INTRODUCTION TO THE ASCOMYCETES IB 371 GENERAL MYCOLOGY

INTRODUCTION TO THE ASCOMYCETES IB 371 - 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 anamorph asexual imperfect conidia mitospore entire teleomorph sexual perfect ascospores meiospore 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 1 N 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 wall Forcibly opening Ascus (deliquescence) of the ascus shot out through an apical 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 opening. - completely closed, no preformed Perithecium - often flask-shaped, with an apical Apothecium - ascomata open and saucer-shaped at opening. 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 cells - thick-walled resistant

IN-CLASS ACTIVITY What, if any, characteristics do the Ascomycetes and Basidiomycetes have in common? How do the Ascomycetes and Basidiomycetes differ?