Aflatoxin Contamination: Occurrence and Management

Thomas Isakeit

Cooperative Extension, The Texas A&M University System

AFLATOXINS: WHAT ARE THEY?

- TOXIC CHEMICALS PRODUCED BY FUNGI (

Aspergillus flavus

and

A. parasiticus

) GROWING IN CROPS - CAUSE DISEASE IN ANIMALS AND HUMANS ( MYCOTOXICOSIS ) - MAY BE PRODUCED IN THE FIELD OR AFTER HARVEST - AFFECT MANY TYPES OF CROPS

TYPES OF AFLATOXINS STRUCTURE OF B 1 , THE MOST POTENT AFLATOXIN, SPECIFICALLY REGULATED IN SOME COUNTRIES

•

B 2 , G 1 AND G 2 ALSO:

•

M 1 AND M 2 IN MILK: SPECIFICALLY REGULATED

AFLATOXIN TOXICITY - HUMANS

•

HEPATIC AND GASTROINTESTINAL INJURY

•

IMMUNOSUPPRESSIVE

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TERATOGENIC

•

ONCOGENIC

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SEVERE LIVER INJURY, SOMETIMES FATAL (2-6 MG/DAY FOR A MONTH)

AFLATOXIN TOXICITY - ANIMALS LUNG LESIONS IN A PIG POISONED BY AFLATOXIN

•

VARIOUS SYMPTOMS: FROM REDUCED GAIN TO DEATH

•

VARYING SENSITIVITY AMONG SPECIES

AFLATOXIN POISONING FROM CORN – RECENT CASES

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TEXAS, 1998: 25 DOGS DIED 100-200 PPB, FULL DIET FOR 90 DAYS

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KENYA, 2004: 125 PEOPLE DIED, 192 POISONED DAMP STORAGE OF CORN, UP TO 8,000 PPB

LOSS FROM AFLATOXIN IN TEXAS CORN IN 1998

•

YIELD LOSS FROM DROUGHT

•

PRICE DROP ($2.20/BU vs. $2.80)

•

$407 MILLION VALUE W/O TOXIN

•

18 – 31% CROP CONTAMINATION

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TOXIN VALUE: $1.30 - $1.40 / BU

$17 - $40 MILLION LOSS

HISTORY IN TEXAS LOSING TURKEYS: “I CUT THEM OPEN AFTER THEY DIE AND FIND A BIG LIGHT COLLORD LIVER; THE GIZZARD IS ENLARGED, ALSO THE GALL IS TWICE AS LARGE AS SHOULD BE.” - LETTER TO FARM AND RANCH, MAY 19, 1917 FROM VAN ZANDT COUNTY, TX

AFLATOXIN?

HISTORY IN TEXAS J.J. Taubenhaus documents A. flavus as a pathogen

ASPERGILLUS EAR ROT PHOTO: G. ODVODY A. FLAVUS IS A WEAK PATHOGEN THAT DOES NOT ALWAYS PRODUCE SYMPTOMS

…CONSEQUENTLY, AFLATOXIN DETECTION REQUIRES A CHEMICAL ANALYSIS EXTRACTION PURIFICATION ANALYSIS DETECTION IS DIFFICULT!

SAMPLING IS MORE DIFFICULT!

CONTAMINATION IS NOT UNIFORM: - WITHIN A REGION - WITHIN A FIELD - ON A PLANT - WITHIN AN EAR - WITHIN A SEED

AFLATOXIN DISTRIBUTION IN TEXAS 2002 CORN ACREAGE 2003 CONTAMINATION

COMPILED BY: OFFICE OF THE TEXAS STATE CHEMIST

COMPILED BY: OFFICE OF THE TEXAS STATE CHEMIST

AFLATOXIN IN AN EAR OF CORN PHOTO: G. SCHUSTER CONCENTRATIONS ARE DIFFERENT FOR EACH KERNEL

WHERE AFLATOXIN OCCURS IN A CORN SEED (SHOWN IN RED) PHOTO: N. KELLER AS SHOWN BY THE RED COLOR MUTANT, AFLATOXIN IS FOUND IN THE ALEURONE

A SMALL PROPORTION OF CORN IS HIGHLY CONTAMINATED: 1 KERNEL WITH 400,000 PPB WILL MAKE A 10-LB SAMPLE MEASURE 26 PPB

WHERE DOES THE FUNGUS COME FROM?

