|Munkvold, Gary - IOWA STATE UNIVERSITY|
|Showers, William - RETIRED|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 1997
Publication Date: N/A
Interpretive Summary: Fusaria are among the most common fungal associates of corn plants, causing diseases of seedlings, roots, stalks and kernels. At least two types of fusaria produce toxins called fumonisins that cause potentially fatal diseases in horses and swine. Injuries to plants caused by insects such as the European corn borer are often the initial infection sites for Fusaria. Corn borer larvae infect corn plants by carrying the fungi from plant surfaces into corn stalks and ears. Genetically-engineered (or transgenic) corn plants have a high level of resistance to corn borer larvae. The objective of this research was to learn whether kernels of transgenic corn have reduced occurrence and severity of Fusarium ear rot. Results suggest that most transgenic corn hybrids have less corn borer kernel damage and less Fusarium ear rot compared with their non-transgenic counterparts. Reduced Fusarium infection in transgenic genotypes resulted in better grain nquality (less mold damage) and decreased potential for the development of fumonisins. Corn producers should benefit from this research since reduced ear rot will improve grain quality. Reduced Fusarium infection also may result in higher seed quality in transgenic corn grown for seed production.
Technical Abstract: Corn hybrids genetically engineered for resistance to European corn borer, Ostrinia nubilalis, were evaluated in 1994, 1995, and 1996 for occurrence and severity of Fusarium kernel rot and occurrence of symptomless Fusarium infection. The transgenic corn hybrids expressed a delta-endotoxin CryIA(b) protein that originated from a soil-borne bacterium, Bacillus thuringiensis (Bt). Treatments included Bt corn and nonBt (near isogenic) corn, manual and natural infestations with O. nubilalis larvae, and standard insecticide applications. Fusarium infection was affected by the specific CryIA(b) gene present, which determines tissue-specific expression of CryIA(b) in corn hybrids. In hybrids expressing CryIA(b) in kernels, occurrence and severity of Fusarium kernel rot and occurrence of symptomless kernel infection were reduced compared with near-isogenic hybrids lacking CryIA(b) genes. In plants that were manually infested with O. nubilalis, kernel rot occurrence was reduced by 87%, 58%, and 68%, severity was reduced by 96%, 54%, and 64% and occurrence of kernel infection by Fusarium spp. was reduced by 17%, 38%, and 38% in 1994, 1995, and 1996, respectively. Reductions in symptoms and infection were similar in treatments that were not manually infested with O. nubilalis larvae. Most kernel infection was due to F. moniliforme, F. proliferatum, and F. subglutinans (Section Liseola) collectively and it was within this group that transgenic hybrids experienced reduced infection. Disease severity and kernel infection were positively correlated with O. nubilalis damage to kernels. Insecticide applications also reduced Fusarium symptoms and infection when applied to nontransgenic plants.