Biological control of ragi blast disease by chitinase producing fluorescent Pseudomonas isolates

The role of antibiotics in biological control of soilborne pathogens, and more generally in microbial antagonism in natural disease-suppressive soils, often has been questioned because of the indirect nature of the supporting evidence. In this study, a protocol for high pressure liquid chromatography/mass spectrometry is described that allowed specific identification and quantitation of the antibiotic 2,4-diacetylphloroglucinol (Phl) produced by naturally occurring fluorescent Pseudomonas spp. on roots of wheat grown in a soil suppressive to take-all of wheat. These results provide, for the first time, biochemical support for the conclusion of previous work that Phl-producing fluorescent Pseudomonas spp. are key components of the natural biological control that operates in take-all—suppressive soils in Washington State. This study also demonstrates that the total amount of Phl produced on roots of wheat by P. fluorescens strain Q2-87, at densities ranging from approximately 105 to 107 CFU/g of root, is proportional to its rhizosphere population density and that Phl production per population unit is a constant (0.62 ng/105 CFU). Thus, Phl production in the rhizosphere of wheat is strongly related to the ability of the introduced strain to colonize the roots.

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Antifungal characteristics of a fluorescent Pseudomonas strain involved in the biological control of Rhizoctonia solani

Microbiological Research ◽

10.1016/s0944-5013(00)80038-5 ◽

2000 ◽

Vol 155 (3) ◽

pp. 233-242 ◽

Cited By ~ 27

Author(s):

K.K. Pal ◽

K.V.B.R. Tilak ◽

A.K. Saxena ◽

R. Dey ◽

C.S. Singh

Keyword(s):

Biological Control ◽

Rhizoctonia Solani ◽

Fluorescent Pseudomonas

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Biological control of damping-off of sugar-beet and cotton with Chaetomium globosum or a fluorescent Pseudomonas sp.

Canadian Journal of Microbiology ◽

10.1139/m88-104 ◽

1988 ◽

Vol 34 (5) ◽

pp. 631-637 ◽

Cited By ~ 25

Author(s):

D. Walther ◽

D. Gindrat

Keyword(s):

Biological Control ◽

Sugar Beet ◽

Seed Treatment ◽

Pythium Ultimum ◽

Chaetomium Globosum ◽

Pseudomonas Sp ◽

Damping Off ◽

Antifungal Metabolites ◽

Fluorescent Pseudomonas

Seed treatment with ascospores of Chaetomium globosum reduced damping-off of sugar-beet caused by seed-borne Phoma betae and soil-borne Pythium ultimum or Rhizoctonia solani in growth chamber experiments. Seed treatment with a fluorescent Pseudomonas sp. controlled Ph. betae and P. ultimum but not R. solani. Coating cotton seeds with ascospores controlled P. ultimum and R. solani damping-off. In some experiments, biological seed treatments were equally or more effective than seed treatment with captan. However, greater variability in disease control occurred with the antagonists than with captan. Fifty percent of freshly harvested ascospores of C. globosum germinated in 8 h on water agar. When ascospores were stored under air-dried conditions for 3 days to 2.5 years, germination increased to > 90%. Under same storage conditions, survival of Pseudomonas sp. was detected after 4 months. Antagonistic activities observed in vitro were hyphal coiling of C. globosum on R. solani, and mycostasis was induced by C. globosum or Pseudomonas sp. on agar and soil. The presumed cause of mycostasis is the diffusible antifungal metabolites which may also be involved in the biological control of damping-off.

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Biological control for rice blast disease by employing detachment action with gelatinolytic bacteria

Biological Control ◽

10.1016/j.biocontrol.2010.07.008 ◽

2010 ◽

Vol 55 (2) ◽

pp. 85-91 ◽

Cited By ~ 19

Author(s):

Saki Shimoi ◽

Kanako Inoue ◽

Hiroko Kitagawa ◽

Masanori Yamasaki ◽

Seiya Tsushima ◽

...

Keyword(s):

Biological Control ◽

Rice Blast ◽

Rice Blast Disease ◽

Blast Disease

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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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