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In this article we will discuss about the economic importance and somatic structures of deuteromycetes.
This is a heterogenous group of many types of fungi whose normal sexual stage (also called perfect stage) is absent or unknown. But in many of them heterokaryosis and pansexuality have been reported. Due to lack of information about the normal sexual stage these fungi cannot be assigned to the three main classes of fungi which have already been described.
Since these fungi apparently lack sexual stage, they are called Fungi Imperfecti or Deuteromycetes and have been taxonomically categorized as Form-class Deuteromycetes adding the prefix form to the taxonomic category class and categories below the rank—class. The use of the prefix form indicates an entirely artificial and temporary grouping of these fungi.
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This form-class is entirely artificial and has been created for the temporary grouping of these fungi pending discovery of perfect stage that they belong either to the Ascomycetes or the Basidiomycetes. Many of these fungi may be reduced forms and might have lost the power to reproduce sexually.
But, in general, it has been seen that a large number of fungi whose sexual stage was not worked out and hence are grouped for long time under the Form-class Deuteromycetes. In course of time and investigation perfect stages of some of them have been worked out.
When the perfect stage of a fungus previously referred to the Deuteromycetes is discovered, depending on the nature of spore produced by karyogamy and meiosis, the organism is transferred to the appropriate class of fungi. According to the rules of nomenclature, a name based on the perfect stage always takes precedence over one based on an imperfect stage, regardless of which name is the older.
In the phvlogenetic classification scheme based upon the oospore, zygospore, ascospore, and basidiospore there is no space for the fungi solely reproducing asexually. They have been given the name Fungi Imperfecti or Deuteromycetes.
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By this was formerly meant that these forms were ‘incomplete’ in their life cycles, lacking the sexual or perfect stage. It also meant that they were incompletely known but that the future would bring us more complete data regarding the sexual stage.
It is very much established that these imperfect stages are not autonomic (i.e., independent) species, but are connected with a sexual stage, whether this stage is known or not. It must not be overlooked, however, that some of them may lack the perfect stage, i.e., that the fungus always lives in its asexual stage, the reason being that they never produced spores by sexual method or that this power has been lost.
In the broadest sense the Fungi Imperfect include all the existing fungi which reproduce solely by asexual means and even those of the fungi which produce no spores at all. These organisms are placed in so-called form-genera with form-species, which are based on certain morphological characters.
But their true relationships being not known and hence they do not represent natural groups of fungi. The form-genera are included under form families which are again placed under form-orders of which the highest taxonomic category is form-class.
A large proportion of the fungi which have been removed from the Deuteromycetes on discovery of the perfect stage prove to be Ascomycetes but some, on the contrary, are Basidiomycetes.
Even though the zygospore or oospore stages of certain Phycomycetes have never been observed, these species are commonly placed among the Phycomycetes rather than among the Deuteromycetes. This is because of the aseptate nature of hyphae. Besides these, many rusts are known only in the aecial or uredial stage.
They are classified under an artificial group ‘Uredinales Imperfecti’ in which are included the form-genera: Aecidium, Peridermium, Caeoma, Roestetia, and Uredo.
The Deuteromycetes occur as saprophytes and parasites. The parasitic Deuteromycetes cause diseases of plants, animals and human beings.
Economic Importance of Deuteromycetes:
The Deuteromycetes are of great economic importance since, in addition to causing plant diseases, they cause several diseases of human beings. Again some are useful in controlling some of the soil-borne plant diseases.
i. Plant Pathogens:
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A number of species is parasitic on higher plants, causing serious diseases of leaves and fruits.
Special mention may be made of, Alternaria solani causes early blight of potatoes, Helminthosporium oryzae causes brown spot of rice, Pyricularia oryzae causes blast of rice, Septoria tritici causes leaf blotch of wheat, Colletotrichum gloeosporioides causes anthracnose of mango, Fusarium oxysporum var. cubense causes panama wilt of banana, Fusarium udum causes wilt of pigeon pea, and Cercospora personata causes leaf spot or tikka disease of ground-nut.
ii. Human Pathogens:
Most of the mycoses are induced by the Deuteromycetes. Fungi causing diseases of the skin of human beings, animals, or both are known as the dermatophytes or ringworm fungi and the diseases are dermatomycoses (sing, dermatomycosis). These fungi cause ringworm of the scalp (found chiefly in children) or other hairy parts of the smooth skin, of the nails and of the hands and feet.
Ringworm of the feet is known popularly as athlete’s foot. Trichophyton gypseum and T. purpurium cause athlete’s foot. Another disease, called moniliasis, chiefly of the fingers, is caused by Candida albicans. Species of Candida also cause a throat and mouth disease called thrush, pulmonary infections, infection of the mucous membranes of the genital organs, and various other diseases.
iii. Biological Control of Soil-Borne Diseases:
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Several of the Deuteromycetes are able to trap nematodes (microscopic roundworms that often infest the roots of crop plants) by forming hyphal rings which constrict about the nematode when stimulated by contact.
Special mention may be made of Arthrobotrys oligospora, Dactylella cionopaga whose mycelia form sticky processes, loops or branches to which nematodes adhere, other hyphae then invade and digest them. Thereby these Deuteromycetes reduce the disease incidence due to nematode of the crop plants.
Somatic Structures of Deuteromycetes:
The thallus of the Deuteromycetes is composed of well-developed mycelium of septate branched hyphae, exception being false yeasts (Cryptococcus, Torulopsis, and Brettanomyces) which possess yeast-like somatic body. The hyphae may be simple and short, or long and much branched. The hyphal cells are usually multinucleate. They possess perforated septa.
Through these perforations cytoplasmic streaming and nuclear migration take place from cell to cell. The nature of septa is very much similar to that of the Ascomycetes which suggests affinities between the Deuteromycetes and the Ascomycetes.
