2008 Annual Report
1a.Objectives (from AD-416)
Objectives are to (1) identify genes and genome regions controlling key traits in diverse maize germplasm using multiple populations and novel genetic mapping methods; (2) identify and characterize new sources of resistance to southern leaf blight (SLB), gray leaf spot (GLS), northern leaf blight (NLB), and Fusarium ear rot by developing new near-isogenic line sets, identifying QTL conferring resistance to multiple foliar diseases, and evaluating the known genetic diversity among public maize inbreds; and (3) incorporate favorable alleles from exotic maize into adapted maize lines, with particular emphasis on improvement of resistance to Fusarium ear rot and fumonisin contamination.
1b.Approach (from AD-416)
Develop genetic mapping populations appropriate for identification of favorable alleles in exotic maize by identifying genome regions and specific genes controlling the response to photoperiod in multiple tropical maize inbreds. Develop interconnected multiple populations and novel statistical methods to map specific genes controlling quantitative trait variation in diverse maize. Fine-map QTL for SLB, NLB, GLS, Fusarium ear rot and fumonisin contamination resistance. Characterize specific disease resistance QTL using near-isogenic line pairs. Identify QTL conferring resistance to multiple foliar diseases. Complete multiple environment screening of a 302-line population encompassing the known genetic diversity among public maize inbreds for resistance to SLB, NLB and GLS. Identify new sources of resistance to SLB, Fusarium ear rot, and fumonisin contamination from the GEM program and the NCSU tropical maize breeding program. Develop new lines with elite agronomic performance and enhanced resistance to Fusarium ear rot by backcrossing. Test if selection for resistance to Fusarium ear rot results in improved resistance to contamination by the associated mycotoxin fumonisin.
New genetic mapping lines that will allow higher resolution mapping of genes for response to photoperiod were constructed. Analysis of 14 complex traits measured on 26 new genetic mapping populations was completed, permitting very high-resolution analysis of this diverse population for genes controlling these traits. More than 20 genome regions containing southern leaf blight resistances were identified in this population. The best 80 backcross-derived families were tested in two locations for resistance to Fusarium ear rot and in four locations for hybrid yield potential. The best 20 lines from a new genetically diverse population segregating for resistance to Fusarium ear rot were intermated to form a new cycle population for continued selection in the future. 50 advanced lines from the USDA Germplasm Enhancement of Maize project and the North Carolina State University maize inbred development programs were tested for resistance to Fusarium ear rot and fumonisin resistance.
The analysis of several near isogenic lines in controlled growth chamber conditions was begun and have shown that resistance observed in the field is also usually observed under control environment conditions (with much younger plants). Fine-mapping two quantitative trait gene regions for southern leaf blight using F2:3 populations was begun.
This progress addresses Component 3 (Genetic Improvement of Crops), Problem Statement 3C (Germplasm Enhancement/Release of Improved Genetic Resources and Varieties) of the National Program 301 Action Plan (Plant Genetic Resources, Genomics, and Genetics Improvement).
Identification of genes conferring multiple disease resistance.
Previous research suggested but did not prove that some resistance genes can confer resistance to multiple pathogens. Several loci conferring resistance to multiple disease resistance in three different genetically restricted populations were identified. In a very genetically diverse population of maize, a gene statistically associated with resistance to three foliar diseases was identified. This discovery will lead to a better understanding of the function of resistance genes and better capability to improve durable resistance to multiple diseases in maize.
This progress addresses Component 2 (Crop Informatics, Genomics, and Genetic Analyses), Problem Statement 2C (Genetic Analyses and Mapping of Important Traits) of the National Program 301 action plan (Plant Genetic Resources, Genomics, and Genetics Improvement).
5.Significant Activities that Support Special Target Populations
Ruiz Corral, J., Duran Puga, N., Sanchez, J., Ron Parra, J., Gonzalez, D., Holland, J.B., Medina, G. 2008. Climatic Adaptation and Ecological Descriptors of 42 Mexican Maize (Zea Mays L.) Races. Crop Science. 48:1502-1512.
Buckler Iv, E.S., Yu, J., Holland, J.B., Mcmullen, M.D. 2008. Genome-wide complex trait dissection through nested association mapping. Genetics. 178:539-551.
Holland, J.B., Roberston-Hoyt, L.A., Kleinschmidt, C.E., White, D.G., Payne, G.A., Maragos, C.M. 2007. Relationships of resistance to Furarium ear rot and fumonisin contamination with agronomic performance of maize. Crop Science. 47(5):1770-1778.
Balint Kurti, P.J., Zwonitzer, J., Wisser, R., Pe, E., Pea, G., Lee, M., Cardinal, A. 2008. Identification of Quantitative Trait Loci for Resistance to Southern Leaf Blight and Days to Anthesis in Two Maize Recombinant Inbred Line Populations. Phytopathology. 98:315-320.
Wooten, D.R., Livingston, D.P., Lyerly, J., Holland, J.B., Fellon, E.N., Marshall, D.S., Murphy, P.J. 2008. Quantitative Trait Loci and Epistasis for Oat Winter Hardiness Component Traits. Crop Science. 48:149-157.