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1.
Increases in populations of fluorescent pseudomonads on wheat roots are usually associated with take-all decline, natural control of take-all, a disease caused by the fungus Gaeumannomyces graminis var. tritici (Ggt). Colonisation by Pseudomonas fluorescens strain Pf29A was assessed on the roots of healthy plants and of plants with take-all, and the effect of this bacterium on indigenous populations of fluorescent pseudomonads was studied. The efficacy of Pf29A as an agent for the biocontrol of take-all on five-week-old wheat seedlings was tested in non-sterile conducive soil in a growth chamber. RAPD (random amplification of polymorphic DNA) fingerprinting with a decamer primer was used to monitor strain Pf29A and culturable indigenous rhizoplane populations of fluorescent pseudomonad. Pf29A decreased disease severity and accounted for 44.6% of the culturable fluorescent pseudomonads on healthy plant rhizoplane and 75.8% on diseased plant rhizoplane. Fewer RAPD patterns were obtained when Pf29A was introduced into the soil with Ggt. In the presence of Ggt and necrotic roots, Pf29A became the dominant root coloniser and dramatically changed the diversity and the structure of indigenous fluorescent pseudomonad populations. The results show that Ggt and reduced lesion size on roots can trigger a specific increase in antagonist populations and that the introduction of a biocontrol agent in soil influences the structure of indigenous bacterial populations.  相似文献   

2.
Rhizoctonia cerealis causes sharp eyespot in cereals and the pathogen survives as mycelia or sclerotia in soil. Real-time Polymerase Chain Reaction (qPCR) assays based on TaqMan chemistry are highly suitable for use on DNA extracted from soil. We report here the first qPCR assay for R. cerealis using TaqMan primers and a probe based on a unique Sequence Characterised Amplified Region (SCAR). The assay is highly specific and did not amplify DNA from a range of other binucleate Rhizoctonia species or isolates of anastomosis groups of Rhizoctonia solani. The high sensitivity of the assay was demonstrated in soils using a bulk DNA extraction method where 200 μg sclerotia in 50 g of soil were detected. DNA of the pathogen could also be amplified from asymptomatic wheat plants. Using the assay on soil samples from fields under different crop rotations, R. cerealis was most frequently detected in soils where wheat was grown or soil under pasture. It was detected least frequently in fields where potatoes were grown. This study demonstrates that assays derived from SCAR sequences can produce specific and sensitive qPCR assays.  相似文献   

3.
ABSTRACT Strains of fluorescent Pseudomonas spp. that produce the antibiotic 2,4-diacetylphoroglucinol (2,4-DAPG) are among the most effective rhizobacteria controlling diseases caused by soilborne pathogens. The genotypic diversity that exists among 2,4-DAPG producers can be exploited to improve rhizosphere competence and biocontrol activity. Knowing that D-genotype 2,4-DAPG-producing strains are enriched in some take-all decline soils and that P. fluorescens Q8r1-96, a representative D-genotype strain, as defined by whole-cell repetitive sequence-based polymerase chain reaction (rep-PCR) with the BOXA1R primer, is a superior colonizer of wheat roots, we analyzed whether the exceptional rhizosphere competence of strain Q8r1-96 on wheat is characteristic of other D-genotype isolates. The rhizosphere population densities of four D-genotype strains and a K-genotype strain introduced individually into the soil were significantly greater than the densities of four strains belonging to other genotypes (A, B, and L) and remained above log 6.8 CFU/g of root over a 30-week cycling experiment in which wheat was grown for 10 successive cycles of 3 weeks each. We also explored the competitive interactions between strains of different genotypes inhabiting the same soil or rhizosphere when coinoculated into the soil. Strain Q8r1-96 became dominant in the rhizosphere and in nonrhizosphere soil during a 15-week cycling experiment when mixed in a 1:1 ratio with either strain Pf-5 (A genotype), Q2-87 (B genotype), or 1M1-96 (L genotype). Furthermore, the use of the de Wit replacement series demonstrated a competitive disadvantage for strain Q2-87 or strong antagonism by strain Q8r1-96 against Q2-87 in the wheat rhizosphere. Amplified rDNA restriction analysis and sequence analysis of 16S rDNA showed that species of Arthrobacter, Chryseobacterium, Flavobacterium, Massilia, Microbacterium, and Ralstonia also were enriched in culturable populations from the rhizosphere of wheat at the end of a 30-week cycling experiment in the presence of 2,4-DAPG producers. Identifying the interactions among 2,4-DAPG producers and with other indigenous bacteria in the wheat rhizosphere will help to elucidate the variability in biocontrol efficacy of introduced 2,4-DAPG producers and fluctuations in the robustness of take-all suppressive soils.  相似文献   

