Feb 18 2009

AscomyetesReview of sexual reproduction strategiesAsexual reproductionRepresentative disease cycles

** Images and lecture material were not entirely ** Images and lecture material were not entirely created by J. Bond. created by J. Bond. Some of this material was created by others.** Some of this material was created by others.**

ASCOMYCETESCharacteristics cont. 6. Asexual spores - conidia, chlamydospores. These

fungi produce both sexual and asexual spores.

The sexual stage produced by a fungus is termed the "perfect stage". Ascomycete fungi also produce asexual spores (conidia). This termed the "imperfect stage".

Conidia can be produced in several different sporocarps (aka arrangements), and each fungus generally (but not always) produces conidia in only one arrangement:

Conidia Arrangementa. Free and independent (aka naked) - one conidium or

chain of conidia at end of conidiophore.Ex: Taphrina deformans - peach leaf curlEx: Sphaerotheca pannosa - powdery mildew of rose

Conidia Arrangementb. Synnema - upright bundle of conidiophores, all

cemented together.Ex: Ophiostoma ulmi - Dutch elm disease

Conidia Arrangement

c. Acervulus - a depressed mat of hyphae with short conidiophores.

Ex: Venturia inaequalis - apple scab

Acervulus

Conidia Arrangementd. Sporodochium - conidiophores are

produced on a pin cushion-shaped stroma.Ex: Monilinia fructicola - brown rot of stone

fruitsEx: Claviceps purpurea - ergot of grains

Conidia Arrangemente. Pycnidium - a structure, round or flask-shaped,

with conidia and conidiophores within.Ex: Guignardia bidwellii - black rot of grapeEx: Cryphonectria parasitica - chestnut blight

Leaf Curl DiseasesLeaf Curl DiseasesPeach leaf curl – Peach leaf curl – Taphrina deformansTaphrina deformansLeaf blister on oaks – Leaf blister on oaks – Taphrina Taphrina caerulescenscaerulescens

Plant Pathology, G.N. Agrios

Powdery MildewsPowdery Mildews• Obligate biotrophsObligate biotrophs• Anamorph: conidiaAnamorph: conidia

• Teleomorph: asci Teleomorph: asci in cleistotheciain cleistothecia

• Host specificHost specific

Plant Pathology, G.N. Agrios

Ergot of Cereals and Ergot of Cereals and GrassesGrasses

Most common on rye and pearl Most common on rye and pearl milletmillet

Grain susceptible only when Grain susceptible only when floweringflowering

Sclerotia mature as seed in grain Sclerotia mature as seed in grain head maturehead mature

Sclerotia contain many toxic Sclerotia contain many toxic alkaloids including LSDalkaloids including LSD

Rye susceptible when deficient of Rye susceptible when deficient of coppercopper

Ergot of RyeErgot of Rye

Sclerotium (pl. sclerotia) – a mass of hyphae that is so compacted that Sclerotium (pl. sclerotia) – a mass of hyphae that is so compacted that hyphae have lost their individuality. Can survive adverse conditions – hyphae have lost their individuality. Can survive adverse conditions – overseasoning structures. Germinate by producing stalked stroma (closely overseasoning structures. Germinate by producing stalked stroma (closely woven somatic hypha)woven somatic hypha)

Plant Pathology, G.N. Agrios