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The presence or the
severity of Fusarium Head Blight (FHB) in an oat crop is next to
impossible to identify in the field prior to crop maturity. As
such, FHB in oat can, and should only be assessed by sampling the
harvested grain for FHB components such as infestation of seed by
Fusarium fungi and contamination by mycotoxin(s).
Compared to wheat and barley, oat seed has lower average levels of both
total Fusarium and Fusarium graminearum, the principal
producer of the mycotoxin deoxynivalenol (DON, vomitoxin)
contamination.
Compared to wheat and barley, oat seed is infected or contaminated with
much higher levels of Fusarium poae, and occasionally of
Fusarium sporotrichioides. These two species are not known to
produce deoxynivalenol (DON, vomitoxin), but are capable of producing
and contaminating grain with other trichothecene mycotoxins, such as T-2
and HT-2.
While oat normally has much lower levels of Fusarium graminearum
on seed, the proportional amount of deoxynivalenol (DON, vomitoxin)
contamination in oat is considerably higher than that which occurs in
wheat or barley.
Oats
often contain levels of deoxynivalenol higher than 1.0 ppm (all
cultivars tested in 2001, several cultivars in each of 2002 and 2003),
and occasionally may harbour much higher levels of DON (4 - 8 ppm in
many of the cultivars tested in 2001).
Laboratory processing of oat grain, involving dehulling (= groats),
steaming, kilning and rolling, significantly reduces the initial level
of DON, usually to levels below 1.0 ppm, even when the initial levels
are in the 5 - 10 ppm range.
Differences in oat cultivar performance to FHB are relatively minor;
however, in general, hulless lines, i.e. AC Belmont, AC Gwen, Boudrias
and Lee Williams, sustain a lower accumulation of deoxynivalenol in the
grain (and in the case of AC Belmont, also lower levels of Fusarium
graminearum). This lower level of DON is likely due to the loss of
the hulls, in which more than 50% of the DON (and F. graminearum)
usually resides, during experimental or commercial harvesting and
threshing operations.
Oat
grain should be tested routinely for FHB to assess whether the disease
and its accompanying mycotoxin(s) are present, prior to the grain being
used for its intended purpose as food or feed.
Based on the dichotomy between the lower levels of Fusarium in
oat grain, but the higher relative levels of deoxynivalenol
contamination compared to wheat or barley, it is difficult to assign an
FHB ‘resistance’ rating for oats, whether as a crop to compare this to
wheat or barley, or to differentiate individual cultivars. As a
starting point, hulless varieties of oat may be considered to have
‘fair’ resistance (albeit likely morphological rather than genetic) to
FHB, while hulled oats should be considered as ‘poor’, on the provincial
5-category ‘very good’ to ‘very poor’ scale (VG, G, F, P, VP). These
designations need to be refined further, before definitive resistance
ratings can be published for producer information.
The
entire oat ‘community’, from primary producers, to processors, to
manufacturers, and researchers, has been kept informed regarding the
findings of this project - through presentations, workshops,
conferences, published articles, the internet, and direct
communication. As such, FHB in oat is now on the ‘map’ and the disease
can be considered to be one of several diseases of major importance (in
addition to crown rust and stem rust) in oat grown in Manitoba.
Breeding for improved FHB resistance in oat should be pursued to assure
that the crop retains its status as a high quality Manitoba product for
use by both the food and feed industries. The finding that processing
reduces DON levels in oat to near negligible levels is significant, and
is a most positive development uncovered from this study. However, this
has little impact on the feed industry where whole oats, and/or the
hulls removed from food oats may be utilized in livestock nutrition.
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