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Spore Release

Active Spore Release

For a fungus to effectively disperse, the spores must first be released from the sporophore (spore holding structure). Spores may be actively released or passively separated from the sporophore. Two types of active release are recognised: ballistospore release and spore discharge.

Ballistospore Release

In ballistospore release, a spore is first held in an unstable configuration at the tip of a sterigma. A drop of fluid called "Bullers drop" expands at the lower end of the spore during spore maturation. Once the drop reaches a size that enables contact over a hydrophobic bridge on the spore, the drop rapidly coalesceses with the spore, suddenly changing the centre of mass of the spore. Contact with the sterigma is broken, and the spore is immediately released into the air. The energy is provided from the release of surface tension at the coalescence of the drop and spore surface. Ballistospore release is observed in basidiomycetous yeasts, rust fungi, and from various basidiocarps that open above ground.

Ballistospores may be sprung up to 1.5 mm from the sterigma. This enables spores in gilled or poroid basidiocarps to clear the vertical structures and fall free in the air space between gills or within pores. The distance spores are released and the distance within gaps is highly correlated. Spores rarely impact on opposing gills.

It is of interest that various genera of fungi found inside and outside Australia, include species with sequestrate hymenophores. Closely related European species have upright agaric basidiocarps with caps that open above ground to expose the hymenium. Spores are released by ballistic discharge. The Australian species in these genera include fungi that do not open the cap, and many remain below ground at maturity (hypogeous). LINK

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Spore Discharge

Spore discharge can be seen in a range of Ascomycota and a few aseptate dung fungi. The spore is released from a turgid cell. The spore(s) becomes airborne because of hydrostatic pressure blasting the spores away from the sporangiophore at the moment of separation. In some apothecial and perithecial fungi, asci emerge above the surface of the hymenium, or through the ostiole. The tip of the ascus bursts and spores are ejected great distances. Successive asci emerge and discharge their spores for as long as conditions remain suitable, and mature asci remain in the hymenophore. Some spores are carried great distances. Dung fungi are thought to eject spores up to 3m. LINK In some cases, the asci direct their spores toward the light, thus increasing the likelihood of spores clearing surrounding vegetation.

Pilobolus (Mucorales), a fungus commonly found on dung, forms a sporangium on a tall sporangiophore. The sporangium is attached to a turgid vesicle by a gel-like matrix. As the gel dries, the tension between the sporangium and vesicle increases. Eventually the gel cracks and the sporangium is released violently to the air. Again, the sporangiophore is oriented towards the light, and sporangia are released through these gaps.

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Passive Spore Release

Spores that are passively released tend to be in one of two forms: dry or in mucilage. Dry spores are produced on or in a structure that is subsequently exposed to the wind. The drying action of the wind causes the spores to separate and disperse. Spores in gels tend to ooze from the enclosed sporocarp or form as sticky caps on conidiophores. Fungi that release spores in mucilage are commonly dispersed by insects. LINK

Spore release is the essential stage between formation and dispersal. The mechanisms of release are diverse, and many appear adapted to specific habitats. Release and dispersal are closely related.

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References

Ingold CT & Hudson HJ 1993 The Biology of Fungi 6 th Ed Chapman Hall, pp119 - 131.

Pringle A, Patek SN, Fischer M,Stolze J & Money NP (2005) The captured launch of a ballistospore. Mycologia 97: 866-871.

Moore D & Novak Frazer LA 2002 Essential Fungal Genetics. Springer.

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