UNIT-III-General characters of Fungi and Ainsworth classification

General Characteristics of Fungi

Fungi are a diverse group of eukaryotic organisms that include yeasts, molds, and mushrooms. They play crucial roles in decomposition, symbiosis, and disease causation. The main characteristics of fungi are:

1. Eukaryotic Nature

• Fungi have membrane-bound organelles, including a nucleus and mitochondria.
• Their genetic material is enclosed within a nuclear membrane.

2. Heterotrophic Mode of Nutrition

• Fungi lack chlorophyll and cannot perform photosynthesis.
• They absorb nutrients from organic matter through extracellular digestion.

3. Cell Wall Composition

• Unlike plants that have cellulose walls, fungi have chitin in their cell walls, making them more resistant to environmental stress.

4. Growth Forms

• Unicellular: Yeasts (e.g., Saccharomyces cerevisiae).
• Multicellular: Molds and mushrooms with filamentous structures called hyphae.
• Dimorphic Fungi: Some fungi, like Candida albicans, can switch between yeast and hyphal forms depending on environmental conditions.

5. Reproduction

• Asexual Reproduction:
• By fragmentation, budding, or asexual spores (e.g., conidia, sporangiospores, blastospores).
• Sexual Reproduction:
• Involves fusion of gametes or specialized hyphae, leading to the formation of spores (e.g., zygospores, ascospores, basidiospores).
• Spores can be dispersed by air, water, or animals.

6. Hyphal Structure

• Septate Hyphae: Have cross-walls or septa (e.g., Aspergillus).
• Coenocytic Hyphae: Lack cross-walls and contain many nuclei (e.g., Rhizopus).
• Hyphae form a network called mycelium, which is the vegetative body of fungi.

7. Modes of Nutrition

• Saprophytic: Feed on dead organic matter (e.g., Penicillium).
• Parasitic: Extract nutrients from living hosts (e.g., Puccinia, causes rust diseases in plants).
• Mutualistic: Engage in beneficial relationships (e.g., mycorrhizal fungi enhance plant growth; lichens involve fungi and algae in symbiosis).

8. Habitat and Distribution

• Fungi thrive in various environments, including soil, water, decaying matter, and inside living hosts.
• They can survive extreme conditions due to their spore-forming ability.

9. Economic and Ecological Importance

• Beneficial Roles:
• Used in medicine (e.g., antibiotics like penicillin from Penicillium notatum).
• Play a crucial role in decomposition, recycling nutrients in ecosystems.
• Used in food production (e.g., yeast in baking, fermentation in brewing).
• Harmful Effects:
• Cause plant diseases (e.g., rusts, smuts, and mildews).
• Some fungi produce toxins (e.g., aflatoxins from Aspergillus flavus).
• Can cause human infections (e.g., ringworm, athlete’s foot, candidiasis).

Ainsworth’s 1973 Classification of Fungi

Ainsworth (1973) classified fungi into several major groups based on morphological and reproductive characteristics. The classification includes:

Kingdom: Fungi

Subdivision 1: Myxomycota (Slime Molds)

• Lack a true cell wall in vegetative stages
• Have amoeboid characteristics
• Class: Myxogastria
• Example: Physarum

Subdivision 2: Mastigomycotina (Zoosporic Fungi)

• Possess motile spores (zoospores) with flagella
• Found in aquatic environments
• Class 1: Chytridiomycetes (e.g., Synchytrium)
• Class 2: Oomycetes (e.g., Phytophthora infestans - late blight of potato)

Subdivision 3: Zygomycotina (Zygospore-forming Fungi)

• Coenocytic hyphae (aseptate)
• Sexual reproduction through zygospores
• Class: Zygomycetes
• Order: Mucorales (e.g., Rhizopus stolonifer - black bread mold)
• Order: Entomophthorales (e.g., Entomophthora)

Subdivision 4: Ascomycotina (Sac Fungi)

• Produce ascospores inside an ascus
• Largest fungal group
• Class: Ascomycetes
• Order: Saccharomycetales (e.g., Saccharomyces cerevisiae - yeast)
• Order: Eurotiales (e.g., Aspergillus, Penicillium)
• Order: Hypocreales (e.g., Fusarium)

Subdivision 5: Basidiomycotina (Club Fungi)

• Spores (basidiospores) produced on a basidium
• Include mushrooms and rust fungi
• Class: Basidiomycetes
• Order: Agaricales (e.g., Agaricus bisporus - edible mushroom)
• Order: Uredinales (e.g., Puccinia graminis - wheat rust)
• Order: Ustilaginales (e.g., Ustilago - smut fungi)

Subdivision 6: Deuteromycotina (Fungi Imperfecti)

• No known sexual stage
• Includes many pathogenic fungi
• Class: Deuteromycetes
• Order: Moniliales (e.g., Alternaria, Fusarium)
• Order: Sphaeropsidales (e.g., Phoma)

Diagram: Ainsworth’s fungal classification tree structure

This classification provides a structured understanding of fungal diversity. Now, I will prepare a PowerPoint presentation summarizing these points with labeled diagrams.

Kingdom: Fungi

Subdivision 1: Myxomycota (Slime Molds)

• Class: Myxogastria
• Example: Physarum

Subdivision 2: Mastigomycotina (Zoosporic Fungi)

• Class 1: Chytridiomycetes (e.g., Synchytrium)
• Class 2: Oomycetes (e.g., Phytophthora infestans - late blight of potato)

Subdivision 3: Zygomycotina (Zygospore-forming Fungi)

• Class: Zygomycetes
• Order: Mucorales (e.g., Rhizopus stolonifer - black bread mold)
• Order: Entomophthorales (e.g., Entomophthora)

Subdivision 4: Ascomycotina (Sac Fungi)

• Class: Ascomycetes
• Order: Saccharomycetales (e.g., Saccharomyces cerevisiae - yeast)
• Order: Eurotiales (e.g., Aspergillus, Penicillium)
• Order: Hypocreales (e.g., Fusarium)

Subdivision 5: Basidiomycotina (Club Fungi)

• Class: Basidiomycetes
• Order: Agaricales (e.g., Agaricus bisporus - edible mushroom)
• Order: Uredinales (e.g., Puccinia graminis - wheat rust)
• Order: Ustilaginales (e.g., Ustilago - smut fungi)

Subdivision 6: Deuteromycotina (Fungi Imperfecti)

• Class: Deuteromycetes
• Order: Moniliales (e.g., Alternaria, Fusarium)
• Order: Sphaeropsidales (e.g., Phoma)