1985 - Mycological Society of America

34
features seen by light microscopy were reflected in
the distinctive ultrastructural appearance of the
cytoplasm. Studies are underway to compare this
chemically-induced cell death with death induced in
the same cell type by Cochliobolus heterostrophus
Race 0, a non~athonen of cowDeas that ~enetrates
and kills epiderrnai cells. A
Miller, Jr.. 0. K., see Flynn, T. M.
Miller, 0. K., Jr., see Vilgalys, R.
Miller, 0. K., Jr., see Vilgalys, R., et. al.
STEVEN L. m. Department of Biology, Virginia
Polytechnic Institute and State University, Blacksburg,
VA 24061. Early basidiosporogenesis and spore release
mechanisms in the gasteroid and agaricoid Russulales.
Ballistosporic discharge appears to be a conservative
phenomenon in most basidiomycetes, resulting from a
prescribed sequence of biochemical and developmental
processes. Ultrastructural characterization of
sterigma formation, spore orientation and development,
and spore release mechanisms may provide valuable
systematic information to aid the understanding of
evolution in the basidiomycetes. Morphologically and
ecologically the Russulales are a homogeneous group.
However, this order contains both ballistosporic and
statismosporic, agaricoid and gasteroid taxa. Spore
symmetry and ability to forcibly discharge spores are
therefore fundamental systematic characteristics, yet
ballistosporic and statismosporic basidiosporogenesis
has not been critically examined. Early
basidiosporogenesis, spore-wall tegumentation, and
differentiation of the hilar appendix were
ultrastructurally compared in eight genera of agaricoid
and gasteroid Russulales. Six layers were present in
all developing spores, two of which were associated
with an evanescent pellicle and four were derived from
the sterigma and young spore. Ontogeny of spore-wall
ornamentation was similar in all genera, however
diversity in the degree of ornamentation resulted from
differentiation of the four enduring wall layers.
Developmental anatomy associated with spore release
mechanisms was also examined. Systematic implications
of basidiosporogenesis in the evolution of the
Russulales and other secotioid and gasteroid
basidiomycetes will be discussed.
STEVEN L. MILLER. Department of Biology, Virginia
Polytechnic Institute and State University,
Blacksburg, VA 24061. Ectomycorrhizae in the
Russulales-a systematic interpretation.
The morphology and anatomy of ectomycorrhizae reflect
many characteristics present in the fruiting
structures and vegetative mycelium of a particular
fungal symbiont. In addition, ectomycorrhizae may
possess characteristics which are not present in the
fungus alone or are ignored in the taxonomy and
systematics of the fungus. Ectomycorrhizal
morphology has not been used to evaluate the
systematic position of a particular taxon or group of
ectomycorrhizal fungi.
Ectomycorrhi zae of several genera of gasteroid and
agaricoid Russulales were synthesized in the
laboratory using the growth-pouch technique.
Mycel ial plugs were used as the source of inoculum.
Mantle morphology and anatomy were compared using
one micrometer thick cross and longitudinal plastic
sections. Sulfo-aldehyde staining of the ectomycorrhizal
root1 ets indicated the presence of sesquiterpenoid
lactones. Lateral rootlets showed a tendency
to grow toward the inoculum plugs, contact the plugs
and become ectomycorrhizal. The implications of
ectomycorrhizal formation, ectomycorrhizal morphology
and anatomy, and host lateral root behavior in the
evolution of the Russulales will be discussed.
C.W. MIMS ano N.L. NICKERSON. Department of Biology,
Stephen F. Austin State University, Nacogdoches,
TX 75962, and Research Station, Agriculture Canada,
Kentville, Nova Scotia, B4N 155. Ultrastructure of
the host-pathogen relationship in red leaf disease
of lowbush blueberry.
Red leaf disease of blueberry is caused by the basidiomycetous
fungus Exobasidium vaccinii Wor. This
fungus produces a p e m e l i u m that invades the
rhizomes of Vaccinium angustifolium Ait. Symptoms
are seen on infected shoots soon after buds break in
the spring and the reddish leaves for which the
disease is named soon become apparent. In this
study TEM was used to examine the host-pathogen
relationship in infected leaves.
Exobasidium vaccinii produced a system of slender,
branched, septate hyphae within infected leaves.
Although hyphae were routinely observed within cells
of the lower epidermis, elsewhere hyphae grew almost
exclusively in an intercellular fashion. Hyphae typically
filled the intercel lular spaces near the
lower epidermis but were rather sparse elsewhere
in the leaf. The haustorial apparatus consisted of
short, finger-like or lobed structures that arose
from intercellular hyphae in close association with
host cells. Each haustorium contained distinctive
membranous inclusions and had one or more electronopaque
haustorial caps. Haustoria usually appeared
to be ensheathed by host cell wall material although
some haustorial caps appeared to penetrate the host
wall.
Mohan, M., see Meyer, R. J., et. al.
Molina, R., see Castellano, M. 4.
GARETH MORGAN-JONES. Department of Botany,
P l a n t P m g y Microbiology, Auburn
University, ~iabama 36849. ~oncerni ng
Dia orthe phaseolorum f.sp. caulivora, and
-!+-
sov ean stem canker in the southeastern
~n?ted States.
Incidence of soybean stem canker has greatly
increased in the southeastern U.S. during
the last five years and losses
*
from the disease
are estimated at over 40 million dollars.
Southeastern biotypes of g. haseol orum f. sp.
caulivoia, which have the abi ity to kill the
soybean plant well before harvest, differ
from northern isolates in cultural characteristics
in vitro, including colony appearance
and color, growth rate at different temperatures,
stroma size and perithecial and ascospore
morphology. Some differences in morphology
of the anamorphic Phomo sis state,
particularly conidiophore 77- ranching, are also
evident between southeastern and northern
isolates. These facts, together with data
from host inoculation experiments, using
several soybean cul tivars, indicate that a
separate, easily distinguishable, forma
speciales exists in the s0utheast.r
symptoms induced by this organism are demonstrated
and an account given of its morphology