Duan Jiahao, Yang Liuyan, Liu Xingke, Du Kang, Liu Yang, Wang Youhua, Hu Wei, Chen Binglin, Meng Yali, Zhao Wenqing
[Objective] At the seedling stage, plant growth regulators and their appropriate concentrations were screened to improve the high temperature tolerance of cotton, and the alleviating effects were determined at the flowering and boll setting stage. [Method] In this study, the cotton cultivar Zhongmian 425 was selected as the test material. Two kinds of temperature treatments were set: normal temperature (average temperature was 28 ℃, and maximum/minimum temperature were 24 ℃/32 ℃) and high temperature (average temperature was 38 ℃, and maximum/minimum temperature were 42 ℃/34 ℃). Water, 200, 400, 600 μmol·L-1 1-methylcyclopropene (1-MCP), 0.01, 0.02, 0.05 μmol·L-1 coronidine (COR) and 0.5, 1.0, 2.0 μmol·L-1 2, 4-epibrassinolide (EBR) spraying treatments were set at the seedling stage. Water and 400 μmol·L-1 1-MCP spraying treatment were set at the flowering and boll setting stage. The effects of different plant growth regulators on the dry mass, leaf photosynthetic characteristics, chlorophyll content, antioxidant enzyme activity, yield and fiber quality of cotton under the normal temperature and high temperature conditions were explored. [Result] The results showed that the suitable concentrations of three plant growth regulators could improve the high temperature tolerance of cotton. Under high temperature stress at the seedling stage, compared with water treatment, spraying 400 μmol·L-1 1-MCP could significantly increase the dry mass of aboveground and underground parts of cotton, and increase the net photosynthetic rate, the contents of chlorophyll a and chlorophyll b, and the activities of antioxidant enzymes (superoxide dismutase, peroxidase, glutathione peroxidase and ascorbate peroxidase), and decrease malondialdehyde content in newly expanded cotton leaves. Principal component analysis proved that 400 μmol·L-1 1-MCP could effectively improve the high temperature tolerance of cotton. Meanwhile, under high temperature stress at the flowering and boll setting stage, spraying 400 μmol·L-1 1-MCP could significantly improve the net photosynthetic rate, stomatal conductance and transpiration rate of subtending leaves to cotton bolls, the number of bolls per plant, boll weight, seed cotton yield per plant and fiber quality compared with spraying water. [Conclusion] 400 μmol·L-1 1-MCP can increase the chlorophyll content, photosynthetic capacity and antioxidant enzyme activity, and reduce the accumulation of malondialdehyde and other harmful substances in cotton leaves, thus enhancing the high temperature tolerance of cotton, and finally improve the cotton yield and fiber quality to a certain extent.