Effects of ethephon on flower bud initiation and fruit quality of five pineapple varieties

Abstract:【Objective】Pineapple, originating in South America, is renowned for the rich flavor and nutrition, which is one of the most distinctive and competitive tropical fruits in China. Flower induction was a crucial step in pineapple cultivation and a technical guarantee to ensure a year- round supply of pineapple. Currently, it has been proven that ethylene is the only endogenous hormone that can directly initiate the reproductive growth of pineapple. Ethephon has been widely utilized to induce pineapple flowering for attaining the higher flowering rate, uniformity rate, cost-effectiveness and convenient application. However, different varieties of pineapples exhibit varying sensitivities to ethephon induction, and thus it is necessary to identify the appropriate ethephon concentrations for each variety and explore appropriate flowering induction ways for different pineapple varieties in order to accelerate their popularization and demonstration. In this study, different pineapple varieties were chosed as research objects to explore the influence of ethephon concentrations on the flowering and fruit quality of pineapple to screen out the appropriate flowering concentrations for each variety, so as to provide a theoretical basisfor production and application.【Methods】Five cultivars including Josapine, Tainong 4, MD-2, Tainong 21 and Tainong 22 were used as sample materials. Ethephon concentrations was set at 25, 50, 100, 200, 400, 800 and 1000 mg·L-1 , respectively, to induce pineapple flowering with three repetitions per concentration treatment. Each plant was treated with a volume of 30 mL solution with clean water serving as the control. The floral bud emergence of each variety was recorded, and flowering rate and floral bud emergence uniformity rate were calculated. All ripe fruits were investigated for the number of crown bud, height of crown bud, weight of crown bud, length and diameter of fruit, fruit weight, perimeter of fruit and number of fruitlets. The contents of total soluble solids, soluble sugar, titratable acid and vitamin C were determined by random selection of three fruits as a treatment with three repetitions. If the flowering rate was too low, all fruits were collected as samples. Excel 2016 was used to sort out the data, Origin 2021 was used for plotting, and SPSS 23 was used for analysis of variance.【Results】Except for Tainong 22, the flowering rate of all pineapple varieties increased significantly with increase of ethephon concentrations. The best ethephon concentration for Josapine and Tainong 4 was 400 mg ·L^-1 , and for MD-2 and Tainong 21 was 800 mg ·L^{- 1} . In summary, the sensitivity of different pineapple varieties to ethephon was as follows: Josapine, Tainong 4, MD- 2, Tainong 21 and Tainong 22 from strong to weak degrees. The floral bud emergence time of Tainong 4 decreased with the increase of ethephon concentrations, while the floral bud emergence time of Josapine, MD- 2 and Tainong 21 did not change. And the floral bud emergence time of these varieties were 29, 31 and 31 days, respectively. When the ethephon concentration was greater than 400 mg · L^-1 , the floral bud emergence stage of Josapine, Tainong 4 and Tainong 21 was shortened, while the floral bud emergence stage of MD-2 was prolonged. The influence of ethephon concentration on the appearance quality varied with varieties. When the concentration of ethephon was greater than 200 mg ·L^-1 , the morphological indexes of Josapine, MD-2 and Tainong 22 showed a downward trend. When the concentration was greater than 400 mg·L^-1 , the length, diameter and fruit weight of Tainong 4 showed a downward trend. The height of crown bud of Josapine, Tainong 21 and Tainong 22 increased with the increase of ethephon concentrations. Simultaniously, the influence of ethephon concentration on the intrinsic quality of different varieties was also different. With the increase of ethephon concentration, the titrable acid content of all pineapple varieties showed a decreasing trend, while the total soluble solid content of all varieties showed an opposite trend. In addition, the malformed fruit was produced in five varieties induced by ethephon. And Josapine was more sensitive to high concentration of ethephon, whose malformation rate reached 65.52%. The malformation rate of Tainong 4 and Tainong 22 increased first and then decreased with the increase of ethephon concentrations. Tainong 21 had deformed fruits at all concentrations. However, the malformation rate of MD-2 was only 6.67%.【Conclusion】According to various indexes, the optimal concentration of ethephon used in flower induction for Josapine was 400 mg ·L^-1 , and Tainong 4, MD-2 and Tainong 21 was 800 mg·L^-1. However, ethephon applied alone could not induce Tainong 22 to initiate flower buds.