In this article we will discuss about:- 1. Introduction to Polyporus 2. Vegetative Structure of Polyporus 3. Reproduction.
Introduction to Polyporus:
The genus is named Polyporus (Gr. poly — many; poros — pores) because of the presence of numerous fine pores on the under-surface of the fruit bodies. For the above reason, members of the family Polyporaceae are commonly called pore fungi and the outer margin of the fruit body looks like first brackets and thus called bracket fungi.
Out of many, 159 species are found in India. The genus has both harmful and useful members.
The harmful members cause damage to both living trees and dead logs (Fig. 4.64). Important wood-rotting parasites are:
1. P. sulphureus, the sulphur mushroom grows on oak, base of bamboo plants and can be easily recognised because of its bright yellow surface.
2. P. abietinus. It causes decay of Abies sp.
3. P. cinnarbarinus. It causes decay of oak branches and is easily recognised by their cinnabar red colour with corky fruit bodies.
4. P. betulinus. It causes heart rot of birch trees.
5. P. squamosus. It causes heart rot of elms and sycamore.
6. P. glomerata. It causes wood decay of red maple.
The useful members are:
7. P mylittae. It is found in Australia and known as ‘black fellow’s bread’ where sclerotia are edible. The sclerotia attain a weight of 13.5-18 kg (30-40 lbs) or more.
8. P. frondosus, P. leucomelas and P. umbellatus are the edible members.
Vegetative Structure of Polyporus:
The vegetative body is mycelial and composed of slender, branched and septate hyphae. Initially, the mycelia are monokaryotic, those developed from germination of spore. The hyphae are much branched and soon become dikaryotic as a result of somatogamy. The dikaryotic hyphae bear clamp connection at the septa.
Reproduction in Polyporus:
Polyporus reproduces by both asexual and sexual means.
1. Asexual Reproduction:
It is very rare. It takes place by conidia developed either on dikaryotic mycelium or on sterile fructifications. On germination they develop dikaryotic mycelia.
2. Sexual Reproduction:
Sexual reproduction is somatogamous. The species are heterothallic and the fusion between two somatic and monokaryotic mycelia (somatogamy) of opposite strains results in the formation of dikaryotic mycelium. The dikaryotic or secondary mycelium is perennial, which may survive for several years. At regular interval, during favourable condition, fruit bodies or basidiocarps are developed.
Development of Fruit Body (Basidiocarp) in Polyporus:
The development of basidiocarp from the secondary mycelium is not clearly understood. Initially, it appears as a spherical knob-like structure which gradually comes out by bursting the bark or soil. With further development the knob may differentiate into either stalked or sessile sporophore.
The stalked sporophore (P. betulinus) has definite stalk or stipe of about 5-15cm in height, bearing a pileus of about 2 cm in diametre. In most species, sporophores are sessile (P. sulphureus, P. consor, P. adustus, P. borealis etc.) and attached laterally with the substratum. At maturity, the fruit bodies may look like bracket, shelf or knob.
Structure of Fruit Body (Basidiocarp) in Polyporus:
In stipitate fruit body, the stipe bears an apical umbrella-shaped pileus. In sessile type, the fruit bodies are attached directly with the substratum and then projected outwardly and form various shapes.
On the ventral surface, the pileus is studded with many fine pores, leading into hollow tube-like structures. The tubes are lined internally with hymenium, composed of basidium bearing basidiospores and sterile paraphyses.
The basidiocarp is made up of three types of hyphae:
These are:
1. Generative hyphae. Hyphae are thin-walled with dense cytoplasm and may or may not have clamp connections (Fig. 4.65A).
2. Binding hyphae. Hyphae are much branched, narrow and thick-walled (Fig. 4.65B).
3. Skeletal hyphae. Hyphae are unbranched, thick walled with narrow lumen (Fig. 4.65C), developed as lateral branch from generative hyphae.
Based on the types of hyphae present, the basidiocarps are of three types.
These are monomitic, dimitic and trimitic:
1. Monomitic. This type consists of only generative hyphae (P. adustus).
2. Dimitic. This type consists of generative hyphae along with either binding or skeletal hyphae (P. sulphureus).
3. Trimitic. This type consists of all the three kinds of hyphae (P. versicolor).
V.S. of Fruit Body in Polyporus:
V.S. of the fruit body shows the following five layers from upper to the lower side (Fig. 4.66):
1. Pileus Surface:
It is the upper surface of fruit body and consists of a thin zone of thick- walled hyphae.
2. Context:
Next to pileus is the context, it consists of very fine anastomosing hyphae with large and irregular spaces between them. Sometimes the context is differentiated into upper soft and lower hard and firm layer, called duplex.
3. Tube Layer:
Next to context is the tube layer, it consists of vertically placed tubes which vary in length according to the size of the fruit body. The tissue lying between the pore tubes consists of generative and skeletal hyphae, called dissepiment (Fig. 4.67).
4. Pore Surface:
It is the lower surface of the fruit body, where tubes open.
5. Hymenium:
The hymenium is lined in the inner surface of the pore, consists of basidium along with paraphyses and rarely with cystedia (Fig. 4.67).
Section of Pore Tube in Polyporus:
From the dissepiment tissue, short branches of hyphae develop at right angles throughout the length of the tube, those form the hymenial layer.
The hymenial layer consists of the following (Fig. 4.67):
1. Basidium:
These are fertile, clavate and single celled structures, slightly project out from the hymenial layer. The basidium bears four sterigmata at its apex from which four basidiospores are abstracted.
2. Paraphyses:
These are sterile structures, remain intermixed with basidium in the hymenial layer and help in spore dispersal.
3. Cystedia:
These are sterile structures, usually conspicuous, larger than basidium, remain intermixed with basidium in the hymenial layer and help in spore dispersal. Young basidia are single celled and binucle- ate (dikaryotic). With maturity both the nuclei undergo fusion, followed by meiosis.
Four sterigmata are developed at the apex of basidium, those bear single haploid basidiospores. The spores are discharged in the pore tube and gradually come out through the pore tubes. Discharge of spores continues from weeks to months and during this period millions of spores are liberated. On germination the spores develop into monokaryotic mycelium.
The life-cycle of Polyporus is given in the Fig. 4.68.
Some common Indian species:
Polyporus betulinus, P. agariceus, P. circinatus, P. gilvus, P. cubensis etc.