Page 10 - Vol.38-No.3

CROP PROTECTION

MEASURING UP TO

MYCOTOXINS IN FEED GRAIN

Other fungal moulds prefer it hot and and where it is grown. However, the
dry. Classic cases are the aflatoxin-pro- appearance of one mycotoxin can often
ducing Aspergillus fungi and mainly A. act as a ‘marker’ for others because
flavus and A. parasiticus. Aspergillus both are produced by closely-related
are predominantly storage fungi and do moulds enjoying similar field condi-
not generally contaminate cereal grain tions for infection and mycotoxin pro-
prior to harvest. However, incidence duction which means, for example,
of drought stress and insect infestation that DON and ZEA frequently occur
and damage, and typically high for hot together. These two mycotoxins are
and dry growing conditions, may allow commonly produced by Fusarium
infection of standing cereal crops by graminearum and also by a number
Aspergillus fungi, and therefore the of other closely related Fusarium fungi
DR. TERRY MABBETT production of aflatoxin, prior to harvest. which infect a range of cereal crops.
Proper grain cleaning to remove all
Getting the measure of mycotoxins crop debris and especially the glumes
is no easy task especially for cereal (integuments surrounding small grain
crop commodities which are used as cereals like wheat) go a long way in
feed grain and as a key component preventing mycotoxins and fungal
of finished livestock feed. Many field moulds from entering the post-harvest
fungal pathogens and storage moulds and grain processing stages. The ex-
synthesise mycotoxins. Each group of tents to which mycotoxin-producing
fungi, including the aflatoxin-produc- moulds become active in store, and
ing Aspergillus moulds or the large to contaminate feed grain and subse-
number of Fusarium fungal pathogens quently finished animal feed, will de-
delivering a broadside of Deoxyniva- pend on the grain moisture content and
lenol (DON), Zearalenone (ZEA), T-2 the conditions of storage.
and HS-2 mycotoxins, has its own en- Maintaining the balance
vironmental requirements.
Twelve per cent grain moisture is
Each mycotoxin is the ‘signature’ generally given as the figure below
chemical and ‘calling card’ left by a which fungal mould activity ceases, but
specific fungus or group of related the situation is more complex than that.
fungi. Many of these highly versatile Moisture level within the grain and in
microbes ‘start life’ as disease causing Fungus infections can begin on the surrounding air is dependent on
pathogens on cereal crops and subse- the green wheat leaves, with the temperature because warmer air has
quently extend into grain spoilage and mycotoxin-producing pathogen a greater water-holding capacity
mycotoxin contamination at any stage subsequently infecting and
along the supply chain from on-farm contaminating the panicles and grain Moisture inside the kernels of stored
later in the wheat crop
storage to bags of finished animal feed. (Picture Dr Terry Mabbett) grain establishes an equilibrium lev-
el (balance) with the air outside and
Mycotoxins in the field the resulting relative humidity (R.H.)
Field factors including fungicide Mycotoxins moving
treatment (by seed dressings or fo- into store
liar sprays), fertiliser treatments and Mycotoxin first appears on the pan-
irrigation regimes, as well as the inher- icles of standing cereal crops but
ent disease resistance of the maize or cleaned grain arriving at the farm silo
wheat variety grown, will play a part in or loaded onto trucks for off-farm ship-
the nature and magnitude of mycotoxin ment is the first opportunity to test for
contamination. And watching over all what and how much mycotoxin is there.
this cereal agronomy is the weather as a Getting a measure of mycotoxins from
‘wild card’. The majority of cereal path- now on is matter of what to test for, at
ogens, and certainly Fusarium spp such what stage and how often.
as Fusarium graminearum responsible Wheat is prone to infection by a wide
for wheat head blight and stalk and ear Farmers and traders generally know range of mycotoxin-producing
rot in corn, respond favourably to cool, the range of mycotoxins they need to fungal pathogens
cloudy, moist and humid conditions test for in relation to the type of cereal (Picture courtesy Dr Terry Mabbett)
8 Vol. 38 No. 3