Aphanomyces euteiches Inoculum Potential: A Rolled-Towel Bioassay Suitable for Fine-Textured Soils

A sensitive measure of soil inoculum potential is needed to evaluate field management of common root rot (Aphanomyces euteiches) in peas (Pisum sativum). A modified rolled-towel (RT) bioassay had been proposed to measure soil inoculum potential in fine-textured soils used for pea production in Minnesota. Homogenized soil was used because organic debris containing the inoculum could not be separated by wet sieving. The poor precision prompted an evaluation of procedures to improve this modified RT bioassay. Seed treatment with a 5% solution of sodium hypochlorite before pea seed germination and plant isolation procedures during the RT bioassay preparation/incubation reduced seedborne contamination and seedling loss to less than 5%. Tests conducted with pasteurized soil that was artificially infested with oospores showed the region of the pea taproot 1 to 2 cm below the seed to be more susceptible to infection (33% compared with 15% infected seedlings) than the region 1 to 2 cm above the root tip. A soil volume of 1.0 cm3 increased inoculum potential compared with 0.5 cm3 applied to each seedling but did not influence the random error; the 40-seedling compared with the 20-seedling RT bioassay reduced random error from 18 to 12%. The modified RT bioassay conducted on soil that was artificially infested after steam treatment or without steam treatment showed superior performance when using 40 seedlings compared with 20 seedlings when evaluated for accuracy and precision. Multiple infection theory demonstrated more multiple infections in the RT bioassay with a 0.5 cm3 soil volume applied to each seedling, which shows that soil mass is a factor preventing a higher percentage of infected seedlings. These modifications to the RT bioassay improved the method enough to reduce the random error by one-half compared with using homogenized soil without the proposed modifications.

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Effect of Sugar Beet Variety and Nonhost Plant on Rhizoctonia solani AG2-2IIIB Soil Inoculum Potential Measured in Soil DNA Extracts

Phytopathology ◽

10.1094/phyto-12-15-0318-r ◽

2016 ◽

Vol 106 (9) ◽

pp. 1047-1054 ◽

Cited By ~ 5

Author(s):

Sascha Schulze ◽

Heinz-Josef Koch ◽

Bernward Märländer ◽

Mark Varrelmann

Keyword(s):

Sugar Beet ◽

Rhizoctonia Solani ◽

Soil Samples ◽

Resistant Variety ◽

Winter Rye ◽

Inoculum Potential ◽

Soil Dna ◽

Soil Inoculum ◽

Sugar Beet Variety ◽

Soil Inoculum Potential

A direct soil DNA extraction method from soil samples (250 g) was applied for detection of the soilborne sugar-beet-infecting pathogen Rhizoctonia solani anastomosis group (AG) 2-2IIIB using a newly developed real-time polymerase chain reaction assay that showed specificity to AG2-2IIIB when tested against various R. solani AG. The assay showed a good relation between cycle threshold and amount of AG2-2IIIB sclerotia detected in three spiked field soils and was also able to detect the pathogen in naturally infested field soil samples. A field trial was conducted to quantify R. solani AG2-2IIIB soil inoculum potential (IP) before and after growing a susceptible and a resistant sugar beet variety as well as after subsequent growth of an expected nonhost winter rye. Plants of the susceptible sugar beet variety displayed a higher disease severity. A more than sixfold increase of the R. solani AG2-2IIIB soil IP was observed in contrast to the resistant variety that resulted in a constant IP. Growing winter rye significantly reduced soil IP to the initial level at sowing. Further research is required to better understand the interaction between disease occurrence and soil IP as well as the environmental influence on IP development.

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(115) Soil Inoculum Potential and Mycorrhizal Colonization of Acer rubrum in Forested and Developed Landscapes

HortScience ◽

10.21273/hortsci.40.4.1079d ◽

2005 ◽

Vol 40 (4) ◽

pp. 1079D-1079

Author(s):

P. Eric Wiseman ◽

Christina Wells

Keyword(s):

Forest Soils ◽

Mycorrhizal Fungi ◽

Acer Rubrum ◽

Chemical Properties ◽

Soil Disturbance ◽

Native Forest ◽

Inoculum Potential ◽

Soil Inoculum ◽

Forest Sites ◽

Soil Inoculum Potential

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test the hypotheses that: 1) landscape trees show lower levels of AMF colonization than forest trees; and 2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% vs. 22%; P= 0.0002). However, soil-sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% vs. 4%; P= 0.0081). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between forest and landscape maples appeared to reflect differences in soil chemical properties rather than in soil inoculum potential.

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A Sensitive Assay for Rapid Detection and Quantification of Aphanomyces euteiches in Soil

Phytopathology ◽

10.1094/phyto-09-13-0265-r ◽

2014 ◽

Vol 104 (10) ◽

pp. 1138-1147 ◽

Cited By ~ 13

Author(s):

Christophe Gangneux ◽

Marc-Antoine Cannesan ◽

Mélanie Bressan ◽

Lisa Castel ◽

Anne Moussart ◽

...

