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Background and Objectives:
Fusarium head blight (FHB) is a major disease of
wheat and barley in southern Manitoba. It can have a devastating effect
on crops and on producer returns. FHB not only reduces grain yield and
quality, but also lowers the quality of seed, compromises end-use
choices because of mycotoxin (DON) contamination (particularly important
to the feed industry), and impacts on the grain trade due to tight or
nil tolerances imposed by customers. FHB currently is the most
important constraint to sustainable or enhanced cereal production in the
province, and as such merits the highest attention and research
priority.
High severities of
this disease can develop in certain environments (typically the Red
River Valley, the Interlake, and South-Central region) in most years
(since 1993), and therefore strategies to minimize damage must be
developed and implemented to maintain producer and industry
profitability. Fortunately, currently-registered cultivars of wheat and
barley, developed without consideration for FHB, are not all highly
susceptible to the disease, and the most resistant (or least
susceptible) ones can be sown as the cornerstone of an integrated FHB
management strategy. A sound management strategy would also include the
use of foliar fungicides, either registered (Bravo) or having emergency
registration (Folicur), cultural amendments (rotations, straw
incorporation/sanitation), and staggered seeding dates and/or use of
cultivars of differing heading/maturities.
The objectives of this
research were as follows:
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Test registered varieties of barley and wheat
suitable for production in Manitoba for their reaction (performance)
to Fusarium head blight (FHB), under natural conditions, and in the
Agriculture and Agri-Food Canada, Cereal Research Centre inoculated
Fusarium Head Blight Nursery at Glenlea, Manitoba (the 'Variety
Performance Trials'- VPT).
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Inspect and sample barley and wheat varieties in
Manitoba Crop Variety Evaluation Trials (MCVET) and/or other regional
trials to supplement testing outlined in “1” and use MCVET/other
trials to assess the FHB performance of a few selected varieties over
a wide geographic region.
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Incorporate data on varietal performance of barley
and wheat to FHB in the 1998 and subsequent annual Manitoba Seed
Guides for the information of producers.
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Disseminate information on barley and
wheat performance to FHB to producers and the industry by
participating in producer field days and at winter industry meetings.
Procedure and
Project Activities:
Varieties
Twenty-two (22) varieties of each of barley and
wheat were tested over three field seasons (1998, 1999, and 2000) at
multi-locations for their performance to FHB. The varieties included:
Barley
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2-row (9) - Condor (hulless or ‘H’), CDC Dawn (H),
CDC Gainer (H), Harrington, CDC Lager, AC Metcalfe, AC Oxbow, AC
Sterling, CDC Stratus
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6-row (13) - B1602, AC Bacon (H), CDC Earl, Excel,
Falcon (H), Foster, AC Lacombe, Legacy, Robust, AC Rosser, CDC Silky
(H), CDC Sisler, Stander.
Wheat
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CWRS – bread wheats (9) - Bacup, AC Barrie, AC
Cadillac, AC Cora, AC Elsa, AC Intrepid, McKenzie, AC Majestic, Roblin
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CPS – noodle, flatbread wheats (2) - AC Taber, AC
Vista
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ES – extra strong (frozen dough) wheats (4) –
Amazon, AC Corinne, Glenlea, Laser
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CWAD – durum or pasta wheats (5) – AC Avonlea,
Kyle, Medora, AC Morse, Plenty
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SWS – soft white, cookie wheat (1) – AC Reed
Locations
1998
1999
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VPT: Altona, Carman, Kelburn, Morris, East Selkirk,
Glenlea (Nursery)
2000
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VPT: Altona, East Selkirk, Grosse Isle, Kelburn
Farm/St. Norbert, Rosebank, Glenlea (Nursery)
Field Plan
Plots were 1m x 5m, planted as 4 rows with 0.3m
spacing, with two replications. They were seeded with a small-plot
4-row seeder as soon as conditions at individual sites were suitable for
planting. Plots were trimmed and weeded by hand, as necessary. At
maturity, heads from a single 5m row were hand harvested, heads dried
further in a warm greenhouse, and then subsequently hand-threshed to
obtain all seed. Seed was analyzed for various FHB parameters (level of
Fusarium species, levels of Fusarium damaged kernels or FDK by number
and weight, and for contamination by deoxynivalenol or DON).
Due to very low levels of natural FHB developed at
the three VPT sites in 1998, (due to lack of rainfall and/or low levels
of inoculum at those sites during heading of plants in the test plots),
the protocol was changed in subsequent years to improve chances of FHB
development. Therefore, in 1999 and 2000, plots were ‘inoculated’ with
Fusarium graminearum by applying 40g of infected corn kernel
inoculum per square meter to the soil surface approximately 3 weeks
prior to heading. While sufficient moisture is required to ‘activate’
the fungus infesting the corn kernels, thereby producing the fruiting
bodies (perithecia) and primary inoculum (ascospores), no supplementary
moisture could be applied at the test sites and natural rainfall was
relied upon. Nonetheless, this was sufficient in most cases to generate
at least light, and more often moderate to severe FHB epidemics at the
trial locations.
