Location: Plant Science Research2010 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.
3. Progress Report
We continue to make progress in fine mapping of a Southern Leaf Blight resistance gene on chromosome 3 and have identified about 50 recombination events within sub-centiMorgan region that contains the underlying gene. We have also fine-mapped a Southern Leaf Blight resistance gene on chromosome 6 to a region of about a centiMorgan. We have intiated a new project to develop a robust gene silencing system in maize in collaboration with the Noble Foundation. In collaboration with scientists at Purdue, we have identified several loci that affect the strength of the maize defence response. We implemented genome-wide association tests using 1.6 million DNA markers to identify about 50 genes associated with Southern Leaf Blight resistance in the maize Nested Association Mapping population. Many of these genes have previously been shown to impact pathogen responses in plants. We also used association analysis in a diverse sample of maize inbred lines to identify a gene involved in multiple disease resistance. We demonstrated that tropical lines with similar photoperiod responses (late flowering under long daylengths) carry photoperiod response genes with quantitatively distinct effects. Superior backcross-derived lines combining resistance to Fusarium ear rot and hybrid yield potential were identified. 50 advanced lines from the USDA Germplasm Enhancement of Maize (GEM) project and the North Carolina State University maize inbred development programs were tested for resistance to Fusarium ear rot and fumonisin contamination resistance. 100 lines and 50 GEM lines were tested for resistance to southern leaf blight and gray leaf spot respectively.
1. Genome-wide association analysis identifies genes involved in Southern leaf blight resistance. Southern leaf blight is a potentially devastating disease of maize, the primary staple crop in many parts of the world. Identification of the numerous genes responsible for quantitative resistance to this disease represents an important step toward ensuring global food security. ARS researchers in Raleigh, NC used the tremendous genetic resources that have recently become available for complex trait analysis in maize to identify Southern leaf blight resistance genes. These resources include the nearly complete and well-annotated maize reference sequence, the maize Nested Association Mapping population, and the maize Haplotype Map, which provides 1.6 million DNA markers segregating in this population. Genome-wide analysis methods developed specifically for the maize Nested Association Mapping were used to pinpoint specific DNA sequence variations associated with Southern leaf blight resistance throughout the genome. A high proportion of these variants are inside of, or adjacent to, genes that have been previously demonstrated to affect disease resistance in plants.