scholarly journals Seed-Colonizing Microbes from Municipal Biosolids Compost Suppress Pythium ultimum Damping-Off on Different Plant Species

2008 ◽  
Vol 98 (9) ◽  
pp. 1012-1018 ◽  
Author(s):  
M.-H. Chen ◽  
E. B. Nelson
Keyword(s):  
Plant Species ◽  
Pythium Ultimum ◽  
Disease Suppression ◽  
Microbial Consortia ◽  
Damping Off ◽  
Microbial Species ◽  
Pathogen Suppression ◽  
Municipal Biosolids ◽  
Leaf Compost ◽  
Biosolids Compost

Composts are known for their suppressive properties toward many different seed- and root-infecting pathogens and diseases. Although disease and pathogen suppression induced by composts is believed to be mediated by microbial activities, the nature of the microbial species and processes responsible for suppressiveness remain unknown. We demonstrated previously that seed-colonizing microbial consortia from leaf compost could explain the observed levels of Pythium ultimum-induced damping-off suppression on cotton. The aim of the present work was to determine whether seed-colonizing microbial consortia could explain Pythium damping-off suppression in municipal biosolids compost on three different plant species. Significant levels of disease suppression were observed on cucumber, wheat, and pea at water potentials of –2 kPa. The suppression of damping-off on cucumber and wheat could be eliminated by autoclaving the compost prior to sowing. High levels of suppressiveness were expressed both on cucumber and on wheat seed surfaces within 8 h of sowing. However, the expression of damping-off suppression on the surface of pea seeds was inconsistent and highly variable. Our results demonstrate that compost-induced suppression of P. ultimum damping-off of cucumber and wheat can be explained by the microbial consortia colonizing seeds within 8 h of sowing. These results further suggest that disease suppression in composts is related to microbial species that interact with the pathogen in its infection court and not in the bulk compost.

scholarly journals Seed-Colonizing Bacterial Communities Associated with the Suppression of Pythium Seedling Disease in a Municipal Biosolids Compost

2012 ◽  
Vol 102 (5) ◽  
pp. 478-489 ◽  
Author(s):  
Mei-Hsing Chen ◽  
Allison L. H. Jack ◽  
I. Cristina McGuire ◽  
Eric B. Nelson
Keyword(s):  
Restriction Fragment ◽  
Bacterial Communities ◽  
Rna Extraction ◽  
Pythium Ultimum ◽  
Disease Suppression ◽  
Seedling Disease ◽  
Treated Seed ◽  
Municipal Biosolids ◽  
The Impact ◽  
Biosolids Compost

This study was designed to characterize seed-colonizing microbial communities that were previously shown to be involved in the suppression of seedling disease caused by Pythium ultimum in a municipal biosolids compost. Selective microbial inhibitors were employed to inactivate portions of the microbial community associated with seed germinated in a compost medium to evaluate their impact on disease suppression. After initial screenings for toxicity to both cucumber and P. ultimum, six selective inhibitors were eventually used to assess the impact of seed treatment on the reduction of bacterial and fungal populations and on disease suppression. Rifampicin was the most effective inhibitor for inactivating disease suppression. Bacterial communities that colonized cucumber seed sown in compost medium for 8 h and seed sown in compost medium for 8 h followed by a 3-h treatment of either rifampicin at 500 ppm or water were dislodged from seed surfaces and subjected to RNA extraction and reverse transcription to cDNA. Differences in the composition of seed-colonizing bacterial communities were assessed using terminal restriction fragment length polymorphisms (T-RFLP) of polymerase chain reaction-amplified 16S rDNA genes. T-RFLP profiles revealed a diversity of distinct bacterial taxa, a number of which dominate seed surfaces within 8 h of sowing. Analysis of similarity (ANOSIM) using terminal restriction fragment (T-RF) presence or absence showed that community profiles of nontreated and water-treated seed were quite similar whereas community profiles from rifampicin-treated seed were distinct. Differences in community profiles based on T-RF abundance (peak height and peak area) indicated that all treatments were unique (ANOSIM, all pairwise comparisons P < 0.05) Peaks heights and areas of relatively few T-RFs were reduced to zero following rifampicin treatment and 34 T-RFs explained 85% of the observed difference between treatments. Tentative taxon assignments for each of the T-RFs that contributed to the treatment differences revealed a preponderance of sequences with affinities to the α-, β-, and γ-Proteobacteria and Firmicutes. Limited sequencing of clones associated with water-treated and rifampicin-treated seed revealed the presence of similar taxa dominated by members of the γ-Proteobacteria. Many species within these taxa (such as Pseudomonas spp., Enterobacter spp., and Bacillus spp.) are known to be suppressive to Pythium diseases. Results of our study have confirmed that Pythium disease suppression in a municipal biosolids compost is mediated by compost-associated bacteria that colonize seed within hours after sowing. By focusing on actively growing microbes in the infection court during important stages of pathogen infection, we believe we can more efficiently determine the mechanisms of disease suppression and the microbes involved. Although specific to this pathosystem and compost, our results have a much broader scope of inference and illustrate the utility of such a targeted approach in identifying a relatively small subset of microbial taxa from complex communities likely to be involved in disease suppression.

