GENETIC-MAPPING OF TURNIP MOSAIC-VIRUS RESISTANCE IN LACTUCA-SATIVA

Presence of the dominant Tu gene in Lactuca sativa is sufficient to co nfer resistance to infection by turnip mosaic virus (TuMV). In order t o obtain an immunological assay for the presence of TuMV in inoculated plants, the TuMV coat protein (CP) gene was cloned by amplification o f a cDNA corresponding to the viral genome using degenerate primers de signed from conserved potyvirus CP sequences. The TuMV CP was overexpr essed in Escherichia coli, and polyclonal antibodies were produced. To locate Tu on the L. sativa genetic map, F-3 families from a cross bet ween cvs 'Cobbham Green' (resistant to TuMV) and 'Calmar' (susceptible ) were genotyped for Tu. Families known to be recombinant in the regio n containing Tu were infected with TuMV and tested by the indirect enz yme-linked immunosorbent assay (ELISA) using the anti-CP serum. This a ssay placed Tu between two random amplified polymorphic DNA (RAPD) mar kers and 3.2 cM from Dm5/8 (which confers resistance to Bremia lactuca e). Also, bulked segregant analysis was used to screen for additional RAPD markers tightly linked to the Tu locus. Five new markers linked t o Tu were identified in this region, and their location on the genetic map was determined using informative recombinants in the region. Six markers were identified as being linked within 2.5 cM of Tu.