Abstract:  【Aim】 To investigate the effects of seed soaking with different concentrations of calcium chloride (CaCl₂) on rice defense enzyme activities and resistance to the brown planthoppers (BPH), Nilaparvata lugens. 【Methods】Rice seeds were respectively soaked in 10, 20, 30, 40 and 50 mmol/L CaCl₂ solution for 48 h, and the control seeds were soaked in distilled water. At the tillering stage, the activities of phenylalanine ammonia lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO) and β-1, 3-glucanase (β-1,3-GA) in leaf sheaths of rice plants pretreated by soaking seeds in various concentrations of CaCl₂ with or without infestation by the 3rd instar nymphs of BPH were tested, and the survival rates of the 2nd instar nymphs of BPH fed on rice plants subjected to seed soaking treatment with different concentrations of CaCl₂, calcium chelator ethylene glycol tetraacetic acid (EGTA)(1 mmol/L) plus 20 mmol/L CaCl₂ and ion channel inhibitor lanthanum chloride (LaCl₃)(1 mmol/L) plus 20 mmol/L CaCl₂, respectively, for 7 d were examined as well.【Results】 Without BPH infestation, the activities of PAL, POD, PPO and β-1,3-GA in rice leaf sheaths in seed soaking treatments with various concentrations of CaCl₂ showed no significant differences from those of the control. When the rice plants were infested by the 3rd instar nymphs of BPH, the activities of these four defense enzymes in leaf sheaths of CaCl₂-pretreated rice plants and the control rice plants all increased significantly, while the ascending degrees of all enzyme activities in CaCl₂-pretreated rice plants were higher than those in the control plants. The effects of seed soaking with different concentrations of CaCl₂ on the activities of various enzymes in leaf sheaths of rice plants under BPH infestation were different, the activities of PAL, POD and PPO in seed soaking treatment with 30 mmol/L CaCl₂ were 104.88%, 94.32% and 61.84% higher than those in their respective controls, respectively, and the β-1,3-GA activities in seed soaking treatment with 10 and 20 mmol/L CaCl₂ were 27.75% and 33.04% higher than those in their respective controls, respectively. After 7 d, the survival rates of the 2nd instar nymphs of BPH fed on the rice plants subjected to seed soaking treatment with 10, 20 and 30 mmol/L CaCl₂ were 32.68%, 22.54% and 30.28% lower than that fed on the control plants, respectively, but the survival rates of BPH nymphs fed on the plants subjected to seed soaking treatment with 40 and 50 mmol/L CaCl₂ showed no significant differences from that fed on the control plants. Additionally, calcium chelator EGTA (1 mmol/L) and ion channel inhibitor LaCl₃ (1 mmol/L) significantly inhibited the effects of CaCl2 (20 mmol/L) on induced resistance in rice plants to BPH, and the survival rates of nymphs fed on rice plants subjected to seed soaking treatment with EGTA+CaCl₂ and LaCl₃+CaCl₂ were 25.80% and 22.12% higher than that fed on rice plants subjected to seed soaking treatment with CaCl₂, respectively.【Conclusion】 Seed soaking treatment with CaCl₂ can prime rice plants in a stage of preparing for defense, resulting in higher enzyme activities when attacked by BPH, and thus increasing rice resistance against BPH.

Key words: Nilaparvata lugens, rice, CaCl₂, seed soaking treatment, defense priming