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

2. A. Robertson, 2006 © What is aflatoxin? Poisonous substance produced by the fungi Aspergillus flavus and A. parasiticus. - once produced, they are VERY stable

3. Production of toxins highly variable: fungal strain and species storage temperature + moisture content length and type of storage other unknown factors A. Robertson, 2006 © Therefore mold ≠ aflatoxins

4. Usually thought of as a storage pathogen BUT fungal contaminations starts in the field Life Cycle of Aspergillus flavus A. Robertson, 2006 © Survives as conidia and sclerotia in soil and crop debris Wind and insects

5. Population dynamics of A. flavus Shearer et al., 1992; McGee et al. 1996 A. Robertson, 2006 © 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

6. Through the silks: Yellow/brown = germination and colonization Pollination = changes in physiology and structure of silk  A. flavus continues growth as a saprophyte A. Robertson, 2006 © Aspergillus : Disease cycle 1. Infection

7. 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 A. Robertson, 2006 © 2. Colonization

8. 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 A. Robertson, 2006 © 3. Colonization and aflatoxin production

9. A. Robertson, 2006 © Optimum conditions for Aspergillus growth and aflatoxin production Aspergillus growthAflatoxin production Temperature (range) 77-108 F (45-118 F) 81-86 F (55-104 F) Moisture18-18.5% (> 14%)> 17 % Relative humidity (range) 85 % (62-99 %) -

10. A. Robertson, 2006 © Optimum conditions for Aspergillus growth and aflatoxin production Temperature Moisture 13%30% 45F120F Aspergillus growth Aflatoxin production 17% 55F 104F ? % So, the fungus can grow at higher and lower temperatures & moistures and not produce aflatoxin

11. 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 A. Robertson, 2006 ©

12. Identification Powdery olive green mold 1. Aspergillus flavus

13. A. Robertson, 2006 © 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

14. A. Robertson, 2006 © 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)

15. 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.stmhttp://aes.missouri.edu/delta/croppest/aflacorn.stm

16. A. Robertson, 2006 © Thank You