Development of diagnostic PCR markers closely linked to the tomato powderymildew resistance gene Ol-1 on chromosome 6 of tomato

Lycopersicon hirsutum G1.1560 is a wild accession of tomato that shows resi stance to Oidium lycopersicum, a frequently occurring tomato powdery mildew . This resistance is largely controlled by an incompletely dominant gene Ol -1 near the Aps-l locus in the vicinity of the resistance,genes Mi and Cf-2 /Cf-5. Using a new F-2 population (n=150) segregating for resistance, we ma pped the Ol-1 gene more accurately to a location between the RFLP markers T G153 and TG164. Furthermore, in saturating the Ol-1 region with more molecu lar markers using bulked segregant analysis, we were able to identify five RAPDs associated with the resistance. These RAPDs were then sequenced and c onverted into SCAR markers: SCAB01 and SCAF10 were L. hirsutum-specific; SC AE16, SCAG11 and SCAK16 were L. esculentum-specific. By linkage analysis a dense integrated map comprising RFLP and SCAR markers near OI-I was obtaine d. This will facilitate a map-based cloning approach for Ol-1 and marker-as sisted selection for powdery mildew resistance in tomato breeding.