A Database for Triticeae and Avena
CEREAL DISEASE LABORATORY
(formerly CEREAL RUST LABORATORY)
USDA-ARS, University of Minnesota, 1551 Lindig, St. Paul,
MN 55108, USA.
D.L. Long, K.J. Leonard, D.V. McVey, M.E. Hughes, D.H. Casper,
and L. Wanschura.
Z.A. Pretorius et al. (Plant Dis 84:203) reported virulence
to Sr31 (T1BL·1RS) in a new pathotype of wheat stem rust
from Uganda. Tests performed at the Cereal Disease Laboratory
during the winter 1999-2000 were in agreement with those reported
by Pretorius et al. Additional sources of resistance to the Sr31-virulent
pathotype identified at the Cereal Disease Laboratory were the
cultivars Waldron (CI 13958), Triumph 64 (CI 13679), and Kota
(CI 5878). Seedling tests of 183 entries in the 2000 winter wheat
Regional Performance Nurseries (Eastern and Southern Soft Red;
and Northern, Southern, and Western Plains Hard Red Nurseries)
for resistance to stem rust, yielded three entries susceptible
to the Sr31 virulent isolate alone. All other entries susceptible
to the Uganda isolate were susceptible to various other of the
five selected highly virulent isolates of wheat stem rust. With
the limited use of Sr31 in the U.S., this isolate does
not appear to provide a threat to U.S. wheat production. For more
information, contact Don McVey (phone: 612-625-5291, E-mail: email@example.com).
Stem rust (Puccinia graminis f. sp. tritici).
In 1999, wheat stem rust severities were generally light in varietal
plots and fields throughout the southern U.S. During mid-May,
a few late-maturing wheat varieties were rusted heavily in southern
Louisiana nursery plots. In late May, severe stem rust was observed
during harvest on late maturing susceptible wheat in central Texas
plots. Wheat stem rust development was much lighter than normal
throughout the southern U.S in 1999.
During the first week in June, stem rust foci were found on
the cultivar Mit, and traces of rust were found scattered on other
cultivars such as Onaga and 2174 in southcentral Kansas nurseries.
In mid-June, wheat stem rust was light on susceptible cultivars,
e.g., Onaga, throughout central and northcentral Kansas plots.
In late June, trace-10 % severities of stem rust were observed
at the hard-dough stage in northcentral Kansas and southcentral
Nebraska fields, but losses were negligible. Wheat stem rust developed
late in the Central Plains. Most of the cultivars were early maturing
and, therefore, escaped the rust. The stem rust-infected areas
in the Central Plains provided spores for susceptible wheats farther
In late June, foci of wheat stem rust, 1 m in diameter at 10
% severity, were found in plots of the susceptible spring wheat
Baart in southcentral and westcentral Minnesota and in plots of
winter wheat cultivars, e.g., 2137, in central and eastcentral
South Dakota. In much of the central and northern Great Plains,
the temperatures were near normal, and moisture was ideal for
the spore infection process to occur. During the second week of
July, stem rust severities of 5-80 % were reported in a winter
wheat field of 2137 in central South Dakota. A significant yield
loss to stem rust occurred in this field. In other fields in central
South Dakota, trace-20 % severities were observed, but incidence
was low. In mid-July, trace-20 % severities were observed in winter
wheat plots in eastcentral South Dakota and southeastern North
Dakota. By mid-July, check plots of highly susceptible spring
wheat cultivars such as Baart had 20 % stem rust severities in
southcentral Minnesota and eastcentral South Dakota, and traces
of stem rust were found in southeastern North Dakota. In late
July, 30 % severities were reported on Baart in northcentral North
Stem rust was unusually prevalent in the Northern Plains this
year. The number of stem rust samples received at the Cereal Disease
Lab this year was twice as great as in recent years. The increased
severity of stem rust in the Northern Plains can be attributed
to the large amount of inoculum produced on winter wheat cultivars,
e.g., 2137, farther south in the Central Plains, and to the warm
temperature and good moisture, which were ideal for stem rust
infection in the Northern Plains this year. If current spring
wheat cultivars were susceptible to stem rust, a serious epidemic
with substantial yield losses would have occurred.
