Submitted to: Aflatoxin Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 10/19/2006
Publication Date: 10/16/2006
Citation: Dowd, P.F., Johnson, E.T., Pinkerton, T.S., Behle, R.W., Berhow, M.A. 2006. Examination of genes newly introduced into plants for control of corn insects associated with mycotoxin problems [abstract]. 2006 Annual Multicrop Aflatoxin/Fumonisin Elimination and Fungal Genomics Workshop. p. 89. Interpretive Summary:
Technical Abstract: Corn ear damage by insects can greatly enhance the levels of mycotoxins. Currently, only commercial corn hybrids with the CryIA(b) Bt protein provide sufficient control to reliably reduce levels of mycotoxins when European corn borers or Southwestern corn borers are the principal insect pests. Appropriate combinations of plant-derived genes, preferably from corn, may lead to effective and stable broad-spectrum control of corn insects that can result in consistent mycotoxin reductions and thus provide a more acceptable material for consumer use and export. We are exploring new genes and gene combinations for corn insect control using plant-derived or readily available models for gene analogs that occur in plants. Previously, in vitro assays of plant-derived hexosaminidase demonstrated high activity against the fall armyworm. Mortality of fall armyworms fed tassels of Hi-II plants that expressed an Arabidopsis gene putatively coding for the enzyme died at a significantly greater rate than those fed tassels from GUS transformants. The mortality level was inversely correlated to levels of enzyme expression. Leaves of some Oh43 plants that expressed the Arabidopsis enzyme killed significant numbers of fall armyworms and corn earworms as compared with essentially no mortality for these insects when fed leaves from negative transformants. Mean fall armyworm feeding on positive transformant leaves were significantly lower than for negative transformants. Newly emergent silks of Hi-II corn plants that expressed a putative corn silk promoter regulated P1 gene (which can enhance levels of secondary metabolites that defend against insects) caused significantly higher mortality of corn earworms compared to wild-type Hi-II plants. Maysin levels were significantly higher in silks that browned when cut, but additional factor(s) appear to have contributed to activity against insects in newly emergent nonbrowning silks. Silks approximately three weeks old did not cause any mortality above five percent, but weights of survivors were significantly less when compared to those of larvae fed wild-type silks. The P35 protein that is produced by A.c. nuclear polyhedrosis virus significantly retarded larval growth rates and enhanced activity of other virus species tested during in vitro assays. Some Oh43 plants that expressed the gene caused significant mortality of corn earworms and fall armyworms compared to negative transformants in the absence of applied virus. Overall, T1 plants that expressed the gene caused significantly higher mortality of corn earworms and fall armyworms when A.g. virus (which does not contain the P35 gene) was added to leaves compared to negative transformants. Related studies in progress include examination of a potential corn-derived selectable marker gene, determining functionally compatible combinations of resistance genes using gene introductions, array-based detection of potentially useful directly active or regulatory genes producing products active against insects, and pathway genes that may produce novel secondary resistance compounds when introduced/upregulated into corn.