scholarly journals Effect of Antibiosis on Antagonist Dose-Plant Disease Response Relationships for the Biological Control of Crown Gall of Tomato and Cherry

1999 ◽  
Vol 89 (10) ◽  
pp. 974-980 ◽  
Author(s):  
K. B. Johnson ◽  
J. A. DiLeone
Keyword(s):  
Biological Control ◽  
Dose Response ◽  
Crown Gall ◽  
Plant Pathogens ◽  
Experimental Treatment ◽  
Pathogen Resistance ◽  
Disease Suppression ◽  
Disease Response ◽  
Similar Dose ◽  
Prunus Mahaleb

The crown gall pathosystem was used to evaluate a model that describes the dose-response relationship between biological control agents and plant pathogens. The model predicts that this relationship can become asymptotic, such that increased antagonist doses cannot compensate for deficiencies in disease suppression. Wounded roots of tomato (Lycopersicon esculentum) and cherry (Prunus mahaleb) plants were dipped into different concentrations of the biological control organism Agrobacterium radiobacter strain K84 prior to inoculation with the pathogen A. tumefaciens. Pathogen strains sensitive or resistant to the antibiotic agrocin 84 were used, and for tomato experiments, a derivative of A. radiobacter strain K84 that does not produce agrocin 84 also was included as an experimental treatment. As predicted by the dose-response model, the amount of disease suppression per unit of antagonist decreased with increasing antagonist dose and became asymptotic at high antagonist densities. Control of crown gall of tomato was nearly complete with the combination of A. radiobacter K84 and an agrocin 84-sensitive strain of A. tumefaciens. Pathogen resistance to agrocin 84 or lack of agrocin 84 production by A. radiobacter resulted in antagonist dose-crown gall incidence relationships that were apparently asymptotic at levels of control significantly less than 100%. For field-grown cherry, similar dose-response relationships were observed with higher asymptotic levels of disease suppression obtained when trees were inoculated with an agrocin 84-sensitive A. tumefaciens strain compared with an agrocin 84-resistant pathogen strain. The differences among bacterial strain combinations in the magnitude of the asymptote defined by the dose-response relationships suggest that A. radiobacter impacts a smaller proportion of the pathogen population when the activity of agrocin 84 is muted.

scholarly journals Fatty Acid Competition as a Mechanism by Which Enterobacter cloacae Suppresses Pythium ultimum Sporangium Germination and Damping-Off

2000 ◽  
Vol 66 (12) ◽  
pp. 5340-5347 ◽  
Author(s):  
Karin van Dijk ◽  
Eric B. Nelson
Keyword(s):  
Fatty Acids ◽  
Biological Control ◽  
Fatty Acid ◽  
Linoleic Acid ◽  
Plant Pathogens ◽  
Enterobacter Cloacae ◽  
Pythium Ultimum ◽  
Plant Diseases ◽  
Disease Suppression ◽  
Acid Uptake

ABSTRACT Interactions between plant-associated microorganisms play important roles in suppressing plant diseases and enhancing plant growth and development. While competition between plant-associated bacteria and plant pathogens has long been thought to be an important means of suppressing plant diseases microbiologically, unequivocal evidence supporting such a mechanism has been lacking. We present evidence here that competition for plant-derived unsaturated long-chain fatty acids between the biological control bacterium Enterobacter cloacae and the seed-rotting oomycete, Pythium ultimum, results in disease suppression. Since fatty acids from seeds and roots are required to elicit germination responses ofP. ultimum, we generated mutants of E. cloacaeto evaluate the role of E. cloacae fatty acid metabolism on the suppression of Pythium sporangium germination and subsequent plant infection. Two mutants of E. cloacaeEcCT-501R3, Ec31 (fadB) and EcL1 (fadL), were reduced in β-oxidation and fatty acid uptake, respectively. Both strains failed to metabolize linoleic acid, to inactivate the germination-stimulating activity of cottonseed exudate and linoleic acid, and to suppress Pythium seed rot in cotton seedling bioassays. Subclones containing fadBA or fadLcomplemented each of these phenotypes in Ec31 and EcL1, respectively. These data provide strong evidence for a competitive exclusion mechanism for the biological control of P. ultimum-incited seed infections by E. cloacae where E. cloacaeprevents the germination of P. ultimum sporangia by the efficient metabolism of fatty acid components of seed exudate and thus prevents seed infections.

