Q.1. Give life history of a mushroom you have studied.
Related Questions -
Q. Write short note on Basidium. (2012)
Q. Describe the development and structure of the fruiting body of any edible fungus studied by you. (2007)
Q. Basidiocarp of Agaricus. (2013)
Q. Describe the internal structure of gill of Agaricus. (2005)
Q. Draw neat and labelled diagram of V. S. of Agaricus gill. (2007)
Q. Give the systematic position of Agaricus. (2007)
Q. Write systematic position and important characters of Agaricus (2011)
Ans. Systematic Position
Division - Mycota
Sub-division - Eumycotina
Class - Basidiomycetes
Sub-class - Homobasidiomycetes
Series - Hymenomycetes
Order - Agaricales
Family - Agaricaceae
Genus - Agaricus
It is an edible fungus and is commonly called as mushroom. In U. P. it is called Kukarmutta and in Punjab as ‘Khumb’. It is commonly found during the rainy season and grows in moist and shady places as a saprophyte. It grows on dead organic substances particularly on humus soil, rotten logs of wood, tree trunks, in open fields, lawns etc. The most common species is Agaricus campestris or Psalliota campestris grows in open fields and is called as field mushroom. Agaricus rodmani is found growing in lownsand called as roadman’s mushroom. Fairy rings as commonly seen in grass lawns ands are considered as the dancing path of the fairies are nothing but Agaricus praerimosus and Marasmius oreades.
Structure:-
The mature plant body of common field mushroom is generally differentiated into two parts:
1. Somatic mycelium (grows in the soil)
2. Basidiocarp or fruiting body (The edible part grows above the soil).
1. Vegatative or Somatic Mycelium :-
The mycelium is subterranean and remains hidden in the soil. The primary mycelium is composed of simple hyphae. The hyphae are septate hyaline and form a thick tangled interwoven mass called the rhizomorph. The septa are perforated with a central pore to maintain the continuity of protoplasm of adjacent cells.
The cells of primary mycelium are uninucleate with oil globules and vacuolated cytoplasm (monokaryotic mycelium).
The two hyphae of opposite strain i.e. of (+) and (-) strain come in contact with each other. Plasmogamy results in the formation of dikaryotic cell or binucleate cell. The dikaryotic cell finally results in the formation of dikaryotic or secondary mycelium by clamp connections.
The underground dikaryotic mycelium is perennial and grows centrifugally i.e. it has the tendency to grow from a central point to the periphery, increases in diameter year after year. The old portions of mycelium decay and at the tips the mycelium collects to form spawns. On maturation the fruitification develop from it and appear in a ring. Such circles of mushrooms are often called as “fairy ring” the perfect rings are generally of 5 meters in diameter.
2. Fruitification (Basidiocarp):-
It is the aerial part of mushroom. It is the edible part and is very conspicuous measuring about 6-9 cm in height. It has two parts (i) stipe or stalk and (ii) Pileus or cap.
(i) Stiple or Stalk :-
The basal part of fruitification where maximum growth occurs is fleshy, cylindrical and pinkish white, swollen stipe.
(ii) Pileus or Cap:-
It is the umbrella like circular part found above the stipe. In the young condition the margins of pileus remain attached with the stipe by a thin membrane called velum. The velum breaks as the pileus increases in size and remains attached on stipe and this remaining part on stipe is called annulus. During young stage the pileus is convex and encloses a cavity called as gill cavity. From the roof of the gill cavity or from the under surface of pileus a large number of vertical plate like structures the gills or lamellae are given out. The gills or lamellae radiate from the margin of the pileus towards the stipe but are not joined to the stipe. A hymenial layer develops on smooth surfaces of gill and bears basidia and basidiospores. The pileus at maturity is 2-5 inches in diameter. The gills are fleshy and pink in the begining but becomes dark brown at maturity.
Internal structure of Stipe:-
Stipe consists of pseudoparenchymatous tissue made up of interwoven hyphae. The hyphae are more compact in the outer region and this region is called cortex whereas the inner region is made up of loose hyphae called medulla.
Internal Structure of Gill:-
The cross section of gill shows a central part called trama. The trama is made up of parallely interwoven mass of hyphae. On both sides of trama, is found a closely and compactly arranged tissue of pseudoparen chymatous cells called sub-hymenium. It is made up of short lateral branches given off by hyphal mass of trama. The cells of sub - hymenial layer gives rise to hymenium. Hymenium is fertile layer and consists of parallely arranged basidia intermingled with paraphysis in a palisade like manner. Each basidium is a club- shaped aseptate structure with four basidiospores borne on sterigmata terminally.
