Effects of five plant growth regulators on fruit quality of Ziziphus jujuba‘Huizao’

【Objective】Huizao is an important variety of red Chinese jujuba (Ziziphus jujuba) in Xinjiang. Improvement of yield and fruit quality will increse economic benefits and market competitiveness. Plant growth regulators have shown unique advantages in regulating crop growth and development, enhancing resistance and improving quality. The study aimed to screen out the effective plant growth regulators that could improve the fruit quality of Huizao.【Methods】This experiment was carried out in the Chines Jujuba Germplasm Resource Collection of Kashgar Mageti County, Fruit and Vegetable Research Institute, Xinjiang Uygur Autonomous Region Academy of Agricultural Sciences. The Huizao trees were used as the test material, and five plant growth regulators, namely, Diethyl aminoethyl hexanoate (DA-6), Oligochitosan (AS), Sodium Nitrophenolate (CSN), Phthalanilic acid (PA), and Paecilomyces variotii extracts (ZNC), were sprayed during the period of fruit expansion. 15 treatment groups were set up with different concentration gradients for each regulator, and a clear water control (CK) was set up. We selected the test trees with good growth, consistent flowering and growth, and sprayed the leaves evenly with different agents and concentrations, 2 L liquit sprayed for each treat-ment. The first spray was made in July 10, and the second spray was made 10 days later. During the fruit ripening period, the morphological indexes (single fruit mass, single kernel mass, longitudinal and transverse diameter of fruit, longitudinal and transverse diameter of jujube kernel, etc.), nutrient content (soluble solids, soluble sugar, soluble protein, vitamin C, titratable acid, etc.) and key secondary metabolites (anthocyanin, total phenolics, total flavonoids, etc.) were measured, and correlation analyses were carried out on the various indexes, and the affiliation function method was used to calculate the integrated scores. The correlation analyses of each index were conducted, and the scores were calculated using the affiliation function method to comprehensively evaluate the fruit quality.【Results】In terms of fruit morphology, the differences in the edible rate (95.11%- 97.31% ) and fruit shape index (1.38- 1.54) among treatments were not significant, but the kernel shape index of ZNC T1 (2000 times 250 mg ·L-1 ZNC), CSN T2 (20 mg·L-1 CSN) and ZNC T2 (1500 times 250 mg·L-1 ZNC) treatments were significantly higher than that of the control. In terms of nutrient content, the DA-6 T1 (20 mg·L-1 DA-6) and DA-6 T2 (30 mg·L-1 DA-6) treatments significantly increased soluble solids content, and the CSN T2 and AS T3 (600 times 5% AS) treatments had the highest SSC content. The DA-6 T3 (25 mg ·L- 1 DA-6) treatment had the highest soluble sugar content, but the difference with the control was not significant; and several treatments significantly increased soluble protein content, the DA-6 T2 and CSN T3 (25 mg·L-1 CSN) treatments increased by 7.285% and 5.16%, respectively, compared with the CK; vitamin C content was significantly higher than that of the control in all treatments except CSN T3, of which the vitamin C contents of the AS T1 (1000 times 5% AS), AS T3 and ZNC T1 treatments were the highest, increased by 89%, 77% and 89%, respectively, compared with the CK. The DA-6 T2 and ZNC T3 (1000 times 250 mg·L-1 ZNC) treatments significantly increased the content of titratable acid. In terms of key secondary metabolites, DA-6 T3, ZNC T2, and ZNC T3 treatments significantly increased anthocyanin content, with ZNC T3 treatment having the highest anthocyanin content. The CSN T1 (15 mg · L- 1 CSN), PA T2 (1200 times 20% PA), and ZNC T1 treatments had the highest total pericarp phenol content. The DA-6 T3 treatment had the highest total phenolic content in the pulp, which was enhanced by 83% compared with the CK. The PA T2 treatment significantly enhanced the total flavonoid content in the pericarp, and the AS T3 treatment significantly enhanced the total flavonoid content in the pulp. The correlation analysis between the indicators showed that fruit transverse diameter and fruit longitudinal diameter, kernel longitudinal diameter and kernel weight, and kernel transverse diameter and kernel weight were all highly significantly and positively correlated (P＜0.01), i.e., an increase in kernel weight was often accompanied by an increase in kernel longitudinal and transverse diameter. And the kernel longitudinal diameter and fruit weight, kernel transverse diameter and anthocyanin content, were significantly and positively correlated with kernel transverse diameter (P＜0.05). Through the comprehensive evaluation of the affiliation function method, the comprehensive score of fruit quality of each treatment ranged from 0.293 to 0.722, with the PA T2 treatment scoring the highest, followed by DA-6 T2 and ZNC T2, and the order of the comprehensive score was PA T2＞DA-6 T2＞ZNC T2＞AS T3＞ ZNC T3＞ZNC T1＞CSN T2＞PA T1 (1400 times 20% PA) ＞DA- 6 T3＞PA T3 (1000 times 20% PA)＞CSN T3 ＞CK＞AS T2 (800 times 5% AS)＞CSN T1＞DA-6 T1＞AS T1.【Conclusion】The five plant growth regulators had certain regulatory effects on the fruit quality of Huizao, among which PA T2 treatment had the most prominent effect in improving fruit quality. DA-6 T2 also had a more satisfactory effect. Therefore, it would be recommended to choose PA T2 treatment to effectively improve the fruit quality of Huizao and enhance its market competitiveness.