Sampling
Two to three weeks after heading (in late July to
early August, depending on seeding date and crop development), spikes
were sampled for severity of FHB by collecting 40 heads at random (10
from each row) from each plot and storing these in plastic bags at -10°C
until analyzed. At maturity, one complete row per plot was harvested
and spikes stored in paper bags in a warm greenhouse until fully dry.
Analysis
FHB severity was assessed by counting the number
of heads out of 40 (as a %) having symptoms of FHB (= disease
incidence), and on affected heads, the number of bleached (infected)
spikelets out of the total number (as a %), and multiplying these two
numbers and dividing by 100 to obtain the Fusarium Head Blight Index
(FHB-1). For example, 10 heads out of 40 affected (= 25% incidence),
and an average of 3 out of 15 spikelets infected on ‘positive’ heads (=
20% severity), result in an FHB-1 of 5.0% (25 x 20 / 100).
Fusarium measurements on mature seed included
level (%) of Fusarium spp. infecting seed and Fusarium
identity to species, levels of Fusarium damaged kernels (FDK,
tombstone), measured by their number and weight, and contamination by
deoxynivalenol (DON, vomitoxin). Levels of Cochliobolus sativus,
causal agent of the foliar diseases spot blotch, and a common spike/seed
invader, also were monitored.
Results and Discussion:
For objectives 1
and 2 the results indicate that:
Wheat
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As
classes, durum and CPS wheats are particularly susceptible to FHB.
These generally showed higher levels of DON, total Fusarium spp.
and F. graminearum on seed, and FDK. Visual disease severity
(FHB-1) was not always higher than or as high as other measurements
would suggest. This likely was due to the fact that wheats of these
classes have a longer maturity and head several days later than most
bread wheats. Because severity in all wheats was sampled on the same
day (due to time and labour constraints), it is likely that for these
wheats, severity was determined several days earlier than ‘optimum’.
Most varieties of durum and CPS wheats tested here should be rated as
having ‘very poor’ (VP) resistance to FHB, for purposes of the
Manitoba Seed Guide. The newer variety AC Vista, although desirable
for reasons of quality, was one of the most FHB-susceptible genotypes
tested. This cultivar will sustain significant losses of yield and
quality and is not suitable for production in regions where FHB is
endemic and disease inoculum is plentiful (i.e., south-central and
south-eastern Manitoba).
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Based
on the single variety tested, the SWS wheat AC Reed also is
susceptible to FHB. Soft white spring wheat is not normally grown in
Manitoba, but was included here to ‘complete’ the portfolio of wheat
classes produced in western Canada.
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Bread wheats were generally less affected
by FHB than other classes; however, at least one cv. Roblin, was as
susceptible as the durum and CPS cultivars tested (rating VP). The
poor performance of Roblin relative to others in this class was
particularly evident in environments where FHB pressure was light to
moderate. By contrast, cultivars AC Barrie, AC Cadillac, AC Cora, AC
Majestic were the most resistant to FHB in the majority of tests
(rating Fair or F). The American bread wheats Bacup and Gunner
performed similarly (F). AC Elsa and AC Intrepid were somewhat poorer
overall, and these likely should be rated as poor (P) in performance
to FHB.
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The four extra-strong wheats tested, were
generally situated in the ‘middle of the pack’ and would be rated as P
to FHB.
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Fusarium
graminearum was the primary pathogen isolated from FHB-affected
wheat crops, comprising more than 90% of the Fusarium spp.
present on wheat kernels. Average F. graminearum levels were
as high as 50%, while in individual cultivars, these could approach
70-85%. High levels of Fusarium infestation of seed have been
shown to greatly reduce germination and plant emergence in subsequent
crops.
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Levels of FDK also could be quite high as
found at Grosse Isle and Selkirk in 2000. Levels of FDK higher than
10% would impact grade significantly, rendering the grain as ‘sample’
and unmarketable in regular commercial channels.
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Cochliobolus sativus,
a common foliar
and spike pathogen of cereals in Manitoba was isolated from wheat
kernels in all cases, but usually at levels of < 20%. This pathogen
can cause ‘black point’ in wheat (a downgrading factor), but its
potential to cause this disorder, and its role, if any, in altering
Fusarium
levels on seed, was not explored.
