Further isolation of AFLP and LMS markers for the mapping of the Ol-2 locus related to powdery mildew (Oidium neolycopersici) resistance in tomato (Solanum lycopersicum L.)

Tomato powdery mildew (Oidium neolycopersici) is a new plant disease that in recent years has frequently occurred in open field and protected environments to cause serious damage to tomato crops. Currently, the development of resistant cultivars appear to be the best eco-compatible solution to control the fungus. Several studies are in progress to increase knowledge on a recessive gene named ol-2 that confers complete resistance to powdery mildew. In this paper, we report results of research aimed at further isolation of new PCR-based markers linked to ol-2. This goal was pursued by means of bulk segregant analysis (BSA) applied to an F2 population segregating for the ol-2 gene and derived from the pair cross between a resistant line of Solanum lycopersicum L. var. cerasiforme and the susceptible cultivar Super Marmande. Eight new amplified fragment length polymorphism (AFLP) markers tightly linked to ol-2 were isolated, adding useful mapping information to the chromosome four region where Ol-2 locus is located. Results from the application of the ligation-mediated suppression PCR (LMS-PCR) technique are also reported for the first time in plant material. These results, combined with those obtained applying low ionic strength single strand conformation polymorphism (LIS-SSCP) analysis, were of value to detect polymorphism between parents characterised by high genetic similarities and also useful in avoiding ‘‘linkage drag’’ during marker assisted selection (MAS) programs.