Components contributing to dilatory resistance to Puccinia polysora Underw. in corn


Zummo, N.

Phytopathology 76(10): 1098

1986


Four characters of southern corn rust, pustule incidence, size, tumescence, and rupture were evaluated in the field and greenhouse to determine relative consistency on individual corn genotypes and their contribution to dilatory resistance. Inoculated plants of a susceptible genotype consistently had greatest pustule incidence. Pustules on this genotype were significantly larger, more tumid, and ruptured earlier than pustules produced on more resistant corn genotypes. A genotype from a cross of susceptible parents followed a similar pattern of susceptibility when compared to genotypes from crosses of parents with dilatory resistance.

and
Eugene
McClain,
Dept.
of
Agronomy
and
Soils,
Clemson
Uni-
Plant
Pathology
and
Weed
Science,
Miss.
State,
MS
39762
versity,
Clemson,
SC
29634-0377.
Yields
of
maize
dwarf
mosaic
virus
-infected
sorghum
[Sorghum
bicolor
(Linn.)
Moench]
plants
(avg
39
g/plant)
and
adjacent
symptomless
plants
(avg
49
g/plant)
of
four
varieties
seeded
17
May
were
not
different.
Yields
were
different
(P=0.05)
when
seeded
31
May
(35
g/plant
and
46
g/plant,
respectively)
and
14
June
(avg
20
g/plant
and
38
g/plant,
respectively).
Numbers
of
diseased
plants
increased
(P=0.05)
to
the
12
July
rating
for
all
four
varieties
seeded
on
the
three
dates.
Incidence
averaged
13
and
8%
on
12
July
in
plots
seeded
17
and
31
May,
respectively.
Incidence
did
not increase
in
these
plots
subsequent
to
12
July.
Incidence
increased
to
an
averaged
of
42%
on
13
August
in
the
plots
seeded
14
June.
Infection
(or
symptom
expression)
may
have
been
limited
by
stage
of
host
maturity
for
plants
in
plots
seeded
17
and
31
May
in
this
experiment.
325
AMELIORATION
OF
TAN
SPOT
OF
WHEAT
WITH
NITROGEN.
D.M.
Huber,
T.S.
Lee,
M.A.
Ross,
and
T.S.
Abney.
Botany
and
Plant
Pathology
Department
and
USDA,
ARS,
Purdue
University,
West
Lafayette,
IN
47907.
The
effect
of
N
rate
and
form
on
tan
spot
were
evaluated
with
wheat
cultivars
Auburn,
Caldwell,
and
Blazer
(resistant,
mod-
erately
susceptible,
and
susceptible
to
Pyrenophora
tritici-rep-
entis,
respectively)
planted
in
a
randomized,
complete
block
design
field
experiment.
The
severity
of
tan
spot
decreased
and
yields
increased
as
the
rate
of
N
increased.
Disease
severity
was
reduced
further
by
inhibiting
nitrification
with
nitrapyrin
which
prevented
overwinter
loss
of
N
and
increased
the
proportion
of
ammonium
N
taken
up
by
plants.
The
rate
of
lesion
development
was
markedly
reduced
as
the
N
rate
increas-
ed,
and
the
pin
-point
lesions
developing
on
Blazer
at
the
highest
rate
of
stabilized
N
were
similar
to
those
on
the
resistant
Auburn.
This
research
indicates
that
both
the
rate
and
form
of
N
influence
the
severity
of
tan
spot
of
winter
wheat,
and
that
N
management
may
be
an
important
cultural
control
of
this
disease.
326
THE
RD
LE
OF
WATER
STRESS
IN
THE
DEVELOPMENT
OF
FUSARIUM
FOOT
ROT
OF
BARLEY.
T.
R.
Gordon,
Department
of
Plant
Pathology,
University
of
California,
Berkeley,
CA
94720.
Barley
(Hordeum
vulgare
L.
cv.
CM
72)
was
grown
in
a
soil
