Genome-wide association mapping reveals loci for enzymatic discoloration on cut lettuce

Enzymatic discoloration is a major postharvest flaw in cut lettuce, leading to significant food waste. Identifying the genetic determinants and factors associated with this physiological process can facilitate the development of cost-effective and environmentally friendly methods that minimize the loss of product. In this study, a diverse panel of 376 lettuce accessions was investigated for the relationship between enzymatic discoloration and agronomic traits, as well as the genetic characteristics of the discoloration process. The discoloration did not correlate significantly with plant developmental rate, resistance to yellow spot malady, bacteria leaf spot, or downy mildew; but it showed a significant although not strong correlation with the initial levels of brownness (r = -0.146, p < 0.05) and greenness (r = -0.255, p < 0.001) in midribs, and the deterioration rate (r = 0.391, p < 0.001) of fresh-cut lettuce packaged in modified atmosphere. The trait exhibited a relatively high broad-sense heritability (H-2 = 0.669) in four trials conducted at three locations in three years. The genome-wide association study (GWAS) revealed the significant effects of six loci (qDis1.1, qDis4.1, qDis6.1, qDis8.1, qDis8.2, and qDis9.1) defined by eight SNP markers. A total of 965 genes were predicted in the identified chromosomal regions, with three quinone oxidation-reduction (redox) enzymes and 19 transcription factors being potentially the most promising candidate genes involved in regulating postharvest discoloration.