Effects of different plant growth regulators on abscission and quality of Lonicera caerulea Berel fruit

Abstract:【Objective】Fruit abscission is a major limiting factor in the production of blue honeysuckle (Lonicera caerulea L.). Cultivars with different maturity periods can cause economic losses during mechanical harvest. Plant growth regulators can regulate fruit abscission and quality. However, the effects of plant growth regulators on fruits in blue honeysuckle remain largely unclear. In this work, we ex-plored the effect of 2, 4-dichlorophenoxyacetic acid (2, 4-D), gibberellin (GA3), ethephon (ETH) and abscisic acid (ABA) with different concentrations on fruit abscission and quality of blue honeysuckle, and screened the most suitable spraying concentrations for blue honeysuckle production. Our research will  rovide theoretical basis for high quality and efficient cultivation of bule honeysuckle and increase eco-nomic benefit.【Methods】Berel, a main cultivar in China was selected as the experimental material. The leaves of Berel were sprayed with different concentrations of 2, 4-dichlorophenoxyacetic acid (25 mg·L^-1, 50 mg·L^-1, 75 mg·L^-1, 100 mg·L^-1 2, 4-D), gibberellin (25 mg·L^-1, 50 mg·L^-1, 75 mg·L^-1, 100 mg ·L^-1 GA3), ethephon (50 mg ·L^-1, 100 mg ·L^-1, 150 mg ·L^-1, 200 mg ·L^-1 ETH) and abscisic acid (50 mg·L^-1, 100 mg·L^-1, 150 mg·L^-1, 200 mg·L-1 ABA). Water was used as the control (CK). For each treat-ment, three plants with the same growth potential and without pests and diseases were used. The plants were sprayed once every 7 days, a total of 4 times. Three branches in different directions of each tree were selected to calculate abscission rate, and the number of fruits was investigated every five days from the fruit expansion period. The mature fruits with different treatments were randomly selected for fruit quality measurement experiments. We investigated the appearance indicators (fruit weight, vertical diameter, horizontal diameter, hardness) and nutrient contents (soluble solids, total acid, chlorophyll, total phenols, flavonoids, anthocyanin, soluble pectin, propectin) of the fruits. In addition, SPSS software was used to conduct principal component analysis on 11 fruit quality indexes under different treatments of plant regulators.【Results】The GA3 and 2, 4-D treatments had lower fruit abscission rate than that of the CK. There were significant differences between 2, 4-D and the CK, and the effect of delayed abscission increased with the increase of 2, 4-D concentration. Comprehensive analysis showed that 100 mg·L^-12, 4-D treatment had the best effect on delayed Berel fruit abscission, while 75 mg·L^-1 GA3 treatment had the most obvious effect on reducing Berel fruit abscission. There was no significant difference in abscission rate between ABA treatment and the CK. The total abscission rates of 50 mg·L^-1 and 200 mg·L^-1ETH treatments were higher than the natural abscission rate, which were 93.99% and 85.44%, respec-tively. The results of appearance quality showed that the fruit weight under different plant regulator treatments was higher than that of the CK except for the ABA treatment. Among them, the fruit weight (1.2 g) under 50 mg ·L^-1 ETH treatment is the largest, while the control was 0.85 g. The fruit hardness treated with 2, 4-D and GA3 was higher than that under the CK, while that with ABA and ETH treat-ments was slightly lower than that of the CK, suggesting that ABA and ETH treatments might acceler-ate the softening of Lonicera caerulea fruits. The hardness of the fruits treated with 100 mg ·L^-1 2, 4-D reached 2.06 N, which was 1.4 times higher than that of the control. The effect of 50 mg·L^-1 GA3 on the appearance quality of the fruits was relatively better. The contents of soluble solids and total acid of the fruits treated with 50 mg·L^-1 GA3 were significantly higher than that of the control. The total phenols content of the fruits treated with 50 mg·L^-1 2, 4-D was significantly higher than that of the CK. The con-tent of phenols was 3.60 OD·g^-1, which was 119% of the CK. The content of the total phenols of the fruits treated different concentrations of GA3 was significantly higher than that in CK. The relative content of total flavonoids of the fruits treated with 75 mg·L^-1 GA3 was significantly higher than that of the CK, while the other treatments had no significant difference with or was significantly lower than that of the CK. The anthocyanin contents of the fruits treated with mg·L^-1 2, 4-D and 75 mg·L^-1 GA3 were significantly higher than that of the CK, and the anthocyanin content of the fruits treated with 50 mg·L^-1 2, 4-D was 123% of the CK. The anthocyanin content of the fruits treated with 75 mg·L^-1 GA3 reached the maximum value 3.27 OD·g^-1, which was 124% of the CK. In addition, 75 mg·L^-1 2, 4-D, 100 mg·L^-1 2, 4-D and 50 mg ·L^-1 GA3 treatments had high content of propectin, and did not change or decreased the content of soluble pectin compared with the control, resulting in the increase of the fruit hardness. The changes of fruit quality indexes of each treatment were comprehensively evaluated and their effects on improving fruit quality were compared. The results showed that the effect of GA3 treatment＞2, 4- D treatment＞CK＞ABA treatment, and the effects of ETH with different concentrations on fruit quality were different.【Conclusion】100 mg·L^-1 2, 4-D and 50 mg·L^-1 GA3 treatments would be the best choices for delaying fruit ripening and abscission without undesirable effects on fruit quality, while 100 mg ·L^-1ABA and 50 mg·L^-1 ETH treatments would be the best choices for promoting fruit ripening and abscission. Among them, 50 mg·L^-1 GA3 treatment had the best effect on improving fruit quality. Key words: Lonicera caerulea L.; Plant growth regulators; Abscission rate; Fruit quality