In mid-June, light stem rust was found in wheat plots in southwestern
Stem rust races. In 1999, eight Pgt races were identified
from 73 collections made in the U.S. (Table 1) as compared to
six Pgt races identified from 47 collections in 1998. Pgt-RCRS
was the most commonly identified race both in 1999 and 1998. From
1993 to 1997, race Pgt-TPMK had been the most common wheat stem
rust found in the U.S.. and in 1999 it was number three. Pgt-QCCJ,
the race that attacks barley and the second most commonly identified
race, was not identified in 1998, but from 1991-95 the QCCJ race
comprised 10-27 % of the identified isolates. Race RCRS was the
most frequently identified race in the Southern and Central Plains
states, but in the Northern Plains, Pgt-QCCJ was predominant.
Table 1. Races of Puccinia graminis
f. sp. tritici identified from wheat in 1999.
Wheat leaf rust (Puccinia triticina). During mid-March,
wheat leaf rust severities ranged from traces on flag leaves to
60 % on the lower leaves of cultivars in nursery plots throughout
southern Texas (Fig. 1).
For example, plots of Custer had traces of leaf rust, but Karl
92 had 60 % severities. Commercial wheat fields in southern Texas
had rust severities ranging from trace-20 % on the lowest leaves.
In southern Texas, rust increased on the lower leaves when moisture
was abundant, but rust increase farther up the plant was limited
because of dry weather. In southern Texas in early April, leaf
rust was severe on spring wheats like Norm (30 %).
In central Texas during early April, leaf rust was much more
severe and widely distributed than normal in wheat fields and
plots. The mild winter and moist conditions in February and March
contributed to the rust development in much of this area. In mid-April,
leaf rust severities of 80 % were observed in central Texas plots
of TAM 107. During the last week in April, wheat leaf rust severities
in northcentral Texas and southern Oklahoma ranged from trace-80
% in plots, and in fields where rust overwintered, severities
were as high as 70 % on flag leaves. Leaf rust was more severe
than last year in this area.
During November in Oklahoma, leaf rust was severe on some of
the commonly grown cultivars. However, a hard freeze in mid- to
late December, followed by dry conditions through January and
early February, eliminated this leaf rust in many of these fields.
Most of the rusted leaves died without the rust spreading to the
younger leaves because of the dry weather in February, so leaf
rust was less severe by early March. Moist conditions in late
March allowed rust to increase again and provided inoculum for
the wheat-growing areas farther north.
During the last week in April, wheat leaf rust severities in
southern Oklahoma ranged from trace-80 % in plots and were as
high as 70 % on flag leaves in fields where rust overwintered.
Leaf rust was more severe than in 1998 in this area and provided
rust inoculum for wheat grown in Kansas and Nebraska.
By the third week in May, leaf rust was severe in plots and
light in most fields in north central Oklahoma. In plots in north
central Oklahoma, 60 % severities were reported on flag leaves
of susceptible cultivars such as Chisholm, Karl 92, and Jagger.
However, severities of less than 2 % were observed on cultivars
like 2163, Custer, and Tomahawk. Rust was severe in some fields
in central Oklahoma where wheat was planted early, which allowed
an autumn infection and overwintering of leaf rust.
During the last week in April, traces of leaf rust were found
on Ae. cylindrica plants growing along the roadside in northcentral
Texas. The pathotype (race) SBD generally identified from these
collections normally does not infect the commonly grown wheat
cultivars. By the third week in May, leaf rust severities ranging
from 10-40 % were observed on Ae. cylindrica plants growing alongside
the road in northcentral Oklahoma.
Central Plains. In Kansas, the autumn of 1998 was long
and warm with frequent rains, which allowed for the buildup of
leaf rust on susceptible varieties. The winter was relatively
mild, but a cold snap in late December killed many of the leaves.
By early March, overwintered leaf rust was found in northwestern
and northeastern Kansas, but overwintering was generally light
and localized. Cool weather in late April and early May slowed
rust development. In early May, traces of leaf rust were found
on the flag leaves of susceptible wheat cultivars in fields in
the southern half of Kansas. During the third week in May, in
a southcentral Kansas nursery plot, 40 % leaf rust severities
were reported on the flag leaves of susceptible cultivars (e.g.,
TAM 107). Severities of 10 % were found on flag-1 leaves in fields
of the cultivar Jagger in southeastern Kansas in mid-May. In some
central Kansas fields, the flag leaves were clean, but the flag-1
leaves had leaf rust severities of trace-5 %. The northward development
of leaf rust into the Great Plains states was slow because of
the cooler than normal weather and moist conditions, which kept
the spores within the crop canopy. However, with the advent of
weather conditions more favorable for spore increase, trace-80
% severities were reported in southcentral Kansas nurseries during
late May. In fields in the same area, 20 % severities were observed
on flag leaves of susceptible cultivars like Jagger, but severities
were much lower on most of the other cultivars. In northcentral
Kansas, 20 % severities were observed on the lower leaves.
