Effect of nutritional stress on control of Longidorus elongatus by nematicidal chemicals

Studies were made to determine the effect of starvation on the susceptibility of Longidorus elongatus to nematicidal chemicals. In vitro studies, using stylet protraction as a measure of susceptibility, showed that the EC₅₀ for nematodes exposed to oxamyl for 5 min was 6-5 μg cm^-3 for starved nematodes and 7-7 μg cm^-3 for well-fed specimens. In pot studies aldicarb and oxamyl, applied at half the normal commercial rates, decreased the numbers of starved, but not of well-fed, L. elongatus. In a field study aldicarb, oxamyl and the fungicide quintozene decreased the numbers of starving and well-fed L. elongatus. Oxamyl was more effective than aldicarb and the numbers of L. elongatus were decreased more in plots previously fallowed than in those cropped with a grass/clover mixture. A significant interaction between oxamyl treatment and initial crop was found. Starved L. elongatus appear to be more susceptible to carbamate nematicides than well-fed ones. Quintozene decreased numbers of L. elongatus more, and for a longer period of time, than either of the systemic nematicides. The mode-of-action of the nematicidal chemicals is discussed.     

Impact of fumigants on soil microbial communities.

Agricultural soils are typically fumigated to provide effective control of nematodes, soilborne pathogens, and weeds in preparation for planting of high-value cash crops. The ability of soil microbial communities to recover after treatment with fumigants was examined using culture-dependent (Biolog) and culture-independent (phospholipid fatty acid [PLFA] analysis and denaturing gradient gel electrophoresis [DGGE] of 16S ribosomal DNA [rDNA] fragments amplified directly from soil DNA) approaches. Changes in soil microbial community structure were examined in a microcosm experiment following the application of methyl bromide (MeBr), methyl isothiocyanate, 1,3-dichloropropene (1,3-D), and chloropicrin. Variations among Biolog fingerprints showed that the effect of MeBr on heterotrophic microbial activities was most severe in the first week and that thereafter the effects of MeBr and the other fumigants were expressed at much lower levels. The results of PLFA analysis demonstrated a community shift in all treatments to a community dominated by gram-positive bacterial biomass. Different 16S rDNA profiles from fumigated soils were quantified by analyzing the DGGE band patterns. The Shannon-Weaver index of diversity, H, was calculated for each fumigated soil sample. High diversity indices were maintained between the control soil and the fumigant-treated soils, except for MeBr (H decreased from 1.14 to 0.13). After 12 weeks of incubation, H increased to 0.73 in the MeBr-treated samples. Sequence analysis of clones generated from unique bands showed the presence of taxonomically unique clones that had emerged from the MeBr-treated samples and were dominated by clones closely related to Bacillus spp. and Heliothrix oregonensis. Variations in the data were much higher in the Biolog assay than in the PLFA and DGGE assays, suggesting a high sensitivity of PLFA analysis and DGGE in monitoring the effects of fumigants on soil community composition and structure. Our results indicate that MeBr has the greatest impact on soil microbial communities and that 1,3-D has the least impact.     

The use of fumigants and anticoagulant rodenticides on game estates in Great Britain

Several studies have highlighted the potential risk to nontarget wildlife associated with accidental exposure to vertebrate control agents. In order to provide information that may assist in the mitigation of this problem, we questioned 215 gamekeepers in Great Britain about the use of vertebrate control agents on the land for which they were responsible. Fumigants were used to control Rabbits Oryctolagus cuniculus by 59% of gamekeepers. Use of fumigants was more common than on farms in general. 91% of gamekeepers reported the use of rodenticides, 95% of which were anticoagulants. Patterns of rodenticide use were similar to those on arable farms, though chlorophacinone and warfarin were used more commonly on game estates. Future studies of the exposure of nontarget wildlife to anticoagulants should be expanded to include these compounds. Rodenticides were apparently used in accordance with label recommendations in most cases. However, better information and guidelines for users may improve standards of agent application and reduce potential risks to nontarget wildlife.     

