Fungal Spores, Spore Dormancy, and Spore Dispersal - Study Notes

Fungal Spores, Dormancy, and Dispersal

Fungi and Fungal Spores

  • Fungi are prime examples of spore-producing organisms, generating millions of spores with diverse shapes, sizes, and surface properties.
  • Sexual spores often remain dormant through seasonal changes.
  • Types of spores (asexual and sexual) differ across fungal classes.

Types of Asexual Spores: Mastigomycotina

Class Chytridiomycetes
  • Asexual reproduction via zoospores with a single posterior whiplash flagellum.
  • Example: Synchytrium endobioticum causing Potato Wart Disease.
  • Sexual reproduction involves thick-walled dormant resting spores called oospores.
Class Oomycetes (Water Molds)
  • Aquatic fungi that are significant plant pathogens (e.g., Phytophthora infestans causing Potato Blight).
  • Mycelium is coenocytic with cellulose walls and diploid life cycle.
  • Asexual reproduction by biflagellate zoospores produced in zoosporangia.

Life Cycle of Oomycetes

  • Sexual reproduction is heterogamous (fusion of male nuclei into eggs) through gametangial copulation.
  • Asexual reproduction involves zoospores that promote rapid spread.

Types of Asexual Spores: Zygomycotina

Class Zygomycetes
  • e.g., Rhizopus stolonifer (Bread Mold) - Asexual reproduction through sporangiospores in sporangia.
  • Hyphae fuse to form zygosporangium, resulting in zygospore development.
Unique Features of Pilobolus
  • Known as the hat-thrower fungus, utilizes explosive dispersal mechanisms.
  • Sprangium can be ejected up to 3 meters to ensure distance from contaminated environments.

Types of Asexual Spores: Ascomycotina

Class Ascomycetes
  • Largest phylum with over 64,000 species; includes yeasts and medicinally important fungi (e.g., Penicillium).
  • Asexual spores known as conidia are produced on conidiophores.
  • Important human pathogens: Aspergillus and Candida albicans.

Sexual Reproduction in Ascomycetes

  • Involves the fusion of hyphae from different mating types to form dikaryotic structures which develop into asci containing ascospores.
  • Ascocarps are fruiting bodies containing fungal spores.

Types of Asexual Spores: Basidiomycotina

Class Basidiomycetes (Club Fungi)
  • Includes mushrooms, puffballs, and decaying wood fungi.
  • Asexual reproduction via budding or conidial spores, with unique club-shaped basidia as the site of sexual reproduction leading to basidiospores.

Deuteromycotina (Fungi Imperfecti)

  • Lack known sexual stages; reproduce only by conidia.
  • Includes industrially relevant fungi like Penicillium and Aspergillus species.

Transmission of Fungal Spores

  • Various vectors exist, such as zoospores for plant viruses.
  • Airborne spores dispersed by wind/rain can settle via:
    • Sedimentation: Heavy spores settle first in calm conditions.
    • Impaction: Large spores are removed from air by colliding into surfaces.
    • Washout: Rain removes spores from the air.

Air Sampling Devices

  • Rotorod sampler: Basic air sampling device.
  • Burkard sampler: Continuous monitoring tool.
  • Anderson sampler: Emulates human respiratory tract deposition of spores.
Common Fungal Diseases in Humans
  • Candidiasis: Infection from Candida species.
  • Dermatomycoses: Infections of skin, nails, and hair from dermatophytes.
  • Respiratory Fungal Infections: Infections caused by airborne fungal pathogens such as Aspergillus and Histoplasma.