MODIFIED FROM: WICKLOW, 1983, SO. COOP. SER. BUL. 279 BROWN & BROTZMAN, 1979, U. OF MO.

•

airborne infective spores

•

survival in soil

SCLEROTIA OF A. FLAVUS DETAIL: RED BAR IS APPROX. 1 MM

HOW THE FUNGUS ENTERS THE EAR

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SPORES FALLING INTO WOUNDS CAUSED BY INSECTS (E.G. CORN EARWORM AND SOUTHWESTERN CORN BORER), OR CARRIED ON THEM CAN GROW DOWN SILKS (NO WOUNDING NECESSARY), SHORTLY AFTER POLLINATION

HOW THE FUNGUS ENTERS THE SEED A WOUND IS USUALLY NEEDED

SILK CUT PHOTO: G. ODVODY STRESS-RELATED LOSS OF KERNEL INTEGRITY

PREDISPOSING FACTORS FOR CONTAMINATION

•

DROUGHT

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HIGH TEMPERATURES AT FLOWERING

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INSECT INJURY

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STRESS ON PLANT + INCREASE IN PATHOGEN REPRODUCTION

FACTORS AFFECTING AFLATOXIN PRODUCTION

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ACTIVITY DOES NOT START UNTIL KERNEL MOISTURE <32%

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BEST RANGE IS 16-20% MOISTURE, 18% IS OPTIMAL

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OPTIMAL 77-86 o F, BUT FUNGUS GROWS WELL AT 97 o F

AFLATOXIN MANAGEMENT IN THE FIELD (PRE-HARVEST) - host resistance - insect control - cultural practices - biological treatment USE OF SEVERAL APPROACHES

HOST RESISTANCE - TO INSECT, CONVENTIONAL & TRANSGENIC (Bt): NOT ENOUGH - TO FUNGUS: SOURCES IN LINES, NOT EASY TO INTRODUCE INTO HYBRIDS - IMPROVED HOST TOLERANCE TO STRESS

HUSK COVER IS A TRAIT ASSOCIATED WITH LESS AFLATOXIN PHOTO: G. ODVODY

HUSK COVER AND AFLATOXIN

3000.0

2500.0

2000.0

1500.0

1000.0

500.0

0.0

1.0

1.5

2.0

2.5

Husk Cover

3.0

3.5

4.0

A TREND TOWARDS MORE AFLATOXIN WITH AN OPEN HUSK BETRAN & ISAKEIT, 2004. AGRON. J. 96:565

3000.0

2500.0

2000.0

1500.0

1000.0

500.0

0.0

CS

Aflatoxin Content (ppb)

WE

Locations AFLATOXIN AND HYBRID Aflatoxin Content (ppb) MATURITY

Across 3000.0

2500.0

2000.0

1500.0

1000.0

500.0

0.0

FULL INTERM.

EARLY CS WE

Locations

Across

BETRAN & ISAKEIT, 2004. AGRON. J. 96:565 MORE AFLATOXIN WITH EARLY-MATURING VARIETIES

FULL INTERM.