4.
Organic management of soils is generally considered to reduce the incidence and severity of plant diseases caused by soil-borne pathogens. In this study, take-all severity on roots of barley and wheat, caused by Gaeumannomyces graminis var. tritici, was significantly lower in organically-managed than in conventionally-managed soils. This effect was more pronounced on roots of barley and wheat plants grown in a sandy soil compared to a loamy organically-managed soil. Fluorescent Pseudomonas spp. and in particular phlD+ pseudomonads, key factors in the take-all decline phenomenon, were represented at lower population densities in organically-managed soils compared to conventionally-managed soils. Furthermore, organic management adversely affected the initial establishment of introduced phlD+ P. fluorescens strain Pf32-gfp, but not its survival. In spite of its equal survival rate in organically- and conventionally-managed soils, the efficacy of biocontrol of take-all disease by introduced strain Pf32-gfp was significantly stronger in conventionally-managed soils than in organically-managed soils. Collectively, these results suggest that phlD+ Pseudomonas spp. do not play a critical role in the take-all suppressiveness of the soils included in this study. Consequently, the role of more general mechanisms involved in take-all suppressiveness in the organically-managed soils was investigated. The higher microbial activity found in the organically-managed sandy soil combined with the significantly lower take-all severity suggest that microbial activity plays, at least in part, a role in the take-all suppressiveness in the organically-managed sandy soil. The significantly different bacterial composition, determined by DGGE analysis, in organically-managed sandy soils compared to the conventionally-managed sandy soils, point to a possible additional role of specific bacterial genera that limit the growth or activity of the take-all pathogen.  相似文献   

5.
生防菌哈茨木霉FJAT-9040的GFP标记及土壤定殖示踪   总被引：1，自引：1，他引：0  
哈茨木霉Trichoderma harzianum FJAT-9040对茄科尖孢镰刀菌具有较强拮抗作用。为跟踪分析该菌株在土壤中的存活与定殖特性,利用PEG-CaCl2介导的原生质体转化体系,筛选获得1株荧光性状稳定的菌株FJAT-9295,该菌株在生长速率、产孢量、对酸碱度和温度的适应性及对尖孢镰刀菌的抑菌活性等方面与野生型菌株FJAT-9040无显著差异（P〉0.05）。同时,研究了菌株FJAT-9295在4种类型土壤中的定殖能力以及作物生长对该菌株在土壤中定殖的影响。结果表明：菌株在育苗土中定殖最好,其次为沙土及菜园土,黄泥土中定殖最差;种植茄子比未种植作物的土壤更有利于菌株的存活;菌株FJAT-9295在不同类型土壤中的菌落数随时间的延长均略有下降,16天后趋于稳定,维持在105 CFU/g,较初始接菌量下降了约1个数量级。  相似文献   

6.
ABSTRACT The role of antibiotics in biological control of soilborne pathogens, and more generally in microbial antagonism in natural disease-suppressive soils, often has been questioned because of the indirect nature of the supporting evidence. In this study, a protocol for high pressure liquid chromatography/mass spectrometry is described that allowed specific identification and quantitation of the antibiotic 2,4-diacetylphloroglucinol (Phl) produced by naturally occurring fluorescent Pseudomonas spp. on roots of wheat grown in a soil suppressive to take-all of wheat. These results provide, for the first time, biochemical support for the conclusion of previous work that Phl-producing fluorescent Pseudomonas spp. are key components of the natural biological control that operates in take-all-suppressive soils in Washington State. This study also demonstrates that the total amount of Phl produced on roots of wheat by P. fluorescens strain Q2-87, at densities ranging from approximately 10(5) to 10(7) CFU/g of root, is proportional to its rhizosphere population density and that Phl production per population unit is a constant (0.62 ng/10(5) CFU). Thus, Phl production in the rhizosphere of wheat is strongly related to the ability of the introduced strain to colonize the roots.  相似文献   