In early June, only traces of leaf rust were found in eastern
Colorado. The leaf rust was less than in prior years, partly because
less acreage of the common susceptible cultivar TAM 107 was grown.
By mid-June in the central plains, 80 % leaf rust severities were
common on susceptible cultivars such as TAM 107 from southeastern
Colorado to northcentral Kansas. Leaf rust developed late, but
still managed to kill the flag leaves of susceptible cultivars
during the soft dough stage throughout much of this area.
The overall estimated loss from leaf rust in Kansas in 1999
was 3.4 %, (Table 4),
which is below the 10-year average of 5 %, but above last year's
estimate of 2.5 %. Yield losses were estimated from fungicide
plot data, cultivar surveys, cultivar disease ratings, and disease
surveys. Several varieties such as Big Dawg, Custer, Dominator,
Heyne, and Jagger showed significant losses of resistance compared
to last year in most Kansas plots.
During the first week in June, traces of leaf rust were found
in a southeastern Nebraska winter wheat nursery. By mid-June,
leaf rust was light in many fields in southern Nebraska and severe
in some fields of susceptible cultivars, where rust had infected
early in the spring or had overwintered.
Northern Plains. In late May, traces of leaf rust were
found in winter wheat plots in Brookings, South Dakota. Growth
stages ranged from emergence of the flag leaf to late boot. On
27 May, traces of leaf rust were observed on the lower leaves
of the winter wheat cultivar Norstar in a southeastern North Dakota
plot. On 3 June, trace-1 % severities were found in a plot of
the winter wheat Roughrider in eastcentral Minnesota. Traces of
rust also were observed on other winter wheat cultivars. The rust
development in the northern Great Plains states probably originated
from rust spores hat were deposited with rain in mid-May. This
rust development was earlier than normal. During the first week
in June, 5-30 % severities were reported in a winter wheat nursery
and traces in spring wheat fields in southeastern South Dakota.
By mid-June, 20 % severities were observed on the flag leaves
of susceptible winter wheats and 30 % on lower leaves of susceptible
spring wheats in east central South Dakota. Leaf rust developed
faster in this area than in 1998.
During the final week in June, leaf rust severities ranged
from trace-60 % on flag leaves of susceptible winter wheat cultivars
in central and eastern South Dakota plots and fields. Winter wheat
flag leaves dried up quickly because of heavy leaf rust infection
throughout South Dakota and southern Minnesota. These rust infections
probably originated from inoculum sources in Oklahoma and Nebraska.
During the final week in June, leaf rust severities were 10% on
the flag leaves and 60% on lower leaves of susceptible spring
wheat cultivars, e.g., 2375, in plots in southwestern and westcentral
Minnesota. In fields, severities ranged from trace-10 % on the
lower leaves of spring wheats in western Minnesota and northeastern
South Dakota. Leaf rust was more severe and concentrated in the
upper Midwest in 1999 than it has been in the last 20 years. Abundant
inoculum from the south was deposited with the frequent rains,
and weather conditions favored infection. The spring wheat cultivars
currently grown are more susceptible than those in previous years.
By mid-July, 40 % severities were common on flag leaves of
spring wheat cultivars, e.g., Oxen, growing in plots in west central
Minnesota. In spring wheat fields, 20 % severities at the early
berry stage were common throughout west central Minnesota and
east central South Dakota. By late July, severities were 40 %
in spring wheat cultivars in a northeastern Montana nursery and
10% in spring wheat fields in north central North Dakota. This
year, total yield losses from leaf rust of 2-4 % per state (Table 4 and Table 5) were common in both winter and spring
wheats in the Northern Plains.
Southeast. In February, heavy rainfall in Louisiana
did not allow the rust spores to move up the plants, so rust development
was limited. By mid-March, wheat leaf rust was increasing in plots
of southern SRWW cultivars in southern Louisiana.
