System-wide Rewiring Underlies Behavioral Differences in Predatory and Bacterial-Feeding Nematodes

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Highlights? Massive neural circuit rewiring between nematodes with divergent feeding behavior ? Striking patterns correlate with known functional differences ? Motor synapse differences indicate a substantial change in information flow ? Correlates of predatory feeding behavior are identified     

Effects of Peanut Genotypes on Meloidogyne Species Interactions

A 3-year microplot study was conducted to characterize the interaction between Meloidogyne arenaria race 1 (MA1) and M. hapla (MH), as affected by the five peanut genotypes: Florigiant, NC 7, NC 6, NC Ac 18416, and NC Ac 18016. The interactive effects on infection (total parasitic forms per root unit) and reproduction potentials of each nematode species and crop damage were determined. As a single population, MA1 had greater infection capacity and caused more crop damage than did MH, but both species had similar reproduction potentials. In mixed infestations, MA1 was more competitive than MH, as reflected by incidence of infection. Infection and reproduction potentials, and crop-damage capabilities of the mixed populations were similar to those of MA1 alone. All peanut genotypes were susceptible to infection by both nematodes. NC 6 was less susceptible to damage by MA1 and the mixed populations than other genotypes. A nematode treatment x genotype interaction was detected for root infection and crop damage, but not for population density or reproduction. With high preplant nematode levels (Pi), the populations reached their peak by midseason, whereas those with low Pi peaked after midseason. Crop damage in the second and third years was correlated with Pi level.     

Nematicides Increase Grain Yields in Spring Wheat Cultivars and Suppress Plant-Parasitic and Bacterial-Feeding Nematodes

Grain yields of spring wheat (Triticum aestivum L. cvs. AC Barrie, AC Walton, AC Wilmot, Belvedere, Glenlea) in field plots over a 3-year period were increased (P < 0.001) by an average of 0.56 (25.1%) and 1.17 (52.5%) tonnes/ha in comparison to untreated check plots when aldicarb at 2.24 kg or fosthiazate at 13.5 a.i./ha, respectively, were broadcast and incorporated into the soil to suppress nematodes. The planned F test using orthogonal coefficients indicated that the mean response of grain yields to nematicide treatments of AC Barrie and Glenlea, which are grown primarily in the prairie provinces of Canada, was greater (48.5%) than the mean response of Belvedere, AC Walton, and AC Wilmot (33.7%), which are more common in the Maritime region of Canada (P < 0.001). Root lesion nematodes (primarily Pratylenchus penetrans) in wheat roots and in root zone soil at harvest were reduced by the nematicide applications (P < 0.001). Bacterial-feeding nematodes (primarily Diplogaster lheritieri (Maupas)) in root zone soil were also suppressed by fosthiazate (P < 0.01) but not by aldicarb. These data indicate that root lesion nematodes cause substantial yield losses in spring wheat in the Maritime region of Canada.     

接种促生菌对花生根际土壤微生物及营养元素的影响

植物根际促生菌是一类可促进植物生长的有益细菌,有效的根际促生菌剂可以减少化肥施用。以束村氏菌属(Tsukamurella sp.)P9、伯克霍尔德氏菌属(Burkholderia sp.)P10、以及P9和P10混合菌液作为接种菌株,研究促生菌对花生生长、植株及土壤营养、根际土壤微生物类群及功能的影响。30 d盆栽实验结果表明,接种组的花生鲜重、株高及根长均显著提高;根际土壤细菌总数、固氮菌和溶磷菌数均明显高于未接种组;氮循环功能菌群数量有不同程度提高,土壤蔗糖酶、脲酶及过氧化氢酶均高于对照;土壤碱解氮及速效钾显著提高,植株营养指标有所提升,尤以P10接种效果更优。本研究初步结论表明2株促生菌通过活化土壤微生物、提高植株的有效营养元素含量,促进了花生的生长。     

Effect of Volatile Organic Compounds from Bacteria on Nematodes

The five studied bacterial strains could produce volatile organic compounds (VOCs) that kill nematodes. Based on their 16S rRNA sequences, these strains were identified as Pseudochrobactrum saccharolyticum, Wautersiella falsenii, Proteus hauseri, Arthrobacter nicotianae, and Achromobacter xylosoxidans. The bacterial VOCs were extracted using solid‐phase micro‐extraction (SPME) and subsequently identified by GC/MS analysis. The VOCs covered a wide range of aldehydes, ketones, alkyls, alcohols, alkenes, esters, alkynes, acids, ethers, as well as heterocyclic and phenolic compounds. Among the 53 VOCs identified, 19 candidates, produced by different bacteria, were selected to test their nematicidal activity (NA) against Caenorhabditis elegans and Meloidogyne incognita. The seven compounds with the highest NAs were acetophenone, S‐methyl thiobutyrate, dimethyl disulfide, ethyl 3,3‐dimethylacrylate, nonan‐2‐one, 1‐methoxy‐4‐methylbenzene, and butyl isovalerate. Among them, S‐methyl thiobutyrate showed a stronger NA than the commercial insecticide dimethyl disulfide. It was reported for the first time here that the five bacterial strains as well as S‐methyl thiobutyrate, ethyl 3,3‐dimethylacrylate, 1‐methoxy‐4‐methylbenzene, and butyl isovalerate possess NA. These strains and compounds might provide new insights in the search for novel nematicides.     

