Mycology Quick Reference (Biol 358)

Introduction to Mycology

  • Mycology: branch of biology studying fungi; origins tied to study of mushrooms; systematic study began in 17th century with the microscope. Pier Antonio Micheli credited as founder; published Nova Plantarum Genera (1729).
  • Fungi: diverse, occupy unique kingdom; most are microscopic; once thought to be plants, now recognized as distinct group with fungi-specific features.

General features of fungi

  • Fungi are eukaryotic, spore-bearing, achlorophyllous, usually filamentous with cell walls containing chitin (and sometimes cellulose).
  • True nuclei present; reproduction mainly via spores; sexual and asexual mechanisms exist.
  • Vegetative body is hyphae forming a mycelium; hyphae are generally non-motile.
  • Nutrition: absorptive, secreting enzymes onto substrates; store glycogen and lipids; lack photosynthesis.
  • Growth conditions: optimum growth typically 20−30∘C20-30^{\circ}C; pH around 6; light aids sporulation/dispersal but is not strictly required for growth.
  • Many fungi tolerate extreme storage: dormant states and cryogenic storage up to −196∘C-196^{\circ}C.

Thallus and hyphae (ultrastructure)

  • Protoplast has typical eukaryotic features: nuclei with envelopes, nucleolus, chromatin.
  • Cytoplasm contains mitochondria, vacuoles, ER, Golgi bodies (not always present in all fungi).
  • Hyphae elongate apically; growth behind the tip; cross walls (septa) divide hyphae into compartments; septa can be simple or complex; nuclei may migrate through septal pores.
  • Septa types: primary septa (associated with nuclear division) and adventitious septa (not tied to division).
  • Dolipore septum (in Basidiomycota) has a complex pore apparatus.
  • Hyphal branching: often subapical; dichotomous branching is rare.

Hyphal fusion and tissue organization

  • Hyphal fusion (anastomosis) is common in higher fungi and important for colony-wide transport of cytoplasm.
  • Three main fusion types: Hyphal-to-Hyphal, Hyphal-to-Peg, Peg-to-Peg.
  • Result: a continuous tube allows protoplasm transport within the colony.
  • Tissues formed by aggregation: prosenchyma (loose, parallel hyphae) and pseudoparenchyma (dense, parenchyma-like; hyphae lose individuality).
  • Specialized tissues/tunics include mycelial strands, rhizomorphs, sclerotium, stroma, and infection cushions.

Specialized somatic structures

  • Rhizoids: substrate-anchoring/absorbing hyphae.
  • Appressorium: flattened hyphal pressing organ for host entry.
  • Haustorium: absorptive infection structure inside host cells.
  • Hyphal traps: predatory structures (nematophagous fungi) for capturing nematodes; include adhesive hyphae, networked hyphae, knobs, rings.
  • Hyphopodium: attachment organ.

Habitat, life style, and nutrition

  • Fungi occur in soil, water, air; many saprophytic; some obligate parasites; many facultative parasites.
  • Mycorrhiza: mutualistic association between fungal hyphae and plant roots; improves nutrient and water uptake, often essential for forest trees.
  • Lichens: symbiosis between fungi (mycobiont) and algae (phycobiont); form a single thallus; widespread and ecologically important.

Mycorrhizae: endomycorrhiza vs ectomycorrhiza

  • Endomycorrhiza (vesicular-arbuscular): intracellular hyphae penetrate root cortical cells; vesicles and arbuscules function in nutrient exchange; common in many plants (often AM fungi, e.g., Glomeromycota).
  • Ectomycorrhiza: hyphae form mantle around root tip with Hartig net in the cortex; hyphae do not penetrate plant cells; widespread in woody plants; often Basidiomycetes.
  • Benefits: improved uptake of N, P, K; better water uptake; disease resistance; plant growth hormones; nutrient solubilization.

Lichens: morphology and importance

  • Lichen = symbiosis between a fungus (mycobiont) and algae/cotos? (phycobiont) forming a single thallus.
  • Thallus types: homoiomerous (uniform distribution of algae) and heteromerous (distinct algal layer).
  • Growth forms: crustose, foliose, fructicose (squamulose variants).
  • Lichens are indicators of air quality; contribute to soil formation; historically used for dyes and perfumes.
  • Anatomy: algal layer, medulla, cortex; many ascomycetous mycobionts; no lichenized Phycomycetes.

