Submitted to: Corn Utilization Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2012
Publication Date: N/A
Interpretive Summary: not required
Technical Abstract: Ear-colonizing insects and diseases, which reduce yield and impose health threats via mycotoxin contaminations, are critical impediments for maize production in the southern US states. To address this problem a combination of basic and applied research approaches are being conducted by the interdisciplinary team to understand maize genetics and breeding, spatial ecology of maize, its insect pests, and subsequent defense responses to insect infestations and fungal infections. For germplasm development, over 200 crosses have been made in the last three years with emphasis on improving both biotic stress (i.e., multiple insects and diseases) and abiotic stress (i.e., heat and drought) resistance and improving yield potential. The important diseases are Aspergillus flavus ear rot, and ear smut, Ustilago maydis (DC) Corda, while the key insect pests at the Tifton location are the whorl-feeding fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), the cob-feeding corn earworm, Helicoverpa zea (Boddie), and the kernel-feeding maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Significant progress has been made on maize germplasm improvement for whorl- and ear-feeding insect resistance with reduced aflatoxin levels. To understand the spatio-temporal ecology of insect damage and aflatoxin contamination under field conditions, gene by environment (G*E) interactions were examined three one-acre maize fields planted with a commercial hybrid. A five-year examination (2005-2009) demonstrated that aflatoxin levels were distributed in clusters in maize fields with genetically identical plants. The aflatoxin levels were more closely correlated with damage caused by kernel-feeding maize weevils than by cob-feeding corn earworms. A strong field edge effect exists for both insect damage and aflatoxin contamination, which could be used as potential aflatoxin and insect damage management tactics to protect crop yield and quality. For maize defensive mechanisms against pathogen and insect attacks, two complex and previously unknown classes of phytoalexins were identified, namely acidic sesquiterpenoids and diterpenoids, termed zealexins and kauralexins, respectively. Physiologically relevant levels of zealexin A1 can reduce the growth of A. flavus by over 80%. To understand dynamics in ears, a time course study of pollinated maize kernels inoculated with A. flavus and Fusarium graminerum was conducted. This work clearly demonstrates the capacity of infected developing kernels to dynamically accumulate high levels of these defensive phytoalexins. The presence of inducible zealexins and kauralexins is predicted to greatly influence fungal growth and kernel mycotoxin accumulation. Studies are currently underway to examine these relationships in detail.