The effect of fumigants on soil recolonization in the glasshouse by organisms colonizing the spermosphere

Germinating turnip seeds were used as baits to measure changes in colonizing floras of the spermosphere in glasshouse soil boxes following fumigation. The spermosphere mycoflora of the untreated soil was always dominated by Fusarium, Pythium, and Gliocladium spp. Methyl bromide, chloropicrin, and MBC₃₃ (a 67:33 mixture of methyl bromide and chloropicrin), applied in polyethylene bags at a rate of 2·5 ml/cubic foot of soil, greatly reduced colonization by Fusarium and Pythium spp. for 120 days. Fungi and actinomycetes recolonizing treated soils were more active than in untreated soils, and each fumigant induced a characteristic recolonization pattern. The spermosphere of methyl bromide-treated soil was initially dominated by actinomycetes and later by Penicillium spp. In chloropicrin-treated soil, Trichoderma and later Penicillium spp. dominated, and in soil treated with MBC ₃₃, Penicillium and Trichoderma spp. were co-dominant. Dilution plates, made at the same time from the same soil, indicated a close correlation between inoculum density of different fungi in the soil and their inoculum potentials towards the spermosphere.     

不同熏蒸剂对草莓连作土壤养分和微生物群落的影响

【背景】草莓连年栽培导致土传病害问题突出,施用熏蒸剂进行土壤消毒因效果显著得以广泛应用。但不同熏蒸剂对土壤病原微生物的影响存在较大差异,同时对非靶标微生物和土壤理化性质也会有不同程度的影响。【目的】明确不同熏蒸剂对草莓连作土壤养分和土壤细菌、真菌群落结构的影响,为合理选择熏蒸剂提供科学依据。【方法】以连作土壤为材料设置5个处理：未熏蒸、石灰氮熏蒸、石灰熏蒸、棉隆熏蒸、威百亩熏蒸,测定熏蒸处理后土壤养分含量;采用PacBio测序平台分析土壤微生物多样性的变化。【结果】石灰氮和威百亩处理均增加了碱解氮含量,降低了有机质、有效磷和速效钾含量;棉隆处理土壤中各养分含量均增加;石灰处理除有机质含量增加外,碱解氮、有效磷和速效钾含量均降低;棉隆、石灰和威百亩处理显著降低pH值。5个处理草莓连作土壤样本中获得了1 164个细菌OTU和444个真菌OTU。细菌多样性和丰富度分析发现,4种熏蒸剂处理均增加了土壤细菌群落的丰富度,石灰氮、石灰和威百亩处理增加了土壤细菌菌落的多样性。4种熏蒸剂处理真菌菌落的丰富度低于对照;石灰、棉隆处理真菌菌落的多样性高于对照和石灰氮、威百亩处理低于对照,但差异不显著。在物种组成分析中,从门水平看,变形菌门(Proteobacteria)和芽单胞菌门(Gemmatimonadetes)为优势细菌门;与对照相比,石灰氮、石灰、棉隆处理变形菌门相对丰度增高,威百亩处理相对丰度降低。4种处理均降低了芽单胞菌门的相对丰度。其他门类中,4种处理均增加了浮霉菌门(Planctomycetota)、疣微菌门(Verrucomicrobia)的相对丰度。优势细菌群落分析表明土壤熏蒸减少了芽单胞菌属(Gemmatimonas)、藤黄单胞菌属(Luteimonas)、中慢生根瘤菌属(Mesorhizobium)等细菌的相对丰度,增加了噬几丁质菌属(Chitinophaga)、苍白杆菌属(Ochrobactrum)的相对丰度。子囊菌门(Ascomycota)为优势真菌,石灰氮、石灰、棉隆、威百亩4种处理均增加了子囊菌门的相对丰度。另外还检测到引起草莓根部土传病害的枝孢属(Cladosporium)和镰刀菌属(Fusarium)病菌,熏蒸处理后均降低了枝孢属和镰刀菌属的相对丰度,其中枝孢属在石灰氮、石灰、棉隆、威百亩处理中分别降低了1.35%、1.11%、0.90%和1.31%,镰刀菌属分别降低了0.71%、0.85%、0.19%和0.65%,但差异不显著。4种土壤熏蒸剂均增加了有益真菌毛壳菌属(Chaetomium)的相对丰度。【结论】采用熏蒸剂处理连作土壤改变了微生物群落构成,减少或灭杀土壤中的大部分致病菌属,起到有效防治草莓土传病害的作用,但不能灭杀所有病菌,而且对有益菌和土壤理化性质有不同程度的影响,因此处理后补充有益微生物非常关键。根据对病原菌的灭杀效果,石灰氮、威百亩处理的效果优于其他处理,可作为轮换施用的熏蒸剂,本试验条件下,棉隆是一种弱的处理剂。     

Effect of certain chemicals on soil fungistasis

Summary Fungistatic property of soil sample amended with certain chemicals has been studied. The fungistatic property was found to be highest in soil samples amended with potassium permanganate and copper sulphate. The remaining chemicals also caused different levels of fungistasis. Thus presence of various chemicals in the microbial products seems to be the possible cause of soil fungistasis.     