Effect of Nematodes on Rhizosphere Colonization by Seed-Applied Bacteria

There is much interest in the use of seed-applied bacteria for biocontrol and biofertilization, and several commercial products are available. However, many attempts to use this strategy fail because the seed-applied bacteria do not colonize the rhizosphere. Mechanisms of rhizosphere colonization may involve active bacterial movement or passive transport by percolating water or plant roots. Transport by other soil biota is likely to occur, but this area has not been well studied. We hypothesized that interactions with soil nematodes may enhance colonization. To test this hypothesis, a series of microcosm experiments was carried out using two contrasting soils maintained under well-defined physical conditions where transport by mass water flow could not occur. Seed-applied Pseudomonas fluorescens SBW25 was capable of rhizosphere colonization at matric potentials of −10 and −40 kPa in soil without nematodes, but colonization levels were substantially increased by the presence of nematodes. Our results suggest that nematodes can have an important role in rhizosphere colonization by bacteria in soil.     

Interactions Between Nematodes and Other Factors on Plants

The distinction between qualitative and quantitative interactions is stressed as it helps to elucidate differences between two current definitions of the term synergism and how multifactorial experiments should be designed, analysed statistically, and their results interpreted. Factorial design and analyses are strongly advocated so that interactions can be detected. It is suggested that interactions involving nematodes are common in nature and should be included, where appropriate, in hypotheses. Methods for testing the hypothesis that environment influences tolerance are suggested.     

细菌在线虫生防中应用的研究进展

在具有杀线虫能力细菌的特征、作用方式及其在线虫生防中的潜在应用等方面,结合作者的研究工作,对国内、外的一些研究进展进行了综述,并提出了研究展望。     

Interactions between Diatoms and Bacteria

Summary: Diatoms and bacteria have cooccurred in common habitats for hundreds of millions of years, thus fostering specific associations and interactions with global biogeochemical consequences. Diatoms are responsible for one-fifth of the photosynthesis on Earth, while bacteria remineralize a large portion of this fixed carbon in the oceans. Through their coexistence, diatoms and bacteria cycle nutrients between oxidized and reduced states, impacting bioavailability and ultimately feeding higher trophic levels. Here we present an overview of how diatoms and bacteria interact and the implications of these interactions. We emphasize that heterotrophic bacteria in the oceans that are consistently associated with diatoms are confined to two phyla. These consistent bacterial associations result from encounter mechanisms that occur within a microscale environment surrounding a diatom cell. We review signaling mechanisms that occur in this microenvironment to pave the way for specific interactions. Finally, we discuss known interactions between diatoms and bacteria and exciting new directions and research opportunities in this field. Throughout the review, we emphasize new technological advances that will help in the discovery of new interactions. Deciphering the languages of diatoms and bacteria and how they interact will inform our understanding of the role these organisms have in shaping the ocean and how these interactions may change in future oceans.     

Saprozoic Nematodes as Carriers and Disseminators of Plant Pathogenic Bacteria

The plant pathogenic bacteria Agrobacterium tumefaciens (Smith and Townsend) Conn. (strain 5-14 Deep), Erwinia amylovora (Burill) Winslow et al., E. carotovora (Jones) Holland and Pseudornonas phaseolicola (Burk.) Dows. (ICPB-PM3) and the red-pigmented non-pathogen Serratia marcescens Bizio were hosts for the saprozoic nematode Pristionchus Iheritieri (Maupas, 1919) Paramonov. Viable bacteria survived passage through the nematode and produced typical colonies on nutrient agar plates. Female nematodes ingested more bacterial cells and retained them longer than did males. It was hypothesized saprozoic nematodes may disseminate pathogenic bacteria to new infection courts.     

昆虫病原线虫共生菌杀虫毒素研究进展

对昆虫病原线虫共生菌杀虫毒素的种类、与口服毒性有关的杀虫毒素以及口服毒性与杀虫毒素基因的关系等研究进展进行了综述,并对未来的研究方向提出了作者的见解。     

七种我国昆虫病原线虫共生菌的分离与鉴定

昆虫病原线虫共生菌是一类具有广阔发展前景的生物防治资源, 由于这类菌的分类鉴定工作起步晚, 存在分类混乱和不系统的现象, 在本土资源十分丰富的我国尤为突出。本文对本实验室分离的7个共生菌菌株进行了分类描述, 建立了以生理形态, 生化特征为分类基础, 结合16S rDNA序列分析的有效鉴定方法。     

Effects of Hydroclytic Enzymes on Plant-parasitic Nematodes

Proteases, lipase, and chitinase killed Tylenchorhynchus dubius in vitro and in soil. Tylenchorhynchus dubius was more susceptible to the enzymes than Pratylenchus penetrans. Papain was the most effective protease, and other enzymes were less effective. Heating enzymes to 80 C for 10 min greatly reduced nematicidal effectiveness. Scanning electron micrographs showed that papain and chitinase produced structural changes in the cuticle of T. dubius. Lipase removed a thin outer layer. Papain removed material filling the striata, or furrow, between the horizontal bands. When added to soil, chitinase, lipase, collagenase, and proteases (papain and bromelain) decreased motility of T. dubius populations up to 75%. Bromelain was the most active in soil against T. dubius, and collagenase was the most active in soil against P. penetrans.     

