INTRODUCTION TO THE ASCOMYCETES IB GENERAL MYCOLOGY LECTURE 16 Tuessday, October 21, 2003

ASCOMYCOTA  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 CYCLE  anamorphteleomorph  asexualsexual  imperfectperfect  conidiaascospores  mitosporemeiospore  entire organism is the holomorph

ASCOMYCETE LIFE CYCLE  HOW DOES ONE PROVE THAT A PARTICULAR ANAMORPH BELONGS TO A PARTICULAR TELEOMORH?

ASCOMYCETE LIFE CYCLE  anamorph (mitospore) holomorph teleomorph (meiospore)

ASCOMYCETE 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  2 o 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 INCOMPATIBILITY  Homogenic incompatibility- controlled by mating type genes (unifactorial)  Somatic or vegetative incompatibility

SEXUAL REPRODUCTION  Gametangial copulation  Gametangial contact and fusion  Hyphal fusion (somatogamy)  Spermatization

SEXUAL 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

ASCOSPOROGENESIS  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 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 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 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 ACTIVITY  What, if any, characteristics do the Ascomycetes and Basidiomycetes have in common?  How do the Ascomycetes and Basidiomycetes differ?