s - Mycological Society of America

F. A. Wclrer, -tic Botany and -logy
-t=Y, =* -, me*
Beltsville,, MD 20705.
Paraphyses in Phanoesis
Phaoopsis iavanica on AsDarsqus fraa Lndoaesia
(Java) differs fram other P-is in that it
prcducss~paraphyses. Since the disoovery of this
distinctive character two other &Utes and a few
herbarim specimens have been fcnuxl that exhibit
it. The morphology, taxoncmy, and g-hic
distribution of the paraphysate species are
discussed.
&UARDO M. VADELL, MICHAEL T . HOLMES , AND JAMES C.
CAVENDER. Department of Botany, Ohio University,
Athens, OH 45701 - A Natural-Historical Approach to
the Cellular Slime Molds of Tikal
rhe Mayan archeological site of Tikal (Peten district,
Guatemala; 17.5 North Latitude) offers an unusual
abundance and richness of dictyostelids, in agreement
uith the great plant and.anima1 diversity of the semi-
evergreen rainforest which surrounds the ruins.
Twenty-five species were isolated from several
soil collections. Four were undescribed species. The
known species were determined using the morpnological
criteria of Raper (1984) and Hagiwara (1988). These
conjugated physiological, morphological and behavior-
al criteria include optimal media and temperature for
growth; aggregation pattern; habit and brancning pat-
tern; sorophore base and tip shape; dimensions of
sori, branches and sorocarps; phototropic response;
chemotaxis to cyclic AW; slug behavior; and spore
size, shape, color and morphology.
The ecological conditions of the Tikal forest
region such as alternative wet and dry seasons allov
some insight into the evolution of dictyostelids.
For example, the seasonal variation of species may
provide clues to the polarity of characteristics
which have been selected over time.
One of the species isolated is probably an ances-
tral Dictvostelium discoideum. This isolate will pro-
vide an opportunity for studying adaptative strategies
and evolution of this species.
C. GERALD VAN DYKE and CHARLES W. MIMS,
Department of Botany, North Carolina State
University, Box 7612, Raleigh, NC 27695, and
Department of Plant Pathology, University of
Georgia, Athens, 30602. Light and electron micro-
scopy of conidium germination and appressorium
development in Colletotrichum truncatum.
Colletotrichum truncatum has been used for bio-
control of the weed 5esbianiaexaltata. Light and
electron microscopic techniques were used to
study events occurring during conidium germ-
ination and appressorium formation. Events were
observed at 22 C up to 12 hrs after conidia were
placed on host tissue and artificial membranes.
Ndclear division occurred 1-2 hrs after place-
men;, followed 5!. formation of a central conidial
septum. A germ tube (GT) emerged 2-3 hrs later;
the nucleus of the germinated conidial cell
divided, one nucleus remained in the conidium, the
other migrated into the GT. A swollen, terminal
appressorium formed 2-3 hrs later; the GT
nucleus divided in the appressorium, now de-
limited from the GT by a septum. An extracellular
matrix coated conidia, GTs, and appressoria and
appeared to stick fungal structures to host tissue
and membranes. Infection pegs formed from
appressoria 9-1 2 hrs after germination.
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E. VAN EECKHOUT., I. BLACKWELL, and H.C. RUSH. Depsrtment of
Botany and Depsrtmt of Plant Pathology and Crop Physiology,
Louisiana State University, Baton Rouge. LA 70603.
In vitro effects of propicanazole on morphology and ultrastructure
of Rhizocton~a solani.
--
Rhizoctonia solani Kbn (AG1) is the causal agent of rice sheath
blight, the mst inportant rice disease in the southern riceproducing
areas of the United States. Propiconazole, a sterol
synthesis inhibitor. is one of the fungicides currently registered
for use in cmtrolling this disease. Agar incorporation of
propiconatole shod good in vitro activity against R. solani. EC
50 values ranged from 0.1 to 0.3 ppn depending on tim after
irwcuiatia. Colony growth uas conpletely inhibited at 10 ppn.
Exposure of R. solani to propiconazole induced rhythmic growth in
culture which can be related to the node of action of
propiconazole. Control and propiconatole treated hyphse were
premred for scanning and transmission electron microscopy.
Morphological changes in response to fungicidal activity included
(a) irregular branching uith decreased intervals between branches.
(b) short, stubby branches, (c) abnormal thickenings and
constrictions, end (d) ruotures in usually inflated hyphal parts.
Electron microsco~ic examination of freeze-substituted and
chemically fix- hyphal tip sections revealed disrupted apical
vesicle configuraticns and abnormal wall inclusions as most
obvious effects of propiconazole on ultrastructure of R. solani .
Rytas Vilgalys. Department of Botany, Duke University,
Durham, NC 27706.
The application of genetic data tor interpretive
mycogeography.
As more becomes known about diverse geographic
distributions of fungi, new sources of independent data will
be necessary to evaluate competing histor~cal hypotheses.
Evidence from macromolecular data should benefit studies
on interpretive mycogeography for several reasons: 1)
Molecular data represent an unlimited source of characters
for phylogenetic analysis at almost any taxonomic level; 2)
Different modes of inheritance and recombination in nuclear
and mitochondria1 genomes provide two alternative sources
of information; 3) Recent technical advances in molecular
biology now make DNA-level analyses possible with minute
tissue samples from natural material. I will discuss the
application of data for examining vicariance biogeography in
macrofungi. The relatively high rate of genome evolution in
many members of the Basidiomycotina should also make it
possible to examine intraspecific phylogeography and its
relation to gene flow, genetic divergence and speciation.