Harmful Effects of Fungi

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Harmful Activities of Fungi

There are many fungal activities which are harmful to mankind. Fungi incite many diseases in plants, animals and human beings. They cause considerable loss to food, vegetable and fruit crops. They destroy valuable timbers and cause spoilage of food and many other useful articles.

Fungi as Pathogen:

1. Plant Disease

Most of the parasitic fungi cause diseases in plants, especially to flowering plants. The common fungal diseases of plants are smuts, rusts, mildews, blights, rots and wilts. They are responsible for destroying crops worth billions of rupees. They may result even into a catastrophe if allowed to run their course unchecked. Disastrous Irish potato famine of 1845-49 caused by Phytophthora infestans was responsible for taking lives of approximately one million people. Similarly, tobacco yield was reduced by over 60% in North Africa and Middle East in 1962 because of the infection of Peronospora tabacina. In England over five million elm trees were destroyed during 1967-77 because of the infection of Ceratocystis ulmi.

Plant diseases caused by fungi:

Fungi-    Plant disease

  1. Synchytrium endobioticum- Wart disease of potato
  2. Pythium aphenodermatum- Stem rot of papaya
  3. Phytophthora infestans- Late blight of potato
  4. Erysiphe polygoni- Powdery mildew of peas
  5. Erysiphe graminis- Powdery mildew of wheat
  6. Peronospora pisi- Downy mildew of peas
  7. Albugo candida- White rust of crucifers
  8. Sclerospora graminicola- Green ear of bajra
  9. Puccinia graminis tritici- Black rust of wheat
  10. Urocystis tritici- Flag smut of wheat
  11. Ustilago tritici- Loose smut of wheat
  12. Ustilago hordei- Covered smut of barley
  13. Ustilago nuda- Loose smut of barley
  14. Ustilago kolleri- Covered smut of oat
  15. Ustilago scitamineae- Whip smut of sugarcane
  16. Sphacelotheca sorghii- Grain smut of jowar
  17. Tolyposporium penicillari Smut of bajra
  18. Alternaria solani- Early blight of potato
  19. Cercospora personata- Tikka disease of groundnut
  20. Colletotrichum falcatum- Red rot of sugarcane
  21. Pyricularia oryzae- Blast disease of rice
  22. Fusarium udum- Wilt of arhar
  23. Plasmodiophora brassicae- Club root disease of crucifers
  24. Protomyces macrosporus- Stem gall of coriander
  25. Haemelia vastatrix- Leaf rust of coffee

2. Animal diseases 

Several fungal species live parasitically on/in animals and they cause various disease. Some important animal diseases caused by fungi are given in Table.

Disease of animals caused by fungi:

Fungus Animal disease
1. Tinea rubrum Athelete foot
2. Trichophyton, Microsporum, Epidermophyton Ring worm
3. Mucor, Rhizopus Mucomycosis
4. Aspergillus Aspergillosis
5. Penicillium Penicillosis

Actinomycosis and black leg disease in animals are also caused by fungi. Members of Entomophthorales (e.g. species of Entomophthora) are parasites on insects and other animals. Similarly, members of Saprolegniales (e.g. species of Achlya and Saprolegnia) are parasitic on the fish. The fish of domestic aquaria are commonly infected by Saprolegnia ferax and S. parasitica. Ichthyophorus haferi is commonly known as a fish destroying fungus.

3. Diseases of human beings

Several fungi infect human beings, causing diseases of skin, respiratory tract, lungs, viscera, nasal sinuses, eye, liver and kidney. Some common diseases caused by fungi in human beings are listed in Table.

Wind borne spores of several fungi (e.g. Alternaria, Aspergillus, Chaetomium, Helminthosporium, Monilia, Phoma, Trichoderma) are allergic and cause distressing symptoms.

Table: Some common diseases of human beings caused by fungi

Fungus Human disease
1. Aspergillus flavus, A. fumigates, A. niger Aspergillosis
2. Elastomyces dermatitidis Blastomycosis
3. Candida albicans Candidiasis
4. Cladosporium corrionii Chromomycosis
5. Coccidiodes immitis Coccidiomycosis
6. Lipomyces neoformans Cryptococcosis
7. Geotrichum candidum Geotrichosis
8. Histoplasma capsulatum Histoplasmosis
9. Mucor pusillus Neuritis
10. Trichophyton purpureum Onychomycosis
11. Sporotrichum schenkii Sprotrichosis

Spoilage of Food Stuffs

A large number of food articles, if not properly stored, are spoiled by fungi, like Mucor, Rhizopus, Aspergillus, Penicillium and yeast. Species of Mucor and Rhizopus are commonly seen on the bread and pickle. Dairy products are spoiled by the species of Mucor, Oidium Torula, Penicillium and Cladosporium. Mucor mucedo and Rhizopus stolonifer spoil frozen meat by causing black spot disease. Some fungi can infect food stuffs even at a very low temperature, for instance, Cladosporium herbaceum can grow on meat stored at 6°C.

Several species of Alternaria, Aspergillus and Rhizopus cause post harves diseases in fruits and vegetables thus shortening their storage life. Oranges are destroyed by Penicillium digitatum and dried prunes and figs by Zygosaccharomyces. Debromyces and Zigopichid. Some common disease of fruits in storage are listed in Table 5.

Table : Some common diseases of fruits in storage caused by fungi.