Effect of soil fumigants on Fusarium wilt and nodulation of peas (Pisum sativum L.)

Chloropicrin, dazomet, formaldehyde, and D-D soil treatments all decreased the incidence of Fusarium wilt in a wilt-susceptible variety of pea grown in wilt-infested soil, but only chloropicrin and dazomet gave satisfactory control of the disease. All four fumigants decreased root nodulation, but no adverse effects on plant growth were detected. With dazomet, formaldehyde, and D-D, decreased nodulation is largely attributed to the extra soil nitrogen mineralized, whereas with chloropicrin the almost complete suppression of nodulation probably reflects the lethal effect of this material on the Rhizobium bacteria.     

Management of common scab of potato in the field using biopesticides,fungicides, soil additives,or soil fumigants

Common scab, caused by Streptomyces scabiei is an economically important potato disease worldwide. The potato industry in New Brunswick, Canada experience $1.2 million loss every year due to this disease. Superficial, raised, or deep-pitted brownish lesions on infected tubers reduce the quality and marketability of both fresh-market and processing potatoes, and hence, common scab is considered a priority disease for which adequate control measures are lacking. The objective of this research was to compare various potential treatments in suppressing the disease. Two field experiments were conducted at McCain's Research Farm, Florenceville-Bristol, New Brunswick, Canada, in 2008 and 2009 to assess the efficacy of Bacillus subtilis, Enterobacter cloacae, Chloropicrin, Pic-Plus, manganese sulphate and mustard meal in comparison with the chemical controls fludioxonil and mancozeb against common scab of potato. The disease incidence was significantly reduced by 36% due to the addition of mustard meal to the soil; 35.4% due to fludioxonil seed treatment; 30.0% due to soil fumigation with Pic-Plus; or by 27.2% due to soil fumigation with Chloropicrin. Potato tubers with scab severity ≥5% which are considered unmarketable in Canada were significantly reduced by 56.1% due to seed treatments with B. subtilis; by 57.8% due to fludioxonil; or by 63.1% due to the soil addition of mustard meal. The same treatments significantly increased marketable yield by 32.5%, 24.6%, and 24.6%, respectively. Soil fumigation with Chloropicrin or Pic-Plus increased marketable yield by 9.5% or 7.1%, respectively. These findings indicate that, in addition to the fludioxonil seed treatment, the seed treatment with the biopesticide containing B. subtilis and the soil addition of mustard meal treatments are potential alternatives for managing common scab of potatoes.     

Insecticidal and nematicidal properties of microbial metabolites

Summary Metabolites from 942 microbial isolates were screened for insecticidal and nematicidal properties. The isolates included 302 streptomycetes, 502 novel actinomycetes including representatives of 18 genera, 28 unidentified aerobic actinomycetes, 70 fungi and 40 bacteria other than actinomycetes. When diluted 10-fold, the metabolites from 55 isolates caused nearly 100% mortality in mosquito larvae (Aedes aegypti) within 24 h. These isolates included 27 isolates ofStreptomyces, four ofActinoplanes, three isolates each ofActinomadura andStreptoverticillium, two isolates each ofMicromonospora, Bacillus andPaecilomyces, and one isolate each ofMicropolyspora, Nocardiopsis, Streptosporangium, Oerskovia, Thermomonospora, Chainia, Pseudomonas, Fusarium, Monilia andSyncephalestrum. Two fungal isolates could not be identified to the generie level. Extracts from the culture broth of 18 isolates caused 100% mortality in mosquito larvae within 15 min to 24 h at a concentration of 1000 ppm. The LC₅₀ of partially purified products from two isolates was 1–2.5 ppm and that of the semipurified preparations from four other isolates was 50 ppm. Valinomycin was identified as an active component in the culture broth from one isolate. The culture broth from 15 isolates of aerobic actinomycetes and 4 of fungi were toxic toPanagrellus redivivus (Nematoda); these included 12 isolates with selective nematicidal properties.Michigan Agriculture Experiment Station, Journal Article No. 12321.     

