2017 ASHS Annual Conference

Lettuce (Lactuca sativa L.) is widely used as the main ingredient of packaged leafy vegetable salads. Salad lettuce can have short shelf life decaying as early as eight days after harvest and reducing the nutritional quality. Decayed lettuce is not marketable, produces extra waste, and needs more lettuce to be grown, processed, and transported. Lettuce cultivars with extended shelf life will help reduce waste products and increase efficiency. Genetic diversity, population structure, and a genome-wide association study (GWAS) were performed on a set of 498 lettuce accessions of mostly romaine types. All but 12 accessions underwent single-seed increase before genotyping using the genotyping-by-sequencing technique. A total of 4,615 high-quality polymorphic SNP (single-nucleotide polymorphism) markers were used for analysis. For shelf life assessment, lettuce heads were harvested from a single replicated field, processed into three salad bags (340 g each) per accession, and stored at 4°C for evaluation. Salad bags were evaluated on weekly intervals using the scale of 0 through 10, where the rating corresponds to 1/10^th of the estimated percentage of decayed tissue. Area under deterioration progress stairs (AUDePS) was calculated for each accession. GWAS with shelf-life data was performed by general linear model (GLM) and mixed linear model (MLM) analyses. Information about the genetic relationships among the individuals was incorporated in the analyses using principal component analysis (PCA) in GLM and PCA and kinship in MLM. Significant marker-trait association (SMTA) was detected on Linkage Group 4 (LG4) in both methods. P-value was as low as 3.55E-14 in MLM which explained 16% of the variation and lowest P-value with GLM was 1.11E-53 explaining 42% of the variation. Markers associated with this SMTA can be used for marker-assisted breeding for improved salad processing efficiency. Major quantitative trait loci (QTL) for decay of fresh-cut lettuce have been previously reported in LG4 in a recombinant inbred line population of Salinas 88 x La Brillante. Thus, information on these SMTA and QTL can be used for further studies leading to the identification and functional studies of gene(s) responsible for extended shelf life of lettuce.