A. Robertson, 2006 © Science of aflatoxin growth and identification Alison Robertson Extension Field Crops Pathologist.

A. Robertson, 2006 ©

Science of Science of

aflatoxin growth and identificationaflatoxin growth and identification

Alison RobertsonExtension Field Crops Pathologist

A. Robertson, 2006 ©

What is aflatoxin?

Poisonous substance produced by the fungi Aspergillus flavus and A. parasiticus.

- once produced, they are VERY stable

Production of toxins highly variable:

• fungal strain and species• storage temperature + moisture content• length and type of storage• other unknown factors

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Therefore mold ≠ aflatoxins

Usually thought of as a storage pathogen

BUT

fungal contaminations starts in the field

Life Cycle of

Aspergillus flavus

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Survives as conidia and sclerotia

in soil and crop debris

Wind and insects

Population dynamics of A. flavusShearer et al., 1992; McGee et al. 1996

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Populations measured once a month

Populations in soil significantly greater in

July vs June, Aug & Sept

1992 & 1993 - A. flavus recovered at greater frequencies in CC and no till

Through the silks:Yellow/brown = germination and colonization

Pollination = changes in physiology and structure of silk

A. flavus continues growth as a saprophyte

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Aspergillus : Disease cycle

1. Infection

Enhanced by damage by birds/insects

Physical damage allows further spread

Broken pericarp allows invasion

Moisture content drops rapidly <35%

A. flavus competes successfully with other MOs (e.g. Fusarium spp.)

grows best at 17-20% grain moisture

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2. Colonization

High max, min and ambient temp (esp. July and Aug) – particularly night – more important than

moisture

Very low rainfall

Stressed plants = altered nutritional status of developing kernels

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3. Colonization and aflatoxin production

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Optimum conditions for Aspergillus growth and aflatoxin production

Temperature

Moisture

13% 30%

45F 120FAspergillus growth

Aflatoxin production17%

55F 104F

? %

So, the fungus can grow at higher and lower temperatures & moistures and not produce aflatoxin

Managing Aspergillus and aflatoxin

1. Early planting (April v May)

2. Reduce plant stress

3. Harvest early

4. Avoid damage during harvest

5. Dry grain a.s.a.p. to 13% moisture (inhibits growth at any temperature)

6. Cool grain a.s.a.p. to <45F (very slow growth <55F)

7. Ensure storage facilities are clean

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A. Robertson, 2006 ©

Identification

Powdery olive green mold

1. Aspergillus flavus

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Identification

2. Aflatoxins

a.Black light

# BGYF particles ≠ aflatoxin = false positive

The black light should no longer be used for any type of mycotoxin screening

http://archive.gipsa.usda.gov/pubs/mycobook.pdf

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b.Test kits

- immunoassay strips

- ELISA assays

- detect +/- 20ppb

USDA GIPSA approved list://151.121.3.117/techservsup/metheqp/testkit.htm

c.HPLC

- quantitative

- list of labs

www.iowagrain.org

(detection)

(identification)

References

Diener et al. 1987. Ann. Rev. Phytopathol. 25: 249-70

Jones et al. 1980. Plant Disease 64: 859-863

Jones et al. 1981. Phytopathology 71: 810-816

Marsh and Payne. 1984. Phytopathology 74: 1284-1289

Schindeer et al. 1967. Applied Microbiology 15: 1006-1009

Wicklow and Donahue. 1984. Trans. Br. Mycol. Soc. 82: 621-624

Aflatoxins in Corn. Pm1800. Iowa State University Extension

Aflatoxin in Corn. http://aes.missouri.edu/delta/croppest/aflacorn.stm

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Thank You