General Characteristics of Molds

Ascomycetes

(septate) form sexual spores known as ascospores, which are formed after a union of 2 cells from the same mycelium or from separate mycelia

Mold

- eukaryotic, multicellular, filamentous fungi by its fuzzy or cottony appearance - main part of the growth commonly appears white but may be colored or dark or smoky - thallus or vegetative body, characteristic of thallophytes, which lack true roots, stems & leaves

Coenocytic (nonseptate)

- with the hyphae apparently consisting of cylinders without cross walls - have nuclei scatterd throughout their length & are considered multicellular

Reproductive Parts or Structures

Asexual spores and Sexual spores

sclerotia

Few kinds of molds produce this which are tightly packed masses of modified hyphae, often thick walled, within the mycelium.

Fungi Imperfecti

Imperfect molds (typically septate) have only asexual spores.

PHYSIOLOGICAL CHARACTERISTICS

Moisture requirements Temperature requirements Oxygen & pH requirements Food requirements Inhibitors

mycelium

Molds can grow from a transplanted piece of

Sexual spores

Molds which can produce sexual spores are classified on the basis of the manner of formation of these spores & the type produced.

sexual spores

Oospores zygospores ascospores, basidiospore

Inhibitors

Penicillin → Penicillium chrysogenum Clavacin/Patulin → Aspergillus clavatus

asexual spores

Reproduction of molds is chiefly by means of

Molds are divided into 2 groups:

Septate Coenocytic nonseptate

sporangium

a sac that encloses the sporangiospore

sporangiospores

enclosed in a sac called called sporangium (sporangia) which is at the tip of a fertile hyphae (sporangiophore)

Basidiomycetes

form basidiospore, includes most mushrooms, plant rusts, smuts, etc.

Zygomycetes

form zygospores by the union of the tips of 2 hyphae which often appear similar & which may come from the same mycelium or from different mycelia

arthrospores or oidia (oidium)

formed by fragmentation of a hypha, so that cells of the hypha become arthrospores

chlamydospores

formed by many species of molds when a cell in the mycelium stores up reserve food, swells & forms a thicker wall than that of a surrounding cells - resting cell, can withstand unfavorable conditions better than ordinary mold mycelium can & later under favorable conditions, can grow into a new mold

Oospores

formed by the union of a small male gamete & a large female gamete mostly aquatic, but important plant pathogens are also included in this group (i.e. downy mildew

fragmentation

how arthrospores are formed

Hyphae

mass of branching intertwined filaments of mold thallus

perfect

molds also form sexual spores Oomycetes or Zygomycetes if nonseptate Ascomycetes or Basidiomycetes if septate

Oomycetes or Zygomycetes

nonseptate

Asexual spores

produced in large numbers & are small, light & resistant to drying - readily spread through the air to alight & start new mold thallus where conditions are favourable

Ascospores

resulting from cell division after conjugation, are in an ascus or sac, with usually 8 spores per ascus, formed by branching & intertwining adjacent hyphae.

Ascomycetes or Basidiomycetes

septate

Oomycetes

sexual spore nonseptate molds that produce oospores

conidia (conidium)

type of asexual spore cut off or bud from special fertile hyphae called conidiophores & are usually open (i.e. not enclosed in any container)

Colored spores

typical of mature mold of some kinds & give color to part or all of the growth

thallus

vegetative body, characteristic of thallophytes, which lack true roots, stems & leaves

Mycelium

whole mass of these hyphae

Septate

with cross walls dividing the hypha into cells - increase in length by means of division of the tip cell (apical growth) or of cells within the hypha (intercalary growth), the type of growth being characteristic of the kind of mold