关键词: 直播早稻, 氯化钙, 低温胁迫, 种子萌发, 幼苗耐冷性, 品种差异

Abstract:

To improve the quality of germinated seeds and cultivate vigorous seedlings, and to overcome the obstacles posed by low-temperature stress during germination and the seedling stage of direct-seeded early rice in southern China, this study used two high-quality conventional indica rice varieties Yushanzhan and Yumeijinzhan as experimental materials. Seeds were primed with 0, 5, 10, and 20 mmol/L calcium chloride (CaCl₂) solutions and subsequently subjected to low-temperature stress (15 ℃) or normal temperature conditions (25 ℃). The effects of exogenous calcium ions on seed germination (germination energy, germination rate, and germination index), seedling morphology, and physiological indices were investigated, with an analysis of varietal response differences. The results showed that low temperatures (15 ℃) significantly inhibited seed germination and seedling growth, reduced antioxidant enzyme activities, increased malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents, and exacerbated cell membrane lipid peroxidation damage. Under these low-temperature conditions, treatment with 5-10 mmol/L CaCl₂ significantly improved the germination index, promoted root and shoot growth, enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), reduced H₂O₂ and MDA content, and increased soluble protein content, effectively alleviating cold stress injury. Yushanzhanwas sensitive to high concentrations of CaCl₂; under 20 mmol/L treatment, its germination, growth, and physiological indices decreased. In contrast, Yumeijinzhan demonstrated relative tolerance to 20 mmol/L CaCl₂; although indices declined compared to the 10 mmol/L treatment, no significant growth collapse occurred. Under normal temperature conditions (25 ℃), seed germination, seedling growth, and physiological indices of both varieties initially increased and then decreased with rising CaCl₂ concentration. The optimal priming concentration was 5-10 mmol/L; however, 20 mmol/L treatment induced oxidative stress, leading to a substantial increase in MDA and H₂O₂ contents. In conclusion, significant differences exist in the response of different rice varieties to CaCl₂ priming concentrations. When applying CaCl₂ priming to direct-seeded early rice before sowing, the appropriate concentration must be selected based on specific varietal characteristics: 5-10 mmol/L is recommended for Yushanzhan, while 10-20 mmol/L can be adopted for Yumeijinzhan. These findings provide technical support for cultivating strong seedlings and enhancing cold tolerance in direct-seeded early rice.

Key words: direct-seeded early rice, calcium chloride, low-temperature stress, seed germination, seedling cold tolerance, varietal difference