Nutrition and growth requirements

  • Fungi are heterotrophs with absorptive nutrition; most capable of degrading wide range of substrates; require carbon, nitrogen, inorganic ions, vitamins.
  • Carbon sources: glucose is preferred; carbon ~50% of fungal dry weight.
  • Vitamins: many fungi require water-soluble vitamins (B group, vitamin H); some auxotrophs can synthesize all vitamins (auxoautotrophs) while others require external vitamins (auxoheterotrophs).
  • Medium: sterile conditions; commonly use agar (PDA) with yeast extract supplying vitamins and trace elements.
  • Elements: macroelements (C, N, O, S, P, H; K, Mg; Ca limited); microelements (Fe, Zn, Cu, Mn, Mo).

Reproduction and life cycles

  • Fungi reproduce sexually and asexually; asexual cycles often dominate in propagation; sexual cycles may occur less frequently.
  • Asexual methods: fragmentation, fission, budding, production of spores (sporangiospores, conidia).
  • Sexual reproduction stages: plasmogamy (fusion of protoplasts), karyogamy (nuclear fusion), meiosis (reduction to haploid).
  • Life cycles can be haplobiontic (single haploid phase) or diplobiontic (alternation of haploid and diploid phases).
  • Sex organs: gametangia (antheridium male, oogonium female); isogamy (isogametes), anisogamy (different-sized gametes), heterogamy (motile/ non-motile gametes).
  • Homothalism: self-fertile; heterothalism: requires mating type of another thallus.
  • Planogametic copulation: fusion of two naked gametes; isogamy/anisogamy/heterogamy variants.
  • Somatogamy: fusion of undifferentiated vegetative cells; can lead to dikaryotic tissues.

Fungal spores and germination

  • Spores: microscopic, unicellular or multicellular; various shapes, colors; many spores produced in multiple forms.
  • Sporangiospores: produced in sporangia on sporangiophores (motile zoospores in some groups; aplanospores are non-motile).
  • Conidia: spores formed at hyphal tips or sides.
  • Germination: typically via germ tube; two-layered spore walls; moisture is critical (often > 95% RH); temperature, wind, light, and nutrients also influence.

Fungal taxonomy overview

  • Taxonomic hierarchy: Kingdom, Division (-mycota), Class (-mycetes / -mycetidae), Order (-ales), Family (-aceae); Genus and species with binomial names.
  • Five divisions (older system): Mastigomycota, Zygomycota, Ascomycota, Basidiomycota, Deuteromycota.
  • Lower vs higher fungi: basal groups have simpler morphology; higher fungi form fruit bodies (mushrooms, etc.).
  • Notable groups and concepts: chytridiomycetes (Chytridiales), oomycetes (Pythiaceae, Peronosporaceae) within Diplomastigomycotina; Zygomycota (Mucorales, Entomophthorales, Zoopagales); Ascomycota (Ascomycetes; yeasts; molds; cup fungi; morels; truffles); Basidiomycota (mushrooms, rusts, smuts); Deuteromycota (fungi Imperfecti).
  • Pathogenic and economic examples: Phytophthora (oomycete) causes potato blight and cocoa black pod; Aspergillus/Penicillium produce mycotoxins and fermentations.

Mycotoxins

  • Mycotoxin: toxic secondary metabolites produced by fungi contaminating foods/feeds.
  • Common toxins: aflatoxins (A. flavus), patulin, ochratoxin, zearalenone, citrinin, etc.
  • Determinants of production: intrinsic fungal factors, contamination level, extrinsic factors (temperature, humidity, oxygen, pH), insect vectors.
  • Effects: mycotoxicosis in humans/animals; variability among species.
  • Control strategies: crop/storage management, sanitation, fungicides; some biocontrols (e.g., Trichoderma, Geniculosporum, Pseudomonas).

Economic and applied aspects

  • Cocoa diseases: Black Pod disease caused by Phytophthora spp.; significant global impact; management includes copper-based fungicides (Bordeaux mixture, Cu oxychloride), crop sanitation, and cultural practices.
  • Mushroom farming (e.g., in Ghana) as an applied industry.
  • Damping-off and rusts/smuts as important plant diseases.
  • Industries rely on fungal fermentation, enzyme production, antibiotics (Penicillium, Aspergillus).

Quick reference terms

  • Hypha, mycelium, septa, coenocytic
  • Spore types: zoospore, sporangiospore, conidium
  • Plasmogamy, karyogamy, meiosis
  • Homothallic vs heterothallic; haplobiontic vs diplobiontic
  • Endomycorrhiza vs ectomycorrhiza
  • Lichens: mycobiont vs phycobiont; homoiomerous vs heteromerous; crustose vs foliose vs fructicose
  • Dolipore septum, septal pores, hyphal anastomosis

Note

  • This is a condensed, exam-focused synthesis of the provided content intended for quick recall and review.