Wheat – Other
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In 1998, when FHB levels at the 5 designated VPT
tests sites were low to very low, wheats at three MCVET sites
(Hamiota, Rosebank, Treherne) were sampled to provide supplementary
data. Two sites contained some wheats not tested in the VPT group,
and none contained all the VPT cultivars. At Hamiota, FHB severity
was rated as light - mod.; AC Vista (CPS) and Laser (ES) wheats
performed worst and had DON levels of 8-10 ppm. Some durums were
included, but seed of these was obtained late and DON tests were not
performed. At Rosebank, FHB was moderate - severe, and again the cvs.
AC Vista and Laser performed worst (DON 19 - 24 ppm). The
American-bred, non-registered wheats, Hagar, and Hamer had DON at 8 -
9 ppm, and based on this one trial would be rated as P. Bread wheat
5600HR was quite good and would rate as F. At Treherne FHB severity
was light, and the severity index (visual disease) very low. Three
durum wheats and the American wheats Hagar, Hamer and Lars performed
worst (DON 2 - 5 ppm).
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At all sites where FHB severity was light or very
light, the data obtained were only useful in differentiating the worst
performing cultivars - usually these were AC Vista, Roblin, at times
Laser, and the durum wheats.
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At sites where FHB severity was moderate to severe,
better differentiation among cultivars was possible and F, P, and VP
performers could be identified and classified.
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In wheat, the various measurements of FHB, i.e.,
DON level, FHB-Index, Fusarium levels and FDK appeared to be
positively correlated, and each gave a reasonable indication of
cultivar performance. Because of the concern re: mycotoxins in the
grain, and the impact of DON on feed and food quality and livestock
and human health, the ranking of cultivars is based on increasing
levels of DON, that is, lowest (= best) to highest (= worst).
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At two sites where FHB
developed to severe levels based on DON, Fusarium spp. and to a
lesser extent FDK (Grosse Isle and Selkirk in 2000), the visual
severity (FHB Index was very low). This anomaly suggests that in 2000
at these sites, FHB development was somewhat delayed (perhaps due to
temperature or moisture conditions), but that conditions subsequently
became optimal, resulting in high levels of the disease in the mature
grain. In situations where only a visual in-crop estimate of the
disease can be made (lack of facilities, funds, and/or expertise in
determining Fusarium levels, doing DON tests, etc.) assessing FHB in
the field as late as possible would be desirable. However, this
should be done prior to the crop ‘turning’, as at this time
differentiation between healthy green spike tissue and infected
bleached tissue becomes difficult if not impossible.
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It would be erroneous and undesirable to base FHB
performance of wheats on a single trial or environment. This was
demonstrated convincingly in several instances during the tenure of
this project, e.g., the better ranking of Kyle durum at the Glenlea
VPT Nursery in 1998, a similar high ranking for several durums at
Altona in 1999, the high ranking for Amazon ES wheat at Kelburn in
1999 and the top ranking for Laser ES wheat at Grosse Isle in 2000.
These results all are anomalous and in isolation would lead to
wrongful conclusions.
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The relatively low levels (compared to those in
barley) of C. sativus infestation of wheat kernels in most of the
trials suggest that this pathogen did not have a role in the
‘production’ of FDK kernels. In wheat these are relatively easy to
distinguish as they are visibly shriveled, smaller and chalk-coloured
compared to healthy kernels. Kernels infected by C. sativus are
typically darkly-stained at the embryo end of the kernel, or over a
larger area (= black point and smudge) but are neither shriveled nor
chalky in colour.
Barley
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As found for wheat,
the barley cultivars tested differed in performance to FHB and
severity levels, as measured by DON, ranged from less <1 to 15 ppm.
Such differences were particularly evident when FHB pressure was
high, such as at Grosse Isle and Selkirk in 2000. In general, two-row
barleys performed better than six-row types.
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For hulless barleys,
the loss of most hulls during harvesting/threshing could be expected
to reduce levels of FHB, as both DON and Fusarium fungi have been
shown to preferentially occupy tissues near the seed surface.
However, hulless barleys were not more resistant to FHB than some
hulled cultivars, although, six-row hulless barleys did perform better
than hulled six-rows in most cases.
- Based on DON accumulation following FHB
infection, most two-row barleys could be rated as F to FHB, while many
six-row cultivars would be VP. The latter category would include cvs.
CDC Earl, AC Lacombe, AC Rosser and Stander, six-rowed barleys that
consistently performed poorly to FHB. The six-row cultivars CDC Sisler
and Legacy, sometimes performed somewhat better than others of their
type, suggesting a P rating, or potentially F, pending further
testing.
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As a rule, FHB levels,
measured by DON, FHB Index, Fusarium spp. and FDK, in barley
were always lower than in wheat. However, in some environments levels
of Fusarium spp. were similar (i.e., high) to those in wheat,
although resulting DON levels were much lower. This suggests that
this crop is generally less susceptible to the DON development and
accumulation phase of FHB than is wheat.