The use of bacteria as probes for lectins in preparations of solubilized human tonsil cell membranes

In earlier work we have shown that some bacteria bind naturally to lymphocyte subpopulations and that this binding may be due to lectin-carbohydrate interactions. Here we determined the possibility of using bacteria to probe for these lectins in solubilized tonsil cell membrane preparations. Since lectins are capable of agglutination, we determined the ability of human tonsil cell membrane extract (TCME) to agglutinate bacteria. We used Escherichia coli strain YS57 which does not bind to human lymphocytes and a mutant strain derived from it, E. coli UI 2023, which binds to about 50 percent of human lymphocytes. The UI 2023 was agglutinated while the YS57 was not; this agglutination was not due to antibodies or DNA. When E. coli UI 2023 was treated with periodate, it lost its ability to be agglutinated. The agglutination of E. coli UI 2023 was not blocked by any of the monosaccharides and disaccharides used but was blocked by the E. coli LPS, more specifically, by its carbohydrate moiety. Also, the E. coli UI 2023 absorbed the agglutinating factor while its parental strain, YS57, did not. Sodium dodecylsulfate-polyacrylamide gel electrophoresis of TCME after absorption with bacteria showed that a band around 67kD was absent in the TCME absorbed by E. coli prevented the absorption by E. coli UI 2023 whereas Na2IO4-treated LPS did not. In addition, tonsil cell membrane was radioiodinated before obtaining the TCME; sodium dodecylsulfate-polyacrylamide gel electrophoresis of the radioiodinated TCME recovered after elution from E. coli UI 2023, but not from E. coli YS57, showed again a band around 67 kD.(ABSTRACT TRUNCATED AT 250 WORDS)     

Behavior of fresh vs. aged chemicals in soil

Existing data indicate that chemicals freshly added to soils are more amenable to losses, including biodegradation, than chemicals that have been in contact with soils for extended periods of time. This review presents the results of studies that indicate that increased soil‐chemical contact time increased the resistance of chemicals to desorption, volatilization, biodegradation, and extraction. Thus, results from studies conducted on chemicals freshly added to soils should not be used to predict the behavior of chemicals that have been in contact with soils for extended periods of time. In addition, a measure of the total chemical concentration present in a soil does not adequately indicate the availability of the chemicals for biodegradation or release, and does not indicate the potential for the chemical to be transported to and have an adverse effect on a human or ecological receptor.     

An assay procedure for solubilized thyroid hormone receptor: use of Lipidex

A method using Lipidex-1000 is reported for the assay of thyroid hormone receptor activity. The receptor was extracted from rat liver nuclei, incubated with [125I]T3, and applied to 1-ml disposable pipet tip columns containing a small volume of Lipidex. The resin absorbed the free hormone, and the receptor-bound hormone was recovered in the eluate. The method allowed accurate assay of the receptor activity, satisfying a linear relationship between the activity and the receptor protein concentration. The usefulness of this method was demonstrated by determining the pH optimum and the Kd and Bmax of T3 binding by the receptor. The Lipidex column can be used for the preparation of an unoccupied receptor after dissociation of the endogenously bound hormone.     

The combined use of self-organizing maps and Andrews' Curves

The use of self-organizing maps to analyze data often depends on finding effective methods to visualize the SOM's structure. In this paper we propose a new way to perform that visualization using a variant of Andrews' Curves. Also we show that the interaction between these two methods allows us to find sub-clusters within identified clusters. Perhaps more importantly, using the SOM to pre-process data by identifying gross features enables us to use Andrews' Curves on data sets which would have previously been too large for the methodology. Finally we show how a three way interaction between the human user and these two methods can be a valuable exploratory data analysis tool.     

The use of thin soil sections for the study of soil micro-organisms

Summary Modifications of Alexander and Jackson's¹ technique for the preparation of thin soil sections are described.The distribution of bacterial colonies within soil aggregates has been examined using this technique and it has been demonstrated that distinct distribution patterns may occur.