Part 2:Part 2:Disease Causing Agents

Agents of DiseaseAgents of Disease

Fungi: 8,000 known pathogenic species 

i 100 000 dicausing 100,000 diseases

Viruses: 1000 differentViruses: 1000 different viruses causing 10,000 or more diseasesmore diseases

Nematodes: 500 species 

Bacteria: 275 species

Parasitic Plants: only 5‐6 yplants that are of concern

Agents of DiseaseAgents of Disease

Single crops are affected by many diseases!

Tomatoes can be attackedTomatoes can be attacked by more than 40 species of fungi, 7 spec es o u g ,bacteria, 16 viruses, and several nematodes!

Agents of Disease FungiCharacteristics of Fungi

Agents of Disease ‐ FungiCharacteristics of Fungi• Filamentous eukaryotic 

organisms that have chitinand glucans in the cell walland 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 stagesstages

• Many faces of fungi –mushrooms, diseases, wood rotters, etc.

Agents of Disease ‐ FungiAgents of Disease  Fungi

Ecology of Fungi:

• Saprophytic fungi breakdown woody biomass (majority)– Recycle organic matter

– Forested ecosystems, ycompost piles

• Some parasitic fungi can  “White Rotter” “Brown Rotter”p gcause disease and some can be beneficial

White Rotter Brown Rotter

Photos from: 

– Mycorrhizae, endophyteshttp://monticellolabs.com/FungalStain.html

Agents of Disease Fungi

Bi h i f f i

Agents of Disease ‐ Fungi

Biochemistry of fungi• Produce many “extracellular 

metabolites”:metabolites :– Enzymes– ToxinsToxins– Hormones

• Compounds when associated pwith plant disease are called virulence factorsC l i i l d i• Complex organisms involved in many processes – necessary for life on Earth – “Garbage men” of gthe ecological world

Agents of Disease FungiAgents of Disease ‐ Fungi

Fungi and Plant Disease• Disperse through spores, 

fragmented hyphae, contaminated soil and tools, vectors and many morevectors, and many more

• Survive as spores, sclerotia, rhizomorphs and myceliumrhizomorphs, and mycelium infested plant debris

• Cause plant symptoms of p y psmuts, molds, cankers, galls, leaf curls, soft rots, root rots, scabs, and more… 

Agents of Disease FungiAgents of Disease ‐ Fungi

Classification of fungal pathogens

• Ascomycetes

• Basidomycetes

• Chytridiomycetes

• Zygomycetes

• Imperfect fungi

• “Fungal‐Like” organismsGroups of fungi are differentiated by 

– Oomycetesp g y

morphological features, and by DNA sequences.

Tree from: www.pfdb.net/myhtml/genosp_dermato.html

Agents of Disease FungiAscomycetes

Agents of Disease ‐ FungiAscomycetes

– Sac fungi – produce sexual spores in a sac

• Typically have 8 ascosporesin an ascus

– Reproduces asexually asReproduces asexually as well

– Produces very distinct structures that are used forstructures that are used for identification

– Imperfect fungi are typically grouped with ascomycetes

– Most common fungalMost common fungal diseases

Agents of Disease FungiDiseases caused by Ascomycetes

Agents of Disease ‐ Fungi

Agents of Disease FungiDisease cycle of Brown Rot (Monilinia fructicola)

Agents of Disease ‐ Fungiy ( f )

Agents of Disease ‐ FungiDisease cycle of Brown Rot (Monilinia fructicola)

Agents of Disease ‐ Fungi

Agents of Disease FungiDisease cycle of Apple Scab (Venturia inaequalis)

Agents of Disease ‐ Fungi

Agents of Disease ‐ FungiDisease cycle of Apple Scab (Venturia inaequalis)

Agents of Disease ‐ Fungi