7.
To reduce Fusarium Basal Rot caused by Fusarium oxysporum f.sp. cepae (Foc) through crop rotation, plant species should be selected based on Foc multiplication in their roots. Foc multiplication rates in 13 plant species were tested in a greenhouse. All plant species enabled Foc multiplication. The lowest Foc levels (cfu g?1 dry root) were found for wheat, sunflower, cowpea and millet, the highest for black bean. The highest Foc levels per plant were calculated for sudan grass. These data were used to calibrate the model Pf?=?Pi/(α?+?βPi) relating final (Pf) and initial (Pi) Foc levels in the soil. The rate of population increase at low Pi (1/α) was highest for onion and black oat and smallest for sunflower. The pathogen carrying capacity (1/β) was highest for black oat and black bean, and lowest for wheat, cowpea and foxtail millet. Foc soil population dynamics was simulated for crop sequences by concatenating Pi-Pf values, considering instantaneous or gradual pathogen release after harvest. Different soil Foc populations were attained after reaching steady states. Foc populations in the sequence onion –foxtail millet - wheat – cowpea were 67 % lower than in the sequence onion – sudan grass - black oat - black beans. In this work, by combining detailed greenhouse experiments with modelling, we were able to screen crops for their ability to increase Foc population and to explore potential crop sequences that may limit pathogen build-up.  相似文献   

8.
Mazzola M  Gu YH 《Phytopathology》2000,90(2):114-119
ABSTRACT Studies were conducted to assess the impact of short-term rotations of wheat on microbial community composition and growth of apple in soils from replant orchard sites. Soils from two orchards were cultivated with three successive 28-day growth cycles of 'Eltan', 'Penewawa', or 'Rely' wheat in the greenhouse and subsequently planted to 'Gala' apple seedlings. Cultivation of orchard replant soils with any of the three wheat cultivars enhanced growth of apple relative to that achieved in untreated soils. Improved growth was associated with a marked reduction in apple root infection by species of Rhizoctonia and Pythium. Populations of plant-parasitic nematodes were below damage threshold levels in these orchard soils; however, apple seedlings grown in wheat-cultivated soils had significantly lower root populations of Pratylenchus spp. than did seedlings grown in untreated soils. Growth of apple in 'Penewawa'-cultivated soils often was superior to that observed in soils planted with 'Eltan' or 'Rely'. In untreated orchard soils, fluorescent pseudomonad populations isolated from soil and the apple rhizosphere were dominated by Pseudomonas fluorescens biotype C and Pseudomonas syringae. Cultivation of replant soils with wheat induced a characteristic transformation of the fluorescent pseudomonad population, and Pseudomonas putida dominated the population of this bacterial group recovered from wheat-cultivated replant orchard soils. Results from this study suggest that use of short-term wheat cropping sequences during orchard renovation could be useful in management of replant disease and that this disease-control option may operate, in part, through modification of the fluorescent pseudomonad community.  相似文献   

9.
小麦条锈菌新菌系V26的SCAR检测标记   总被引：2，自引：0，他引：2  
 建立小麦条锈菌生理小种的快速分子检测技术体系对小麦条锈菌的监测和防治策略的制定具有重要价值。条锈菌V26是近年来出现的,对我国目前小麦抗病育种中普遍应用的抗条锈病基因Yr26具有毒性的新菌系。该菌系的出现,对我国当前小麦生产、抗病育种都造成了严重威胁。本研究选用189条随机引物对CYR29、CYR31、CYR32、CYR33、T4、Su11-4和V26等7个条锈菌生理小种(菌系)进行了扩增,筛选V26的特异性RAPD片段,并对其进行克隆和测序。根据测序结果,设计并合成SCAR特异性引物, 将V26的RAPD标记转化为稳定的SCAR标记。使得对该菌系的快速检测成为可能,同时也将会为条锈菌新小种的监测提供更为准确的科学依据。  相似文献   

10.
小麦叶锈菌生理小种MFR的分子鉴定研究   总被引：2，自引：0，他引：2  
 用AFLP方法对来自中国和墨西哥的23个小麦叶锈菌生理小种进行分析,共筛选了64对引物,获得一对引物(M05/E03)可在MFR小种中扩增出一条特异性DNA片段,进行回收、克隆、测序,结果表明该片段具有325个碱基。根据特异性片段序列设计出SCAR标记引物,对60个叶锈菌生理小种分离物进行回检结果表明,研制的SCAR标记能够准确区分MFR生理小种。本实验结果为小麦锈菌生理小种分子检测体系的建立奠定了基础  相似文献   