In much of the southeastern U.S., dry weather through March
and some of April was a limiting factor in rust development. In
mid-April, leaf rust was severe in plots of susceptible southern
SRWW cultivars within approximately 75 miles of the Gulf Coast,
and some cultivars that previously were resistant showed significant
rust development this year. During the last week in April in the
southeastern U.S., severities of 60 % were observed in plots of
susceptible soft red winter cultivars, although in fields, 1 %
severities were common on the flag leaves. The drier and cooler
than normal conditions during the last part of April slowed the
rust development. Because of low relative humidities during the
last half of April, there was little dew formation, which is needed
for rust infection to occur. Therefore, the numbers of spores
released as inoculum for areas farther north were lessened. Losses
to leaf rust in the southeastern SRWW area were less than normal
this year (Table 4).
During mid-April, traces of leaf rust were found in southern
Arkansas. By the third week in May, leaf rust was heavier than
normal, but wheat in the southern part of the state was too mature
for rust to cause much loss. In northern Arkansas (north of I-40),
losses occurred in fields that were later than normal in maturity.
This area provided a source of inoculum for areas to the north.
In some fields in this area, leaf rust development was stopped
by severe Septoria infection of leaves.
In mid-April, 40 % severities of leaf rust were found on wheat
in eastcentral South Carolina plots.
Midwest. By the first week in June, 20-30 % leaf rust
severities were observed on susceptible wheat cultivars at the
late milk growth stage in southwestern Indiana and western Kentucky
plots. Leaf rust severities of 40 % were observed in wheat fields
at full berry stage in northeast Missouri on 7 June, and severities
in plots ranged from trace-40 %.
By the second week in June, 40 % leaf rust severities were
reported in plots of susceptible wheat cultivars from northeastern
Missouri to northeastern Indiana. In fields of the susceptible
cultivar Clark in southern Illinois, 80 % rust severities were
common during the second week in June. In plots and fields in
places like east central Indiana, 20 % severities were noted on
only 10 % of the wheat plants, because there was not enough dew
or rainfall in late May to allow the infection process to occur
and, therefore, rust did not spread from wheat plants infected
During the third week in May, traces of leaf rust were reported
in southcentral Michigan. Leaf rust (low to moderate incidences
and low severities) was found in southwest Michigan fields by
8 June. The infections were predominantly on the lower leaves.
East. During the last week in May, 80 % leaf rust severities
were observed on susceptible winter wheat cultivars in eastern
Virginia plots, and traces of rust were found on wheat in west
central New York fields. Leaf rust was not a problem in the eastern
U.S. this year, because conditions were so dry limited rust infection
California. In early May, 20 % leaf rust severities
were reported on wheat lines growing in a nursery in the northern
Sacramento Valley. By mid-May, late infections of wheat leaf rust
occurred throughout the Central Valley, but because the infections
were so late, losses were minimal. Disease levels were much lower
in 1999 than in previous years because of the cool spring and
a cold spell in late December, which killed some of the early
Pacific Northwest. By the third week in May, leaf rust
was just starting to show in nurseries in western Oregon, but
none was found in commercial fields. In eastern Oregon, wheat
leaf rust was light because of the cool dry May.
During mid-April, leaf rust was light in wheat plots in the
Skagit valley of western Washington. Because of the cool dry May,
leaf rust increased at a slow rate in the state of Washington.
By the second week in June in western Washington plots, 50 % severities
were reported on winter wheats and traces on the spring wheats.
In mid-June, traces of leaf rust were found on spring wheats in
eastern Washington plots. By late June, wheat leaf rust was increasing
on spring wheats in the Mount Vernon area of western Washington.
In early July, traces of leaf rust were found in eastern Washington
and northern Idaho fields. In mid-July, leaf rust was increasing
on spring wheats in western Washington. Leaf rust was very light
east of the Cascades in Washington. The cool dry conditions in
early spring were not conducive for leaf rust to develop, and
losses were light this year in the Pacific Northwest (Table 4 and Table
Leaf rust races. Virulence formulas for the leaf rust
races collected in 1999 are shown in Table 2. The four most common
leaf rust races found in the U.S. in 1999 were MBDL, MCDL, MCRQ,
and THBL (Table 3).
Races MBDL and MCDL comprised a significant part of the race population
in the Great Plains states from Oklahoma northward to North Dakota.
These two races (Lr17 virulence) overwintered in Oklahoma
and increased on cultivars like Jagger that have Lr17 resistance.
Jagger is grown on significant acreage in Oklahoma and Kansas.
From the initial inoculum source, the rust spores then infected
other wheats along the Great Plains Puccinia pathway. Another
significant change this year was the increase in the number of
T races (Lr1,2a,2c,3 virulence) that
were identified. For example, the second most commonly identified
race was THBL, which was found in the northern Great Plains area.
