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Biological Control of Plant Diseases


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Biological Control of Plant Diseases

  1. 1. What is biological control of plant diseases ? Biological control involves the use of one living organism to control another. This management technology has received much attention in recent times.
  2. 2. Pros •Specific to a particular pest. •Cheap after startup. •It works most of the time. Cons •Does not have a broad-spectrum as insecticides. •Expensive at startup. •Doesn't completely destroy a pest
  3. 3. A Parasitoids Biological Control Agents B Pathogens C Predators Entomopathogenic micro-organisms (Bacteria, Fungi, Viruses ,Protozoa and Nematodes). Antagonists of Plant Diseases D E
  4. 4. Parasitoids Each parasitoids requires only one host, which it kills for its development into a free living adult. Parasitoids are of the same size as the hosts , or sometimes even smaller. Mechanism The Female parasitoid lays eggs inside or on an insect host. Legless larva on hatching feed on the hosts internally or externally. Many adult parasitoids feed on nectar or pollen and serve as important pollinators. Eggs of female Trichogramma chilonis Examples Trichogramma,Ichneumoid,Scelionoid,Braconid, Encryrtid,Eulophid,Chalcid wasps and Tachinid Flies
  5. 5. Revolution of Trichogramma chilonis Trichogramma chilonis has been successfully released in Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana, Gujrat , Uttrakhand , Uttar Pradesh, Bihar , Karnataka, Tamil Nadu ,Maharashtra and few other states. It has given 56-82% protection against the sugarcane tissue borers.
  6. 6. Pathogens Pathogens are disease causing organisms e.g. Bacteria, Fungi, Viruses ,Protozoa and Nematodes in Insect Pests which kill their host or debilitate the future generation. Mechanism The infected insects are unable to feed properly ,remain stunted, lose their body colour and get paralysed. Dead insects are often found hanging on the plants, or a fungal growth on the body of dried insect could be easily located in the field. Caterpillar, Pseudoplusia includens , killed by entomopathogenic fungus Nomuraea rileyi , white-disease in soybean crop.
  7. 7. Predators These are free living and larger in size than their prey, requiring several preys to complete their life cycle. Some smaller predators release a powerful poison, use a trap or hunt in groups to be more effective. Mechanism Green lacewings (very common and important predator of crop pests). The female lays small pale green, oval shaped eggs at the end of long silken stalks, which ultimately turns grey.The larva have well developed legs and pincer like jaws with which they suck the body fluids from the prey
  8. 8. Antagonists of Plant Diseases The microorganisms used in biological suppression of plant diseases which grow in association with plant diseases are termed as antagonists. An antagonist microorganism adversely affects the disease causing organism by following:- Competition:- the competition which takes place between two organisms in terms of nutrients etc. Antibiosis:-an association between organisms that is injurious to one of them. Antibiosis, is provided by marigold (Tagetes species) roots, which release terthienyls, chemicals that are toxic to several species of nematodes and fungi.
  9. 9. Hyperparastism:-the parasitic habit of one species upon another parasitic species which is harmful to one of them. Mycoparasitism:-a parasitism of a fungus(host) by another fungus(mycoparasite). Trichoderma harzianum, used as seed treatment against pathogenic fungus(Sclerotium rolfsii) on chickpea and sugarbeet
  10. 10. Field Release Methods Inoculative Release:- The release of relatively small numbers of natural enemies that are expected to colonize, reproduce, and spread naturally throughout an affected area. Augmentation(growing larger) of Natural Enemies:- It is a method of increasing the population of a natural enemy that attacks a pest. This can be done by mass producing a pest in laboratory and releasing it into the field a the proper time. Application of microorganisms:-Antagonists like Trichoderma and Glicladium spp. introduced with planting material such as seeds and seedlings of vegetable crops to suppress damping off and root rots are one kind of inoculative release.