Download pb372 – general mycology laboratory - fungi

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INTEGRATIVE BIOLOGY – 371
GENERAL MYCOLOGY LABORATORY
FUNGI IMPERFECTI-II
November, 4 2003
In this laboratory, you will examine fungi that produce some type of conidioma
or synnemata, and fungi that produce no conidia or conidiomata. You will also observe
some special groups of Fungi Imperfecti: the predaceous, aquatic and aeroaquatic fungi.
COELOMYCETES - These fungi form their conidia in a variety of enclosed
conidiomata, which frequently develop just beneath the surface of their plant
substrates. The first type is the acervular conidioma. In the older literature, these fungi
were included in the Melanconiales; they are now included in the Coelomycetes. In
these fungi, fungal hyphae aggregate and produce a flat, fertile layer of conidiophores
that produce many conidia. The pressure of accumulating conidia, and often of
accessory mucilage, eventually ruptures the host integument and allows the conidia to
escape. Laboratory example - Dinemosporium sp. Examine the culture provided with
the dissecting microscope. Look for a slimy mass of conidia surrounded by stout, black
setae. Mount a single conidioma on a slide in a drop of water and examine with the
compound microscope. What is your immediate impression? How could you go about
locating the conidiogenous cell? Proceed and draw and label the conidiogenous cell.
The type of conidioma that completely surrounds the conidiogenous cells and
conidia is called a pycnidium. Fungi that form pycnidia were previously called the
Sphaeropsidales; they are now included in the Coelomycetes. Included in the
pycnidial fungi are a large number of plant pathogens in the genera Diplodia, Phoma,
Phomopsis, Phyllosticta, and Septoria. Laboratory examples - Herbarium specimens of a
variety of pycnidial fungi are provided. Examine the specimens provided with the
dissecting microscope to observe the variation in pycnidial morphology. Select one
species and follow the directions given for acervular fungi.
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AGONOMYCETALES - These fungi do not form conidia at all, although some species
produce chlamydospores or sclerotia. There are about 28 good genera with about 200
species in this group. Rhizoctonia and Sclerotium are two genera that include some
important plant pathogens. Laboratory example - Sclerotium rolfsii - Examine the
culture with the dissecting microscope and locate the sclerotia. Remove one to a slide
and make a thin section through it with a razor blade. What color is the inside? Can
you find any conidia? Describe the make-up of the inside of the sclerotium.
SYNNEMATOUS FUNGI - These fungi produce structures known as synnemata.
These structures consist of groups of conidiophores united at the base. Laboratory
example - Penicillium claviforme. Examine a plate with the dissecting microscope and
locate the synnemata. Mount some material in lactic acid and locate the united
conidiophores, condiogenous cells, and conidia. Describe the type of conidiogenesis
and the conidial morphology.
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PREDACEOUS HYPHOMYCETES - Nematode-trapping fungi have evolved a variety
of mechanisms for trapping nematodes: sticky hyphae, sticky knobs and nets, and
constricting and non-constricting rings. Laboratory examples - After nematodes have
been added to a culture of Arthrobotrys, examine plates with the dissecting microscope.
Locate a trapped nematode and remove it to a slide in a drop of water and determine
how the nematode was trapped.
AQUATIC (INGOLDIAN) HYPHOMYCETES - This group of fungi have conidia that
are modified to decrease sinking rates and maximize the probability that they will
become entangled with a substrate (leaves and/or wood). The most common shapes
are long sigmoidal, tetraradiate and branched. Laboratory examples – submerged
leaves have been collected from Sangamon River at Nattie Hart forest (This is one of the
University research sites). Using a hole puncher, leaf discs have been incubated in
water and conidia have been produced on the leaves. Conidia of aquatic hyphomycetes
are easily trapped on the surface of air bubbles. Examine the dish of leaf discs with the
dissecting microscope and locate the suspended conidia. You may also mount a leaf
disk in water on a slide and examine the edges with the compound microscope. You
should see conidia attached to conidiophores. What is the ecological role of these
fungi? Using the identification book, see if you can identify any species to genus.
AEROAQUATIC HYPHOMYCETES - The conidia of aeroaquatic fungi are specialized
for trapping air so that they float to the surface of water bodies. In some cases, the
conidia are coiled to make a cylinder that holds air and in other cases a rounded basket
or pouch which contains air is formed. Laboratory examples – Unidentified helicosporus
species - Wet a transfer needle and pick up some of the white mass of conidia. Place
them in a drop of water and try to sink them. Treat them with alcohol and see if you
can sink them. Helicoon giganteum - Examine the specimen of this fungus. Look for
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the rounded pouch-like structures. Remove some of the bulbils and try to sink them in
a drop of water. Treat with alcohol and then stain with lactic acid and cotton blue.
Describe the composition of the bulbil. Where would you find these kinds of fungi?
Why are the conidia hydrophobic?