BIOCONTROL AGENT - Pseudomonas fluorescens

 BIOCONTROL AGENT - Pseudomonas fluorescens

General Characteristics of Pseudomonas fluorescens

• Gram’s classification – Gram negative
• Shape – Rod shape
• Arrangement – Single in arrangement
• Size – Measures approximately 0.5 μm in width and 2.0 - 2.5 μm in length
• Family – Pseudomonadaceae
• Motility – Motile (due to presence of several Polar flagella)
• Capsule – Absent
• Endospores – Absent
• Respiration – Obligate aerobe.
• Optimum Temperature – 25 °C to 30 °C.
• Optimum pH – 7.0
• Pseudomonas fluorescens secretes a soluble Greenish fluorescent pigment called Fluorescein, particularly under conditions of low iron availability.
• Pseudomonas fluorescens can able to produce Fluorescent pigment on King’s B Medium and shows positive reaction for Gelatin liquefaction, Catalase test, Oxidase test, Starch hydrolysis, Levan formation from sucrose, Citrate utilization, etc.
• Pseudomonas fluorescens have been shown to be potential agents for the biocontrol and are known to enhance plant growth promotion and reduce severity of many fungal diseases.

Habitat of Pseudomonas fluorescens

• Pseudomonas fluorescens as non-pathogenic saprophytes that colonize soil, water and plant surface environments.

Pseudomonas fluorescens as Plant disease control agent

• Many strains of Pseudomonas fluorescens show potential for biological control of phytopathogens especially root pathogens. They had strong inhibitory on Rastonia solanacearum, Fusarium oxysporum and Rhizoctonia solani, etc.
• Pseudomonas fluorescens have been mostly studied for protection of crop plants from phytopathogenic Oomycetes (particularly Pythium spp.) and fungi (Fusarium oxysporum, Gaeumannomyces graminis, Rhizoctonia solani, etc.), and to a lesser extent bacteria (e.g. Pectobacterium carotovorum) and nematodes (e.g. Meloidogyne spp.).
• Biocontrol agents from Pseudomonas fluorescens are rather non-specific in their ability to protect plants from soil phytopathogens. Indeed, each biocontrol strain can typically act in more than one pathosystem, i.e. protect more than one plant species from often distinct pathogens.
• Disease suppression by Pseudomonas fluorescens often entails inhibition of phytopathogens in soil or on roots, by competition and antagonism. Plant protection may also result from direct interactions with the host plants, especially in the case of Induced Systemic Resistance (ISR).
• Pseudomonas fluorescens suppress plant diseases by production of number of Secondary metabolites including

a)   Antibiotics and Antifungal compounds – Inhibit fungal spore germination and lysis of fungal mycelia.

b)     Siderophores – Low molecular weight compound, chelate irons and limited the supply of iron to the rhizosphere. 

c)     Hydrogen cyanide – Inhibits the growth of phytopathogens and non-toxic to host plants.

•      Pseudomonas fluorescens has the unique ability to enter the plant vascular system, reach the various parts of the plant system and act as a systemic biocontrol agent against various fungal and bacterial diseases.
•    Competitive exclusion of pathogens (Competition) as the result of rapid colonization of the rhizosphere by Pseudomonas fluorescens may also be an important factor in disease control.
•   Pseudomonas fluorescens is also involved in the production of Plant growth promoting Phytohormones (Indole acetic acid, Auxins and Gibberrelins) and Phosphate solubilization.

Crop Recommendation

• Potato, Cucumbers, Eggplant, Tomatoes, Chilli, Cut flowers, Orchards, Vineyards Ornamentals in greenhouses, lawns and nurseries.

Target Diseases

• Pythium sp., Phytophtora sp., Rhizoctonia solani, Fusarium sp., Botrytis cinerea, Sclerotium spp., Sclerotinia sp. and Ustilogo sp.

Isolation of Pseudomonas fluorescent

• Pseudomonas fluorescens are isolated from the soil sample by Serial Dilution Method (Spread Plate Method or Pour Plate Method).
• The common culture medium used for the isolation of Pseudomonas fluorescens is King’s B Agar medium.

Microscopic characteristics of Pseudomonas fluorescent

• Gram staining – Pseudomonas fluorescens was observed as Pink coloured, rod shaped Gram negative bacteria, arranged as single.
• Motility test (Hanging Drop Method) – Motile rods.

Cultural characteristics of Pseudomonas fluorescent

• In King’s B Agar medium, Pseudomonas fluorescens shows individual, small, round, irregular and fluorescent pigmented colonies.

Figure – 1: Colony morphology of Pseudomonas fluorescens in King’s B Agar medium

Biochemical characteristics of Pseudomonas fluorescens

a)     Catalase test – Positive

b)     Oxidase test – Positive

c)     Urease test – Positive

d)     Indole test – Negative

e)     Methyl Red (MR) test – Negative

f)      Voges Proskauer (VP) test – Negative

g)     Citrate utilization test – Positive

h)    Starch hydrolysis test – Negative

i)      Casein hydrolysis test - Positive

j)      Gelatin hydrolysis test – Positive

k)     Esculin hydrolysis – Negative

l)      Nitrate reduction – Negative

m)   Glucose fermentation – Acid produced and Gas not produced

n)    Sucrose fermentation – No fermentation

o)     Mannose fermentation – Acid produced and Gas not produced

p)     Mannitol fermentation – Acid produced and Gas not produced

q)     Arabinose fermentation – Acid produced and Gas not produced

Formulation of Pseudomonas fluorescent

• Commercial preparations of Pseudomonas fluorescens comes in various forms such as solids, liquids, powders, tablets, granules, ball agents, liquid suspensions, and oil emulsions.