七种我国昆虫病原线虫共生菌的分离与鉴定

昆虫病原线虫共生菌是一类具有广阔发展前景的生物防治资源,由于这类菌的分类鉴定工作起步晚,存在分类混乱和不系统的现象,在本土资源十分丰富的我国尤为突出.本文对本实验室分离的7个共生菌菌株进行了分类描述,建立了以生理形态,生化特征为分类基础,结合16 SrDNA序列分析的有效鉴定方法.     

植物寄生线虫生防细菌及其作用机制研究

对具有较大潜在应用价值的植物寄生线虫生防细菌的种类、特征和作用方式及其在分子生物学水平上的最新研究进展进行了综述.     

Molecular Analysis of the Interactions between Cyst Nematodes and Their Hosts

In order to complete its life cycle, a cyst nematode must stimulate the production of a specialized syncytial feeding site within host root tissues. This process is characterized by major changes in local root morphology, including enlargement of affected nuclei and nucleoli, cell wall degradation, and proliferation of subcellular organelles. At the molecular level very little is known about the processes involved in this host response, but recent evidence suggests that cyst nematodes are able to regulate specific host genes. The host-parasite model system provided by Arabidopsis thaliana and Heterodera schachtii will be fundamental to our future understanding of the formation of syncytia. Molecular biology now offers us the opportunity to study this complex host-parasite interaction in great detail. A better understanding of the host genes regulated by cyst nematodes and the mechanisms by which this regulation is achieved will facilitate the engineering of crop cultivars that possess novel forms of resistance to these adept parasites.     

昆虫病原线虫共生菌杀虫蛋白的研究进展

昆虫病原线虫共生菌杀虫蛋白对许多农业害虫都有很明显的毒杀作用,作为一种新型的具有开发潜力和应用前景的生物防治资源,已经引起科学家们的关注并成为国内外研究的热点之一.综述了昆虫病原线虫共生菌杀虫蛋白基因的结构和功能及其杀虫机制方面的研究进展.     

Interrelationships between Root-nodule Bacteria,Plant-parasitic Nematodes and their Leguminous Host

The effect of infection by Meloidogyne javanica and Heterodera trifolii on number, size, structure and efficiency of nodules formed by Rhizobiurn trifolii on white clover roots was investigated. Introduction of nematodes one week before, simultaneously, or one week following inoculation with Rhizobium bacteria did not hinder nodule formation. Nodule size did not differ between nematode-infected and nematode-free plants. Formation of nodules on M. javanica galls and gall formation on the nodules have been reported. The structure of nodular tissues was not disturbed by nematode infection, even though giant cells were formed inside the vascular bundles. The nitrogen-fixation efficiency of nematode-infected nodules was not impaired; however, earlier disintegration of nodules as a result of M. javanica infection ultimately deprived the plants of nitrogenous materials. The drastic reduction of the total-N in H. trifolii-infected plants reflected stunting of the entire plant due to nematode infection. Both nematodes invaded the entire root system, uniformly showing preference for nodules.     

Effects of Fixation and Dehydration Procedures on Marine Nematodes

Different combinations of fixation and dehydration procedures for the preparation of permanent mounts of marine nematodes of the subfamily Oncholaiminae were tested and compared. Qualitatively, the best specimens resulted from Seinhorst''s killing method and fixation in FAA; the dehydration procedure was of less significance. Quantitatively, no significant modification of measurements resulted from any of the methods used. Sources of error in measurements are discussed.     

Interactions Among Selected Endoparasitic Nematodes and Three Pseudomonads on Alfalfa

Meloidogyne hapla, Pratylenchus penetrans, and Helicotylenchus dihystera, reduced the growth of ''Saranac AR alfalfa seedlings when applied at concentrations of 50 nematodes per plant. All except P. penetrans reduced seedling growth when applied at 25 per seedling. M. hapla reduced growth when applied at 12 per seedling. Nematodes interacted with three pseudomonads to produce greater growth reductions than were obtained with single pathogens, suggesting synergistic relationships. Ditylenchus dipsaci, applied at 25 or 50 nematodes per seedling, reduced plant weight compared with weights of control plants, but did not interact with test bacteria. All of the nematodes except D. dipsaci produced root wounds which were invaded by bacteria.