Comprehensive evaluation and analysis of cold tolerance in Neopyropia yezoensis strains based on multiple traits

Neopyropia yezoensis, an important economic macroalga, is cultivated in the coastal regions of Northeast Asia, where the farming season spans the cold winter. The low temperatures during this period severely impacting its growth and yield. Given these challenges, selecting high-quality strains with enhanced cold tolerance is essential for improving both yield and quality. To achieve this, it is crucial to establish a set of evaluation criteria and methods to effectively screening for cold-tolerant germplasm. In this study, the cold tolerance of 60 N. yezoensis strains was evaluated by assessing 13 traits, including growth rate, photosynthetic parameters, and pigment contents. Under low temperature, most traits were depressed, with the daily growth rate (DGR) being particularly affected. Principal Component Analysis (PCA) and weight analysis identified thalli area, DGR, chlorophyll a (Chl a), phycoerythrin (PE), allophycocyanin (APC) and photochemical efficiency (Φ_PSII) as primary contributors to cold tolerance. A comprehensive index (D) was developed based on the membership function and weight of each trait to rank the 60 strains into five cold tolerance levels. Over 65.0 % of strains exhibited a certain extent of cold tolerance, which aligning with the nature N. yezoensis as cold-water species. The optimal evaluation model was established as D = 0.387a rea + 0.122Chl a + 0.242F_v/fm + 0.066APC - 0.086, with R² of 0.955 (where F_v/fm represents the maximum photochemical efficiency). This research establishes a comprehensive evaluation system for cold tolerance in N. yezoensis, enabling the rapid screening of cold-tolerant strains and enhancing breeding efforts in the industry.