(1) Plant Diseases:
These are incited by different agents — bacteria, viruses, cell-worms and fungi; of these the fungi cause the most severe losses. They destroy field crops, forage crops, fruit and nut crops, vegetable crops, drug plant crops and ornamental crops.
Disease causing fungi are found in class Phycomycetes, Ascomycetes, Basidiomycetes and Fungi Imperfecti. No species of Myxomycetes are known to cause disease in plants, except mushrooms. Some of the important diseases are listed in the given table.
Fungi infect many economically important plants and minimize the yield of food grains considerably. In 1945 late blight of potato (caused by Phytophthora infestans) destroyed millions of acres of potato crop and caused famine in Ireland, it resulted in the death of about a million people and almost the same number of people migrated to other continents. Similarly, the 1942 Bengal famine which resulted in the death of two million people was due to destruction of rice crop by brown leaf spot disease caused by Helminthosporium oryzae.
(2) Human Diseases:
Several fungi are responsible formycoses and tropical diseases of man and animals. Some of the important diseases caused by fungi are given in the related table.
(3) Destruction of timber and timber products:
Several fungi like Polyporus, Chloros-plenium, Penicilium divaricatum, Fusarium negundi. Pori microspora, Lentinus lepidens are responsible for decay of standing trees, decay of felled timber, sap stains and decay of wood in various uses.
(4) Tropical Deterioration:
This term applies to the destruction of such articles as textile, wool, tent age, binoculars, gunsights, cameras, leather goods, plastic articles, photographic films, paper and paper goods, radios, electronic goods etc., which are destroyed by fungi and rendered unfit for use.
(5) Food Spoilage:
Besides microorganisms, members of Mucorales (e.g., Rhizopus, Mucor), yeasts, Moniliales, Aspergillus oryzae. Penicillium digitatum are chief cause of food spoilage. These are saprophytic fungi which grow on food articles such as bread, jam, pickles, meat etc.
For instance, food items are spoiled by yeasts, Aspergillus otyzae, Penicillium digitatum etc.
Dairy products are spoiled by Aspergillus repens, Mucor, Penicillium, Cladosporium, Oiduni lactis, etc.
Fruits and fruit preparations are spoiled by Penicillium digitatum, Debr,omyces, Zygosacchwomyces etc.
Vegetables are spoiled by Rhizopus nigricans and R. tritici.
(6) Spoilage of Stored Grains:
A number of fungi, particularly some Ascomycetes and Fungi imperfecti are highly destructive of food grains like wheat and maize, and make them unfit for human and cattle consumption. Many infected grains carry fungal hyphae which cause seed-borne diseases in crops. Seeds or rye infected with Claviceps purpurea (ergot) causes abortion in pregnant ladies.
(7) Mushroom poisoning:
Deadly poisonous toadstools such as Amantia sp and others have invariably been mistaken for edible mushrooms and have taken a toll of life. Mushroom poisoning is known as mycetimus.
(8) Fungal toxins:
Some fungi produce toxic alkaloids and other toxic compounds.
For instance:
Claviceps purpurea, a parasitic fungus (causing ergot of rye) contains a powerful poison. When eaten it causes gangrenes and convulsions. LSD (Lysergic acid diethylamide), a hallucinogenic and hypnotic compound, is also obtained from claviceps. Besides this, some fungi secrete a group of toxic compounds called aflatoxins. Aspergillus flavus, an important toxin producing fungus frequently infects ground nut. Animals eating such nuts fall sick.