scholarly journals Compost-Induced Suppression of Pythium Damping-Off Is Mediated by Fatty-Acid-Metabolizing Seed-Colonizing Microbial Communities

2003 ◽  
Vol 69 (1) ◽  
pp. 452-460 ◽  
Author(s):  
Mary E. McKellar ◽  
Eric B. Nelson
Keyword(s):  
Fatty Acid ◽  
Linoleic Acid ◽  
Microbial Communities ◽  
Pythium Ultimum ◽  
Disease Suppression ◽  
Microbial Consortia ◽  
Damping Off ◽  
Bacterial Consortia ◽  
Seed Colonization

ABSTRACT Leaf composts were studied for their suppressive effects on Pythium ultimum sporangium germination, cottonseed colonization, and the severity of Pythium damping-off of cotton. A focus of the work was to assess the role of fatty-acid-metabolizing microbial communities in disease suppression. Suppressiveness was expressed within the first few hours of seed germination as revealed by reduced P. ultimum sporangium germination, reduced seed colonization, and reduced damping-off in transplant experiments. These reductions were not observed when cottonseeds were sown in a conducive leaf compost. Microbial consortia recovered from the surface of cottonseeds during the first few hours of germination in suppressive compost (suppressive consortia) induced significant levels of damping-off suppression, whereas no suppression was induced by microbial consortia recovered from cottonseeds germinated in conducive compost (conducive consortia). Suppressive consortia rapidly metabolized linoleic acid, whereas conducive consortia did not. Furthermore, populations of fatty-acid-metabolizing bacteria and actinobacteria were higher in suppressive consortia than in conducive consortia. Individual bacterial isolates varied in their ability to metabolize linoleic acid and protect seedlings from damping-off. Results indicate that communities of compost-inhabiting microorganisms colonizing cottonseeds within the first few hours after sowing in a Pythium-suppressive compost play a major role in the suppression of P. ultimum sporangium germination, seed colonization, and damping-off. Results further indicate that fatty acid metabolism by these seed-colonizing bacterial consortia can explain the Pythium suppression observed.

scholarly journals Mutation of rpiA in Enterobacter cloacae Decreases Seed and Root Colonization and Biocontrol of Damping-Off Caused by Pythium ultimum on Cucumber

2002 ◽  
Vol 15 (8) ◽  
pp. 817-825 ◽  
Author(s):  
Scott M. Lohrke ◽  
Pierre D. Dery ◽  
Wei Li ◽  
Ralph Reedy ◽  
Donald Y. Kobayashi ◽  
...  
Keyword(s):  
Pentose Phosphate Pathway ◽  
Sequence Similarity ◽  
Enterobacter Cloacae ◽  
Pythium Ultimum ◽  
Pentose Phosphate ◽  
Disease Suppression ◽  
Amino Acid Sequence Similarity ◽  
Damping Off ◽  
Isomerase Activity ◽  
Key Enzyme

