grain molds and
TRANSCRIPT
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Grain Molds and
Mycotoxins in Corn
Dr.Kedar Karki
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Grain Mold Pathogens
Molds are fungi that grow by producinglong filaments called hyphae (Figure 1). Ingeneral, hyphae are important to the
survival and dispersal of fungi. Hyphalgrowth allows the fungus to colonize afood source (e.g., a corn kernel) as well asto grow from one food source to another;e.g., from root to root through soil or fromone kernel to an adjacent kernel in a pileof stored grain
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Grain Mold Pathogens
It is usually masses of spores that give the
mold a characteristic color. Spores are
dispersed passively by wind and rain.
Insects can serve as vectors of these fungi
usually by transporting the spores on the
surface of their bodies; this is particularly
important within grain storage bins.
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Grain Mold Pathogens
Managing grain storage insects can
reduce contamination by grain molds and
mycotoxins. Most species of grain mold
fungi are well adapted to the conditions of
grain production and postharvest handling
and storage.
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Grain Mold Pathogens
They can survive long periods in storage
facilities making sanitation of the facility an
important part of a grain mold
management plan.
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Grain Mold Pathogens
The most striking external symptom of
grain mold is the presence of the mold
itself. The degree of growth on the kernels
and the appearance of the mold (e.g.,
color and density) varies with the species
of mold, the quality of the grain being
colonized, and the prevailingenvironmental conditions
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Grain Mold Pathogens
Aspergillus species tend to be more prevalentwhen there is drought during the latter half of thegrowing season. Fusarium verticillioides isassociated with a high proportion of corn kernelsunder most growing conditions but Fusarium earand grain mold develops more often when coolwet weather during silking is followed by hot dryweather. Gibberella grain mold is more prevalent
in hybrids with tight husks. Unlike F.verticillioides, F. graminearum is rarely seed-borne.
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Common Grain Molds
Fusarium Grain MoldFusarium grain mold is probably the most common grainmold pathogen in Nebraska. It is caused by three seed-borne species ofFusarium: F. verticillioides, F.
proliferatum, and F. subglutinans. The role of seed-borneinoculum to the development of grain mold is uncertain.Disease symptoms and severity vary with hybridgenetics and environmental conditions. Moldy kernelsmay be clumped at the tip of the ear or randomly
dispersed across the entire ear. Infected kernels may bepink or show a white starburst pattern radiating from thetop of the kernel.
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Gibberella Grain Mold
Gibberella grain mold is also common inNebraska. It is caused by the fungusGibberella zeae; the asexual stage of the
pathogen is Fusarium graminearum.Unlike F. verticillioides, F. graminearum israrely seed-borne. Disease symptoms andseverity vary with hybrid genetics and
environmental conditions. Infected kernelsare usually clumped at the tip of the earand the mold is reddish in color.
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Penicillium Grain Mold
Penicillium grain mold is probably the second mostcommon grain mold pathogen in Nebraska. It may becaused by several species ofPenicillium, including P.
oxalicum and P. chrysogenum. Which species is themost prevalent in Nebraska is unknown. Penicilliumspecies are well adapted to survival in many types ofstorage facility. Kernel infection can occur in the field orin storage. Symptoms range from external mold
development to internal discoloration ("Blue Eye") of theembryo. Symptoms caused by Penicillium are easy toconfuse with those caused byAspergillus glaucus.
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Aspergillus Grain Mold
Aspergillus grain mold is probably the leastcommon grain mold pathogen in Nebraska. Atleast three species ofAspergillus can causegrain mold in corn, includingA. flavus,A.
parasiticus, andA. glaucus. Like Penicilliumspecies,Aspergillus species are very welladapted to survival in many types of storagefacility. Infection of kernels can occur in the fieldor in storage. Also like Penicillium, symptoms
range from mold development on the surface ofkernels to internal discoloration ("Blue Eye") ofthe embryo.
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Fusarium
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Penicillium
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Diplodia
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Mycotoxins
The nature of the toxic effects caused by mycotoxinsvaries greatly. Some mycotoxins cause acute toxicities(i.e., immediate effect) where a certain organ (e.g., liver,kidney) loses complete or partial function; other
mycotoxins cause chronic toxicities (i.e., long-term)resulting in symptoms such as weight loss andreproductive dysfunction. Still other mycotoxins impairthe immune system predisposing the affected animal toa variety of infections or other ailments. For some
mycotoxins damage is not permanent and affectedanimals can recover from ingestion if the contaminatedfeed is removed from the diet.
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swinereproductive dysfunctionzearalenone
manyacute toxicityvomitoxin
many (not ruminant
s)
many
acute toxicity
immune suppression
trichothecenesFusarium
graminearum
horse
swine
human
blind staggers
pulmonary edema
esophageal cancer
fumonisinFusarium
verticillioides
swine, poultry
human
acute toxicity (kidney)
cancer
ochratoxinAspergillus alutaceus
many
human
humans, animals
acute toxicity (liver)
liver cancer
immune suppression
aflatoxinAspergillus flavus
Species AffectedToxic Effects
Toxin
ProducedGrain Mold Fungus
Table I. Toxigenic fungi, their metabolites and target effects.
G i M ld d M t i
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Grain Mold and Mycotoxin
Management
PreharvestHybrids that are less susceptible to grain mold should be
planted where available in areas with perennial grainmold and/or mycotoxin problems. Identifying the
prevalent grain mold pathogens will be necessary priorto selecting the appropriate hybrids. After planting, theoverall strategy for grain mold management is to
minimize plant stress during and after silking. Commonstresses associated with grain mold include: high
moisture in mid-to-late season after a dry early season,moisture stress early in season and during grain fill, highleaf disease pressure, and insect damage.
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Post harvest
All grain storage facilities should be
monitored regularly to detect grain mold
development. Grain molds rarely developuniformly throughout a storage unit;
development of hot spots is common.
Monitoring requires a systematic samplingplan to account for the unique design
characteristics of each storage facility.
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Ensure Proper Storage
Conditions
To minimize the potential for mold growth and mycotoxinproduction, grain moisture content should be reduced to
less than 15 percent within 48 hours after the grain is
harvested. This may be difficult to achieve in manystorage facilities, especially larger capacity elevators. Astorage temperature of less than 40 F should be
maintained. Good air circulation throughout the storagebin is important. Storage conditions optimal for
maintaining grain quality will minimize mold developmentand mycotoxin contamination.
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Minimize Mechanical Damage
Harvest and postharvest grain handling
should be designed to minimize
mechanical damage. Although most moldpathogens can directly penetrate plant
tissues, mechanical damage provides
additional entry sites, facilitating infectionand spread from kernel to kernel during
shipping and storage.
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2.Ensure proper storage conditions grain moisture, temperature, relative
humidity
3.Minimize mechanical damage harvest and postharvest shipping and handling
4.Minimize insect damage pre-harvest and postharvest storage
5.Plant tolerant hybrids some tolerant hybrids available
6.Sanitation of storage facility critical management practice
7.Chemical management propionic acid, mineral oils
Key management steps to minimize grain mold and mycotoxin
contamination.