Major Quantitative Trait Loci Control Low-Temperature Germination in Lettuce

Low-temperature stress during germination is a major constraint for lettuce establishment in temperate and early-season production systems, causing delayed emergence, poor stand uniformity, and reduced yield. Cold germination represents an adaptive trait that enables seeds to initiate growth under suboptimal temperatures, but its genetic basis in lettuce remains poorly understood. Here, we investigated genetic architecture underlying cold germination using a biparental recombinant inbred line population derived from a cross between Lactuca sativa cv. Salinas and Lactuca serriola (wild lettuce). Phenotypic evaluations revealed substantial variation in germination performance at low temperatures, with cultivated lettuce exhibiting superior cold germination compared with the wild parent. Estimates of heritability indicated that genetic factors accounted for a large proportion of the observed phenotypic variation, demonstrating strong potential for selection. Quantitative trait locus (QTL) analysis identified two genomic regions significantly associated with cold germination ability, together explaining a substantial fraction of phenotypic variance (35%). These regions contained candidate genes involved in hormone signaling, membrane stability, and stress-responsive transcriptional regulation, including components of abscisic acid (ABA), gibberellic acid (GA), and ethylene pathways known to modulate germination under adverse conditions. Together, these results indicate that cold germination is a genetically complex trait that has likely been shaped through domestication and breeding. By elucidating the genetic basis of cold germination in lettuce, this study provides valuable targets for marker-assisted breeding aimed at improving seedling establishment and extending lettuce production into cooler environments.