Strains of Enterobacter cloacae show promise as biocontrol agents for Pythium ultimum-induced damping-off on cucumber and other crops. E. cloacae A145 is a mini-Tn5 Km transposon mutant of strain 501R3 that was significantly reduced in suppression of damping-off on cucumber caused by P. ultimum. Strain A145 was deficient in colonization of cucumber, sunflower, and wheat seeds and significantly reduced in colonization of corn and cowpea seeds relative to strain 501R3. Populations of strain A145 were also significantly lower than those of strain 501R3 at all sampling times in cucumber, wheat, and sunflower rhizosphere. Populations of strain A145 were not detectable in any rhizosphere after 42 days, while populations of strain 501R3 remained at substantial levels throughout all experiments. Molecular characterization of strain A145 indicated mini-Tn5 Km was inserted in a region of the E. cloacae genome with a high degree of DNA and amino acid sequence similarity to rpiA, which encodes ribose-5-phosphate isomerase. In Escherichia coli, RpiA catalyzes the interconversion of ribose-5-phosphate and ribulose-5-phosphate and is a key enzyme in the pentose phosphate pathway. Ribose-5-phosphate isomerase activity in cell lysates from strain A145 was approximately 3.5% of that from strain 501R3. In addition, strain A145 was a ribose auxotroph, as expected for an rpiA mutant. Introduction of a 1.0-kb DNA fragment containing only the rpiA homologue into strain A145 restored ribose phosphate isomerase activity, prototrophy, seedling colonization, and disease suppression to levels similar to those associated with strain 501R3. Experiments reported here indicate a key role for rpiA and possibly the pentose phosphate pathway in suppression of damping-off and colonization of subterranean portions of plants by E. cloacae.

scholarly journals Microbial-Induced Carbon Competition in the Spermosphere Leads to Pathogen and Disease Suppression in a Municipal Biosolids Compost

2012 ◽  
Vol 102 (6) ◽  
pp. 588-596 ◽  
Author(s):  
Mei-Hsing Chen ◽  
Eric B. Nelson
Keyword(s):  
Linoleic Acid ◽  
Microbial Communities ◽  
Germ Tube ◽  
Disease Suppression ◽  
Cucumber Seed ◽  
Seed Exudate ◽  
Municipal Biosolids ◽  
Carbon Competition ◽  
Germ Tubes ◽  
Biosolids Compost

The aim of this study was to understand whether competition for fatty acids in plant seed exudates by compost-derived seed-colonizing microbial communities could explain the suppression of plant infections initiated by sporangia of Pythium ultimum. The germination behavior of P. ultimum sporangia in response to cucumber seeds was measured to determine the impact of seed-colonizing microbes on pathogen suppression. Seed-colonizing microbial communities from municipal biosolids compost utilized cucumber seed exudates and linoleic acid in vitro, reducing the respective stimulatory activity of these elicitors to P. ultimum sporangial germination. However, when sporangia were observed directly in the spermosphere of seeds sown in the compost medium, levels of germination and sporangial emptying did not differ from the responses in sand. The percentage of aborted germ tubes was greater after incubating sporangia in compost medium for 12-h than the level of germ tube abortion when sporangia were incubated in sand. Abortion did not occur if previously germinated sporangia were supplemented with cucumber seed exudate. Furthermore, removal of cucumber seed exudate after various stages of germ tube emergence resulted in an increase in aborted germ tubes over time. Adding increasing levels of glucose directly to the compost medium alleviated germ tube abortion in the spermosphere and also eliminated disease suppression. These data fail to support a role for linoleic acid competition in Pythium seedling disease suppression but provide evidence for general carbon competition mediated by seed-colonizing microbial communities as a mechanism for the suppression of Pythium seed infections in municipal biosolids compost.

scholarly journals Biocontrol of Damping-off of Catharanthus roseus Caused by Pythium ultimum with Trichoderma virens and Binucleate Rhizoctonia Fungi

Plant Disease ◽  
2000 ◽  
Vol 84 (6) ◽  
pp. 644-648 ◽  
Author(s):  
J. R. Burns ◽  
D. M. Benson
Keyword(s):  
Plant Species ◽  
Catharanthus Roseus ◽  
Pythium Ultimum ◽  
Biocontrol Agents ◽  
Trichoderma Virens ◽  
Damping Off ◽  
Binucleate Rhizoctonia ◽  
Biocontrol Efficacy ◽  
Bedding Plant ◽  
Gliocladium Virens

