Lecture #6

Basidiomycetes I: Introduction

very successful group; approx. 20,000 known species

great diversity of :

growth forms: yeasts to filamentous
reproductive structures: lacking basidioma(ta) to highly developed basidioma = basidiocarp (e.g., mushroom)
habitats: marine to terrestrial; tropics to temperate to arctic
nutritional modes: saprobic, pathogenic, symbiotic
symbioses: mycorrhiza, insect symbionts, parasites (host specificity)

regularly septate hyphae (See p. 494)
three groups of septal types; dolipore, smut-type, simple
diversity of septal plugs and associated membrane structures; parenthosomes and pulley wheel occlusions
clamp connections (See p. 492)

compatibility & nuclear status
- homo- & heterothallic species
- bi- & tetrapolar mating types
- mono- & dikaryons
- homo- & heterokaryotic
typical basidiomycete life cycle (See p. ERIC CHECK PAGE)
- mycelium derived from germination of a basidiospore is initially a primary mycelium, i.e., monokaryon
- fusion of two compatible thalli (primary mycelia) result in secondary thallus, i.e., dikaryon (secondary mycelium)
- the entire thallus then becomes dikaryotic via nuclei migration through the pores and/or via clamp connections
- clamp connection; only found in basidiomycetes but not all basidiomycetes (e.g. most boletes lack clamps)
- dikaryotic hyphae is long-lived in most basidiomycetes; major vegetative stage
- basidiomata & young probasidia are dikaryotic
- karyogamy occurs in metabasidium usually immediately followed by meiosis (See p. 496)
- typically produce four haploid nuclei
- haploid nuclei migrate through sterigmata into basidiospore proper
- basidiospore that are forcibly ejected are perched off-center on sterigma; ejected forcibly by tugor pressure; Buller's droplet (See p. 500)
- basidiospores that are not forcibly ejected are usually centered symmetrically on sterigmata

three major groups of basidiomycetes are now recognized based on septal ultrastructure, secondary chemistry and molecular data

Hymenomycetes - dolipore septum

Ustilaginomycetes - smut septum or "simple dolipore"

Urediniomycetes - simple septum