In this article we will discuss about:- 1. Habit and Habitat of Polyporus 2. Mycelium of Polyporus 3. Economic Importance of Polyporus.
Habit and Habitat of Polyporus:
It is a cosmopolitan genus including about 50 species. All grow parasitically on the roots, trunks and larger branches of trees. They are common on dead or dying, standing or fallen tree trunks.
Rarely do they occur on grass and other herbaceous roots. They cause brown wood rot of various forest and shade trees and are known as the wood rotters.
Some attack and destroy timber. Dalbergia, Albizza, Mulberry, birch, oak and other timber trees are the common hosts.
Mycelium of Polyporus:
It is inconspicuous and subterranean. At first, it grows in the soil near the host roots. Eventually it attacks the roots and grows beneath the bark. The mycelium is formed by the germination of basidiospores.
It consists of numerous white, slender, branched and septate hyphae. The cells of the primary mycelium are uninucleate. Soon the cells become binucleate by hyphal fusions.
The binucleate or dikaryotic cells by elongation and division by clamp connections form the dikaryotic mycelium. The secondary or dikaryotic mycelium is long-lived.
As the parasitism becomes more severe the mycelium forms a complete, thick layer of hyphae around the central woody cylinder. The hyphae secrete enzymes which digest the lignified walls of the wood cells.
Basidiocarp (Fig. 15.12 A):
From the dikaryotic mycelium develop the basidiocarps. Each basidiocarp appears as a rounded dense knot of hyphae. It arises from the subterranean mycelium. As the knot grows it bursts through the bark. It gradually increases in size. Soon it becomes differentiated into a short stalk, or the stipe terminated by a rounded cap-like structure, the pileus.
At this stage the basidiocarp is soft and pliable. Towards maturity it becomes woody, corky or leathery. These fructifications in Polyporus last for a single season (annual) and constitute the only visible part of the fungus. In the wood inhabiting species they grow horizontally from the surface of the trunk. Many species of shelf fungi (Fames) have perennial basidiocarps which produce spore forming hyphae in annual layers.
The stipe is brown or dark brown in colour, about 2-6 inches in length. It is made up of numerous hyphae compacted together. At its top it bears an expanded structure, the pileus.
The attachment of the stipes to the pileus varies from a central to an excentric position in different species. The upper surface of the pileus is flat with a slightly undulating or smooth surface. It is brown or lightly coloured. It is marked with a few concentric brown or whitish brown rings near the periphery.
Polyporus versicolor has a zonately marked pileus. The lower surface of the pileus is smooth and flat. It has no radiating gills. Instead it bears numerous, fine pores in the form of minute circular holes. They are the openings of many small tubes (Fig. 15.12B). They give a porous appearance to the undersurface of the pileus. Each pore leads inwards into a hollow tube lined by a fertile layer called hymenium.
The hymenium is made up of sterile cells, the cystidia and the spore producing club-shaped cells, the basidia (Fig. 15.12C). The latter project slightly into the cavity of the tube and are somewhat larger than the cystidia. Each basidium bears four spores, each raised on a short sterigma.
The spore output is enormous rather fantastic. A single basidiocarp may produce several billion spores. They escape through the pores and are dispersed by air and insects. After the discharge of all the basidiospores, the basidiocarp degenerates.
The basidiospores are tiny, oval structures, white or brownish in colour. Each under suitable conditions germinates to form the primary mycelium.
Economic Importance of Polyporus:
The fructifications of Polyporus betulinus are used in the manufacture of charcol crayons. In olden times the upper tissue of the pileus was considered an efficient razor strop. Some parasite species cause disease of forest and shade trees.
A few attack and destroy lumbar. P. squamosus attacks and damages living trees of several genera and destroys structural wood. P. betulinus is a destructive parasite of beach, oak, birch and other conifers. The saprophytic polypores are active agents of wood decomposition. A few soft, fleshy species are edible and sold in local markets. P. tuberaster and P. tunetanus are even cultivated in a primitive way.
