ADVERTISEMENTS:
In this article we will discuss about the economic importance of basidiomycetes.
Many of the Basidiomycetes are of great economic importance because of their beneficial as well as harmful nature. Some of them are the causative agents of most destructive diseases of our cereal crops.
To this category belong the smut diseases of com, wheat, oats, and barley as well as the wheat rusts. They destroy several million rupees worth of crops every year.
ADVERTISEMENTS:
Some of the higher Basidiomycetes such as the pore fungi are the common wood rotters. They destroy lumbar and timber. Mushrooms which also belong to this group are of great economic value as food.
They are regularly cultivated for being delicious. The young fleshy sporophores of many species of puff balls (Lycoperdon and Clavatia) are also edible. Clavatia contains an anticancer substance calvacin.
The toad stools, however, are poisonous. Some of these such as Amanita are fatally poisonous whereas others cause only discomfort. Many members of this class form ectotrophic mycorrhizal associations with the roots of forest trees.
The association is mutually beneficial. The fungus obtains sugars and other organic substances from the roots of the tree partner whereas the mantle of the fungal partner serves to pass on nitrogen, phosphorus, and other elements absorbed by the mycelium to the root.
ADVERTISEMENTS:
The saprophytic Basidiomycetes play a significant role in decomposing the dead fallen leaves and other forest litter converting waste material and returning it to the soil.
Origin and Phylogeny:
Two hypotheses have been put forth to explain the origin of the Basidiomycetes. They are the Ascomycetean hypothesis and Phycomycetean hypothesis. The consensus of opinion now favours the first view.
Ascomycetean Hypothesis:
According to this hypothesis, Basidiomycetes have evolved from Ascomycetes. This view is based on the fact that the Basidiomycetes resemble Ascomycetes more closely than any other class of fungi.
ADVERTISEMENTS:
These resemblances are:
1. Their hyphal structure is similar.
ADVERTISEMENTS:
2. In both the classes plasmogamy is not immediately followed by karyogamy. It is delayed for some time so that the resultant fusion cell contains two nuclei.
ADVERTISEMENTS:
3. Secondary mycelium is homologous to the ascogenous hyphae of the Ascomycetes.
4. Clamp connections of the Basidiomycetes are homologous to the croziers of the Ascomycetes.
5. Asexual reproduction takes place by means of conidia which are produced in the same way in both the classes.
6. Basidia are homologous to the asci. Both have a similar origin and early development. In fact basidium is considered an early evolutionary development from an ascus of the Ascomycetes.
ADVERTISEMENTS:
7. Basidiospores are homologous to the ascospores.
8. Basidiocarps are comparable to the ascocarps.
From the above-mentioned similarities mycologists conclude that the Basidiomycetes have arisen from the Ascomycetes. In fact they believe that a basidium is an evolutionary development from an ascus.
The fact that in some Ascomycetes the ascus produces only four ascospores gives further support to the close affinity between the two classes.
ADVERTISEMENTS:
The views regarding evolution within the Basidiomycetes are rather speculative. Some mycologists think that the Basidiomycetes with septate basidia (phragmobasidia) are nearer to the ancestral Ascomycetes.
On this basis the Heterobasidiomycetidae such as rusts (Uredinales) are considered primitive. The rust spermagonium suggests a relationship to the Ascomycetes.
According to this view, the unseptate basidium (holobasidium) of the Homobasidiomycetidae is more advanced and derived from the septate basidium by simplification in which the septa disappeared.
The massive fructifications of the Homobasidiomycetidae support the view that they are more advanced than the Heterobasidiomycetidae.
Some mycologists, however, maintain that the Heterobasidiomycetidae are more advanced. They have arisen from the simpler members of the Homobasidiomycetidae much like the ancestors of Agaricus.
This viewpoint is supported by the fact that the unseptate basidium (holobasidium) is very much similar to the unseptate ascus. According to this interpretation, Homobasidiomycetidae are more primitive and closer to the ancestral Ascomycetes.
