Agaricus

SYSTEMATIC POSITION

Division	Eumycota
Sub division	Basidiomycotina
Class	Hymenomycetes
Order	Agaricales
Family	Agaricaeae
Genus	Agaricus

OCCURRENCE

• Ø  The genus Agaricus is represented by about 17 species and is cosmopolitan in distribution. Most of them are saprophytic, growing on dead and decaying wood and leaves and on organic rich soil.

• Ø  Agaricus commonly called Mushroom, grow best in moist and shady places and are commonly seen during rainy season. What we ordinarily call the mushroom is not the whole fungus, it is actually the fructification which is technically called basidiocarp and the vegetative part of this fungus remains hidden in the soil.

• Ø  The fruit bodies are the visible part of the fungi (Fig. 1) and are found in rings as in Agaricus arvensis (Horse mushroom), Agaricus tabularis and based on the ancient belief that they marked the path of dancing fairies, these rings are called fairy rings.

• Ø  Though many fleshy Agaricales are edible, whereas some like Amanita phalloides, Amanita muscaria, Agaricus xanthoderma are poisonous in nature. Amanita phalloides also known as Death Cap is highly poisonous organisms on earth, once ingested there is no hope of recovery. Armilleriella mellia grow as parasite on woody trees.

VEGETATIVE STRUCTURE

• Ø  The thallus of Agaricus is made up of tubular, branched, hair like structures called hyphae.

• Ø  A large number of hyphae constitute the mycelium. Three types of mycelia are seen namely primary mycelium, secondary mycelium (dikaryotic) and tertiary mycelium.

 REPRODUCTION

• Agaricus reproduce by vegetative, asexual and sexual methods.

•  Vegetative reproduction: The edible mushrooms are cultivated on a large scale by vegetative method. The small pieces of dikaryotic mycelium are used as inoculum to develop spawns (the mushroom seed). The mass of spawn is grown in rich organic manure soil to obtain the edible mushroom (fruiting bodies/ basidiocarps).

•  Asexual reproduction: Asexual reproduction is rare in Agaricus and it takes place by forming Chlamydospores, Oidia or Conidia.

•  Sexual Reproduction:  Sex organs are absent in Agaricus and mode of sexual fusion is somatogamy (fusion of vegetative cells) and takes place through the following three steps.

• i.     Plasmogamy: Most of the species including A. campestris are heterothallic, but A. bispora is homothallic. Two cells of monokaryotic hyphae of opposite strains (+ & -) come in contact with each other. The cell wall dissolves at the point of contact and a dikaryon (n + n) is formed. This dikaryo­tic cell develops into dikaryotic myceli­um by regular cell divisions through clamp connection (Fig 3). The dikaryotic mycelium is perennial and subterranean. It forms the chief food absorbing phase of the fungus and produces fructifications called the basidiocarp under suitable temperature and sufficient moisture.

• ii.     Karyogamy: It takes place at later stage in the young basidium which develops on gills of the fruiting body. Both the nuclei fuse together and form diploid nucleus.

• iii.     Meiosis: Meiosis takes place soon after karyogamy and leads to the formation of four haploid nuclei. The basidiospores, thus formed on the sterigma of basidium are haploid and either of (+) or (–) type.