) and sown to wheat or pea, and the rhizosphere population dynamics of each strain was monitored. All three strains were similar in ability to colonize the rhizosphere of wheat and pea when introduced alone into the soil; however, when introduced together in equal densities, the outcome of the interactions differed according to the host crop. In the wheat rhizosphere, the population density of strain F113 was significantly greater than that of Q8r1-96 in the mixed inoculation studies, but no significant differences were observed on pea. The population density of strain Q8r1-96 was greater than that of MVP1-4 in the mixed inoculation on wheat, but the opposite occurred on pea. In the wheat rhizosphere, the population of MVP1-4 dropped below the detection limit (log 3.26 CFU g(-1) of root) in the presence of F113; however, on pea, the population density of MVP1-4 was higher than that of F113. When all three strains were present together, F113 had the greatest density in the wheat rhizosphere, but MVP1-4 was dominant in the pea rhizosphere. Finally, eight pea cultivars were grown in soil inoculated with either MVP1-4 or Q8r1-96. The effect of the pea cultivar on rhizosphere colonization was dependent on the bacterial strain inoculated. Rhizosphere population densities of MVP1-4 did not differ significantly among pea cultivars, whereas population densities of Q8r1-96 did. We conclude from these studies that the host crop plays a key role in modulating both rhizosphere colonization by 2,4-DAPG-producing P. fluorescens and the interactions among different genotypes present in the same rhizosphere. 相似文献