mix
infested
with
macroconidia
of
Fusarium
graminearum.
After
four
weeks
under
greenhouse
conditions,
plants
were
transferred
to
a
growth
chamber
where
they
were
subjected
to
an
episode
of
water
stress
lasting
30
days.
This
was
accomplished
by
using
a
two
phase
rooting
medium.
The
upper
phase
was
soil,
and
the
lower
phase
was
a
nutrient
solution
into
which
the
root
system
grew
from
the
soil.
Water
stress
was
imposed
by
amending
the
liquid
phase
with
progressively
higher
concentrations
of
PEG
-3350.
Infected
plants
subjected
to
water
stress
developed
substantial
discoloration
of
the
crown
and
died
before
reaching
maturity.
Healthy
plants
given
the
same
stress
treatment
showed
some
firing
of
the
leaf
tips
but
otherwise
appeared
comparable
to
non
-stressed
plants.
Disease
symptoms
on
infected
plants
not
subjected
to
water
stress
were
restricted
to,
at
most,
discoloration
of
the
lower
leaf
sheaths.
327
AN
EXPLANATION
FOR
THE
PERPETUATION
OF
YIELD
LOSS
IN
MOROCCAN
BARLEYS
FROM
PYRENOPHORA
TERES.
J.
R.
Burleigh,
M.
Tajani,
&
B.
Ezzahiri.
Institut
Agronomique
et
Veterinaire,
Rabat,
Morocco
and
Dept.
of
Pl.
Path.,
Univ.
of
Minn.,
St.
Paul,
MN
55108.
In
Morocco
selection
of
barley
lines
for
resistance
to
Pyrenophora
teres
is
done
when
high
temperatures
and
lack
of
moisture
may
arrest
the
disease
even
though,
early
in
the
season,
it
has
been
severe
on
senesced
lower
leaves.
Studies
of
yield
components
linearly
regressed
on
areas
under
the
disease
progress
curve
(AUDPC)
for
growth
stage
intervals
corresponding
to
when
tillers,
ears,
spikelets,
kernels
and
kernel
weight
are
formed
revealed
that
both
numbers
of
ears
and
kernel
weight
were
inversely
related
to
AUDPC
for
growth
intervals
when
ears
are
formed.
This
indicates
that
our
cultivars,
selected
at
adult
stages
which
show
little
infection,
may
be
damaged
severely
by
early
infections
that
reduce
ear
number
and
kernel
weight.
328
COMPONENTS
CONTRIBUTING
TO
DILATORY
RESISTANCE
TO
PUCCINIA
POLYSORA
UNDERW.
IN
CORN.
Natale
Zummo,
USDA-ARS,
Dept.
of
Four
characters
of
southern
corn
rust,
pustule
incidence,
size,
tumescence,
and
rupture
were
evaluated
in
the
field
and
green-
house
to
determine
relative
consistency
on
individual
corn
genotypes
and
their
contribution
to
dilatory
resistance.
Ino-
culated
plants
of
a
susceptible
genotype
consistently
had
greatest
pustule
incidence.
Pustules
on
this
genotype
were
significantly
larger,
more
tumid,
and
ruptured
earlier
than
pus-
tules
produced
on
more
resistant
corn
genotypes.
A
genotype
from
a
cross
of
susceptible
parents
followed
a
similar
pattern
of
susceptibility
when
compared
to
genotypes
from
crosses
of
parents
with
dilatory
resistance.
329
THE
INHERITANCE
OF
RESISTANCE
IN
SPRING
AND
WINTER
BREAD
WHEATS
TO
TWO
ISOLATES
OF
MYCOSPHAERELLA
GRAMINICOLA.
T.
Danon
and
Z.
Eval,
Dept.
of
Botany,
Tel
Aviv
Univ.,
Tel
Aviv
69978,
Israel.
The
inheritance
of
low
pycnidial
coverage
was
investigated
in
parental
Fl,
F2,
F3
and
backcrossed
populations
derived
from
crosses
among
spring
and
winter
bread
wheats
crossed
in
a
comp-
lete
diallel
scheme.
Field
grown
populations
were
replicated
four
times
within
two
blocks,
each