Losses were much higher than normal in northern plains states
(Table 5). Much of this
loss was due to an increase in virulence of Lr2a, which
is included in the Lr gene resistance of many of the spring
Wheat stripe rust (Puccinia striiformis). The first
report of stripe rust this year in the central part of the U.S.
was in a southcentral Kansas nursery, during the last week in
May. Wheat stripe rust foci were found in some plots (e.g. 2137),
and traces of rust were scattered throughout the central and southern
parts of the state. Where this rust originated from is anybody's
guess. Last year, light amounts of wheat stripe rust were scattered
from the lower Mississippi Valley north to eastcentral Minnesota.
In Kansas, the cool spring weather allowed development of stripe
rust, but the hot temperatures of early June disrupted further
development, so losses were negligible (Table 4).
During the third week in June, traces of stripe rust were found
in east central Colorado fields. Normally, stripe rust is found
at higher elevations in Colorado, i.e., San Luis Valley (7,500
ft) or front range of the Rockies (~5,000 ft).
In early June, light amounts of stripe rust were observed in
wheat plots in west central Indiana.
During mid-April, wheat stripe rust was severe in a field in
the Sacramento Valley of California. In other fields in the same
area, severe rust was expressed in small foci. By the first week
in May, wheat stripe rust was increasing in the Sacramento Valley,
where temperatures remained relatively cool. Disease foci readings
ranged from 1-80 % severities in fields of the autumn-sown HRSW
cultivars Express and RSI 5, the predominant cultivars grown
there. During the third week in May, because of the cool weather,
wheat stripe rust was continuing to increase in fields in the
Sacramento and San Joaquin Valleys. A 7 % yield loss from stripe
rust occurred in California.
In mid-April, wheat stripe rust severities of 30 % were reported
on susceptible winter wheat lines in the Skagit valley nursery
in western Washington. In late May in western Oregon nurseries,
wheat stripe rust was starting to show, but none was found in
commercial fields. During the last week in May, 80 % wheat stripe
rust severities were reported on susceptible winter wheat lines
in northwestern Washington plots at the boot stage. In mid-June,
60 % severities were observed on spring wheats in western Washington.
Wheat cultivars with adult-plant resistance continued to provide
durable resistance in farmers' fields. Stripe rust foci of 60
% severity were found in winter wheat plots in eastern Washington,
but they were few in number. The dry autumn and cool dry May led
to the low rust severities, but the rains in mid-June improved
conditions for rust buildup.
By late June, wheat stripe rust was increasing on spring wheats
in the Pacific Northwest, but rust losses were minimal, because
most of the cultivars have high temperature, adult-plant resistance.
During mid-July, 100 % stripe rust severities were reported on
susceptible spring wheat cultivars in the Mount Vernon area of
western Washington. In mid-July, wheat stripe rust was increasing
in spring wheat fields in the Palouse region, but the adult-plant
resistance of commercial cultivars minimized losses (Table 5).
In early July, significant amounts of wheat stripe rust were
reported in nurseries in the Bozeman area of Montana.
4. Estimated losses in winter wheat due to rust in 1999.
5. Estimated losses in spring and durum wheat due to rust in 1999.
UNIVERSITY OF MINNESOTA AND USDAARS
PLANT SCIENCE RESEARCH UNIT
Department of Agronomy and Plant Genetics, University of
Minnesota and USDAARS, St. Paul, MN 55108, USA.
J. Anderson, R. Busch, G. Linkert, L. Matthiesen, E. Wennerlind,
A. Procopiuk, H. Mickelson, S. Liu, and K. McGowan.
Dr. Sixin Liu joined our project in January, 2000, as a postdoctoral
associate. Kari-Lynn McGowan is a new M.S. student. Ana Maria
Procopiuk finished her Ph.D. in December, 1999. Heidi Mickelson,
a joint graduate student with S. Rajaram (CIMMYT) and R. Busch,
died in September, 1999, after being ill for several years.