Rhizosphere colonization of wheat by selected soil bacteria over diverse environments

1993 ◽  
Vol 39 (3) ◽  
pp. 335-341 ◽  
Author(s):  
Eugene A. Milus ◽  
Craig S. Rothrock
Keyword(s):  
Biological Control ◽  
Plant Pathogens ◽  
Disease Suppression ◽  
Growth And Yield ◽  
Subtilis Strain ◽  
Wheat Roots ◽  
Streptomyces Strain ◽  
Rhizosphere Colonization ◽  
Population Sizes ◽  
Crown Roots

The ability to colonize the rhizosphere is essential for bacteria to function as biological control agents for soil-borne plant pathogens. Eight bacterial strains reported to colonize wheat roots, inhibit root pathogens, and (or) improve wheat growth and yield were applied to wheat seeds that were planted in fumigated and nonfumigated soil in the 1990 and 1991 growing seasons at two locations in Arkansas. Rhizosphere population sizes were highly correlated with population sizes on seeds. Bacillus subtilis strain D-39Sr colonized roots as well in nonfumigated as in fumigated soil, and the other seven strains had rhizosphere populations 0.3 to 1.1 log units higher in fumigated soil. Pseudomonas fluorescens strain 2-79R was one of the best colonizers, and Streptomyces strain D-185S was the poorest. The greatest difference among strains was for relative colonization ability of crown roots in the spring. All strains except Streptomyces strain D-185S appear to have broad adaptation to colonize wheat roots and are able to compete with soil microflora for colonization sites. This research indicates that it is possible to select bacteria in the genera Bacillus, Pseudomonas, or Xanthomonas that will colonize roots well over diverse environments. Rhizosphere colonization by these strains was not associated with disease suppression or enhanced plant growth or yield.Key words: biological control, rhizosphere competence, wheat, Triticum aestivum.

scholarly journals Microbial antagonists against plant pathogens in Iran: A review

2020 ◽  
Vol 5 (1) ◽  
pp. 404-440 ◽  
Author(s):  
Mehrdad Alizadeh ◽  
Yalda Vasebi ◽  
Naser Safaie
Keyword(s):  
Biological Control ◽  
Chemical Control ◽  
Plant Disease ◽  
Plant Pathogens ◽  
Plant Diseases ◽  
Agricultural Products ◽  
Control Measures ◽  
Wide Range ◽  
Plant Disease Management ◽  
Published Research

AbstractThe purpose of this article was to give a comprehensive review of the published research works on biological control of different fungal, bacterial, and nematode plant diseases in Iran from 1992 to 2018. Plant pathogens cause economical loss in many agricultural products in Iran. In an attempt to prevent these serious losses, chemical control measures have usually been applied to reduce diseases in farms, gardens, and greenhouses. In recent decades, using the biological control against plant diseases has been considered as a beneficial and alternative method to chemical control due to its potential in integrated plant disease management as well as the increasing yield in an eco-friendly manner. Based on the reported studies, various species of Trichoderma, Pseudomonas, and Bacillus were the most common biocontrol agents with the ability to control the wide range of plant pathogens in Iran from lab to the greenhouse and field conditions.

scholarly journals The Potential of Rhizoctonia-Like Fungi for the Biological Protection of Cereals against Fungal Pathogens

Plants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 349
Author(s):  
Dominik Bleša ◽  
Pavel Matušinský ◽  
Romana Sedmíková ◽  
Milan Baláž
Keyword(s):  
Biological Control ◽  
Fungal Pathogens ◽  
Plant Pathogens ◽  
Higher Plants ◽  
Fusarium Culmorum ◽  
Suppressive Effect ◽  
Plant Production ◽  
Shoot Biomass ◽  
Organic Substrates

