Q.(a) Write the outline of the life cycle of Agaricus. OR

Agaricus completes its life cycle through: basidiospore germination to monokaryotic mycelium, fusion of compatible mycelia to form dikaryotic mycelium, development of the mushroom (basidiocarp) whose gill-borne basidia undergo karyogamy and meiosis, releasing fresh basidiospores.

Agaricus (the common edible mushroom) belongs to the Basidiomycetes, whose defining feature is the production of sexual spores called basidiospores on club-shaped structures called basidia. Its life cycle proceeds through these stages:

1. Basidiospore germination: a haploid basidiospore, on landing in a suitable substrate, germinates to produce a haploid, monokaryotic (one nucleus per cell) mycelium — the primary mycelium.
2. Plasmogamy (fusion of mycelia): two compatible (genetically different mating-type) monokaryotic mycelia grow toward each other and their hyphae fuse. Their cytoplasms merge (plasmogamy), but the two nuclei do NOT immediately fuse; instead they remain paired within each cell, producing a dikaryotic (two nuclei per cell, n+n) mycelium — the secondary mycelium.
3. Growth of dikaryotic mycelium: this dikaryotic mycelium is the main, long-lived vegetative phase; it spreads extensively through the soil/substrate, absorbing nutrients.
4. Formation of the basidiocarp: under suitable conditions, the dikaryotic mycelium aggregates and organises into the familiar fruiting body — the mushroom (basidiocarp), consisting of a stalk (stipe) and a cap (pileus), with thin, radiating plate-like gills (lamellae) on the underside of the cap. …