REDUCED FUSARIUM EAR ROT AND SYMPTOMLESS INFECTION IN KERNELS OF MAIZE GENETICALLY-ENGINEERED FOR EUROPEAN CORN-BORER RESISTANCE

Field experiments were conducted in 1994, 1995, and 1996 to evaluate t he incidence and severity of Fusarium ear rot and the incidence of sym ptomless Fusarium infection in kernels of maize hybrids genetically en gineered with Bacillus thuringiensis genes encoding for the delta-endo toxin CryIA(b). Treatments included manual infestation with European c orn borer (ECB) larvae and insecticide applications to limit ECB activ ity to specific maize growth stages or mimic standard ECB control prac tices. Fusarium symptoms and infection were affected by the specific c ryIA(b) transformation used in each hybrid that determines tissue-spec ific expression of CryIA(b). In hybrids expressing CryIA(b) in kernels , incidence and severity of Fusarium ear rot and incidence of symptoml ess kernel infection were reduced compared with near-isogenic hybrids lacking cryIA(b) genes. In plants that were manually infested with ECB , ear rot incidence was reduced by 87, 58, and 68%; severity was reduc ed by 96, 54, and 64%; and incidence of kernel infection by Fusarium s pecies was reduced by 17, 38, and 38% in 1994, 1995, and 1996, respect ively. Results were similar in treatments that were not manually infes ted, but differences between transgenic and nontransgenic hybrids were smaller. Most kernel infection was due to F. moniliforme, F. prolifer atum, and F. subglutinans (section Liseola) collectively, and it was w ithin this group that transgenic hybrids exhibited reduced infection. Expression of CryIA(b) in plant tissues other than kernels did not con sistently affect Fusarium symptoms or infection. Disease incidence was positively correlated with ECB damage to kernels. Insecticide applica tions also reduced Fusarium symptoms and infection when applied to non transgenic plants.