Fumonisin content in conventional versus Bt maize and implications of fumonisin contamination on fuel ethanol yield and DDGS quality
Genetic engineering of maize plants with genes (Bt genes) for resistance to Lepidopteran insects reduces the risk of grain contamination with fumonisin mycotoxins. Fumonisins are secondary metabolites of certain Fusarium fungal species that may be present in maize grain and, when consumed, lead to a variety to detrimental health impacts in both humans and animals. Changing insect populations, newly available transgenes, and trends in maize utilization have raised new questions about the scope of Bt effects on fumonisins.
Field trials were conducted at two locations in 2008-2011 to assess the effects of expression of Bt insecticidal proteins Cry1Ab, Cry1F, or Cry1Ab x Vip3Aa on fumonisin contamination in grain following infestations with European corn borer (ECB), Western bean cutworm (WBC), corn earworm (CEW), and natural insect infestation (no insects applied). These maize pests are common in the major maize-producing regions of the United States and their feeding can reduce yields and increase levels of fungal contamination and mycotoxins. Fumonisins have also demonstrated toxic effects on certain yeast strains used in fermentation of maize grain for fuel ethanol production. Additionally, because fumonisins are heat-stable and non-volatile under relevant conditions, they can be enriched up to three-fold in dried distillers' grains with solubles (DDGS), the residual non-fermentable co-product of fuel ethanol processing which is fed to livestock. Therefore, fumonisin contamination in maize is a significant consideration for maize and maize-based ethanol producers.
Grain quality was assessed by visual inspection to determine the extent of kernel injury and Fusarium ear rot, and by ELISA or HPLC to determine the fumonisin content. Visual assessment of maize obtained from field trials revealed significant reductions in kernel injury and Fusarium ear rot in Bt versus non-Bt maize. Both HPLC and ELISA measurements of maize grain demonstrated that fumonisin levels were significantly reduced in Bt as compared with non-Bt maize. Protection against multiple Lepidopteran pests provided by Cry1F or Cry1Ab x Vip3Aa resulted in the most noteworthy improvements in grain quality and reduced fumonisin levels.
Maize obtained from these field trials was used to examine the impacts of grain quality and fumonisin contamination on fermentation outputs including ethanol and DDGS. Naturally and artificially contaminated maize samples ranging from 0-37 mg kg-1 total fumonisins were fermented, ethanol yield determined, and DDGS was collected and analyzed for fumonisin content. Ethanol yield was not affected by fumonisin contamination of maize in the range of concentrations examined. Fumonisins in DDGS derived from Bt hybrids averaged 2.04 mg kg-1 whereas those from non-Bthybrids averaged 8.25 mg kg-1. Enrichment factors (DDGS fumonisin level/ground grain fumonisin level) did not differ significantly from 3.0 for 50 out of 57 hybrid x insect infestation treatment combinations. The seven that differed significantly from 3.0 were
The present study provides evidence for the efficacy of Cry1Ab, Cry1F, and Cry1Ab x Vip3Aa Bt maize reducing feeding from Lepidopteran insects ECB, CEW, and WBC, which resulted in indirect fumonisin reductions in Bt maize compared with non-Bt maize. The present study also provides laboratory-scale validation for the industry assumption of three-fold enrichment of fumonisins in DDGS, with fumonisin measurements traceable to individual samples.