Keyword(s):

Root Rot ◽

Optimal Solution ◽

Inoculum Potential ◽

Infested Soil ◽

Aphanomyces Euteiches ◽

Wide Range ◽

Oomycete Pathogen ◽

Polymerase Chain ◽

Leguminous Crops

Aphanomyces euteiches is a widespread oomycete pathogen causing root rot in a wide range of leguminous crops. Losses can reach up to 100% for pea culture and there is currently no registered pesticide for its control. Crop management remains the most efficient tool to control root rot, and avoidance of infested soil seems to be the optimal solution. A test was developed to identify fields suitable for pea crops, consisting of the determination of the inoculum potential of soil using baiting plants. A new rapid, specific, and sensitive molecular method is described allowing the quantification of less than 10 oospores per gram of soil. This challenge is achieved by a real-time polymerase chain reaction procedure targeting internal transcribed spacer 1 from the ribosomal DNA operons. A preliminary study based on typical soils from northwestern France demonstrated that the A. euteiches oospore density in soil is related to the inoculum potential. Furthermore, this method has proved sensitive enough to accurately study the influence of biotic factors that may govern the actual emergence of root rot.

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Inhibition of Aphanomyces euteiches f. sp. pisi by Volatiles Produced by Hydrolysis of Brassica napus Seed Meal

Plant Disease ◽

10.1094/pdis.1997.81.3.288 ◽

1997 ◽

Vol 81 (3) ◽

pp. 288-292 ◽

Cited By ~ 39

Author(s):

Urszula Smolinska ◽

G. R. Knudsen ◽

M. J. Morra ◽

V. Borek

Keyword(s):

Brassica Napus ◽

Volatile Compounds ◽

Root Rot ◽

Hyphal Growth ◽

Rapeseed Meal ◽

Seed Meal ◽

Inoculum Potential ◽

Aphanomyces Euteiches ◽

Volatile Products ◽

Rot Disease

Seed meal from Brassica napus (rapeseed) produced volatile fungitoxic compounds potentially of value in the control of Aphanomyces root rot of pea. Hyphal growth, germination of encysted zoospores, and oospore survival and inoculum potential, were determined in the presence of volatiles produced from B. napus seed meal. Volatile compounds from B. napus meal completely suppressed mycelial growth and germination of encysted zoospores on agar. In growth chamber bioassays, pea (Pisum sativum) seed inoculated with zoospore suspensions and incubated 24 h in the presence of volatiles from rapeseed meal had 50% lower root rot disease severity than in the absence of meal. Volatile compounds passing through soil also significantly decreased survival and inoculum potential of oospores. Gas chromatographic analysis of rapeseed tissues and the volatile compounds evolved from tissues showed that substrate glucosinolates were hydrolyzed enzymatically to produce mainly isothiocyanates. Non-autoclaved rapeseed meal produced significantly higher levels of volatile compounds than did autoclaved meal. Also, volatile compounds produced from autoclaved meal were dominated by nitriles, whereas isothiocyanates were more common volatile products from non-autoclaved meal. Our results indicate that B. napus allelochemicals responsible for toxic effects toward A. euteiches f. sp. pisi are enzymatic hydrolysis products of glucosinolates.

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Zoospore Homing and Infection Events: Effects of the Biocontrol Bacterium Burkholderia cepacia AMMDR1 on Two Oomycete Pathogens of Pea (Pisum sativum L.)

Applied and Environmental Microbiology ◽

10.1128/aem.66.12.5192-5200.2000 ◽

2000 ◽

Vol 66 (12) ◽

pp. 5192-5200 ◽

Cited By ~ 49

Author(s):

K. Heungens ◽

J. L. Parke

Keyword(s):