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Fusarium graminearum was the principal species isolated from
affected barley crops, but in contrast to wheat, this species was not
as predominant, and other species, especially F. poae and F.
sporotrichioides (and sometimes F. avenae), made up a
sizable portion of the Fusarium isolated.
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FDK levels in barley
were more difficult to characterize and enumerate than those in wheat,
and levels of FDK often did not parallel differences in other FHB
measurements, i.e., DON or Fusarium levels. FDK in barley, for
the purposes of this study, included kernels with dark staining; some
of this discolouration could have been caused by agents other than
Fusarium.
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Levels of Cochliobolus sativus in barley
generally were considerably higher than those found in wheat. There
appeared to be differences in this trait between two-row and six-row
types, with the former having higher levels of this pathogenic fungus
on seed. Levels of C. sativus sometimes averaged near 30%, and
were as high as 92% in individual cultivars. It is likely that some
of the dark staining of kernels (measured as FDK) was caused by the
high (or otherwise) levels of C. sativus. There also may be an
association between levels of C. sativus and those of
Fusarium spp. (and DON) on barley seed, as these appeared to be
negatively correlated in many instances.
Barley – Other
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It is not possible, or would
certainly be undesirable, to evaluate cultivar performance to FHB
based on data from a single environment. To do so would lead to
certain erroneous conclusions; e.g., CDC Earl barley ranked second
best at Kelburn in 2000, but was second worst at Selkirk in 1999.
This disease appears to be very variable in commercial fields as well
as experimental trials, and considerable replication is needed (i.e.,
data from several station-years must be compared and summarized),
before meaningful conclusions can be drawn.
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Severity of FHB can vary considerably among test
sites in any give year, even though such sites are all in ‘southern
Manitoba’, e.g., average DON levels of 0.5 ppm for barley at Altona,
vs. 3.4 ppm at Selkirk, 100 kms apart ‘as the crow flies’.
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When FHB severity was low (average DON levels of
<=0.5 ppm in barley), the data could only distinguish the
worst-performing (VP) cultivars from the remainder, e.g., as at Carman
and Kelburn in 1999 for (VP) barley cvs. AC Lacombe, Robust, Stander
and Falcon.
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When FHB severity was moderate or high
(average DON levels of >=2.0 ppm in barley), better differentiation
among cultivars was possible and more performance ‘classes’ could be
distinguished, e.g., as at Grosse Isle and Selkirk in 2000, where
barley cultivars with DON levels of <=2.0 could be rated as F, those
>2.0 to <=4.0 as P, and those > 4.0 as VP.
For objective 3:
Cultivar performance to FHB based on these trials was summarized and
ratings prepared (F, P, VP) for the varieties under test. These were
supplied annually to Manitoba Agriculture and Food, Soils and Crop
Branch, Carman, Manitoba (Mr. Dave Campbell) and used, along with
supplementary data, to prepare the disease performance tables re. wheat
and barley published in the ‘Manitoba Seed Guide’ for the information of
producers and the agricultural industry. The cumulative data from two
and subsequently the three years of testing, resulted in a number of
changes to cultivar FHB ratings over the years (1998, 1999, 2000, 2001
Seed Guides) as would be expected as additional information (either
confirmatory or contrary) became available.
For objective 4:
Information on progress and
results of these trials was presented at numerous summer field days
(Altona, East Selkirk x 3, Glenlea, Grosse Isle, Kelburn Farm, Warren),
and winter meetings (Roseisle, Selkirk x 2, Stonewall, Teulon) in
co-operation with Manitoba Ag Reps (Mr. Michael Sykes, Mr. Stan Stadnyk,
and others), and distributed to the farm press for inclusion in articles
on FHB in the Manitoba Co-operator, Western Producer, Top Crop Manager
and other publications. As such, producers and the industry were kept
apprised of the research results, and on the performance of adapted
registered varieties to FHB. This information was useful to develop an
FHB management plan, in which varietal selection plays a pivotal role.
Conclusions:
Availability of a highly FHB-resistant wheat or barley cultivar suitable
for production in Manitoba is not imminent (late 2002), despite
optimistic pronouncements in the past. It will likely be at least
4 years before such cultivar(s) are released. At present, the status of
a potential candidate, ‘Alsen’ wheat, is unresolved as it is not
registered pending final assessment of quality, and in addition, its
resistance may not be sufficient. In the interim, an integrated
strategy, as outlined above should be used to combat FHB and minimize
its impact on cereal production in Manitoba. The information on cultivar
performance to FHB obtained in this study has been a valuable and
integral component to the implementation of this approach.
Acknowledgement:
This project was made possible
due to funding from the Governments of Manitoba and Canada through the
Canada-Manitoba Agri-Food Research and Development Initiative (ARDI).
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