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A basidiospore is a reproductive spore produced by basidiomycete fungi, a grouping that includes , shelf fungus, rust fungus, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidium. Typically, four basidiospores develop on appendages from each basidium, of which two are of one strain and the other two of its opposite strain. In gills under a cap of one common species, there exist millions of basidia.
Some gilled mushrooms in the order Agaricales have the ability to release billions of spores. The puffball fungus Calvatia gigantea has been calculated to produce about five trillion basidiospores. Most basidiospores are forcibly discharged, and are thus considered ballistospores. These spores serve as the main air dispersal units for the fungi. The spores are released during periods of high humidity and generally have a night-time or pre-dawn peak concentration in the atmosphere.
When basidiospores encounter a favorable substrate, they may germination, typically by forming hyphae. These hyphae grow outward from the original spore, forming an expanding circle of mycelium. The circular shape of a fungal colony explains the formation of , and also the circular lesions of skin-infecting fungi that cause ringworm. Some basidiospores germinate repetitively by forming small spores instead of hyphae.
The spore wall consists of several layers, from innermost to outermost: the endosporium, episporium, and the ectosporium. These layers are typical for colourless basidiospores. The episporium is made out of interwoven chitin and glucan microfibrils. The ectosporium becomes sticky and slimy in mature spores and is quite thin. The color of the spore print is usually found in a part of the cell wall called the exosporium although in rare instances – like the yellow spores of Clavaria helicoides – the cytoplasm is responsible for the spore color. Coloured spores also have another additional layer called the perisporium, which may be amyloid (contain starches that react with iodine).
Plages are quite variable between different Basidiomycota Rather than simply a flat area above hilar appendix, some fungi have a dimple. This is called a suprahilar depression. These variations may happen because of structural differences in the gills or pores of different species, as they need different volumes of water, to disperse the spore.
There are four types of plages, based on how they react to Melzer's reagant. If the plage turns blue or black in reaction to Melzer's reagant, it can be classified as an amyloid plage. If it does not change colour, it is called an inamyloid plage. If the colour shows up only in the center, it is called centrally amyloid, respectively, if it shows up only on the outer edges of the plage, it is called distally amyloid. (2025). 9789811047688, Springer Singapore : Imprint: Springer. ISBN 9789811047688 These characteristics can be useful in distinguishing between Lactarius species. (2025). 9789072619815, National Botanic Garden of Belgium. ISBN 9789072619815
Passive dispersal uses environmental vectors such as wind, water or animals. Wind dispersal is the most common method of passive basidiospore dispersal of agarics. The shape of the stipe and cap of the fungi are adaptive for the optimal dispersal of basidiospore. For example, bell-shaped caps can prevent spores from being blown back to the hymenium, when the wind turbulence is strong. Taller stipes, and smaller basidiospores allow the basidiospores travel farther. To overcome still air, some fungi create their own draft, by evaporating water which causes differences in air temperature beneath the hymenium.
Basidiospore dispersal by water can occur through rain or mist. For example, in bird's nest fungi, raindrops help carry peridioles (small aggregates of basidiospores) out of the peridium (cup-like structure). Puffball and earthballs rely on the pressure of raindrops, to compress the air inside the peridium to trigger the release of basidiospores through its apical hole.
Basidiospore dispersal through animals can happen through ingestion of the mushroom, or adherence of the spores to skin or fur. Animals that consume mushrooms range from slugs, to insects and small mammals. Basidiospores dispersed through ingestion, must have thick walls to survive the digestive process. Basidiospores of Ectomycorrhiza often get transported through attaching to the cuticle of arthropods.
Additionally, the basidiospores themselves can have characteristics that facilitate them landing in favourable conditions. For example, the rough spore surfaces of spores in the Russula genus, may improve attachment to a substrate. Basidiospores in Agaricus have melanin in the walls of their basidiospores which helps protect them against chemical, enzymic and light damage. Basidiospores can be categorised by whether they have characteristics that optimise dispersal or survival. Memnospores tend to be large, spherical, thick-walled and require specific environmental stimuli to germinate, which optimizes survival. Xenospores, tend to be small, thin-walled, oblong and ornamented, which optimizes dispersal.
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