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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.