Biological control of Stephanodiscus hantzschii (Bacillariophyceae) blooms in a field mesocosm by the immobilized algicidal bacterium Pseudomonas fluorescens HYK0210-SK09

ABSTRACT Forty-seven isolates representing all biovars of Pseudomonas fluorescens (biovars I to VI) were collected from the rhizosphere of field-grown sugar beet plants to select candidate strains for biological control of preemergence damping-off disease. The isolates were tested for in vitro antagonism toward the plant-pathogenic microfungi Pythium ultimum and Rhizoctonia solani in three different plate test media. Mechanisms of fungal inhibition were elucidated by tracing secondary-metabolite production and cell wall-degrading enzyme activity in the same media. Most biovars expressed a specific mechanism of antagonism, as represented by a unique antibiotic or enzyme production in the media. A lipopeptide antibiotic, viscosinamide, was produced independently of medium composition by P. fluorescens bv. I, whereas the antibiotic 2,4-diacetylphloroglucinol was observed only in glucose-rich medium and only in P. fluorescens bv. II/IV. Both pathogens were inhibited by the two antibiotics. Finally, in low-glucose medium, a cell wall-degrading endochitinase activity in P. fluorescens bv. I, III, and VI was the apparent mechanism of antagonism toward R. solani. The viscosinamide-producing DR54 isolate (bv. I) was shown to be an effective candidate for biological control, as tested in a pot experiment with sugar beet seedlings infested with Pythium ultimum. The assignment of different patterns of fungal antagonism to the biovars of P. fluorescens is discussed in relation to an improved selection protocol for candidate strains to be used in biological control.

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Quorum-sensing system influences root colonization and biological control ability in Pseudomonas fluorescens 2P24

Antonie van Leeuwenhoek ◽

10.1007/s10482-005-9028-8 ◽

2006 ◽

Vol 89 (2) ◽

pp. 267-280 ◽

Cited By ~ 96

Author(s):

Hai-Lei Wei ◽

Li-Qun Zhang

Keyword(s):

Biological Control ◽

Quorum Sensing ◽

Pseudomonas Fluorescens ◽

Root Colonization ◽

Sensing System ◽

Quorum Sensing System

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Application of Pseudomonas fluorescens isolates to wheat as potential biological control agents against take-all

Plant Pathology ◽

10.1111/j.1365-3059.1993.tb01536.x ◽

1993 ◽

Vol 42 (4) ◽

pp. 560-567 ◽

Cited By ~ 35

Author(s):

A. L. CAPPER ◽

K. P. HIGGINS

Keyword(s):

Biological Control ◽

Pseudomonas Fluorescens ◽

Biological Control Agents ◽

Take All

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Control of Fire Blight by Pseudomonas fluorescens A506 and Pantoea vagans C9-1 Applied as Single Strains and Mixed Inocula

Phytopathology ◽

10.1094/phyto-03-10-0097 ◽

2010 ◽

Vol 100 (12) ◽

pp. 1330-1339 ◽

Cited By ~ 50

Author(s):

V. O. Stockwell ◽

K. B. Johnson ◽

D. Sugar ◽

J. E. Loper

Keyword(s):

Biological Control ◽

Pseudomonas Fluorescens ◽

Fire Blight ◽

Erwinia Amylovora ◽

Field Trials ◽

Disease Suppression ◽

Biological Control Agents ◽

Population Sizes ◽

Mixed Inocula ◽

Pantoea Vagans

The biological control agents Pseudomonas fluorescens A506 and Pantoea vagans C9-1 were evaluated individually and in combination for the suppression of fire blight of pear or apple in 10 field trials inoculated with the pathogen Erwinia amylovora. The formulation of pathogen inoculum applied to blossoms influenced establishment of the pathogen and the efficacy of biological control. Pantoea vagans C9-1 suppressed fire blight in all five trials in which the pathogen was applied as lyophilized cells but in none of the trials in which the pathogen was applied as freshly harvested cells. In contrast, Pseudomonas fluorescens A506 reduced disease significantly in only one trial. A mixture of the two strains also suppressed fire blight, but the magnitude of disease suppression over all field trials (averaging 32%) was less than that attained by C9-1 alone (42%). The two biological control agents did not antagonize one another on blossom surfaces, and application of the mixture of A506 and C9-1 to blossoms resulted in a greater proportion of flowers having detectable populations of at least one bacterial antagonist than the application of individual strains. Therefore, the mixture of A506 and C9-1 provided less disease control than expected based upon the epiphytic population sizes of the antagonists on blossom surfaces. We speculate that the biocontrol mixture was less effective than anticipated due to incompatibility between the mechanisms by which A506 and C9-1 suppress disease.

