Molecular Markers and Genome Analysis in the Manipulation of Lettuce Downy Mildew

Abstract

We are developing approaches for map-based cloning of disease resistance genes. Specificity between lettuce and its fungal pathogen, Bremia lactucae, is conditioned by an unambiguous gene-for-gene interaction. Classical genetics of host and pathogen has defined 13 resistance genes (Dm) and matching avirulence genes. The resistance genes are clustered in four regions. The current genetic map comprises 319 markers. We are now focusing on saturating the regions containing resistance genes with PCR-based markers using near-isogenic lines, bulked segregant analysis, and deletion mutants. We are also mapping many genes for disease resistance in lettuce to test whether they are all clustered. Random amplified polymorphic DNA (RAPD) markers are being converted to sequence characterized amplified region (SCAR) markers to provide reliable markers flanking each resistance locus. Recombinants selected from large populations are being used to order closely linked markers in the vicinity of resistance genes. We are developing long-range restriction maps around the Dm genes and analyzing recombinants for changes in the map to orientate the physical map relative to the genetic map and to determine the relationship between genetic and physical distance in the region. We are currently preparing various libraries for chromosome walking and will start isolating overlapping clones when a physically close marker has been confirmed.KeywordsResistance GeneDowny MildewDisease Resistance GeneBulk Segregant AnalysisSequence Characterize Amplify Region MarkerThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.