2018 ASHS Annual Conference

Fresh-cut lettuce is widely used in packaged leafy vegetable salads. While there are no current estimates of the retail value of fresh-cut lettuce, the segment represents 25-35% of raw product production in Monterey county of California, which has a farm gate value of approximately 1.5 billion dollars. Most fresh-cut products involve harvesting whole mature heads of romaine or iceberg type lettuce, cutting the leaves to a specified size, and packaging the salad in clear specialized films with modified atmospheres (modified atmosphere packaging, MAP). However, even in MAP, fresh-cut lettuce can have short shelf life and deterioration can occur within a week after processing. Deteriorated lettuce is not marketable, must be disposed, and results in the need for more lettuce to be grown, processed, and transported. Lettuce cultivars with extended shelf life will help reduce waste and increase efficiency. Genome-wide association studies (GWAS) were performed on a set of 498 lettuce accessions. The accessions were genotyped, and 4,615 high-quality, polymorphic, single-nucleotide polymorphism (SNP) markers were used for analyses. For shelf life assessment, four field experiments were performed in three locations in Salinas Valley during 2016 and 2017. Lettuce heads were harvested, processed into fresh-cut salad, and stored at 4°C for evaluations. Salad bags were visually evaluated weekly and deterioration assessed using the scale of 0 through 10, where the rating corresponds to 1/10^th of the estimated percentage of deteriorated tissue. Mean area under deterioration progress stairs (AUDePS) was calculated for each accession. GWAS of shelf life data was performed by mixed linear model analyses; the genetic relationships among the individuals were incorporated into statistical models using principal component analysis and kinship matrix. Significant marker-trait associations (SMTA) were detected on Linkage Group 4 (LG4) in all experiments. The most significant P-value was 8.44E-14 that explained 15% of the total phenotypic variation (R² = 0.15) of the trait. Major quantitative trait loci (QTL) for deterioration of fresh-cut lettuce were reported previously in LG4 in a recombinant inbred line population of Salinas 88 x La Brillante. Molecular markers closely linked with the trait QTL can be applied for selecting lettuce genotypes with a slow rate of deterioration and for identification of gene(s) responsible for extended shelf life of fresh-cut lettuce.