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Evaluation of Bacterial Antagonists for Biological Control of Broccoli Head Rot Caused by Pseudomonas fluorescens

Phytopathology ◽

10.1094/phyto-96-0408 ◽

2006 ◽

Vol 96 (4) ◽

pp. 408-416 ◽

Cited By ~ 5

Author(s):

Xiaohui Cui ◽

Rob Harling

Keyword(s):

Biological Control ◽

Quorum Sensing ◽

Pseudomonas Fluorescens ◽

Virulence Gene ◽

Pathogenicity Test ◽

Bacillus Sp ◽

Inhibitory Effects ◽

Extracellular Metabolite ◽

Head Rot ◽

Tn5 Mutant

Pectolytic strains of Pseudomonas fluorescens are opportunistic pathogens of broccoli, causing head rot in temperate regions of the world. In this study, we investigated the potential of two bacterial isolates, P. fluorescens m6418 and Bacillus sp. A24, for biological control of broccoli head rot caused by P. fluorescens 5064, isolated from diseased broccoli in Scotland, UK. P. fluorescens m6418, a Tn5 mutant of wild-type 5064, is nonpathogenic and overproduces an extracellular metabolite with strong antimicrobial activity. In this study, we identified the anti-microbial metabolite produced by strain m6418 as pyrrolnitrin. P. fluorescens m6418 had significant inhibitory effects against strain 5064 both in culture and on broccoli leaves. In an excised broccoli head pathogenicity test, strain m6418, when coinoculated with P. fluorescens 5064, reduced disease by 41%. Bacillus sp. A24 produces an enzyme that can degrade N-acyl homoserine lactones, signaling molecules employed by bacteria for quorum sensing. Bacillus sp. A24 was capable of out-competing P. fluorescens 5064 when grown together in culture, and could degrade the quorum sensing signal of P. fluorescens 5064 (and thereby attenuate its virulence gene production). However, Bacillus sp. A24 had only a limited biocontrol effect on P. fluorescens 5064 in the excised broccoli head assay.

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Biological control of rice bacterial blight by plant-associated bacteria producing 2,4-diacetylphloroglucinol

Canadian Journal of Microbiology ◽

10.1139/w05-106 ◽

2006 ◽

Vol 52 (1) ◽

pp. 56-65 ◽

Cited By ~ 41

Author(s):

Palaniyandi Velusamy ◽

J Ebenezar Immanuel ◽

Samuel S Gnanamanickam ◽

Linda Thomashow

Keyword(s):

Biological Control ◽

Pseudomonas Fluorescens ◽

Bacterial Blight ◽

Field Experiments ◽

Screening Method ◽

Xanthomonas Oryzae ◽

Rice Bacterial Blight ◽

Fluorescent Pseudomonas ◽

Tn5 Mutants ◽

Bacterial Blight Pathogen

Certain plant-associated strains of fluorescent Pseudomonas spp. are known to produce the antimicrobial antibiotic 2,4-diacetylphloroglucinol (DAPG). It has antibacterial, antifungal, antiviral, and antihelminthic properties and has played a significant role in the biological control of tobacco, wheat, and sugar beet diseases. It has never been reported from India and has not been implicated in the biological suppression of a major disease of the rice crop. Here, we report that a subpopulation of 27 strains of plant-associated Pseudomonas fluorescens screened in a batch of 278 strains of fluorescent pseudomonads produced DAPG. The DAPG production was detected by a PCR-based screening method that used primers Phl2a and Phl2b and amplified a 745-bp fragment characteristic of DAPG. HPLC,1H NMR, and IR analyses provided further evidence for its production. We report also that this compound inhibited the growth of the devastating rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae in laboratory assays and suppressed rice bacterial blight up to 59%–64% in net-house and field experiments. Tn5 mutants defective in DAPG production (Phl–) of P. fluorescens PTB 9 were much less effective in their suppression of rice bacterial blight.Key words: biocontrol, 2,4-diacetylphloroglucinol, Pseudomonas fluorescens, rice, Xanthomonas oryzae pv. oryzae.

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