11.
菲利普孢囊线虫Heterodera filipjevi是禾谷类作物上重要的病原线虫之一,严重影响禾谷类作物的产量和品质。本课题组前期研究发现菲利普孢囊线虫许昌群体是一个新的致病型,其在小麦上的致病力强于其他多个群体,危害更为严重。本研究旨在建立菲利普孢囊线虫许昌群体的快速、准确的分子检测体系,为Heterodera filipjevi许昌群体的监测和防控及抗病品种的选育利用奠定基础。本研究采用随机扩增多态性DNA(RAPD)和序列特征扩增区域(SCAR)的方法,对黄淮麦区5个重要小麦孢囊线虫致病型共9个线虫群体进行RAPD分析和SCAR标记转化,并通过增加除黄淮麦区外的线虫群体验证所获得的致病型相关分子标记的特异性和有效性。本研究共筛选了331条RAPD引物,筛选出2个菲利普孢囊线虫许昌群体相关的RAPD标记,引物S86可以扩增出1条约550 bp的多态性片段,引物S178可以扩增出1条约1 200 bp的多态性片段,并将这2个RAPD标记成功转化为SCAR标记。SCAR标记的特异性检测结果表明这两个SCAR标记只在许昌群体上有特异性扩增,可以用于许昌群体的分子检测。  相似文献   

12.
玉米矮化病株及其根际土壤内线虫的分离与分子鉴定   总被引：2，自引：1，他引：1  
为探究玉米矮化病的病原,采用Ludox TM悬浮法对从吉林和辽宁采集的玉米矮化病株及其根际土壤和健康株根际土壤分离的线虫进行了鉴定和种群比较,并对矮化病株茎基组织PCR产物进行测序分析。结果表明:玉米健康株根际土壤分离出29属线虫,特有线虫是角咽线虫属Actinolaimus和木盾移线虫属Peltamigratus,矮化玉米病株根际土壤分离出28属线虫,特有线虫为锥线虫属Dolichorus,二者相同的线虫属有27个。矮化玉米病株根际土壤中植物线虫种类和数量明显比健康株根际土壤中高,线虫种群数量差异明显的主要是矮化线虫属Tylenchorhynchus、短体线虫属Pratylenchus和刺线虫属Belonolaimus,病株根际土壤中这3个属线虫总数约占病株土壤分离线虫总数的20.23%、11.27%和10.40%。玉米矮化病株茎基组织中短体线虫属和矮化线虫属数量占优势,2个属的线虫数量分别占测序总数的22%、14%(吉林长岭)和16%、20%(辽宁黑山)。表明玉米矮化病的发生与植物线虫相关,很可能是多种线虫共同引起的病害。  相似文献   

13.
The dependence of the behaviour of metsulfuron-methyl on soil pH was confirmed during incubations under controlled laboratory conditions with two French soils used for wheat cropping. The fate of [14C] residues from [triazine-14C]metsulfuron-methyl was studied by combining different experimen-tal conditions: soil pH (8·1 and 5·2), temperature (28 and 10°C), soil moisture (90 and 50% of soil water holding capacity) and microbial activity (sterile and non-sterile conditions). Metsulfuron-methyl degradation was mainly influenced by soil pH and temperature. The metsulfuron-methyl half-life varied from five days in the acidic soil to 69 days in the alkaline soil. Under sterile conditions, the half-life increased in alkaline soil to 139 days but was not changed in the acidic soil. Metsulfuron-methyl degradation mainly resulted in the formation of the amino-triazine. In the acidic soil, degradation was characterised by rapid hydrolysis giving two specific unidentified metabolites, not detected during incubations in the alkaline soil. Bound residues formation and metsulfuron-methyl mineralisation were highly correlated. The extent of bound residue formation increased when soil water content decreased and was maximal [48 (±4)% of the applied metsulfuron-methyl after 98 incubation days] in the acidic soil at 50% of the water holding capacity and 28°C. Otherwise, bound residues represented between 13 and 32% of the initial radioactivity. © 1998 SCI  相似文献   

