In this article we will discuss about the classification of aphyllophorales.
Family Polyporaceae of Aphyllophorales:
The Polyporaceae, or pore fungi grow on both living and dead trees (lignicolous), or less commonly on organic matter in the soil, a few are parasitic on other fungi. They are of enormous importance as they are largely responsible for causing disease of sending timber and decay of logs and timbers. The tremendous destruction of wood by these fungi is probably greater than by any other agencies including fire and man.
Some members of the Polyporaceae are saprophytes after the tree is dead. Again others grow on living trees typically attacking only the dead cells of which the wood is composed, but the enzymes they produce may kill some of the living cells and ultimately contribute to the death of the tree.
They very often do serious damage to mature standing timber, and also to lumber which is kept moist or in contact with the ground.
The visible portion of the fungus is the fruiting body (basidiocarp), produced by vegetative hyphae located in the bark and wood (Fig. 280A & C). Removal of such a basidiocarp from a tree in which the hyphae are living parasitically does not destroy the fungus or constitute a method to control its incidence.
The vegetative hyphae develop extensively in the substrate before a basidiocarp is produced, and appearance of it usually indicates that considerable decay has already occurred. Even after removing the basidiocarp the hyphae will continue to feed upon the wood and will subsequently form new basidiocarps.
The fungus gains entrance through wounds caused by various agencies like, fire, lumbering, prunning, insects, and storms. The hyphae spread into adjoining tissues, which they digest by means of cellulase and other enzymes. The enzymes are the chief weapons with which the hyphae invade the plant cells and bring about damage.
The enzymatic activity is exhibited at different stages of growth of hyphae for example, young vegetative hyphae, hyphae about to bear fruiting bodies, and hyphae with fruiting bodies.
The basidiocarps are usually large bearing pores which are often so small as to be barely visible to the naked eye. In texture they may be fleshy, corky, woody, or gelatinous to cartilaginous. In shape also the basidiocarps are extremely Variable.
They may be:
(i) A flat crust-like thin structure developed on the substrate with the pores on the outer side is known as resupinate,
(ii) A stretched out, partly crust-like and partly turned up at the edge forming a small bracket-like projecting margin is effused-reflexed;
(iii) The entire fruiting body growing erect with broad or narrow base forming an angle with the substrate producing a bracket- or shelf-like structure is termed reflexed; and
(iv) The one possessing a stalk or stipe of sterile tissue is stipitate and depending on the position of the stipe lateral or centrally placed, a stipitate fruiting body may be laterally stipitate or centrally stipitate respectively. The main bulk of the basidiocarp—hymenophore is composed of vertically arranged tubes the ends of which usually appear as pores on the lower surface (Fig. 280B).
The internal surface of the tubes of these pores is lined by the hymenium composed of basidia bearing basidiospores (Fig. 280E). Setae or cystidia are also sometimes present in the hymenium. Mature basidiospores escape through the pores. The pore tubes develop from an interwoven mass of hyphae forming a fibrous tissue which is known as the context (Fig. 280B).
The context may be thick or thin. The pore layer in a fruiting body may or may not be separable from the context. The pore tubes again may be shallow corrugations, uniformly deep-seated, sunken to unequal depths in the context, or the walls of the tubes form into toothed plates.
The shape of the pores may be:
(i) Circular called poroid (Fig. 281D);
(ii) Angular known as hexagonal (Fig. 281 A);
(iii) Intermediate between rudimentary lamellae (gills) and pores termed daedaloid (Fig. 281C); or
(iv) Almost resembling gills called lamellate (Fig. 281B). Pores vary from round to angular in Poria, Polyporus, Trametes, Gonoderma, and Forties-, hexagonal in Hexagonia; and labyrinthiform in Daedalea and Lenzites.
While the number of ports per mm. is an important character for a species, this is governed by the thickness of wall, the number of pores decreasing with increasing width of wall; thus both characters are important. The pore surface often changes in colour on drying.
Therefore its colour when fresh and also on drying should be recorded. The basidiocarps are also extremely variable in colour ranging from deep-red, white, brown, rusty-brown, yellowish-brown, black, or shades of different other colours. The upper surface of a basidiocarp may be smooth, laccate, hairy, zonate, or velvety.
The basidiocarps are annual or perennial. In perennial forms, stratification of horizontal layer of tubes corresponding to each year’s growth takes place (Fig. 280D). It is often possible to count the layers and determine the age of the basidiocarp, encountered in Fomes applanatus. In some cases the cavities of the new tubes are continuous with those of the preceding season.
In others, the new layer is separated from the old by a thin compact layer of hyphae. The spores in perennial forms are’ discharged continuously, day and night, over a period of several months. Stratifications of tubes do not always indicate perennial growth of the basidiocarp.
In Polyporus gilvus where pore tubes are stratified, the new growth is produced from mycelium within the host tissue at the base of the basidiocarp and not from any live mycelium of the previous year’s basidiocarp.
