Progress towards mapping QTLs for pest and disease resistance in lettuce

Quantitative non race-specific resistance may be more durable than resistance based on single dominant genes. However selection for multigenic traits in a breeding programme is difficult. We have produced a lettuce mapping population of recombinant inbred lines using cv. Iceberg, a source of quantitative resistance to downy mildew and peach-potato aphid, and have tested the lines for resistance. We are constructing a genetic linkage map from the population using molecular markers which we will use to identify QTL for the resistances.