14.
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   

15.
ABSTRACT Previously, the zoosporicidal activity and control of Pythium root rot of flower bulbs by Pseudomonas fluorescens SS101 was attributed, in part, to the production of the cyclic lipopeptide surfactant massetolide A. The capacity of strain SS101 and its surfactant-deficient massA mutant 10.24 to suppress populations and root infection by complex Pythium spp. communities resident in orchard soils was assessed on apple and wheat seedlings and on apple rootstocks. Both strains initially became established in soil and persisted in the rhizosphere at similar population densities; however, massA mutant 10.24 typically was detected at higher populations in the wheat rhizosphere and soil at the end of each experiment. Both strains effectively suppressed resident Pythium populations to an equivalent level in the presence or absence of plant roots, and ultimately suppressed Pythium root infection to the same degree on all host plants. When split-root plant assays were employed, neither strain suppressed Pythium spp. infection of the component of the root system physically separated from the bacterium, suggesting that induced systemic resistance did not play a role in Pythium control. Strain SS101 only marginally suppressed in vitro growth of Pythium spp. and growth was not inhibited in the presence of mutant 10.24. When incorporated into the growth medium, the cyclic lipopeptide massetolide A significantly slowed the rate of hyphal expansion for all Pythium spp. examined. Differences in sensitivity were observed among species, with Pythium heterothallicum, P. rostratum, and P. ultimum var. ultimum exhibiting significantly greater tolerance. Pythium spp. populations indigenous to the two soils employed were composed primarily of P. irregulare, P. sylvaticum, and P. ultimum var. ultimum. These Pythium spp. either do not or rarely produce zoospores, which could account for the observation that both SS101 and mutant 10.24 were equally effective in disease control. Collectively, the results showed that (i) Pseudomonas fluorescens SS101 is very effective in controlling diverse Pythium populations on different crops grown in different soils and (ii) production of the cyclic lipopeptide massetolide A does not play a significant role in disease suppression. Other, as yet undefined mechanisms appear to play a significant role in the interaction between P. fluorescens SS101 and soilborne Pythium spp. communities.  相似文献   

16.
Two different molecular tools for the diagnosis of the cereal and legume root-lesion nematode Pratylenchus thornei were developed. A randomly amplified DNA (RAPD) fragment specific to P. thornei was identified. After sequencing the fragment, longer primers were designed that complement the terminal sequences of the RAPD fragment, and this pair of specific primers was used to amplify the sequence-characterized amplified region (SCAR). Using the developed pair of SCAR primers, the SCAR fragment specific to P. thornei was easily amplified with DNA extracts obtained from different life stages of the nematode. The described SCAR-PCR-based assay has the potential to be optimized for routine practical diagnostic tests. In addition, the use of a species-specific satellite DNA sequence to distinguish P. thornei from other Pratylenchus spp. is discussed.  相似文献   

17.
南方、爪哇和花生根结线虫的快速灵敏的PCR鉴定方法   总被引：7，自引：0，他引：7  
 为了研制南方、爪哇和花生根结线虫快速灵敏的检测和鉴定方法,分别分离了4个南方根结线虫和3个爪哇根结线虫特异性的随机扩增多态性DNA (RAPD)片段。在这些RAPD标记DNA序列的基础上,设计了多对SCAR PCR引物,并用源于国内外的南方、爪哇、花生、北方和象耳豆根结线虫群体验证其扩增特异性和灵敏度。最终确定了3对高效扩增的SCAR引物,它们组合使用可以可靠灵敏地鉴定南方、爪哇和花生根结线虫。3对引物的扩增灵敏度达1/3条的二龄幼虫、雄虫或雌虫,这表明本研究研制的PCR鉴定法可用于生产实践中土样和根样中3种根结线虫快速灵敏的鉴定。  相似文献   

