Ecological Groups of Fungi

Ecological Groups of Fungi

• Fungi are heterotrophic organisms
• Heterotrophic life in fungi is categorized into:
  • Saprobic: Feed on dead organic matter
  • Parasitic: Feed on a host organism (algae, plants, fungi, animals)
    • Biotrophic: Colonize a living host
    • Necrotrophic: Kill the host first, then colonize it
  • Symbiotic: Mutualistic relationship benefiting both the fungus and its partner

Symbionts and Endophytes

• Fungi living on the exterior of their hosts are called epiphytes
• Fungi living within host tissue are called endophytes
• Endophytes:
  • Protect host plants from insect herbivores and other fungal pathogens
  • Used as bioregulators to enhance resistance to diseases
  • Provide biological control against certain pathogens and weeds

Methods for Isolation

• Tissue pieces are sterilized:
  • 60 seconds in 70% ethanol
  • 2-5 minutes in NaOCI (1-3%, depending on tissue type)
  • 60 seconds in 70% ethanol (to remove NaOCI)
• Tissue samples are plated on PDA amended with streptomycin (1 mL/L)
• Incubated at 25°C
• Emerging fungal colonies are hyphal-tipped and transferred to PDA slants for identification

B: Symbionts

Lichens

• Lichens are beneficial mutualistic associations between a fungus and an alga.
• Mycobiont: The fungal partner in a lichen
• Photobiont: The photosynthetic partner (either a green alga or cyanobacterium)

Characters of Lichens

• Worldwide distribution, often found in extreme environments (Arctic, Antarctic, deserts)
• Occur on soil, plants, animals, rocks, decorations, etc.
• Rare in polluted areas; intolerant of industrial pollutants (especially sulfur dioxide)
• Mycobiont usually makes up 90% of the thallus and is typically an ascomycete (mostly inoperculate discomycetes), or less commonly a basidiomycete (e.g., Omphalina, Multiclavula)
• Photobiont may be a green alga, cyanobacterium, or both
• Algae and cyanobacteria fix carbon; cyanobacteria fix nitrogen

Advantages to the alga

• Mechanical protection from injuries and high light by being tightly enveloped by hyphae
• Improved water relations and resistance to desiccation
• Provides minerals

Advantages to the fungus

• Organic nutrients (carbon and nitrogen) provided by the photobiont
• Lichenized fungi have greater longevity
• Most lichenized fungi are not found free-living in nature

Structure of Lichens

• Cortex (upper and/or lower)
• Medulla (fungal layer)
• Algal layer

Types of Lichens

• Stratified lichen: Algal cells are not distributed through the lichen
• Non-stratified lichen: Algal cells are distributed throughout the lichen

Uses of Lichens

• Food
• Dyes
• Essential oils for perfumes and soaps
• Bioactive compounds (antiviral, antibacterial)
• Nesting/bedding material
• Poisons

Reproduction of Lichens

• Sexual spores (ascospores & basidiospores)
• Conidia

Mycorrhizae

• Symbiotic association between a fungus and the root of vascular plants
• 95% of all vascular plants are involved in mycorrhizae
• Believed that the symbiotic association of plant roots and fungi led to modern vascular plants

Types of Mycorrhizae

• Ectomycorrhizae
• Ectendomycorrhizae
• Endomycorrhizae
  • Arbuscular mycorrhizae (AM)
  • Ericoid endomycorrhizae
  • Orchid endomycorrhizae

1-Ectomycorrhizae

• Form a sheath (covering the root tip)
• The fungus grows between plant cells, producing a hartig net (extensive network of intercellular hyphae between epidermal and cortical cells)
• Septate fungi (Ascomycetes)

2-Ectendomycorrhizae

• Different from Ectomycorrhizae in that some hyphae actually penetrate into the root cells
• Septate fungi (Basidiomycetes)

3-Endomycorrhizae (Arbuscular mycorrhizae)

• Hyphae enter the plant cells, producing vesicles (swollen spherical or oval structures) or arbuscules (finely dichotomously branching hyphae invaginations) to increase the surface area between hyphae and cytoplasm
• Major site of nutrient exchange between the fungus and plant
• Non-septate fungi (zygomycota)

B) Ericoid Endomycorrhizae

• The fungus penetrates the plant cells, consisting of dense coils of hyphae in the root cells.
• Septate fungi (Ascomycetes)
• Ericoids are trees such as tea and blue berry

C) Orchid Endomycorrhizae

• Hyphae penetrate cells of the embryo and form coils called pelctons
• Septate fungi (Basidiomycetes)
• Orchids are plants which produce flowers like orchids and vanilla (flowering monocot plants)

Functions of Mycorrhizae

• Increase the plant's competitiveness, depending on the environment and improve plant growth
• Wet environments: Increase nutrient availability (especially phosphate)
• Arid environments: Aid in water uptake, increasing transpiration rates compared to non-mycorrhizal plants

Mycorrhization Helper Bacteria

• Symbiotic bacteria trapped within mycorrhizal fungi (cytoplasm of ectomycorrhizae and arbuscular mycorrhizae)
• Play a role in mycorrhizal relationships
• The main function of bacterial symbionts in ectomycorrhizal fungi is to contribute to nitrogen (N) metabolism by assisting in the synthesis of essential amino acids

Explore the diverse ecological roles of fungi with this quiz. Learn about saprobic, parasitic, and symbiotic fungi and their importance in ecosystems. Delve into the fascinating relationships between fungi and their hosts, including epiphytes and endophytes.