Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/26/2012
Publication Date: 9/22/2013
Citation: Simko, I. 2013. Marker-assisted selection for disease resistance in lettuce. In: Varshney, R.K., Tuberosa, R., editors. Translational genomics for crop breeding. Vol. I: Biotic stresses. Ames, IA: John Wiley & Sons, Inc. p. 267-289.
Interpretive Summary: Lettuce is the most popular vegetable from the group of leafy vegetables. Development of new lettuce cultivars is a lengthy process that involves cross-pollination, several rounds of selection, development of homozygous genotypes, and testing of material performance. Use of molecular markers linked to the disease resistance genes allows for rapid and frequently also more accurate selection of desirable genotypes than phenotype-based selection. The chapter describes current status of mapping disease resistance genes and development of assays for marker-assisted selection (MAS) in lettuce. The chapter includes comprehensive description of MAS assays developed at the USDA-ARS in Salinas. These assays are based on the high-resolution DNA melting analysis and are used for identification of alleles linked to the resistance against corky root, lettuce mosaic virus, and lettuce dieback. Discussed is the progress in the study of the lettuce genome and perspectives of MAS in this vegetable crop.
Technical Abstract: Lettuce (Lactuca sativa L.) is the most popular leafy vegetable that is cultivated mainly in moderate climate. Consumers demand lettuce with good visual appearance and free of disease. Improved disease resistance of new cultivars is achieved by combining desirable genes (or alleles) from existing cultivars or by introgressing novel resistance genes from wild Lactuca species sexually compatible with cultivated lettuce. Development of elite lettuce cultivars is a lengthy process that involves cross-pollination, several rounds of selection, development of homozygous genotypes, and testing of material performance. Use of molecular markers linked to the disease resistance genes allows for rapid and frequently also more accurate selection of desirable genotypes than phenotype-based selection. This marker-assisted selection (MAS) is used by both public and private lettuce-breeding sectors. At the present time, MAS for diseases resistance in lettuce is limited to simply inherited traits. Assays were developed to detect genes and alleles for resistance to downy mildew, corky root, lettuce mosaic, and lettuce dieback (description of three assays based on the high-resolution DNA melting approach is provided in this chapter). Resistance genes against Verticillium wilt, turnip mosaic, root downy mildew, powdery mildew, big-vein, Fusarium wilt, and anthracnose have been mapped on the molecular linkage map of lettuce and assays for MAS are under development for several of these genes. The lettuce genome has been recently sequenced paving the way to speedier mapping, cloning and functionally validating genes for disease resistance and for more efficient development of molecular markers used in MAS.