EARLY

AFLATOXIN AND MATURITY

3000.0

2500.0

2000.0

1500.0

1000.0

500.0

0.0

68.0

70.0

72.0

74.0

76.0

78.0

80.0

82.0

Silking date (days) A TREND TOWARDS LESS AFLATOXIN IN HYBRIDS WITH A LONGER MATURITY BETRAN & ISAKEIT, 2004. AGRON. J. 96:565

CORN BREEDING AND AFLATOXIN EVALUATION FOR RESISTANCE REQUIRES MORE TIME AND LABOR THAN OTHER TRAITS

PESTICIDE TREATMENTS INSECTICIDES TARGETED TO: - REDUCE PLANT STRESS (E.G. PRESCRIBE FOR ROOT INSECTS) - REDUCE EAR INJURY FUNGICIDES ARE NOT EFFECTIVE OR PRACTICAL

CULTURAL PRACTICES - PLANTING DATE - PLANT POPULATIONS - WEED & PEST CONTROL

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IRRIGATION

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TILLAGE TO BREAK HARD PAN

-

ADEQUATE FERTILITY

CULTURAL PRACTICES

WHATEVER YOU DO TO GET THE BEST CROP POSSIBLE DOES NOT CONFLICT WITH MYCOTOXIN MANAGEMENT

BIOLOGICAL CONTROL

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AF36 LABELED FOR COTTON IN TX AND AZ

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AFLA-GUARD: GA PEANUTS - APPLIED EARLY SEASON TO COVER FIELD - AREA-WIDE TREATMENT - CARRY OVER (PLACE/TIME)

HARVEST PRACTICES SEGREGATE HARVEST OF “GOOD” AND “BAD” FIELDS

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CHANGE COMBINE SETTINGS TO REMOVE DAMAGED SEED

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EARLY HARVEST, FOLLOWED BY ARTIFICIAL DRYING - CLEANING SEED AFTER HARVEST (E.G. DENSITY SEPARATOR)

MYCOTOXINS IN INTACT AND DAMAGED/DISCOLORED KERNELS “GOOD”: 35 PPB AFLATOXIN 1 PPM FUMONISIN DAMAGED OR DISCOLORED: 270 PPB AFLATOXIN 9.3 PPM FUMONISIN REPRESENTATIVE DAMAGED KERNELS

AFLATOXIN CONCENTRATION CAN INCREASE THE LONGER CORN IS LEFT IN THE FIELD DATA OF G. ODVODY

AFLATOXIN: POST-HARVEST MANAGEMENT

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PROPER STORAGE CONDITIONS TO MINIMIZE INCREASE

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BLENDING WITH “CLEAN” CORN – SUBJECT TO FEDERAL AND STATE REGULATIONS – CHECK FIRST!

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CHEMICAL NEUTRALIZATION IS SUBJECT TO FEDERAL AND STATE LAWS – CHECK FIRST!

STORAGE CONDITIONS

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OBJECTIVE IS TO KEEP THE FUNGUS WITHIN THE GRAIN DORMANT

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STORE CORN AT <15% MOISTURE AND KEEP OUT MOISTURE

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PROPER OPERATION OF VENTILATION TO PREVENT MOISTURE CONDENSATION CAUSED BY UNEVEN TEMPERATURES IN BIN

MOISTURE MIGRATION IN A BIN TEMPERATURE DIFFERENCES WITHIN THE BIN LEAD TO AIR MOVEMENT, WITH MOISTURE CONDENSATION AT THE TOP OF THE BIN. PROPER VENTILATION WILL PREVENT THIS.

DIAGRAM: ROSS ET AL., 1974 U. KY. AEN-20

CHEMICAL TREATMENTS

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AMMONIATION: SUBJECT TO STATE AND FEDERAL REGULATIONS

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OZONATION: NOT COMMERCIALLY AVAILABLE

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ABSORBENT CLAYS ADDED TO FEED (E.G. NOVASIL): NOT YET APPROVED BBY REGULATORY AGENCIES

ENTEROSORBENT CLAY ADDITIVE AFLATOXIN PRESENT IN FEED NOVASIL ADDED TO CONTAMINATED FEED PHOTOS: OFFICE OF THE TEXAS STATE CHEMIST

OZONATION OF CONTAMINATED CORN: EFFECT ON GROWTH CONTROL O3 CK AFLATOXIN AF+O3 APPEARANCE OF LIVERS PHOTO: MCKENZIE ET AL. POULTRY SCI., 1998