Four isolates of Trichoderma (Gliocladium) virens (G-45, G-65, G-85, and G-93) and two isolates of binucleate Rhizoctonia spp. (BNR621 and P9023) were evaluated for biocontrol of preemergence damping-off of Catharanthus roseus (vinca) caused by Pythium ultimum. Putative biocontrol agents were amended to a soilless mix 1, 3, or 6 days prior to seeding and pathogen infestation to determine if colonization of the mix before infestation was important for biocontrol efficacy. Biocontrol of preemergence damping-off of vinca with the four isolates of T. virens was variable. Only isolate G-93 gave control of preemergence damping-off (10 to 18% disease) regardless of the length of time the mix was amended prior to seeding and infestation compared to the infested control (43% disease). In contrast, preemergence damping-off was 10 to 15% with SoilGard (based on isolate GL-21 of T. virens). For isolate G-65, preemergence damping-off of vinca was 0% in lots of mix amended 1 day prior to seeding, but over 60% in lots of mix amended 6 days prior to seeding, compared to 43% in the infested control. With the exception of isolate G-65 in the lot amended 6 days before seeding, the isolates of T. virens were as effective as metalaxyl (19% damping-off) for control of P. ultimum in lots of mix amended 1 to 6 days before seeding. In contrast to T. virens, biocontrol efficacy of isolates BNR621 and P9023 of binucleate Rhizoctonia spp. in a Pesta formulation improved as lots of mix were amended up to 6 days before seeding and infestation. As length of initial amendment increased from 1 to 6 days, preemergence damping-off decreased from 37 to 16% for BNR621, and from 42 to 22% for P9023. Preemergence damping-off was observed in vinca in control treatments with only the putative biocontrol agents (BNR621, 14% disease and P9023, 19.6%); therefore, additional bedding plant species were evaluated for susceptibility to the BNR isolates. In the absence of P. ultimum, isolates BNR621 and P9023 in a Pesta formulation caused an average 82.5, 56.5, and 5.8% damping-off of snapdragon, petunia, and impatiens, respectively. Our results suggest that binucleate Rhizoctonia isolates, although effective for biocontrol of P. ultimum on vinca, should be evaluated for pathogenicity on a crop by crop basis before use on other crops.

scholarly journals Compost Tea as a Container Medium Drench for Suppressing Seedling Damping-Off Caused by Pythium ultimum

2004 ◽  
Vol 94 (11) ◽  
pp. 1156-1163 ◽  
Author(s):  
Steven J. Scheuerell ◽  
Walter F. Mahaffee
Keyword(s):  
Control Plant ◽  
Pythium Ultimum ◽  
Plant Diseases ◽  
Disease Suppression ◽  
Compost Tea ◽  
Damping Off ◽  
Bacterial Populations ◽  
Production Methods ◽  
Tea Production ◽  
Relationship Of

Compost tea is being used increasingly in agricultural production to control plant diseases. However, there has been limited investigation relating disease control efficacy to various compost tea production methods, particularly compost tea produced with active aeration and additives to increase microbial population densities in compost tea. Aerated compost tea (ACT) and nonaerated compost tea (NCT), produced with or without additives, was investigated for the suppression of damping-off of cucumber caused by Pythium ultimum. Compost tea was used to drench soilless container medium inoculated with P. ultimum; effect on damping-off ranged from not suppressive to consistently suppressive depending on the method used to produce the tea. The most consistent formulation for damping-off suppression was ACT produced with kelp and humic acid additives. Producing ACT with a molasses-based additive inconsistently suppressed damping-off; evidence suggests that residual nutrients can interfere with disease suppression. Heating or diluting compost tea negated suppression. Across all compost tea samples, there was no significant relationship of bacterial populations, measured as active cells, total cells, or CFU, to disease suppression. However, for all ACT produced without the molasses-based additive, there was a threshold of bacterial population density (6 log10 active cells per ml, 7.48 log10 total cells per ml, or 7 log10 CFU per ml) above which compost teas were suppressive.

scholarly journals Suppression of Rhizoctonia solani on Impatiens by Enhanced Microbial Activity in Composted Swine Waste-Amended Potting Mixes