Basidiocarp Formation:-
The development of fruitification begins with the formation of a little button like aerial structure made up of interwoven hyphae given out form the sub-terranean hyphae . During growth fertile layer is demarkated in the form of a ring of deeply stained hyphae. Above fertile region the tissue grows rapidly to form pileus or cap. The growth below fertile ring forms the gill cavity. The gill cavity is small in the beginning but gradually enlarges. The gill cavity forms the gills or lamellae. The gill cavity is enclosed by a membrane on the underside by at velume. The velum ruptures at maturity and is seen in the form of annulus on the stipe. The fruitification is umbrella like which is convex in the beginning but becomes flat at maturity exposing the gills fully.
The gills are lined on both sides by fertile layer called hymenium. The hymenium has basidia and paraphysis parallely arranged in palisade like manner.
Development of Basidium and Basidiospores:-
Basidium is holobasidium. The sub - hymenial layer of fruitification is made up of dikaryotic hyphae which forms the basidia. During formation, the tips of sub-hymenial hyphae swell up to form club - shaped structures containing two nuclei of opposite strain. Here the two nuclei fuse (Karyogamy) to form a diploid nucleus. The diploid nucleus moves to the upper part of developing basidium. The diploid nucleus divides by a reduction division to form 4 haploid nuclei of which two are of (+) strain and two of (-) strain.
The basidium remains aseptate and gives out four fingers like out growths at the terminal side, called sterigmata each sterigma gives out a single basidiospore by budding. The haploid nuclei passes into the bud to form two (+) strain and two (-) strain basidiospores.
Fig. Development of basidiocarp.
The basidiospores are thin walled oval or spherical structures with a single haploid nucleus and are liberated by water drop mechanism at regular intervals. In cultivated species only two basidiospores are produced e.g., Agaricus bisporous.
Germination of Basidiospore:-
The basidiospores, when fall on a suitable substract and the atmospheric conditions are favourable germinates. It produces a germ tube and finally a well branched septate monokaryotic mycelium (Primary mycelium). It is either (+) or (-) strain depending upon the nature of the basidiospore. The primary mycelium later on produce secondary mycelium by dikaryotisation.
Q.2. What are fairy rings and how are they formed? (2002, 08)
Related Question -
Q. Write a short note on ‘Fairy Rings’. (2010)
Ans. The mycellium lying within the substratum is perennial and grows from the center with the result that it increases in diameter from year to year. The centrifugal growth of mycellium is followed by the death of older hyphae in the center. At the time of sporulation, the fruiting body or mushrooms are developed in a ring above the ground in lawns and pastures. Such circles of mushrooms are commonly called “fairy rings”, a name based on the ancient belief that mushrooms growing in a ring marked the path of dancing fairies. These fairy rings are best seen in Agricus praeimosus and Marasmius oreades. Fairy rings by Agaricus campestris are less common.The perfect rings of Agaricus are usually less than 5 mts in diameter. Imperfect rings may attains a diameter of 400 mts in certain other Agaricales. The circle of mushrooms or the fairy rings is invarriably accompanied by the concentric zone of deeply green grass some what interiorly. This green colour is due to the accumulation of nitrogenous substances. The mycelium may live for as many as 400 years and produces a crop of mushroom every year.
Q.3. Describe the economic importance of Agaricus. (2006)
Ans. Economic Importance of Agaricus: -
All species of Agaricus are edible. The only two exceptions are Agaricus silircola and Agaricus xanthodermis which are supposed to be slightly poisnous at times but not lethal. Mushrooms are a valuable source of nourishment being rich in high quality proteins ( 5-7%) and amino acids. For this reason they are often known as the vegetarians meat. They also contain a digestive enzymes that aids digestion. Besides they contain folic acid, vitamin B -complex and C several minerals like calcium, phosphorus, potassium, iron and copper. Because of high folic acid content the mushrooms are extremely beneficial for blood formation and thus are good for anaemic patients. The mushrooms being devoid of fat cholesterol and starch are prescribed as excellent diet for diabetes and for those who suffer from high blood pressure. The mushrooms thus being of considerable economic importance are grown commercially and form the basis of food industry. Agaricus bispora, the white spored mushroom, is cultivated to a greater or lesser extent all over the world. The other common cultivated species are A. bitorquis and A. arvensis. Purple-spored agaricus such as Agaricus Compesteris, A. rodmani and A. placomyces are also edible. Agaricus xanthodermis and a few other contain bacteriostatic substances which inhibit development of bacteria.