The use of biological control is becoming a common practice in plant production. One overlooked group of organisms potentially suitable for biological control are Rhizoctonia-like (Rh-like) fungi. Some of them are capable of forming endophytic associations with a large group of higher plants as well as mycorrhizal symbioses. Various benefits of endophytic associations were proved, including amelioration of devastating effects of pathogens such as Fusarium culmorum. The advantage of Rh-like endophytes over strictly biotrophic mycorrhizal organisms is the possibility of their cultivation on organic substrates, which makes their use more suitable for production. We focused on abilities of five Rh-like fungi isolated from orchid mycorrhizas, endophytic fungi Serendipita indica, Microdochium bolleyi and pathogenic Ceratobasidium cereale to inhibit the growth of pathogenic F. culmorum or Pyrenophora teres in vitro. We also analysed their suppressive effect on wheat infection by F. culmorum in a growth chamber, as well as an effect on barley under field conditions. Some of the Rh-like fungi affected the growth of plant pathogens in vitro, then the interaction with plants was tested. Beneficial effect was especially noted in the pot experiments, where wheat plants were negatively influenced by F. culmorum. Inoculation with S. indica caused higher dry shoot biomass in comparison to plants treated with fungicide. Prospective for future work are the effects of these endophytes on plant signalling pathways, factors affecting the level of colonization and surviving of infectious particles.

scholarly journals Restoration of Susceptibility of Intracellular Methicillin-Resistant Staphylococcus aureus to β-Lactams: Comparison of Strains, Cells, and Antibiotics

2008 ◽  
Vol 52 (8) ◽  
pp. 2797-2805 ◽  
Author(s):  
Sandrine Lemaire ◽  
Aurélie Olivier ◽  
Françoise Van Bambeke ◽  
Paul M. Tulkens ◽  
Peter C. Appelbaum ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Dose Response ◽  
Intermediate Phenotype ◽  
Maximal Effect ◽  
Response Curves ◽  
Methicillin Resistant ◽  
Complete Restoration ◽  
Similar Dose ◽  
Dose Response Curves ◽  
Mrsa Strains

ABSTRACT Staphylococcus aureus invades eukaryotic cells. When methicillin-resistant S. aureus (MRSA) ATCC 33591 is phagocytized by human THP-1 macrophages, complete restoration of susceptibility to cloxacillin and meropenem is shown and the strain becomes indistinguishable from MSSA ATCC 25923 due to the acid pH prevailing in phagolysosomes (S. Lemaire et al., Antimicrob. Agents Chemother. 51:1627-1632, 2007). We examined whether this observation can be extended to (i) strains of current clinical and epidemiological interest (three hospital-acquired MRSA [HA-MRSA] strains, two community-acquired MRSA [CA-MRSA] strains, two HA-MRSA strains with the vancomycin-intermediate phenotype, one HA-MRSA strain with the vancomycin-resistant phenotype, and one animal [porcine] MRSA strain), (ii) activated THP-1 cells and nonprofessional phagocytes (keratinocytes, Calu-3 bronchial epithelial cells), and (iii) other β-lactams (imipenem, oxacillin, cefuroxime, cefepime). All strains showed (i) a marked reduction in MICs in broth at pH 5.5 compared with the MIC at pH 7.4 and (ii) sigmoidal dose-response curves with cloxacillin (0.01× to 100× MIC, 24 h of incubation) after phagocytosis by THP-1 macrophages that were indistinguishable from each other and from the dose-response curve for methicillin-susceptible S. aureus (MSSA) ATCC 25923 (relative potency [50% effect], 6.09× MIC [95% confidence interval {CI}, 4.50 to 8.25]; relative efficacy [change in bacterial counts over the original inoculum for an infinitely large cloxacillin concentration, or maximal effect], −0.69 log CFU [95% CI, −0.79 to −0.58]). Similar dose-response curves for cloxacillin were also observed with MSSA ATCC 25923 and MRSA ATCC 33591 after phagocytosis by activated THP-1 macrophages, keratinocytes, and Calu-3 cells. By contrast, there was a lower level of restoration of susceptibility of MRSA ATCC 33591 to cefuroxime and cefepime after phagocytosis by THP-1 macrophages, even when the data were normalized for differences in MICs. We conclude that the restoration of MRSA susceptibility to β-lactams after phagocytosis is independent of the strain and the types of cells but varies between β-lactams.

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