Biological control of three phytopathogenic fungi by Pseudomonas fluorescens isolated from rhizosphere.
M Goud, V Muralikrishnan
biocontrol, chemical fungicides, fungal pathogens., plant protection, pseudomonas fluorescens
M Goud, V Muralikrishnan. Biological control of three phytopathogenic fungi by Pseudomonas fluorescens isolated from rhizosphere.. The Internet Journal of Microbiology. 2008 Volume 7 Number 2.
Plant protection is an important area which needs attention since most of the hazardous inputs added into the agricultural system are in the form of plant protection chemicals.
Research on a more sustainable and environmental friendly agriculture system is the need of the hour, as there is a growing concern on the deteriorating quality of the environment as a result of the intensive agriculture. Despite the many achievements of modern agriculture, certain cultural practices have actually enhanced the destructive potential of diseases. It is true that a huge number of fungal diseases plague the crop plants throughout the year when a farmer fails to take proper preventative measures. Plant disease control, therefore has become heavily dependent on fungicides to combat the wide variety of fungal diseases.
A land mark study published by the us environment protection agency indicates that in the US alone 3000-6000 cancer cases are induced annually by pesticide residues on foods and another 50-150 by exposure to pesticides during application (Goud, 2004).This type of findings have made the governments of many countries increasingly aware of the drawbacks of many chemical pesticides in terms of their effect on the environment, as well as on the grower and consumer of agriculture products.
Plant protection is an important area, which needs attention since most of the hazardous inputs added into the agricultural system are in the form of plant protection chemicals. Studies aimed at replacing pesticides with environmentally safer methods are currently being conducted at many research centers.
Biological control of plant diseases assumes a greater importance at this juncture. The efficient use of rhizosphere microorganisms to control plant pathogens has been reported worldwide in different plants. Soil pseudomonads possess a variety of promising properties, which make them better biocontrol agents (Cook,1993). In the last two decades endophytic bacteria especially
The objectives of the present study were to isolate P.fluorescens from soil, to check its antagonistic activity and effect of its secondary metabolites on three fungal plant pathogens by in vitro techniques.
Material And Methods
Rhizosphere soil suspension was prepared and 10-6 and 10-7 dilutions were spread on King’s B medium (James, 1990). After 2 days incubation the colony which initially colourless and later produced fluorescent pigment when observed under U.V light were subcultured in slants.
Fungal plant pathogens namely
Figure 1- A:
Screening for antagonistic activity
Cross streak assay
A heavy inoculum from an actively growing
Pour plate method
A loopful of
Extraction of antifungal compound.
A loop full of actively growing culture of
Effect of crude antifungal compound on fungal biomass 50ml PD broth was inoculated with 4mm test fungal mat.1ml of crude compound with a concentration of 50mcg/ml, 100mcg/ml and 150mcg/ml in methanol was added and incubated for 5 days at 280C. Control flasks were maintained with out the compound. Dry weight of fungus was taken and compared with control.
Agar well diffusion method
Seeded agar plates of each test fungal organism were prepared. With a sterile borer, 6mm wells were prepared in which 70 micro liters of crude compound with a concentration of 50mcg/ml, 100mcg/ml and 150mcg/ml of methanol was added. These plates were then kept for incubation for 3 days at 280C .Control well was maintained by adding only methanol. Antifungal efficiency was calculated by measuring the zone of inhibition.
Reproducibility of the results
All data are the mean of at least three independent experiments showing consistent results.
Results And Discussion
Fluorescent pseudomonads are of great importance in biotechnology because of the ability of several strains to degrade xenobiotics, control plant pathogens, and act as human pathogens. The ability of some strains to colonize the plant rhizosphere allows its use in rhizoremediation (Brazil et al.,1995; Karlson,1998). The isolation and enumeration of bacteria belonging to the genus
The currently accepted diagnostic medium for the detection of fluorescence is king’s B medium (Djibaoui and Bensoltane,2005). In the present study, the organism is isolated on King’s B medium (fig 2 A&B) and based on the biochemical tests the organism isolated was authenticated as
Cross streak assay and pour plate method are done to test the antagonistic activity of
In pour plate method,
Cross streak assay and pour plate method can be used to observe the interaction between the organisms in natural environments. Results from the above methods indicate that
Dry weight of fungal growth under different concentrations of crude antibiotic was taken as a measure of effect of crude antibiotic on phytopathogenic fungi. In
Growing the pathogenic fungi in the vicinity of compounds on PDA medium can test the efficacy of antagonistic activity of
As the concentration of the compound increased the zone of clearance increased. Pure compounds like pyrrolnitrin decreased the incidence of damping off (Lambert, 1866) and phenazine 1-carboxylic acid controlled take all disease (Zhengyu et al., 2004). This suggests that
As agricultural practices become more sustainable, there is an increasing need for ecologically sound methods of disease control. Biological control, which exploits the natural antagonistic activity of certain root-colonizing bacteria against fungal pathogens, is one such approach. Biological control agents often perform inadequately under field conditions, however, and this has impeded acceptance of the technology as an alternative to chemical pesticides. Soil pseudomonads possess a variety of promising properties which make them better biocontrol agents. Although the present study is not an initiative but helps in better understanding and utilization of
One of the authors (M.J.P.G) is thankful to M. Deiveekasundaram, Head, Department of Soil and Agriculture Microbiology, Annamalai University for providing the necessary facilities and awarding the degree “