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zeae-maydis were examined after exposure to different RH with growth chamber and field studies. Steamed and nonsteamed
regimes. Conidia were atomized onto polysulfone membrane filter soil was used in growth chamber studies. No significant interdiscs
and allowed to germinate for 6 hr. Discs were then sus- actions were found between herbicides and plant growth parspended
above glycerol solutions maintained at 25.0 C to obtain meters in steamed soil. Significant interactions between
39-100% RH. Germ tube elongation and appressorial formation herbicides and inoculum treatments affecting root and hypocotyl
were observed microscopically after staining the discs with acid weight occurred in nonsteamed soil. Root and hypocotyl weights
fuchsin in lactophenol. Appressoria formed in 2 to 3 days when were significantly lower in inoculated soil than in noninocugerminated
conidia were maintained at 95% RH. Appressoria did lated soil in the absence of herbicides. No similar significant
not form at 90% RH even after 15 days. However, when these differences were observed in treatments where herbicides were
conidia were then transferred to 95% RH, appressoria formed in added to the soil. In field studies R. solani infested oats
2 to 3 days. Conidia held at 39-80% RH for 15 days did not con- placed in furrow at planting significantly reduced plant growth
tinue development when transferred to 95% RH. parameters. No significant interactions were observed between
herbicides and inoculum treatments. Effects of R. solani
inoculum were significantly reduced with carboxin-pentachloro-
102 nitrobenezene seed treatments.
THE EFFECTS OF NITROGEN ON CHARCOAL ROT DEVELOPMENT IN
SORGHUM BICOLOR. G.L. Cloud and J.C. Rupe, Dept. of Plant
Pathology, University of Arkansas, Fayetteville, AR 72701. 106 Withdrawn
Colonization of sorghum by Macrophomina phaseolina was
determined at nitrogen fertilization rates of 0, 50, 100,
and 150 lbs/acre in a randomized complete block design with
five replications. Plant tissue and roots were sampled
monthly to determine total nitrogen and percent root
segments colonized by natural infection. Sorghum stalks
also were inoculated with toothpicks infested with M. pLhaseolina,
and four plants were rated monthly for lesion
length. There were no significant differences between the
level of soil nitrogen and incidence of root colonization.
There was a positive correlation between the length of stalk
lesions from the point of inoculation and plant tissue
nitrogen levels at 119 and 139, but not 79 days after
planting.
103
AMBIGUITY OF THE DESIGNATION RACE 4 FOR ISOLATES OF CERCOSPORA
SOJINA. D. V. Phillips and H. R. Boerma, Departments of Plant
Pathology and Agronomy, Georgia Station, University of Georgia, 107
Griffin, GA 30223. CHARACTERIZATION OF COLLETOTRICHUM GRAMINICOLA ISOLATES
Race 3 and Race 4 of Cercospora sojina were described in 1968 WITH
TROPHORESIS
AMINOPEPTIDASE
OF SOLUBLE
PROFILES AND
PROTEINS.
POLYACRYLAMIDE
Ali,
GEL
M.E.K.,
ELECto
designate isolates from North Carolina. In
H.L.
recent
Warren,
years,
D.M. Huter
_C. E.tROPHORES sOFSOBLPR S A atholEgyH
sojina
anrenDMurI
isolates from the southern U.S. include Race 5 and F.E. Lytle, K. Hughes. USDA-ARS, Botany & Plant Pathology,
several
and
of
Che0istry
Race 4.
De-
Since Race 4 was originally tested on only partments; Purdue University, W.
16
Lafayette,
cultivars,
IN 47907.
additional cultivars were tested for reaction to Filter aminopeptidase and gel electrophoresis methods
isolates
were compared
of this
with
race.