Mutant Strain ◽

Burkholderia Cepacia ◽

Field Experiments ◽

Sweet Corn ◽

Inoculum Potential ◽

Aphanomyces Euteiches ◽

Pea Seeds ◽

Roots In Vitro

ABSTRACT Burkholderia cepacia AMMDR1 is a biocontrol agent that protects pea and sweet corn seeds from Pythium damping-off in field experiments. The goal of this work was to understand the effect ofB. cepacia AMMDR1 on Pythium aphanidermatum andAphanomyces euteiches zoospore homing events and on infection of pea seeds or roots. In vitro, B. cepaciaAMMDR1 caused zoospore lysis, prevented cyst germination, and inhibited germ tube growth of both oomycetes. B. cepacia AMMDR1 also reduced the attractiveness of seed exudates to Pythiumzoospores to nondetectable levels. However, when present at high levels on seeds, B. cepacia AMMDR1 had little net effect on zoospore attraction, probably because it also enhanced seed exudation. Seed-applied B. cepacia AMMDR1 dramatically reduced the incidence of infection by Pythium zoospores in situ compared with an antibiosis-deficient Tn5 mutant strain. This mutant strain also decreased Pythium infection incidence to some extent, but only when the pathogen inoculum potential was low. B. cepacia AMMDR1 did not affect attraction ofAphanomyces zoospores or Aphanomyces root rot incidence. These results suggest that B. cepacia AMMDR1 controlsP. aphanidermatum largely through antibiosis, but competition for zoospore-attracting compounds can contribute to the effect. Differences in suppression of Aphanomyces andPythium are discussed in relation to differences in the ecology of the two pathogens.

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Localization of Adenosine Triphosphatase Activity in the Phleom of Nicotiana Tabacum

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100094401 ◽

1972 ◽

Vol 30 ◽

pp. 230-231

Author(s):

James Cronshaw ◽

Jamison E. Gilder

Keyword(s):

Plasma Membrane ◽

Atpase Activity ◽

Adenosine Triphosphatase ◽

Higher Plants ◽

High Surface ◽

Root Tip ◽

Animal Cells ◽

Physiological Processes ◽

Tip Cells ◽

Atpase Localization

Adenosine triphosphatase (ATPase) activity has been shown to be associated with numerous physiological processes in both plants and animal cells. Biochemical studies have shown that in higher plants ATPase activity is high in cell wall preparations and is associated with the plasma membrane, nuclei, mitochondria, chloroplasts and lysosomes. However, there have been only a few ATPase localization studies of higher plants at the electron microscope level. Poux (1967) demonstrated ATPase activity associated with most cellular organelles in the protoderm cells of Cucumis roots. Hall (1971) has demonstrated ATPase activity in root tip cells of Zea mays. There was high surface activity largely associated with the plasma membrane and plasmodesmata. ATPase activity was also demonstrated in mitochondria, dictyosomes, endoplasmic reticulum and plastids.

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In situ TEM Studies of agglomeration of sub-nanometer Ru layers in Ru/C multilayers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121685 ◽

1992 ◽

Vol 50 (1) ◽

pp. 256-257

Author(s):

Tai D. Nguyen ◽

Ronald Gronsky ◽

Jeffrey B. Kortright

Keyword(s):

Layered Structure ◽

Driving Force ◽

High Energy ◽

Superior Performance ◽

In Situ Tem ◽

Rayleigh Instability ◽

Practical Applications ◽

Transmission Electron ◽

Diffraction Patterns

Nanometer period Ru/C multilayers are one of the prime candidates for normal incident reflecting mirrors at wavelengths < 10 nm. Superior performance, which requires uniform layers and smooth interfaces, and high stability of the layered structure under thermal loadings are some of the demands in practical applications. Previous studies however show that the Ru layers in the 2 nm period Ru/C multilayer agglomerate upon moderate annealing, and the layered structure is no longer retained. This agglomeration and crystallization of the Ru layers upon annealing to form almost spherical crystallites is a result of the reduction of surface or interfacial energy from die amorphous high energy non-equilibrium state of the as-prepared sample dirough diffusive arrangements of the atoms. Proposed models for mechanism of thin film agglomeration include one analogous to Rayleigh instability, and grain boundary grooving in polycrystalline films. These models however are not necessarily appropriate to explain for the agglomeration in the sub-nanometer amorphous Ru layers in Ru/C multilayers. The Ru-C phase diagram shows a wide miscible gap, which indicates the preference of phase separation between these two materials and provides an additional driving force for agglomeration. In this paper, we study the evolution of the microstructures and layered structure via in-situ Transmission Electron Microscopy (TEM), and attempt to determine the order of occurence of agglomeration and crystallization in the Ru layers by observing the diffraction patterns.

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Reversion Toward the Mean Independently of Regression Toward the Mean

Methodology ◽

10.1027/1614-2241.5.1.3 ◽

2009 ◽

Vol 5 (1) ◽

pp. 3-6 ◽

Cited By ~ 2

Author(s):

Merton S. Krause

Keyword(s):

Random Error ◽

Evaluation Studies ◽

Internal Validity ◽

Intervention Evaluation ◽

Population Mean ◽

Experimental Intervention ◽

Sample Data ◽

The Mean ◽

Regression Toward The Mean

There is another important artifactual contributor to the apparent improvement of persons subjected to an experimental intervention which may be mistaken for regression toward the mean. This is the phenomenon of random error and extreme selection, which does not at all involve the population regression of posttest on pretest scores but involves a quite different and independent reversion of subjects’ scores toward the population mean. These two independent threats to the internal validity of intervention evaluation studies, however, can be detected and differentiated on the sample data of such studies.

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