2003 ◽  
Vol 93 (9) ◽  
pp. 1115-1123 ◽  
Author(s):  
H. G. Diab ◽  
S. Hu ◽  
D. M. Benson
Keyword(s):  
Rhizoctonia Solani ◽  
Microbial Activity ◽  
Microbial Biomass Carbon ◽  
Pythium Ultimum ◽  
Population Diversity ◽  
Disease Suppression ◽  
Peat Moss ◽  
Biomass Carbon ◽  
Damping Off ◽  
Carbon And Nitrogen

Peat moss-based potting mix was amended with either of two composted swine wastes, CSW1 and CSW2, at rates from 4 to 20% (vol/vol) to evaluate suppression of pre-emergence damping-off of impatiens (Impatiens balsamina) caused by Rhizoctonia solani (anastomosis group-4). A cucumber bioassay was used prior to each impatiens experiment to monitor maturity of compost as the compost aged in a curing pile by evaluating disease suppression toward both Pythium ultimum and R. solani. At 16, 24, 32, and 37 weeks after composting, plug trays filled with compost-amended potting mix were seeded with impatiens and infested with R. solani to determine suppression of damping-off. Pre-emergence damping-off was lower for impatiens grown in potting mix amended with 20% CSW1 than in CSW2-amended and nonamended mixes. To identify relationships between disease suppression and microbial parameters, samples of mixes were collected to determine microbial activity, biomass carbon and nitrogen, functional diversity, and population density. Higher rates of microbial activity were observed with increasing rates of CSW1 amendment than with CSW2 amendments. Microbial biomass carbon and nitrogen also were higher in CSW1-amended mixes than in CSW2-amended potting mixes 1 day prior to seeding and 5 weeks after seeding. Principal component analysis of Biolog-GN2 profiles showed different functional diversities between CSW1- and CSW2-amended mixes. Furthermore, mixes amended with CSW1 had higher colony forming units of fungi, endospore-forming bacteria, and oligotrophic bacteria. Our results suggest that enhanced microbial activity, functional and population diversity of stable compost-amended mix were associated with suppressiveness to Rhizoctonia damping-off in impatiens.

scholarly journals Detection of High Concentrations of Organic Acids in Fish Emulsion and Their Role in Pathogen or Disease Suppression

2009 ◽  
Vol 99 (3) ◽  
pp. 274-281 ◽  
Author(s):  
Pervaiz A. Abbasi ◽  
George Lazarovits ◽  
Suha Jabaji-Hare
Keyword(s):  
Organic Acids ◽  
Sandy Loam ◽  
Pythium Ultimum ◽  
Disease Suppression ◽  
Toxic Substances ◽  
Damping Off ◽  
Cucumber Seedlings ◽  
Loam Soil ◽  
Polymerase Chain ◽  
High Concentrations

Fish emulsion (FE) added to a sandy-loam soil at 1 and 2% rates reduced the viability of Verticillium dahliae microsclerotia by 39 and 74% in 1 day, 87 and 98% in 3 days, and 95 and 99% in 6 days, respectively. The immediate kill of microsclerotia indicated that FE contains toxic substances. We found in FE high concentrations (400 mmol/liter) of organic acids, including some known toxicants. Glycolic, acetic, formic, n-butyric, and propionic acids were the major organic acids detected in FE at the proportions of 52.5, 26.9, 7.9, 7.2, and 4.7%, respectively. In solution assays, the viability of V. dahliae microsclerotia treated for 24 h in 1, 2, 5, and 10% FE (pH 3.6 to 3.0) or a mixture of organic acids (pH 4.1 to 3.9) equivalent to the proportions in FE was reduced by 74, 94, 97, and 99% or 81, 91, 98, and 99%, respectively. The viability of microsclerotia was increased when the treatment solutions were buffered to pH 6.0. The organic acids mixtures and formic (0.025%) and acetic (0.1%) acids were toxic to Pythium ultimum. A mixture of organic acids (1, 2, and 4%) provided immediate protection of cucumber seedlings from damping-off in P. ultimum-infested muck and sandy-loam soils but not in peat-based mix. FE (1 and 2%) provided immediate protection of cucumber seedlings from damping-off in an infested muck soil, and disease protection was consistent when planting was delayed for 7, 14, and 28 days after adding FE. FE (1, 2, and 4%) did not provide immediate protection of cucumber seedlings from damping-off in a P. ultimum-infested peat-based mix; however, disease suppression was evident when planting was delayed for 7, 14, and 21 days after adding FE. Real-time polymerase chain reaction analyses of the peat-based mix indicated that the P. ultimum populations in the FE-amended mix declined over time. This study suggests that these organic acids in FE played a major role in pathogen or disease suppression, depending on the soil and substrate.

