Burt Bluhm Department of Plant Pathology University of Arkansas Division of Agriculture
Aspergillus flavus is a fungus that infects corn ears Produces aflatoxin causes cancer, other illnesses in humans and animals Common in soils throughout Arkansas Periodically a problem in corn Aflatoxin B1
1998 Aflatoxin outbreak cost Arkansas growers > $15,000,000 2010 Wide spread aflatoxin 0 to 6000+ ppb Prolonged heat & drought Some fields mowed down Many loads rejected at grain elevators
Arkansas, 2010: Aflatoxin Outbreak Heat/Drought stress Insect Damage
2011 Aflatoxin: River valley was hit the hardest (heat & drought)
Climate Limited management options Genetic resistance is unavailable Lack of research
Three main areas Best management practices Afla-Guard optimizing for Arkansas Transgenic resistance to aflatoxin
Hybrid Selection Plant Health No reliable genetic resistance Select southern hybrids Use Bt hybrids when possible Good husk coverage
Plant Health Plant early to avoid heat Manage insects Maintain soil moisture Maintain fertility
Pre-harvest Decisions Consider Afla-Guard Scout/test fields before harvest Selectively harvest unstressed vs. stressed fields or areas within fields Dry land fields in high-stress years may not be harvestable
Harvest & Storage Harvest early Do not leave high-moisture corn on trucks overnight Clean bins before storing corn Dry corn as quickly as possible to 15% or lower moisture Beware rainfall during dry down
Hybrid Selection No reliable genetic resistance Select southern hybrids Use Bt hybrids when possible Good husk coverage Plant Health Plant early to avoid heat Manage insects Maintain soil moisture Maintain fertility Minimize Stress!! Pre-harvest Decisions Scout/test fields before harvest Selectively harvest unstressed vs. stressed fields or areas within fields Do not harvest dry land fields in high-stress years Harvest & Storage Harvest early Do not leave high-moisture corn on trucks overnight Clean bins before storing corn Dry corn as quickly as possible to 15% or lower moisture
No commercially available fungicides are labeled for control of Aspergillus in corn Strobilurins (e.g., Headline) for plant health? No proven benefit regarding aflatoxin Inconsistent results regarding benefit to stress (e.g., heat or drought) Serious risk of fungicide resistance in unrelated diseases! Frogeye Leaf Spot (soybean)
* 2010 * 2011
No commercially available fungicides are labeled for control of Aspergillus in corn Strobilurins (e.g., Headline) for plant health? No proven benefit regarding aflatoxin Inconsistent results regarding benefit to stress (e.g., heat or drought) Serious risk of fungicide resistance for unrelated diseases! Afla-Guard, a newly registered bio-control product, shows promise
A non-aflatoxin-producing strain of A. flavus Originally developed for peanut to reduce aflatoxin Registered on corn in US for 2009 crop Apply at V10 or tasseling How does it work? Spores of biocontrol strain outcompete natural strains on corn kernels
Afla-guard (Non-toxigenic strain)
Infection in drought-stressed corn (Natural, aflatoxigenic strains)
Good potential but will not eliminate aflatoxin gives a 60 to 75% reduction at best Can not take a high risk field and make it low risk For example: a dry land field with 2000 ppb potential of aflatoxin would only be reduced to 500 ppb with 75% control More effective in reducing aflatoxin in fields with light to moderate risk -- 20 to 100 ppb for human consumption Fields with some fertility and watering issues in extreme years Loose shuck cover Susceptible to disease and insects Dry land fields in years with stress --- drought, high heat Not practical or economical for highly productive fields where fertility and water is not an issue Stress, especially heat/drought before tasseling
Natural populations of Aspergillus flavus in the Southeastern US generally produce high levels of aflatoxin The fungus does not appear to need aflatoxin to survive We are looking at long-term ways to shift populations away from producing aflatoxin Goal: New biocontrol products more effective and longer lasting
Ultimate Goal: Change the kernel environment (or how the fungus perceives the kernel environment) to block mycotoxin biosynthesis
Two major strategies 1. Engineer corn that produces compounds that are toxic to the fungus 2. Engineer corn that makes the fungus turn off its own genes involved in making aflatoxin
An inhibitor of Aspergillus growth was identified from Hyacinth bean The gene was cloned and transformed into corn Testing is underway to measure the effect
Identified fungal gene targets for silencing Spliced plant and fungal genes to create gene silencing construct Creating transgenic corn Self-pollinate Laboratory/greenhous transgenic lines; e tests increase for aflatoxin seed for resistance testing
Partner with industry and public breeders to distribute resistance Field tests for aflatoxin resistance & impact on yield Move transgenic resistance into elite germplasm via genetics Transgenic lines that test well in the lab Field tests for aflatoxin resistance
Aflatoxin B 1 Deoxynivalenol (DON) Fumonisin B 1
Federal funds for aflatoxin research have been minimal States participating in AMCOE Southeastern states have banded together to launch a research center specifically for aflatoxin in corn AMCOE brings researchers together from multiple states Increases productivity Reduces research overlap The Arkansas Corn and Sorghum Promotion Board has taken a strong leadership role in AMCOE
Aflatoxin continues to be a problem for Arkansas corn production Afla-Guard provides some protection but is not a cure for aflatoxin Minimizing stress on corn is the key message to prevent aflatoxin New research is underway to create resistant hybrids and improved bio-control strains
Contact Information Burt Bluhm Department of Plant Pathology U of A Division of Agriculture Fayetteville, AR 72701 Ph 479-575-2677 Email: bbluhm@uark.edu www.uaex.edu