Cold Resistance Evaluation of Alfalfa during the Germination and Seedling Stages and Analysis of its Relationship with Fall Dormancy

Background: Alfalfa (Medicago sativa L.), a vital forage crop, demonstrates pronounced variability in growth performance and yield in cold regions, largely determined by its cold tolerance. Fall dormancy ratings, a key indicator of alfalfa’s winter dormancy intensity, induce distinct physiological responses and cold tolerance capacities among varieties under low-temperature stress. Therefore, investigating the germination traits and seedling physiological adaptations of alfalfa with varying fall dormancy ratings under cold stress is critical for breeding and cultivating cold-tolerant alfalfa cultivars. Methods: This experiment was conducted in the Key Laboratory of Grassland Resources, Ministry of Education, Inner Mongolia Agricultural University, from March to September 2024. A total of 28 alfalfa materials with 10 different fall dormancy grades were used. Low-temperature stress experiments were conducted to evaluate critical germination parameters, including germination rate, germination index, vigor index, root length and germination coefficient. Concurrently, seedling physiological responses were investigated under 4oC conditions, focusing on biochemical markers: Malondialdehyde (MDA) content, relative conductivity (REC) and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), along with proline (Pro) and soluble sugar (SS) accumulation. Result: Under low-temperature stress, significant reductions were observed in germination parameters, including germination rate, germination index, vigor index, root length and germination coefficient, across alfalfa accessions of different fall dormancy ratings. A strong negative correlation was established between fall dormancy ratings and cold hardiness during germination. Physiological analysis revealed that key biochemical markers-MDA, REC, SOD, POD, CAT, Pro and SS-under 4oC stress conditions. Accessions with lower fall dormancy ratings demonstrated superior cold hardiness, while those with higher fall dormancy ratings showed reduced tolerance. Through comprehensive analysis, REC, SOD, POD and SS were identified as the most critical physiological indicators for evaluating cold hardiness at the seedling stage.