The hymenial configuration may exhibit toothed condition as in Irpex, but such forms are not included in the Hydnaceae, since the growing region is distinctly poroid.
Again, the genera Daedalea and Lenzites exhibit lamelloid or gilled hymenial surface like the Agaricaceae but are not included in the latter since the hymenial configuration in these two genera can be distinctly poroid or at any rate in the younger tubes at the margin.
Further, the consistency of the-fruit body in Daedalea and Lenzites, their persistent nature, lignicolous habit and ability to decay wood place these genera in the Polyporaceae and not in the Agaricaceae where the fruit body is usually fleshy and deliquescent and members do not commonly grow on wood and even then seldom decay.
The conventional genera under Polyporaceae are only treated. The recognition of Polystictus for species under Polyporus having very thin context is arbitrary and is thus no longer valid, and therefore the species usually recognized under Polystictus are placed under Polyporus.
A simplified key to the genera of the family Polyporaceae is presented below:
Basidiocarp always entirely resupinate, completely appressed to the substratum, without any pileus Poria
Basidiocarp pileate, rarely resupinate pore tubes not separate
Basidiocarp perennial, each year a tube layer added to previous layer so that pore tubes appear stratified, distinctly or indistinctly
Spores smooth on inner wall Fomes
Spores rough on inner-coloured wall, outer wall hyaline
Spores ovate to cylindric-ovate with the wall not uniformly thick, apex always thicker, truncate or rounded Ganoderma
Spores globose to subglobose, occasionally oblong with the wall uniformly thick Amauroderma
Basidiocarp annual, pore tubes in a single layer
Hymenium with folds that are joined into shallow pits or pores, over which hymenium is continuous or pores alveolate
Pileus waxy, hymenium with shallow net-like pores
Merulius
Pileus gelatinous, pores alveolate
Laschia
Pores daedaloid or approaching lamellate
Daedalea
Pore surface lamellate
Lamellae concentric
Cyclomyces
Lamellae not concentric
Lenzites
Pores hexagonal Basidiocarp sessile
Hexagonia
Basidiocarp stipitate or substipitate, pores arranged in radiating rows
Favolus
Pore surface with teeth, spine or warts in mature areas, usually poroid near growing region
Irpex
Pores circular to angular
Pore tubes sunk into an even depth into context forming a distinct stratum, their bases forming anunbroken straight line
Polyporus
Pore tubes sunk to unequal depths into context not forming a distinct stratum, their bases do not form a straight line
Trametes
Basidiocarp pileate or sessile, pore tubes isolated, free from each other, spores coloured
Fistulina
Genus Polyporus:
The genus Polyporus includes both saprophytic as well as parasitic species,-some of which are homothallic and others heterothallic. Basidiocarps occur on lumber, logs, living trees, and on ground. They are usually annual, but occasionally surviving for two to three years. The basidiocarps may be effused-reflexed, reflexed, or stipitate being fleshy to tough, leathery or woody in texture.
Pore tubes simple or stratified usually sunken into thick context to equal depths so their bases form a straight line. They are not separable from the surface of the context. Pores are circular to angular but rarely daedaloid. Hymenium forms a distinct layer along the pore tubes. Glavate tetrasterigmate basidia bear hyaline or coloured basidiospores. Cystidia, setae or setal hyphae may or may not be present.
The species Polyporus gilvus (Schw.) Fr. is a parasite on Shorea robusta (sal), Acacia arabica (babul), Dalbergia sissoo (shisham), and many other hardwood trees. It also grows saprophytically on a large number of hardwood trees, of which mention may be made of Quercus sp. The fungus causes a white rot.
It usually gains entrance into the living trees through wounds. It also behaves as a root-parasite and basidiocarps are common on exposed roots. Sometimes it causes severe damage to hardwood trees in conjunction with Ganoderma lucidum or with G. applanatum.
The basidiocarp of Polyporus gilvus is annual usually reflexed and hard to brittle in texture. The upper surface is with shades of yellow, brown or red and are either coarsely hairy with faintly zoned or smooth with concentric zonations. Context is thick yellowish-brown. It is composed of thick-walled yellowish-brown hyphae. Hymenial surface is yellowish-brown with long uniform or stratified pore tubes.
Pores are round and regular. Thick-walled dark-brown setae project into the pore tubes which are lined by basidia. The basidia are hyaline, clavate and tetrasterigmate. Each sterigma bears a single hyaline oval basidiospore.
The basidiospores on germination produce monokaryotic primary mycelia. The monokaryotic compatible mycelia by somatogamy, produce dikaryotic secondary mycelium from which the basidiocarp is developed. Life cycle of a species of Polyporus is presented in Figure 282.
Some Indian species of Genus Polyporus:
Polyporus agariceus Berk.; P. betulinus Fr.; P. circinatus Fr.; P. cubensis Mont.; P. gilvus (Schw.) Fr.