Fungus Storage disease
1. Alternaria sp. Alternaria rot of apple
2. Aspergillus fumigatus Aspergillus rot of apple
3. Alternaria tenuis Alternaria rot of banana
4. Rhizopus stolonifer Soft rot of tomato
5. Rhizopus arrhizus Soft rot of potato

Deterioration of Articles

Many important paper documents, valuable leather articles, textiles, plastic, objects, photographic films, electronic goods, rubber, painted surfaces, etc. are spoiled by fungi. Chaetomium globosum, Aspergillus niger, Stachybotrys atra and species of Alternaria and Cephalosporium are some common fungi which spoil paper. Penicillium purpurogenum and species of Fusarium and Stachbotrys cause spot print on leather goods. Moulds are responsible for the damage of cellulose fibers. They weaken and discolour textiles and alter their affinity for dyes. Myrothecium verrucaria is notorious for its ability to degrade cellulose. The proteins of wool and silk are also degraded by moulds. Paints and painted surfaces like most organic substrates, are subject to attack by various fungi. The fungi mainly responsible for disfigurement or deterioration of paint surfaces are Pullularia pullulans, Phomaglomerata and species of Alternaria and Cladosporium. Several species of moulds are responsible for damaging glass components of optical equipments, electrical cables telephone poles, etc. Amorphotheca resinae may plug the pipers and valves of the fuel tanks of air crafts and might prove dangerous, especially during flight. This fungus also grows luxuriantly on aluminium alloy and may corrode the metal.

Jute articles are destroyed by Chaetomium globosum, Memnoniella echinata and Stachbotrys atra. Rubber products are spoiled by the species of Aspergillus and Penicillium.

Destruction of Timbers

Several fungal species like Polyporus spp. Serpula lacrymans Penicillium divarianum, Fusarium negundi, Coniophora cerebella and Lentinus lapidens are responsible for the destruction of valuable timbers. These fungi break down the components of wood and reduce mechanical strength of the wood. Armillaria mellea causes wood not diseases in several trees. Wood degradation by fungi is usually of two types white rots and brown rots. White rots cause degradation of brownish lignin, leaving white spongy cellulosic mass in the wood. On the other hand, in brown rots, degradation of cellulose takes place and a brown pinkish mass with predominance of lignin is left behind.

Some fungi like Ceratostomella, Chlorosplenium, Fusarium Lasiosphaeria, Penicillium and Trullula grow in sap wood and stain it Chlorosplenium aeruginosum and Penicillium divaricatum impart characteristic green and yellow stain to hard wood and Lasiospharia pezizula imparts grayish olive stain to heart and sap-wood.

Hallucinogenic Fungi

Some fungi, such as Amanita phalloides, A. verna and Boletus santanus, are highly poisonous and if ingested they may prove fatal.

Several mushrooms, such as Amanita muscaria, Psilocybe Mexicana and Panaeolus spp. secrete hallucinogenic substances like psilocybin and psilocin. These substances may destroy brain cells and power of human beings.

Mycotoxins

Many fungi produce mycotoxins which are responsible for food poisoning and other distressing symptoms. These mycotoxins may be broadly classified into the following three categories.

  1. Food toxins :

    These toxins are mainly responsible for food-poisoning. The toxin production can occur in most plant products, but cereal and oil seed crops are mostly contaminated. The following four groups of food toxins are mainly associated with human diseases.

    1. Aflatoxins : Aflatoxins the most potent carcinogens are produced by Aspergillus flavus, A. fumigatus, A. parasiticus and Penicillium islandicum, when they infest dried food and groundnut meal. They are highly oxygenated low molecular weight, heat stable, heterocyclic compounds. Eight forms of aflatoxins, B1, B2, G1,G2, M2, M2, B2a and G2a have been recognized. Of these aflatoxins B1, B2,. are the most important. Aflatoxins are derivatives of furanocoumarin. They bind with DNA and prevent its transcription and as such protein synthesis is inhibited. They cause liver cancer in animals and human beings. The clinical symptoms include jaundice, rapidly developing ascites, portal hypertension, etc.
    2. Ochratoxins : Ochratoxins, closely related derivaties of isocoumarin linked to 1-Bphenylalanine are mainly produced by Aspergillusochraceus and Penicillium viridicatum, when they infest stored maize, pea nuts, beans and mixed animal feeds. Of the nine ochratoxins, ochratoxin A is the most important. It causes tubular necrosis of the kidney, mild degeneration of the liver and enteritis of the small intestine in ducklings.
    3. Zearalenone: Zearalenone, a phenolic resorcyclic acid lactone, is produced by several species of Fusarium, such as F. graminearum and F. moniliforme, growing on maize. It causes esterogenic symptoms in swine.
    4. Trichothecenes : Trichothecenes are produced by several species of Cephalosporium, Fusarium, Myrothecium, Stachybotrys and Trichoderma. They posses a tetracyclic 12, 13- epoxytrichothecoene skeleton. Of the nearly 30 trichothecenes known, T-2 toxin, nivalenol and deoxynivalenol are most important. They are responsible for severe local irritation, inflammation, sub-epidermal haemorrhage and general necrosis.
  2. Ergot toxins-

    The sclerotia of Claviceps purpurea contain some poisonous alkaloids, like ergotamine, ergometrimine, ergocrystinine, ergocristine and ergonovin. Ergot poisoning in human beings causes diarrhoea, abdominal pain and vomiting. It also effects nerves and results in psychiatric disturbances.

  3. Mushroom toxins-

    Several mushrooms produce mycotoxins which cause diarrhea and vomiting in earlier stages, but in severe cases, liver damage, kidney failure complete unconsciousness and even death may lake place.

Amanita phalloides produces about ten toxins of these, phalloidin affects the plasma membrane of liver cells, and a-amanitin causes lesions in stomach and intestine cells. Gyromitrin, a highly fatal toxin is produced by the species of Helvella, such as H. esculenta, H. gigas, H. infula and H. underwoodii. Some species of Inocybe and Clitocybe produce the toxin muscarine. Species of Coprinus produce the toxin coprine, that affects the autonomic nervous system.

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