Insight into postharvest deterioration in fresh-cut lettuce through genetics and physiology

Authors: Simko, Ivan

Submitted to: Plant and Animal Genome Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/31/2024
Publication Date: 1/14/2025
Citation: Simko, I. 2025. Insight into postharvest deterioration in fresh-cut lettuce through genetics and physiology. Plant and Animal Genome Conference, January 14, 2025, San Diego, California.

Interpretive Summary:

Technical Abstract: Fresh-cut lettuce (Lactuca sativa), a key ingredient in ready-to-eat salad mixes, faces significant postharvest challenges, including rapid tissue deterioration and discoloration under modified atmosphere packaging (MAP). Although MAP with low oxygen levels (<3% O2) effectively reduces enzymatic browning, certain lettuce cultivars possess heritable traits that accelerate deterioration in low oxygen conditions, thereby compromising shelf life and food safety. Environmental and processing factors, such as temperature, leaf maturity, and sample size, also influence deterioration rates. Larger cut pieces, lower humidity in MAP, reduced tissue-to-MAP volume ratios, and optimized oxygen concentrations significantly mitigate deterioration. Experimental results revealed that rapid deterioration correlates with sustained respiration under extremely low oxygen levels (<1%), with minimal effects from elevated carbon dioxide (0–14%) or ethylene (0–10 ppm). RNA-seq analysis of contrasting genotypes—slowly deteriorating and rapidly deteriorating—identified distinct transcriptomic responses under MAP conditions. Rapidly deteriorating genotypes showed increased expression of glycolytic enzymes, ATP-consuming pathways, and electron transport chain components, indicative of an inefficient metabolic response to oxygen stress. In contrast, slow-deteriorating genotypes exhibited higher expression of alternative oxidase genes, potentially conserving ATP and reducing oxygen demand. To elucidate the genetic basis of these traits, quantitative trait locus (QTL) mapping was performed on two biparental populations derived from crosses between parents with slow and rapid deterioration rates, and genome-wide association studies (GWAS) were conducted on nearly 500 diverse lettuce accessions. These analyses consistently identified qSL4 on chromosome 4 as the primary locus associated with deterioration. Fine mapping of qSL4 further validated its role, explaining up to 74% of the phenotypic variance in deterioration rates. Marker saturation within this locus identified haplotypes predictive of deterioration rates, enabling efficient genotypic screening. The qSL4 locus was narrowed to a 10 Mbp region containing candidate genes potentially linked to stress resistance and postharvest quality. Transgenic lines with induced mutations in the coding and promoter regions of candidate genes have been developed and are currently being tested for their effects on postharvest deterioration. These findings demonstrate the potential to breed lettuce cultivars with extended shelf life by optimizing metabolic efficiency and oxygen-use strategies. Such advancements could significantly reduce postharvest losses, lower economic and environmental costs, and improve consumer satisfaction with fresh-cut products.