CHROMOSOMAL LOCALIZATION AND MOLECULAR MARKER TAGGING OF THE POWDERY MILDEW RESISTANCE GENE (LV) IN TOMATO

We report the tagging of a powdery mildew [Leveillula taurica (Lev.) A rnaud.] resistance gene (Lv) in tomato using RAPD and RFLP markers. DN A from a resistant (cv Laurica) and a susceptible cultivar were screen ed with 300 random primers that were used to amplify DNA of resistant and susceptible plants. Four primers yielded fragments that were uniqu e to the resistant line and linked to the resistance gene in an F-2 po pulation. One of these amplified fragments, OP248, with a molecular we ight of 0.7 kb, was subsequently mapped to chromosome 12, 1 cM away fr om CT134. Using RFLP markers located on chromosome 12, it was shown th at approximately one half of chromosome 12 (about 42 cM), in the resis tant variety is comprised of foreign DNA, presumably introgressed with the resistance gene from the wild species L. chilense. Further analys is of a backcross population revealed that the Lv gene lies in the 5.5 -cM interval between RFLP markers, CT211 and CT219. As a prelude to ma p-based cloning of the Lv gene, we are currently enriching the density of markers in this region by a combination of RAPD primers and other techniques.