Lettuce is one of the top ten most important crop species in the US and multiple diseases, particularly downy mildew, cause significant losses. The project will increase the efficiency of lettuce breeding, reduce crop losses, and decrease applications of control chemicals. It addresses the NRI Plant Genomics Program priority of the biological role of genomic sequences and links these sequences to function and agricultural processes. We will exploit several new high throughput genomics technologies to identify candidate gene for resistance to eleven different diseases and will map candidate sequences relative to resistance phenotypes. We will demonstrate function for a subset of these candidates using RNAi. By studying several types of resistance genes and resistance to diverse types of diseases, we will identify which genes are critical for which kinds of disease. We will then survey the primary and secondary genepools of lettuce to identify informative polymorphisms. These markers will then be utilized to introgress resistance from wild germplasm. This project builds on the Compositae Genome Project and translates basic information into tools and genotypes useful for lettuce breeding. We have numerous well-defined genetic stocks of plant and pathogen. The outputs will be sets of molecular markers for cost effective high-throughput genotyping and advanced germplasm that is resistant to multiple diseases. In the long-term, this project will lead to a detailed mechanistic understanding of the genes determining resistance in lettuce to diverse diseases.

These studies will have basic and applied impacts. It will provide a detailed mechanistic understanding of the genes determining resistance in lettuce to diverse diseases. In the long term, through the development and release advanced lettuce breeding lines that are resistant to multiple diseases, it will increase the efficiency of lettuce breeding, reduce crop losses, and decrease applications of control chemicals. The use of multiple resistance genes and their introgression into different plant types will fragment the selection pressures on the pathogen and hence increase the durability of resistance.

1. Multiple molecular markers linked to resistance loci for most major diseases of lettuce.
2. Candidate genes for resistance to several diseases.
3. Information on which types of gene are critical for which type of disease.
4. Advanced breeding lines/genotypes with resistance to multiple diseases.