Genetic analysis of resistance to bacterial leaf spot in the heirloom lettuce cultivar Reine des Glaces

Bacterial leaf spot (BLS) is a disease that affects lettuce ( Lactuca sativa L.) worldwide. The disease is caused by the bacterium Xanthomonas campestris pathovar vitians ( Xcv ), which exclusively infects lettuce and is particularly devastating in warm humid climates. Reine des Glaces (RG), an old Batavia-type cultivar, exhibited an uninvestigated partial resistance to Xcv . Quantitative trait loci (QTLs) were analyzed using two recombinant inbred line (RIL) populations derived from RG × Eruption and RG × Delsay using three isolates collected in California and Canada, each representing a different race, and an isolate collected in France. A major QTL was identified in linkage group 2 in both populations; additional, minor QTLs were also detected in other linkage groups. The major QTL collocates with the Xanthomonas resistance 1 ( Xar1 ) and Xanthomonas campestris vitians resistance ( Xcvr ) genes that had previously been identified using RIL populations derived from Salinas 88 × La Brillante and PI 358001-1 × Tall Guzmaine. RG provides another resistance resource for combating BLS using data provided by this study for marker-assisted selection.