Analysis of physiological changes in peanut germination and seedling stages following low-temperature stress

Introduction: Peanut cultivation in high-latitude regions is frequently subjected to low-temperature stress, which adversely affects peanut growth and development. The correlation between physiological changes in peanut during the germination and seedling stages and exposure to low-temperature stress at the harvest period remains unclear, and this research gap limits the in-depth study of peanut cold tolerance. This study aimed to explore the above correlation and identify core physiological indicators for evaluating peanut cold tolerance at germination and seedling stages. Methods: Thirty-six peanut accessions were used as experimental materials and subjected to natural low-temperature stress during the field harvest period. After drying the pods for 3 days, laboratory germination tests were conducted to screen out one extremely cold-tolerant and one extremely cold-sensitive accession from the 36 materials. The two extreme materials were then exposed to artificial low-temperature stress at the germination and seedling stages: the temperature was decreased from 26 °C to target temperatures (8 °C, 4 °C, and 0 °C) at a rate of 2 °C/h, and then increased back to 26 °C at the same rate, with a control group maintained at a constant 26 °C. Physiological indicators of the materials were determined at five time points after they returned to 26 °C and resumed normal growth, and principal component analysis (PCA) was used for comprehensive analysis of the indicators. Results: After low-temperature stress at both germination and seedling stages, the cold-tolerant material had significantly higher contents of proline (Pro) and soluble sugar, as well as higher activities of Superoxide Dismutase (SOD), Peroxidase (POD), and Catalase (CAT) compared with the cold-sensitive material, while its Malondialdehyde (MDA) content was significantly lower. All physiological indicators of the cold-tolerant material recovered to normal levels within 36 hours of recovery, whereas the recovery of the cold-sensitive material was significantly slower. PCA extracted three principal components from the measured indicators, with a cumulative contribution rate of 89.35%. Pro and SOD were ultimately identified as the core indicators for evaluating peanut cold tolerance at the germination and seedling stages. Discussion: This study successfully screened two peanut materials with extreme cold tolerance phenotypes by combining field natural low-temperature stress and laboratory simulated low-temperature stress treatments. The clarification of Pro and SOD as core evaluation indicators fills the research gap in the cross-stage cold tolerance study of peanuts, which links harvest-period low-temperature stress with physiological responses at germination and seedling stages. The screened extreme cold-tolerant and cold-sensitive materials provide important germplasm resources for subsequent peanut cold tolerance breeding, and the identified core indicators lay a solid theoretical foundation for the rapid evaluation and identification of peanut cold tolerance.