18.
ABSTRACT After outbreaks of potato brown rot in three different fields in the Netherlands, the fate of the brown rot pathogen, Ralstonia solanacearum biovar 2, was monitored in soil by immunofluorescence colony staining (IFC) supported by R. solanacearum division-2 specific polymerase chain reaction. In selected areas of all fields, the R. solanacearum population densities were initially on the order 10(4) to 10(6) per g of topsoil. These population densities then declined progressively over time. In two fields, however, the pathogen persisted for periods of 10 to 12 months. The survival of a selected R. solanacearum biovar 2 isolate, strain 1609, in three soils, a loamy sand and two different silt loam soils, was further studied in soil microcosm experiments. The effects of temperature and soil moisture content were assessed. At 12 or 15 and 20 degrees C, a gradual decline of the population densities was observed in all three soils, from the established 10(5) to 10(6) CFU g(-1) of dry soil to significantly reduced levels, occasionally bordering the limit of detection (10(2) CFU g(-1)of dry soil), in periods of approximately 90 to 210 days. Soil type affected the rate of population decline at 20 degrees C, with the greatest decline occurring in loamy sand soil. In all three soils, the survival of IFC-detectable R. solanacearum 1609 cells at 4 degrees C was severely impaired, reflected in an accelerated decline of CFU counts, to undetectable numbers. Moreover, indications were found for the occurrence of viable but nonculturable strain 1609 cells in the loamy sand as well as in one silt loam soil under these conditions. In addition, a single freezing-thawing cycle caused a significant additional reduction of the culturable R. solanacearum 1609 populations in the three soils, though detectable populations remained. Moderate soil moisture fluctuations of approximately pF 2 did not affect the survival of R. solanacearum 1609 in soil. Severe drought, however, drastically reduced the populations of strain 1609 CFU in all three soils.  相似文献   

19.
To elucidate how soft rot disease affects soil characteristics and root-associated, culturable microorganisms in Amorphophallus konjac stands, the responses of soil around roots of A. konjac with soft rot disease were investigated in stands with and without soft rot. Changes in the root-associated culturable microbial community and diversity were investigated by dilution plating. Soil characteristics were compared between stands using standard techniques. A. konjac with soft rot had higher concentrations of available soil P and K, NH4–N, organic matter and water content and lower pH compared with plants without. The community composition of root-associated culturable microorganisms differed between stands with and without soft rot. The microbial community associated with soft rot in A. konjac was characterized by four types of abundant microorganisms (Fusarium solani, Fusarium oxysporum, Pseudomonas chlororaphis subsp. aureofaciens and Stenotrophomonas pavanii) and three types of less-abundant microorganisms (Rhizobium radiobacter, Bacillus thuringiensis and Streptomyces cellulosae), and a small number of Bacillus and Streptomyces species in the rhizosphere and rhizoplane soils. Particular microbial combinations were diametrically opposed between plants with and without soft rot. The richness and diversity of root-associated culturable microorganisms were higher in the stand without soft rot than in the stand with soft rot. A. konjac soft rot led to obvious differences in the diversity and community composition of root-associated culturable microorganisms and in soil characteristics.  相似文献   

20.
A laboratory study was conducted to determine the degradation rates and identify major metabolites of the herbicide metsulfuron-methyl in sterile and non-sterile aerobic soils in the dark at 20°C. Both [phenyl-U-14C]- and [triazine-2-14C]metsulfuron-methyl were used. The soil was treated with [14C]metsulfuron-methyl (0.1 mg kg−1) and incubated in flow-through systems for one year. The degradation rate constants, DT50, and DT90 were obtained based on the first-order and biphasic models. The DT50 (time required for 50% of applied chemical to degrade) for metsulfuron-methyl, estimated using a biphasic model, was approximately 10 days (9–11 days, 95% confidence limits) in the non-sterile soil and 20 days (12–32 days, 95% confidence limits) in the sterile soil. One-year cumulative carbon dioxide accounted for approximately 48% and 23% of the applied radioactivity in the [phenyl-U-14C] and [triazine-2-14C]metsulfuron-methyl systems, respectively. Seven metabolites were identified by HPLC or LC/MS with synthetic standards. The degradation pathways included O-demethylation, cleavage of the sulfonylurea bridge, and triazine ring opening. The triazine ring-opened products were methyl 2-[[[[[[[(acetylamino)carbohyl]amino]carbonyl]amino] carbonyl]-amino]sulfonyl]benzoate in the sterile soil and methyl 2-[[[[[amino[(aminocarbonyl)imino]methyl] amino]carbonyl]amino]sulfonyl]benzoate in the non-sterile soil, indicating that different pathways were operable. © 1999 Society of Chemical Industry  相似文献   

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