Abstract: [Objective] Kiwifruit (Actinidia spp.) originated in China, in the "Big Food View" perspective is an important part of China's fruit food. Kiwifruit has become one of the most popular fruits because of its unique flavor, rich in nutrients such as Vc, amino acids, organic acids, soluble sugars and minerals. Plant growth regulators have many physiological effects, such as enhancing plant resistance, regulating fruit size, pigment accumulation level, saccharic acid component content and maturation and senescence process. Improper use of plant growth regulation can easily lead to high malformed fruit rate, dark skin color, early physiological ripening, large inventory loss, and low quality, which leads to the decline of comprehensive quality of postharvest kiwifruit. To explore the effects of different plant growth regulators on the growth and postharvest quality of kiwifruit. [Methods] The Jinyan kiwifruit was treated with different concentrations of GA3 (50 mg·L-1, 100 mg·L-1, 200 mg·L-1), CPPU (5 mg·L-1, 10 mg·L-1, 20 mg·L-1), triacotanol (5 mg·L-1, 10 mg·L-1, 20 mg·L-1), NAA (50 mg·L-1, 100 mg·L-1, 200 mg·L-1), IAA (20 mg·L-1, 40 mg·L-1, 80 mg·L-1), 6-BA (25 mg·L-1, 50 mg·L-1, 100 mg·L-1), melatonin (10 mg·L-1, 20 mg·L-1, 40 mg·L-1) and tryptophan (100 mg·L-1, 200 mg·L-1, 400 mg·L-1) after 25~30 d of pollination. The water treatment as control (CK), three plants were treated with each concentration of each plant growth regulator as three biological replicates. After 140 d of pollination, 20 fruits were selected every 2 d for the determination of soluble solid content. When the SSC content was greater than 6.5%, it was recorded as the physiological maturity stage of the treatment. At the physiological maturity stage of corresponding treatment, 120 healthy kiwifruit fruits were randomly selected from each plant for index determination. They were placed at room temperature until soft ripe (80% of the fruits were less than 1.2 kg·cm-2 in hardness), and 9 fruits were randomly selected every 2 d for hardness index determination. After soft ripening, soluble solid shape and titrable acid content were determined. The remaining fruits were crushed and mixed with liquid nitrogen and stored at -80℃ for the subsequent determination of physiological indexes. The fruit weight, fruit shape index, fruit hardness and starch content were measured at the physiological maturity stage of Jinyan kiwifruit. The soluble solid content, titrable acid content, ascorbic acid content, sucrose, fructose, glucose, citric acid, quinic acid, malic acid, total phenol and total flavone content were measured at the soft ripening stage of the fruit. The effects of different plant growth regulators and concentrations on the above indexes were compared and analyzed. [Results] Different plant growth regulator treatments can significantly increase the single fruit weight, NAA treatment has the best effect, compared with CK single fruit weight increased by 43.07%~55.78%. Tri and CPPU treatments were followed by 34.56%~43.07% and 24.07%~31.62% respectively. Compared with CK, CPPU treatment can advance the physiological maturity by 18~20 d, and NAA treatment can delay the physiological maturity by 6~8 d. Compared with CK, CPPU treatment can increase starch content by 8.53%~17.32%. Different concentrations of MT, Trp, NAA, 5 mg·L-1 of Tri, 25 mg·L-1 and 50 mg·L-1 of 6-BA treatment can significantly improve fruit hardness. Different concentrations of NAA, 200 mg·L-1 of GA3 and 25 mg·L-1 of 6-BA could significantly reduce the softening rate of fruit. NAA treatment has the best effect, the softening rate is reduced by 10.96%~16.44% compared with CK, and the softening period is extended by 3~5 d. CPPU treatment can promote the softening of fruit, and the softening rate is increased by 13.69%~26.03% compared with CK, and the softening period is advanced by 4~6 d. Different concentrations of NAA, 100 mg·L-1 of 6-BA, 5 mg·L-1 of CPPU, 50 mg·L-1 and 100 mg·L-1 of IAA, 20 mg·L-1 of Tri, 100 mg·L-1 and 400 mg·L-1 of Trp could significantly increase the content of titrable acid in fruit at soft ripening stage. Different concentrations of CPPU, NAA and Trp significantly reduced the ascorbic acid content at the soft ripening stage, and the treatment effect of CPPU was the best, which decreased the ascorbic acid content by 10.53%~14.47% compared with CK. Trp and NAA treatments decreased by 9.21%~11.84% and 6.24%~8.34%, respectively. 200 mg·L-1 of GA3, 200 mg·L-1 of NAA, 10 mg·L-1 and 20 mg·L-1 of MT treatments significantly increased the fructose content in soft ripening stage. The most significant effect was 10 mg·L-1 of MT, the fructose content increased by 17.43%, followed by 200 mg·L-1 of GA3, 20 mg·L-1 of MT and 200 mg·L-1 of NAA, the fructose content increased by 13.47%, 11.82% and 10.64%. Different concentrations of CPPU, 40 mg·L-1 of MT , 5 mg·L-1 of Tri and 400 mg·L-1 of Trp could significantly increase sucrose content in soft ripening stage. Compared with CK, CPPU treatment can increase the sucrose content by 34.23%~41.23%. Different concentrations of MT, 20 mg·L-1 and 40 mg·L-1 of IAA treatment can significantly increase the glucose content in soft ripening stage, and 20 mg·L-1 of IAA treatment has the best effect, followed by 10 mg·L-1 of MT treatment, which can increase the glucose content by 28.39% and 26.59%, respectively. Different concentrations of CPPU and MT significantly reduced the contents of citric acid, quinic acid and malic acid in soft ripening fruits. Compared with CK, the content of citric acid decreased by 8.75%~10.63% and 8.75%~15.01%, the content of quinic acid decreased by 10.77%~15.38% and 9.23%~12.30%, and the content of malic acid decreased by 14.29%~20.01% and 23.8%~24.76%, respectively. Different concentrations of NAA, MT, 20 mg·L-1 of Tri and 80 mg·L-1 of IAA increased the total phenol content. Different concentrations of CPPU and MT increased the accumulation level of total flavonoids by 22.56%~28.75% and 8.75%~15.00%, respectively, compared with CK. [Conclusion] Different concentrations of 6-BA, CPPU, GA3, IAA, MT, NAA, Tri and Trp could significantly increase fruit weight, but decrease fruit shape index. The contents of soluble solid, ascorbic acid, soluble sugar, organic acid, total phenol and total flavone of kiwifruit fruit quality indexes were promoted or inhibited by different plant growth regulators or concentrations. CPPU treatment of 10 mg·L-1 had the best effect on the accumulation of starch and soluble solids, NAA treatment of 100 mg·L-1 had the best effect on the appearance and storage performance of fruits, and MT treatment had the best effect on the improvement of fruit flavor quality. The suitable concentration of CPPU, NAA and MT combined treatment was expected to improve the comprehensive quality of kiwifruit.
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