Abstract
This study investigates the natural variation in zinc (Zn) tolerance across lettuce cultivars, integrating phenotypic assessments at the seedling stage with further testing in a glasshouse trial and genotypic analysis to explore genetic underpinnings. High-throughput screening of seedlings identified cultivars with distinct Zn tolerance levels: Michelle (high-Zn-tolerant), Drunken Woman (medium-Zn-tolerant), and Arianna (Zn-sensitive). Subsequent glasshouse trials confirmed these tolerance rankings at a later stage of maturity, with fresh weight and leaf Zn accumulation reflecting consistent cultivar-specific responses. Arianna exhibited reduced biomass and Zn accumulation under excess Zn, aligning with its sensitivity, while Michelle demonstrated resilience as a Zn accumulator.
Genotyping-by-sequencing (GBS) revealed genetic heterogeneity among cultivars but found no correlation between genetic relatedness and Zn tolerance phenotypes. Limitations of GBS, including restricted genome coverage (63% missing SNPs), challenges in resolving complex traits, and potential inaccuracies in phenotype classification based solely on root growth, were identified as factors hindering genetic relatedness dissection. Despite genetic analysis limitations, the study underscores the utility of high-throughput phenotypic screening for breeding programs.
Implications extend to phytoremediation and biofortification, with Zn-accumulating cultivars like Michelle offering dual benefits for soil remediation and dietary Zn enhancement. Future research should prioritize multi-trait phenotyping, consistent seed sourcing, and investigation of Zn transport from roots to leaves to refine tolerance detoxification. This work establishes a framework for evaluating heavy metal responses in crops, supporting strategies to address Zn toxicity and nutritional security.