scholarly journals Differential Inactivation of Seed Exudate Stimulation of Pythium ultimum Sporangium Germination by Enterobacter cloacae Influences Biological Control Efficacy on Different Plant Species

2003 ◽  
Vol 69 (2) ◽  
pp. 1114-1120 ◽  
Author(s):  
Koji Kageyama ◽  
Eric B. Nelson
Keyword(s):  
Biological Control ◽  
Plant Species ◽  
Enterobacter Cloacae ◽  
Pythium Ultimum ◽  
Damping Off ◽  
Control Efficacy ◽  
Stimulatory Activity ◽  
Seed Exudate ◽  
Pea Seeds ◽  
Stimulation Of

ABSTRACT This study was initiated to understand whether differential biological control efficacy of Enterobacter cloacae on various plant species is due to differences in the ability of E. cloacae to inactivate the stimulatory activity of seed exudates to Pythium ultimum sporangium germination. In biological control assays, E. cloacae was effective in controlling Pythium damping-off when placed on the seeds of carrot, cotton, cucumber, lettuce, radish, tomato, and wheat but failed to protect corn and pea from damping-off. Seeds from plants such as corn and pea had high rates of exudation, whereas cotton and cucumber seeds had much lower rates of exudation. Patterns of seed exudation and the release of P. ultimum sporangium germination stimulants varied among the plants tested. Seed exudates of plants such as carrot, corn, lettuce, pea, radish, and wheat were generally more stimulatory to P. ultimum than were the exudates of cotton, cucumber, sunflower, and tomato. However, this was not directly related to the ability of E. cloacae to inactivate the stimulatory activity of the exudate and reduce P. ultimum sporangium germination. In the spermosphere, E. cloacae readily reduced the stimulatory activity of seed exudates from all plant species except corn and pea. Our data have shown that the inability of E. cloacae to protect corn and pea seeds from Pythium damping-off is directly related to its ability to inactivate the stimulatory activity of seed exudates. On all other plants tested, E. cloacae was effective in suppressing damping-off and inactivating the stimulatory activity of seed exudates.

scholarly journals Induction of Soil Suppressiveness Against Rhizoctonia solani by Incorporation of Dried Plant Residues into Soil

2006 ◽  
Vol 96 (12) ◽  
pp. 1372-1379 ◽  
Author(s):  
Masahiro Kasuya ◽  
Andriantsoa R. Olivier ◽  
Yoko Ota ◽  
Motoaki Tojo ◽  
Hitoshi Honjo ◽  
...  
Keyword(s):  
Rhizoctonia Solani ◽  
Mycelial Growth ◽  
Inhibitory Effect ◽  
Volatile Substance ◽  
Disease Suppression ◽  
Plant Residues ◽  
Infested Soil ◽  
Antagonistic Bacteria ◽  
Damping Off ◽  
Soil Suppressiveness

Suppressive effects of soil amendment with residues of 12 cultivars of Brassica rapa on damping-off of sugar beet were evaluated in soils infested with Rhizoctonia solani. Residues of clover and peanut were tested as noncruciferous controls. The incidence of damping-off was significantly and consistently suppressed in the soils amended with residues of clover, peanut, and B. rapa subsp. rapifera ‘Saori’, but only the volatile substance produced from water-imbibed residue of cv. Saori exhibited a distinct inhibitory effect on mycelial growth of R. solani. Nonetheless, disease suppression in such residue-amended soils was diminished or nullified when antibacterial antibiotics were applied to the soils, suggesting that proliferation of antagonistic bacteria resident to the soils were responsible for disease suppression. When the seed (pericarps) colonized by R. solani in the infested soil without residues were replanted into the soils amended with such residues, damping-off was suppressed in all cases. In contrast, when seed that had been colonized by microorganisms in the soils containing the residues were replanted into the infested soil, damping-off was not suppressed. The evidence indicates that the laimosphere, but not the spermosphere, is the site for the antagonistic microbial interaction, which is the chief principle of soil suppressiveness against Rhizoctonia damping-off.

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