Importance of micro-organism in agriculture with examples of commercially important plant pathogens

Plant Pathology

            It is derived from two Greek words i.e. Pathos= Disease or Suffering and Logos = to study

“It is the study of plant diseases caused by plant pathogens”

Pathogen

            Any organism or micro-organism which lives, feeds and multiplies on host and also cause diseases.

Parasite

            Any organism or insect which lives feeds and multiplies on host and may cause disease.

Disease

Any deviation from normal functioning is called disease. OR

“It is a continuous process due to some biotic or non-biotic factors which cause abnormality in the physiology, morphology and genetics of plant or its part that reduces quality or quantity or both above economic levels”.

            Disease may be caused by

  1. Biotic agents such as plant pathogenic fungi, bacteria and nematodes.
  2. Abiotic agents such as temperature, Relative humidity, Rain fall, Fog, Imbalance of nutrients and pH etc.
  3. Mesobiotic agents such as viruses

What are microorganisms?

            A microorganism or microbe is a microscopic organism, which may be single-celledor multicellular. Microorganisms are very diverse and include all bacteria, archaea and most protozoa. This group also contains some fungi, algae. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists classify viruses and viroids as microorganisms.

Importance of Micro-Organisms

VIRUSES

Harmful aspects

  • Cotton leaf curl disease is caused by CLCuV
  • Tobacco mosaic disease is caused by TMV
  • Sugarcane mosaic disease is caused by ScMV

 

Beneficial aspects

  • Used to kill insects as bio control agents
  • Used in genetic engineering
  • Some viruses are the sources of enzymes such as RNA polymerases
  • Viruses are the most efficient means of gene delivery
  • Color breaking agent in ornamental plants

BACTERIA

Harmful aspects

  • Xanthomonasaxonopodiscauses citrus canker disease in citrus
  • Erwiniaamylovora causes fire blight of pear, peach and apple
  • Soft rot of vegetables caused by Erwiniacarotovora in tomato and Brinjal etc.
  • Most can cause food spoilage
  • Some bacteria can cause process failure by clogging process systems
  • Cause foul smelling gas
  • Different species of Streptococcus, Micro­coccus and Lactobacillus cause spoilage of milk and different milk products

Beneficial aspects

  • Used as a vector in genetic engineering
  • Used for fermentation process (milk to yogurt)
  • The lactic acid bac­teria are used in the preparation of butter, cheese
  • Acetobacteraceti, the acetic acid bacteria are used in the conversion of alcohol to acetic acid
  • Important for symbiosis process e.g. Rhizobium
  • Used for antibiotic preparation e.g. Streptomyces
  • Used in transgenic cotton (BT. Cotton)
  • Disintegrate dead biological materials ( compost)
  • These Can produce useful gas( methane)
  • Can help in digestion
  •  Used in the ret­ting of jute, hemp and flax fibres e.g. Clostridium tetani, C. botulinum 

Nematodes

Harmful aspects

  • Economic losses due to diseases
  • Causes citrus decline in citrus
  • Wheat ear cockle and root-knot disease is caused by nematodes

Beneficial aspects

  • Used to control insects by biological method
  • Improve soil fertility

FUNGI

Harmful aspects

  • Economic losses due to plant diseases e.g. early and late blight of potato.
  • Lather, paper, timber and textile industry has been destroyed by species of Polyporus and Armillaria, Mucor, Trichoderma
  • Food industry specially pickles and pasteurized foods are destroyed
  • Different types of food are destroyed by different fungi like Mucor, Aspergillus, Penicillium, Rhizopus etc.
  • Poisonous mushrooms which called as death caps e.g. Amanita phalloides produce toxinslike α-amanitin causes lesions of stomach cells 
  • Well-known hallucinogenic drug, is extracted from the sclerotia of Clavicepspurpurea.

Beneficial aspects

  • Bakery products are formed by fermentation e.g. yeast
  • Some fungi are edible such as mushroomse.g. oyster mushrooms, Button mushrooms
  • Ganodermalucidum and Agaricussubrufescensenjoy usage as therapeutics in traditional Chinese medicine.
  • The shiitake mushroom is a source of a clinical drug called Lentinan.
  • Fungi are also used to produce industrial chemicals, including citric, malic and lactic acids.
  • Fungi are easy to handle for research purposes
  • Some antibiotics like penicillin is formed from fungus called penicillium
  • Some beneficial fungi are helpful to fertile the soil
  • Some fungi are used as insecticides i.e. biological control e.g. coelomyces is used
  • to kill mosquitoes

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