a laser
Several cultivars reacted differently enhanced aminopeptidase technique to characterize
to
isolates
isolates
of Colletotrichum
designated
gram
as Race 4, indicating that the 16 inicola from three hosts. Filter and laser aminopeptidase profiles
cultivars
and gel
used
electro-
to describe Race 4 are not adequate to phoretic patters of soluble protein indicate that
distinguish
isolates of C. graminicola
Race 4
from
from other apparently new races. The sorghum, corn and barnyard grass can be differentiated
reaction
based
of
on
additional
their host speci-
cultivars to Race 4 cannot be determined ficity. The laser aminopeptidase profiles further separated
because
sorghum
an
isolates
authentic
to
culture is not available. Since at least races, similar to their reactions on sorghum
3 isolates
plants. Corn
designated
isolates showed
as Race
less
4 can be separated from each variability, which is consistent with results from pathogenicity
other and
tests.
from
The
Races
percent
1, 2, 3, and 5 by cultivar reaction, the hydrolysis of f?-napthylamides was highest in sorghum
designation
followed
Race
by
4
corn
is
and
ambiguous and should not be used. barnyard grass. The aminopeptidase assay is a powerful method which is sensitive
104
enough to provide a rapid method of differentiating between isolates of C. graminicola
from sorghum, corn and barnyard grass. Laser enhancement of the aminopeptidase
system permits differentiation of races of C. graminicola pathogenic to sorghum.
STABILITY OF PLASMA MEMBRANE OF WHITE BEAN ASSOCIATED WITH
WHITE MOULD RESISTANCE. J. C. Tu, Agriculture Canada, Research
Station, Harrow, Ontario NOR IGO.
Stability of plasma membrane of white bean to oxalic acid
secreted by Sclerotinia eclerotiorum was associated with
disease resistance. Leaf tissues of a susceptible (Fleetwood)
and a resistant (ExRico 23) cultivar were treated with
different concentrations of oxalic acid for thin sectioning and
freeze fracturing. In thin sections, at a given oxalic acid
concentration, the plasma membrane and chloroplasts of
Fleetwood were affected more and ruptured quicker than those of
ExRico 23. In replicas of freeze-fractured plasma membrane,
protrusions, wrinkles and breakages increased with increasing
oxalic acid concentration. The degree of damage was distinctly
more severe in the plasma membrane of Fleetwood than ExRico
23. Conductivity measurements of the bathing water of leaf
discs showed that Fleetwood had a higher conductivity reading
than that of ExRico 23, indicating that the plasma membrane of
Fleetw~ood was less stable than that of ExRico 23.
105
108
OCCURRENCE AND IMPACT OF VIRAL DISEASES OF
WINTER WHEAT IN NEW YORK STATE. N. R, Miller, G. C.
Bergstrom, and S. M. Gray. Dept. of Plant Pathology, Cornell
Uiest taaY183
Tedsrbtoadicdneocmovrsdsae fetnsf
whie winteri whenatd iniNew York Staten (NYus) wierses dfeterined in
whtwierhatnNwYokSae( S)eedtrmedn
1988 and 1989. Over 100 randomly selected fields were assessed for
wheat spindle streak mosaic(WVSSM), barley yellow dwarf(ByD),soil-
borne wheat mosaic, and wheat streak mosaic using ELISA
techniques and symptom expression. At early stem extension,
symptoms of WSSM were severe in fields planted to susceptible
cultivars. BYDVwas detected byELISAin many fields at this growth
stage, although no symptoms of the disease were observed. At spike
emergence, BYDVwas the only widespreadwheatvirus. In surveyed
fields, as well as in field plot experiments, the cultivar Geneva
consistently incurred a low incidence of WSSM. These findings,
together with experiments examining the effect of WSSM on wheat
yields, contribute to our understanding of the impact of virus diseases
on wheat production in NYS.
INTERACTION OF DINITROANILNE HERBICIDES AND RHIZOCTONIA DISEASE
ON SOYBEAN. E. N. Bauske and H. W. Kirby, 1102 S. Goodwin Ave. 109
University of Illinois, Urbana, Illinois 61801
MANGANESE TOXICITY IN THE MARBLE CULTIVARS OF CHRYSANTHEMUM
The effect of trifluralin, pendimethalin, and ethalfluralin and MORIFOLIUM. I. CYTOcHEMISTRY. R. H. Lawson anid7TM. M.Dienet.
disease caused by Rhizoctonia solani on soybeans was determined UWfSDAARFlorist & Nursery Crops Lab., geltsville, MO.
1148 PHYTOPATHOLOGY