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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETIC IMPROVEMENT OF MAIZE AND PEARL MILLET FOR RESISTANCE TO INSECTS AND AFLATOXIN
2012 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 pearl millet for yield-related traits, resistance to Aspergillus flavus and aflatoxins, and insect pests. Brazilian maize introductions were evaluated for resistance to lepidopteran pests. Temperate corn inbreds were evaluated for corn rootworm and fall armyworm resistance. New elite Genetic 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. The previously evaluated GEM inbreds and hybrids, as well as new additional GEM inbreds and hybrids from Texas and Iowa are evaluated for the foliage feeding insects in 2012. Fall armyworm and southern rust-resistant inbreds from the FAWCC(C5) population were advanced, and test crosses are being evaluated for two possible new releases (FAW 1382 and FAW1430). High maysin experimental hybrids were evaluated for resistance to feeding by ear insects (corn earworm, stink bugs, maize weevil) and fall armyworm, as well as for natural enemy attraction in whorl stage. Introduced Chinese inbreds were evaluated for resistance to ear feeding insects, and rust and smut. The co-occurrence of aflatoxin contamination and maize weevil and stinkbug distributions in fields of AgraTech 760RR was assessed. Inoculation methods to allow for more effective screening for A. flavus and aflatoxin contamination were assessed using elite inbreds and commercial hybrids to understand plant defensive responses to A. flavus infection and aflatoxin production. Approximately 700 grain samples were analyzed for aflatoxin using the Vicam procedure. Approximately 100 experimental hybrids, and 800 of segregating populations at varying stages were evaluated with the goal of combining aflatoxin, insect, and drought resistance in improved genetic backgrounds. In addition, newly-acquired heat- and drought-tolerant maize germplasm from the National Genetic Resources Program, Germplasm Resources Information Network, has also been evaluated for whorl-feeding fall armyworm resistance in the southern Coastal Plain region.


4.Accomplishments
1. Identified corn germplasm that confers resistance to whorl-feeding fall armyworm. Eight corn germplasm lines with known resistance to western corn rootworm and corn earworm were examined for their foliar resistance to fall armyworm and natural enemy attractiveness at V6-V8 (or 6-8 leaf) stages in 2008 and 2009. Inbred lines ‘Mp708’ and ‘FAW7061’ were the most resistant, whereas ‘Ab24E’ and ‘EPM6’ were the most susceptible to fall armyworm feeding. The western corn rootworm-resistant germplasm line ‘CRW3(S1)C6’ and corn earworm-resistant ‘SIM6’ showed moderate resistance to fall armyworm feeding. Surveys for the diversity and abundance of predators of fall armyworm in each experimental plot showed that ‘CRW3(S1)C6’ and ‘Ab24E’ had the highest and lowest predator abundance, respectively. The current study demonstrated the feasibility of developing foliage-, root-, and ear-feeding insect-resistant germplasm covering multiple corn growth stages.

2. Determined 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 level (100 ug/ml) of Zealexin A1 can reduce the growth of fungus (A. flavus) by over 80%. Great variation in phytoalexins was detected in scutella of corn seeds 10-d post-germination among the inbred lines examined. The findings have been utilized for new germplasm development at present.


Review Publications
Hu, X., Dennehy, T.J., Ni, X., Zhao, H., Nichols, R.L., Li, X. 2011. Potential adaptation of a Q biotype whitefly population from poinsettia to field crops. Insect Science. 18:719-728.

Ni, X., Chen, Y., Hibbard, B.E., Wilson, J.P., Williams, W.P., Buntin, G., Ruberson, J.R., Li, X. 2011. Foliar resistance to fall armyworm in corn germplasm lines that confer resistance to root- and ear-feeding insects. Florida Entomologist. 94(4):971-981.

Huffaker, A., Kaplan, F., Vaughan, M.M., Dafoe, N.J., Ni, X., Rocca, J.R., Alborn, H.T., Teal, P.E., Schmelz, E.A. 2011. Novel acidic sesquiterpenoids constitute a dominant class of pathogen-induced phytoalexins in maize. Plant Physiology. 156:2082-2097.

Guo, B., Yu, J., Ni, X., Lee, R.D., Kemerait, R.C., Scully, B.T. 2012. Crop stress and aflatoxin contamination: Perspectives and prevention strategies. In: Venkateswarlu, B., Shanker, A.K., Shanker, C., Maheswari, M., editors. Crop Stress and its Management: Perspectives and Strategies. London, NY: Dordrecht Heidelberg Springer. p. 399-427.

Last Modified: 10/23/2014
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