INTRODUCTION TO INTRODUCTION TO THE ASCOMYCETESTHE ASCOMYCETES

IB 371 - GENERAL MYCOLOGYIB 371 - GENERAL MYCOLOGY

LECTURE 16LECTURE 16

Tuessday, October 21, 2003Tuessday, October 21, 2003

ASCOMYCOTAASCOMYCOTA

products of meiosis contained in a sac called an ascus

well-developed mycelium with septa at regular intervals

septa with simple pores (sometimes numerous micropores) & Woronin bodies

haploid w. restricted diploid life cycle asexual reproduction by conidia

Polysporous Asci (From David Geiser)

ASCOMYCETE LIFE CYCLEASCOMYCETE LIFE CYCLE

anamorph teleomorph asexual sexual imperfect perfect conidia ascospores mitospore meiospore entire organism is the holomorph

ASCOMYCETE LIFE CYCLEASCOMYCETE LIFE CYCLE

HOW DOES ONE PROVE THAT A HOW DOES ONE PROVE THAT A PARTICULAR ANAMORPH PARTICULAR ANAMORPH BELONGS TO A PARTICULAR BELONGS TO A PARTICULAR TELEOMORH?TELEOMORH?

ASCOMYCETE LIFE CYCLEASCOMYCETE LIFE CYCLE

anamorph (mitospore)

holomorph

teleomorph (meiospore)

ASCOMYCETE LIFE CYCLEASCOMYCETE LIFE CYCLE

homothallic - mycelium from a uninucleate 1N ascospore is capable of producing ascospores

heterothallic - requires 2 mycelia, each from a single haploid ascospore of different mating types

2o homothallic - appears homothallic because a single ascospore may contain 2 nuclei (one of each mating type). If an ascospore contains two nuclei of the same mating type, the fungus will be sterile.

SEXUAL SEXUAL INCOMPATIBILITYINCOMPATIBILITY

Homogenic incompatibility- controlled by mating type genes (unifactorial)

Somatic or vegetative incompatibility

SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

Gametangial copulation

Gametangial contact and fusion

Hyphal fusion (somatogamy)

Spermatization

SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

dikaryotic stage is not usually of long duration

after karyogamy, meiosis occurs immediately to produce 4, 8, or more ascospores in an ascus

ascospores are formed by free cell formation within the ascus

ASCOSPOROGENESISASCOSPOROGENESIS

An enveloping membrane system (EMS) that originates from the ascus membrane delimits portions of cytosplasm surrounding a nucleus.

Wall material is deposited between the two membranes to form the ascospore wall.

ASCOSPORE RELEASEASCOSPORE RELEASE

Breakdown (deliquescence) of the ascus wall

Forcibly shot out through an apical opening

Ascus wall layers separate and ascospores are shot out through a pore in the apex of the inner ascus

FRUITING BODIESFRUITING BODIES

General term is ascoma (pl. ascomata). Cleistothecium - completely closed, no preformed

opening. Perithecium - often flask-shaped, with an apical

opening. Apothecium - ascomata open and saucer-shaped at

maturity. Pseudothecium - asci formed in a stromatal cavity.

ASEXUAL REPRODUCTIONASEXUAL REPRODUCTION

Spores produced by mitosis

Spores called conidia (also called mitospores)

Formed by (1) fragmentation, (2) fission, (3) budding, or (4) blastic development.

Chlamydospores - thick-walled resistant cells

IN-CLASS ACTIVITYIN-CLASS ACTIVITY

What, if any, characteristics do the Ascomycetes and Basidiomycetes have in common?

How do the Ascomycetes and Basidiomycetes differ?