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Part 2: Part 2: Disease Causing Agents Agents of Disease Agents of Disease Fungi: 8,000 known pathogenic species causing 100,000 diseases i 100 000 di Viruses: 1000 different Viruses: 1000 different viruses causing 10,000 or more diseases more diseases Nematodes: 500 species Bacteria: 275 species y Parasitic Plants: only 5‐6 plants that are of concern Agents of Disease Agents of Disease Single crops are affected by many diseases! Tomatoes can be attacked Tomatoes can be attacked by more than 40 spec es o u g , species of fungi, 7 bacteria, 16 viruses, and several nematodes! Agents of Disease Fungi Agents of Disease ‐ Characteristics of Fungi Characteristics of Fungi • Filamentous eukaryotic organisms that have chitin and glucans in the cell wall and glucans in the cell wall • Filamentous growth is called hyphae, and a mass of growth is called mycelium Reproduction is by spores – • Reproduction is by spores both assexual and sexual • Classification is by sexual stages • Many faces of fungi – mushrooms, diseases, wood rotters, etc. Agents of Disease ‐ Fungi Agents of Disease Ecology of Fungi: • Saprophytic fungi breakdown woody biomass (majority) – Recycle organic matter – Forested ecosystems, y compost piles • Some parasitic fungi can p g cause disease and some can be beneficial – Mycorrhizae, endophytes “White White Rotter Rotter” “Brown Brown Rotter Rotter” Photos from: http://monticellolabs.com/FungalStain.html Agents of Disease Fungi Agents of Disease ‐ Bi h i Biochemistry of fungi ff i • Produce many “extracellular metabolites : metabolites”: – Enzymes – Toxins – Hormones p • Compounds when associated with plant disease are called virulence factors • Complex organisms involved in C l i i l di many processes – necessary for life on Earth – “Garbage men” of g the ecological world Agents of Disease Fungi Agents of Disease ‐ Fungi and Plant Disease • Disperse through spores, fragmented hyphae, contaminated soil and tools, vectors and many more vectors, and many more • Survive as spores, sclerotia, rhizomorphs and mycelium rhizomorphs, and mycelium infested plant debris • Cause plant symptoms of p y p smuts, molds, cankers, galls, leaf curls, soft rots, root rots, scabs, and more… Agents of Disease Fungi Agents of Disease ‐ Classification of fungal pathogens • • • • • • Ascomycetes Basidomycetes Chytridiomycetes Zygomycetes Imperfect fungi “Fungal‐Like” organisms – Oomycetes Groups of fungi are differentiated by p g y morphological features, and by DNA sequences. Tree from: www.pfdb.net/myhtml/genosp_dermato.html Agents of Disease Fungi Agents of Disease ‐ Ascomycetes – Sac fungi – produce sexual spores in a sac • Typically have 8 ascospores in an ascus – Reproduces Reproduces asexually as asexually as well – Produces very distinct structures that are used for structures that are used for identification – Imperfect fungi are typically grouped with ascomycetes – Most common fungal Most common fungal diseases Agents of Disease Fungi Agents of Disease ‐ Diseases caused by Ascomycetes Agents of Disease Fungi Agents of Disease ‐ Disease cycle of Brown Rot (Monilinia y ( ffructicola)) Agents of Disease ‐ Fungi Agents of Disease ‐ Disease cycle of Brown Rot (Monilinia fructicola) Agents of Disease Fungi Agents of Disease ‐ Disease cycle of Apple Scab (Venturia inaequalis) Agents of Disease ‐ Fungi Agents of Disease ‐ Disease cycle of Apple Scab (Venturia inaequalis)
