An intra-specific linkage map of lettuce (Lactuca sativa) and genetic analysis of postharvest discolouration traits.

Minimally processed salad packs often suffer from discolouration on cut leaf edges within a few days after harvest. This limits shelf life of the product and results in high wastage. Recombinant inbred lines (RILs) derived from a cross between lettuce cvs. Saladin and Iceberg were shown to be suitable for genetic analysis of postharvest discolouration traits in lettuce. An intra-specific linkage map based on this population was generated to enable genetic analysis. A total of 424 markers were assigned to 18 linkage groups covering all nine chromosomes. The linkage map has a total length of 1,040 cM with an average marker distance of 2.4 cM within the linkage groups and was anchored to the ultra-dense, transcript-based consensus map. Significant genetic variation in the postharvest traits ‘pinking’, ‘browning’ and ‘overall discolouration’ was detected among the RILs. Seven significant quantitative trait loci (QTL) were identified for postharvest discolouration traits providing markers linked to the QTL that can be used for marker-assisted selection. Phenotypic stability was confirmed for extreme lines possessing the corresponding QTL parental alleles and which had shown transgressive segregation. This study indicates that a desired phenotype with reduced levels of postharvest discolouration can be achieved by breeding using natural variation.