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United States Department of Agriculture

Agricultural Research Service


Location: Crop Genetics and Breeding Research

2013 Annual Report

1a. Objectives (from AD-416):
The long-term objective of this project is to develop corn and pearl millet germplasm with reduced aflatoxin contamination and insect damage in order to increase the productivity and quality of grains produced in the southeastern United States. Over the next five years we will: 1) Identify new sources of germplasm with resistance to Aspergillus flavus/aflatoxin contamination, and to multiple ear-feeding insect damage; 2) Determine biochemical and physiological bases and associated key phenotypic traits conferring resistance/ susceptibility to chewing and piercing-sucking insects in corn and pearl millet germplasm; 3) Identify quantitative trait loci associated with reduced aflatoxin accumulation in corn; and 4) Develop maize germplasm with desirable agronomic traits and reduced aflatoxin accumulation and increased resistance to ear-feeding insects for use in the Coastal Plain region.

1b. Approach (from AD-416):
In comparison with molecular (gene to trait, or top-down) approach, a trait to gene (bottom-up) approach will be taken for this project. Diverse (exotic and temperate) germplasm will be screened under field conditions for resistance to aflatoxin and insect pests (i.e., corn earworm, fall armyworm, maize weevil, and stink bugs). Field-proven germplasm entries will be further evaluated for key unique phenotypic traits in relation to resistance mechanisms and underlying genetics using both conventional and molecular techniques. Following rigorous field and laboratory screenings, selected germplasm will be further examined for biochemical and physiological bases that confer resistance to multiple insect pests and aflatoxin. Insect resistance mechanisms in the selected corn and pearl millet germplasm will be categorized and the biochemical and physiological processes that confer certain insect resistance will be identified. Segregating populations with resistance to aflatoxin contamination and multiple insect damage will be developed. These new populations will serve as the sources of favorable alleles for ultimately developing aflatoxin- and insect-resistant corn inbred lines with elite agronomic traits, which will improve corn production under biotic and abiotic stresses in our region.

3. Progress Report:
Activities focused on the genetic improvement of corn and sorghum for yield related traits, resistance to Aspergillus flavus infection and aflatoxin accumulation, and insect pest damage. Temperate corn inbreds were evaluated for corn rootworm and fall armyworm resistance. New elite Germplasm Enhancement of Maize (GEM) inbreds and hybrids selected from Iowa, North Carolina, and Texas programs were evaluated for resistance to whorl and ear feeding insects. In addition to the seeds of over 200 newly requested Ex-PVP and other maize germplasm lines from the National Genetic Resources Program, Germplasm Resources Information Network (GRIN) and Maize Stock Center were increased, a total of 150 GEM inbreds and hybrids from Iowa, North Carolina, and Texas were evaluated for the foliar- and ear-feeding insects in 2013. A total of 178 new experimental hybrids made in 2012 utilizing the parents of high level of phytoalexins, and good agronomic traits were also evaluated for insect resistance and yield potential. Over 170 segregating populations at varying stages were evaluated with the goal of combining aflatoxin, insect, and abiotic resistance in the improved genetic backgrounds. In addition, a set of 23 heat- and drought-tolerant maize germplasm from the GRIN has also been evaluated again for whorl-feeding fall armyworm resistance in the southern Coastal Plain region. For sorghum germplasm development, a set of 38 Ex-PVP and 47 anthracnose-resistant sorghum lines were requested and planted for seed increase, and preliminary insect resistant evaluation. In collaborative research efforts with other teams in the region, we participated in Aflatoxin Mitigation Center of Excellence (AMCOE) Research Program 2013 to examine the germplasm lines by focusing on insect damage and aflatoxin accumulation; and participated in a team effort to differentiate plant defensive responses in a maize inbred line and its mutant in fungal infection and aflatoxin contamination in corn ears at pre-harvest. Continuously participated in the South Eastern Regional Aflatoxin Test (SERAT) Program, and processed and analyzed approximately 500 grain samples for aflatoxin using the Vicam procedure. Continuously participated in the State Variety Tests and examined the new corn and sorghum hybrids for insect resistance in 2013. This project was replaced by bridging project #6602-21220-016-00D pending completion of NP 301 OSQR review.

4. Accomplishments
1. Screening of corn germplasm for multiple ear pest resistance. Multiple ear-colonizing pests are important impediment of corn production in the southern US states. Twenty corn lines that had been derived from exotic maize germplasm were examined for insect and disease resistance by ARS researchers in Tifton, GA. Significant differences in insect damage, smut infection, and husk protection traits were detected among the germplasm lines. Three of the 20 germplasm lines were identified as multiple insect and smut resistant. This study has established the baseline information to develop multiple insect and disease resistance in corn with good yield potential and other agronomic traits.

2. Spatial and temporal patterns of insect damage and aflatoxin contamination in a corn field. The spatio-temporal patterns of multiple ear and kernel feeding insect damage and aflatoxin contamination are still not well understood. The corn cob and kernel feeding insect damage, and the levels of aflatoxin contamination at pre-harvest was sampled by ARS researchers in Tifton, GA. The grid-sampling data showed a field edge effect in both insect damage and aflatoxin contamination in both years. Stink bug damage and maize weevil number were more closely associated with aflatoxin level than the corn earworm damage. The strong field edge effect and the spatial and temporal patterns of different insect damage and aflatoxin contamination across a corn field could be utilized to effectively manage insect pests and aflatoxin contamination in the corn production.

Review Publications
Ni, X., Xu, W., Blanco, M.H., Wilson, J.P. 2012. Evaluation of corn germplasm lines for multiple ear-colonizing insect and disease resistance. Journal of Economic Entomology. 105:1457-1464.

Brevault, T., Heuberger, S., Zhang, M., Ellers-Kirk, C., Ni, X., Masson, L., Li, X., Tabashnik, B.E., Carriere, Y. 2013. Potential shortfall of pyramided Bt cotton for resistance management. Proceedings of the National Academy of Sciences. 110:5806-5811.

Last Modified: 06/26/2017
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