Reduced herbivory of the European corn borer ( Ostrinia nubilalis) on corn transformed with germin, a wheat oxalate oxidase gene

The strategy of targeting expression of a constitutively regulated gene to generate H 2O 2 in the extracellular matrix, to reduce herbivory of the European corn borer (ECB) [ Ostrinia nubilalis (Hübner)] was tested by transforming corn with germin, a wheat oxalate oxidase (OXO) gene, regulated by the rice actin promoter elements (pAct-OXO). With two independent transformation events, enzyme activity was stable over seven generations of backcrossing into three maize inbred lines. Enzyme activity remained associated with the cell wall debris fraction of water extracted tissues. Leaf tissue of the germin transgenics had elevated levels of H 2O 2. In vitro leaf feeding bioassays demonstrated that ECB larvae feeding was significantly reduced and larval growth and development were delayed on all ECB infested germin transgenic lines. This reduced ECB feeding was confirmed under field conditions. Most significantly, stalk tunneling damage, measured at plant harvest, was substantially reduced in all germin transgenic lines. The reduction of tunneling by 50% in the transgenic lines is indicative of lower levels of ECB survival which should be significant in ECB epidemiology. Possible mechanisms of resistance include modifications in plant cell wall chemistry, activation of pathogen resistance genes and effects of H 2O 2 and germin on insect physiology are discussed.