Pg:- 20,21. ch:- 1

Parasitic fungi are a diverse group of organisms that derive nutrients by infecting living hosts, including plants, animals, and other fungi.

Hyphae and Mycelium:

• Hyphae: The fundamental structural units of fungi, including parasitic fungi, are hyphae. These are long, thread-like structures composed of tubular cells. Hyphae can be septate (divided by cross-walls called septa) or coenocytic (without septa, containing continuous cytoplasm with multiple nuclei).

• Mycelium: A network of hyphae that forms the main body of the fungus. In parasitic fungi, the mycelium grows within or on the surface of the host tissue, absorbing nutrients.

Appressoria:

• Appressorium: A specialized structure that many parasitic fungi develop to penetrate host tissues. It forms at the tip of a hypha and generates high turgor pressure, allowing the fungus to breach the host’s surface. This is crucial for initial infection.

Haustoria:

• Haustorium: Once inside the host, parasitic fungi often develop haustoria. These are specialized hyphal structures that penetrate host cells without breaking the plasma membrane. Haustoria facilitates nutrient exchange between the fungus and the host cell, siphoning off organic compounds necessary for fungal growth.

Spores and Spore-Producing Structures:

• Spores: Reproductive units of fungi. Parasitic fungi produce various types of spores (e.g., conidia, sporangiospores) that aid in the dissemination and infection of new hosts.

• Sporangia and Conidiophores: Structures that produce and release spores. Sporangia are sac-like structures, while conidiophores are specialized hyphae that bear conidia (asexual spores).

Enzymes and Toxins:

• Lytic Enzymes: Parasitic fungi secrete a range of enzymes (e.g., cellulases, proteases) that break down host cell walls and other structures, facilitating invasion and nutrient absorption.

• Toxins: Some parasitic fungi produce toxins that can kill or weaken host tissues, making them more susceptible to infection and further facilitating nutrient extraction.

Examples of Parasitic Fungi:

• Rusts and Smuts: Plant pathogens that form complex life cycles, often involving different hosts and producing structures like urediniospores and teliospores.

• Cordyceps: Entomopathogenic fungi that infect insects, eventually killing them and emerging from their bodies to release spores.

• Candida albicans: A human pathogen that causes infections ranging from superficial (e.g., thrush) to systemic, often in immunocompromised individuals.