block
inoculated
with
a
dif-
ferent
isolate
of
Mycosphaerella
graminicola
(anamorph,Se
toria
tritici).
The
semidwarf
winter
wheat
cultivars
Aurora,
ezo-
sta
Kavkaz
and
Trakia
were
susceptible
to
isolate
ISR8036
but
not
to
isolate
ISR398
(ATCC48507).
The
semidwarf
spring
wheats
Hazera
2230
and
Lakhish
were
susceptible
to
both
iso-
lates.
Resistance
of
the
four
winter
wheats
to
isolate
ISR398
is
controlled
by
one
or
two
dominant
genes.
There
was
no
indi-
cation
for
maternal
effect
on
the
expression
of
disease
cover-
age.
The
two
isolates
of
M.
graminicola
possess
at
least
two
different
genes
for
virulence.
Low
correlations
were
expressed
between
heading
date,
plant
height
and
pycnidial
coverage
of
septoria
tritici
blotch.
330
Improved
"Single
tillers"
method
for
loss
assessment
in
wheat.
Shtienberg
D.,
D.
Marani
and
A.
Dinoor
Faculty
of
Agriculture,
Rehovot,
Israel
Common
methods
for
loss
assessment
include
(a)
establishment
of
experimentally
derived
damage
functions
expressing
the
relationships
between
disease
level
and
yield.
(b)
estimates,
based
on
the
function,
of
losses
in
other
fields.
There
are
drawbacks
to
that,
like
(1)
the
cost,
preplanning
and
prospects
for
success
of
the
field
trials,
(2)
validy
of
the
function
for
other
fields.
In
the
"Single
tillers"
method
the
function
is
based
on
hundreds
of
tillers.
The
main
drawback
to
it,
is
the
validity
of
estimates
derived
from
single
tillers
to
a
whole
crop.
the
advantages
of
this
method
are:
(1)
it
can
be
applied
simply
in
any
desired
situation
without
preplanning
and
without
allocation
of
field
experiments,
(2)
the
function
is
calculated
for
each
field
evaluated,
(3)
it
is
very
non
-expensive
in
operation.
Attempts
at
standartization
of
procedures
for
improving
the
validy
of
the
method
were
tested
in
field
trials.
The
losses
determined
by
the
improved
method
did
not
differ
significantly
from
the
values
calculated
from
field
trials.
331
IMPORTANCE
OF
SOILBORNE
PLANT
PATHOGENS
ON
WHEAT
AS
INFLUENCED
BY
TILLAGE
AND
CROPPING
SYSTEM.
C.
S.
Rothrock,
Department
of
Plant
Pathology,
University
of
Georgia,
Georgia
Station,
Experiment,
GA
30212.
The
importance
of
soilborne
plant
pathogens
on
wheat
yields
as
influenced
by
no
tillage
and
soybean/wheat
doublecropping
were
examined.
Tillage
and
cropping
treatments
were
split
into
fumigated
(methyl
bromide)
and
nonfumigated
subplots.
Yields
under
no
tillage
were
significantly
lower
than
conventional
tillage
in
1984,
but
were
similar
for
1985,
a
year
with
a
very
dry
spring.
In
1984
yields
were
increased
62%
and
12%
by
fumigation
for
no
tillage
and
conventional
tillage,
respectively.
In
1985
yields
were
increased
15%
and
11%
for
these
same
treatments.
Yields
were
not
affected
by
cropping
system
(wheat/fallow
vs.
wheat/soybean).
The
growth
parameter
most
affected
by
fumigation
was
tillering.
The
most
common
group
of
pathogens
isolated
from
roots
were
Pythium
spp.,
primarily
P.
irregulare.
Isolation
frequency
of
Pythium
spp.
was
lower
under
conventional
tillage.
332
THE
EFFECT
OF
SAND
PARTICLES
SIZE
ON
INFECTION
OF
WHEAT
ROOTS
BY
GAEUMANNOMYCES
GRAMINIS
VAR
TRITICI.
H.M.
El-Nashaar,
R.A.
1098
PHYTOPATHOLOGY