Author: Naresh Kumar
According to the estimate of FAO, the annual losses to crop production due to plant diseases alone are about 12 per cent. The losses are going to increase with change in agricultural practices and our country, which is tropical with warm and humid climate, provides ideal conditions for development and spread of diseases of crops cultivated under good management systems. Therefore, control of plant diseases assumes greater importance. Although several methods are followed for this purpose, disease control by chemicals is the promising one especially under intensive cropping programmes. However, their use poses certain problems of residues left over on crops, which has gained considerable importance in recent years, not only in India but also throughout the world.
The reduction of inoculums density or disease producing activities of a pathogen or parasite in its active or dormant stage by one or more organisms accomplished naturally or through manipulation of the environment, host or by introduction of one or more antagonists.
Biocontrol Agents :
| Fungi (Antagonists) | Pathogen Controlled |
| Trichoderma viride | Macrophomina phaseolina, Pythium, Sclerotium rolfssi |
| Trichodema harzianum | Fusarium oxysporum f.sp. vasinfectum,Fusarium oxysporum f.sp. melonis, Rhizoctonia solani |
| Trichoderma haematum | Pythium sp., Rhizoctonia solani |
| Verticillium laccani | Uromyces dianthi |
| Gliocladium virens | P. ultimum, Rhizoctonia solani |
| Latesaria arvalis | Sclerotinia sclerotiarum, R. Solani, Pythium sp. |
| Bacteria : | |
| Agrobacterium radiobacter | Agrobacterium tumefaciens |
| Azotobacter chrococcum | Rhizoctonia solani |
| Bacillus subtilis | Fusarium spp., Pythium spp., Rhizoctonia spp., Sclerotium rolfsii, Streptomyces scabies, Verticillium spp., |
| Bacillus thuringiensis | Alternaria alternata, Hemileia vastatrix |
| Erwinia herbicola pv. herbicola | Erwinia amylovora |
| Pseudomonas fluorescens | Fusarium spp., Macrophomina phaseolina, Pyricularia oryzae, Pythium spp., Rhizoctonia solani |
| P. cepacia | Cercospora sp. |
| Streptomyces diastaticus | Pythium aphanidermatum |
| S. griseoviridis | Alternaria brassicola, Fusarium oxysporum f. sp. dianthi, Rhizoctonia solani |
1. Parasitism :
The biocontrol agent parasitizes the pathogen by coiling around the hyphae.
Ex – Tricoderma viride parasite derives its nutrition from the
pathogen by puncturing the host hyphae and kills them.
Various bactria and fungi secrete hydrolytic enzymes for the degration of cell wall of pathogen.
2. Lysis :
Bacillus sp. Causes hyphal lysis of gaumanomyces gramini.
The chitinolytic enzymes of Serratia marcescens caused cell wall lysis of Sclerotium rolfsi.
Tricoderma sp. Produces chitineses and B 1-3 glucanases which lysis the cell wall of Rhizoctonia solani.
3. Antibiosis :-
The antibiotic compounds secreted by the biocontrol agent suppress the growth of the pathogen.
Ex – Phenazine-1-carboxylic acid (PCA) produced by Pseudomonas fluorescence play an important role in suppressing the take all disease of wheat, Trichoderma sp. Produces antibiotics Viz- Trichodermin, Gliotoxin and viridian.
4. Competition :-
The biocontrol agent competes for food and essential elements with the pathogen thereby displacing and suppressing the growth of pathogen. Ex.- The competition for nutrients between pythium aphanidermatum, P. ultimum and bacteria suppress the damping off disease in cucumbers.
Fluorescent iron chelator siderophores such as Pseudobactins and pyoverdins produced by P.fluorscence chelate the iron available in the soil, thereby, depriving the pathogen of its Fe requirement
Mode of Application
- Innundative application- The biocontrol agent is applied directly to the infection court at high population level. For Ex. – Tricoderma used for seed treatment.
- Augmentative application – The biocontrol agent is applied at one place at lower multiplies and spreads to other plant part and provides protection. For Ex.- PGPR are used for seed bacterization.
Methods of application
- Seed Treatment
- Seedling root dipping treatment
- Soil application
- Foliar application
Advantage of biocontrol agent :-
- Less costly and cheaper than any other method.
- Give protection throughout the crop period.
- Highly effective against specific plant disease.
- They do not cause toxicity to the plant.
- Application is safer to the environment.
- They can be combined with biofertilizer.
Conclusion:
About Author / Additional Info:
I am doing Ph.D (Agriculture) Plant Pathology from S.K.N. Agriculture University, Jobner (Raj.)