Minnesota produced an estimated 79.2 million bushels (2.67
million metric tons) from 1.99 million acres (0.81 million hectares)
in 1999. Losses from leaf rust were estimated at 4 %. During the
1998-99 crossing cycle, 317 crosses were made. Most of these crosses
involved elite germ plasm from the University of Minnesota HRSW
breeding program and sources of FHB resistance. A total of 1,980
lines were under small-scale increase (8 ft. rows) in the 1998-99
winter nursery in California. A total of 17,000 F3 seeds were
planted in New Zealand in the autumn of 1998 for generation advance
by SSD. During the 1999 growing season, 439 and 140 experimental
lines were evaluated in replicated preliminary and advanced yield
trials, respectively. The preliminary yield and advanced yield
trials were grown at two and three locations, respectively. The
Variety Trial, which contained 31 released varieties and two University
of Minnesota experimental lines, was grown at seven locations.
FHB-inoculated, misted, replicated nurseries were established
at three locations. Approximately 2,500 lines were tested for
FHB resistance in the greenhouse during the past year. Most of
these materials were experimental lines, but also included potential
new resistance sources from China and elsewhere and materials
for genetic studies. McVey (MN93413) was released in 1999. Developed
under the project leadership of Dr. Robert Busch, McVey has shown
high yield levels, even in the presence of FHB.
J.A. Anderson and E. Wennerlind.
We are using SSR markers to saturate genomic regions known
to contain FHB-resistance genes. We are concentrating our efforts
on chromosomes 3BS and 2AL, where we have previously located major
QTLs for this disease using RFLP and AFLP markers. Previous research
identified an AFLP fragment associated with FHB resistance on
3BS. We cloned and sequenced this fragment and designed PCR primers.
Unfortunately, these primers did not reveal polymorphism in either
of two populations. We have continued mapping SSR markers in three
populations of wheat segregating for resistance to FHB: 'Sumai
3/Stoa', 'ND2603/Butte 86', and 'Wuhan/Norm'. Of the 142 microsatellite
markers screened to date, 37 % were polymorphic between Sumai
3 and Stoa and 62 % between ND2603 and Butte 86 or between Wuhan
and Norm. The marker Xgwm533 was mapped in the 'ND2603/Butte 86'
population and explained 24.6 % of the phenotypic variation in
scab resistance in this population. This marker explains the highest
proportion of FHB resistance of those that we have identified
to date for a gene inherited from Sumai 3. Unfortunately, this
microsatellite was not polymorphic between Sumai 3 and Stoa. Based
on a common marker (AFLP locus XEagcMcta.1) mapped on 3BS
in the 'Sumai 3/Stoa' and 'ND2603/Butte 86' populations, we believe
the same gene(s) on chromosome 3BS is contributing to scab resistance
in both populations. Two additional SSRs were mapped on 3BS in
'ND2603/Butte 86', so that this region is now well covered with
A. Procopiuk and R. Busch.
Fusarium spp. can cause an important wheat disease that
has resulted in an estimated $1.3 billion in losses in the Midwest
of the U.S. in the last 6 years. Present methods of screening
wheat for improved resistance to FHB requires adult-plant testing
in the field and in the greenhouse. Our objective was to increase
screening efficiency by determining if seedling tests for FHB
resistance would predict adult FHB reaction of spring wheat genotypes.
Preliminary experiments to determine the best method of inoculating
seed with F. graminearum macroconidia, using vacuum and suspension,
indicated that the suspension method was superior. After preliminary
testing using only Sumai 3 (resistant) and Wheaton (susceptible),
we determined that scoring roots provided little useful information.
Twenty-four genotypes with diverse reactions to FHB then were
evaluated for seedling height and emergence in three separate
greenhouse tests. The reaction of the 24 genotypes to FHB had
been evaluated previously in a FHB-inoculated nursery and in a
natural field epidemic. Genotypes did not differ from the control
for seedling height, indicating that this trait was of little
value in determining FHB reaction. Genotypes also did not differ
for seedling emergence, adjusted for control, when combined over
greenhouses because of a 'genotype x greenhouse' interaction.
Results within each greenhouse trial and for combined greenhouse
trials indicated that emergence percent was reduced more for Pioneer
2375 than for any other genotype. Pioneer 2375 provides some resistance
to FHB and was the most widely grown cultivar in the upper Midwest
during the FHB epidemic years 1994 through 1998. Sumai 3, the
most resistant genotype in the study, also had severely reduced
emergence in two of three greenhouse trials. The seedling leaf
reaction to the toxin DON was tested using six genotypes. The
reactions of the genotypes did not differ from each other but
differed from those of the controls. We concluded that none of
the seedling tests were sufficiently predictive of adult plant
reaction to FHB to justify their use for discarding even the most