Effects of girdling on tree growth and development, and fruit quality of different jujube varieties under protected cultivation

【Objective】Girdling is an important measure to preserve flowers and fruits and improve fruit quality in the cultivation process, but it’s time-consuming and laborious. Most of the studies on girdling used a single variety of materials, and there was a lack of research on the fruit quality and fruit cracking of different varieties. Eight different jujube varieties were used as test materials to explore the effects of girdling on tree growth and development, yield per plant, fruit quality and fruit cracking of different jujube varieties, so as to provide theoretical basis for improving fruit quality, clarifying the pattern of tree growth and development after girdling, and reducing fruit cracking rate.【Methods】Eight fresh jujube varieties, including Zaohongmi, Yingqiuhong, Panzao, Liuyuexian, Lindong 2, Longpandongzao, Beijingsuanzao and Lengbaiyu, were taken as test materials, which were cultivated in a cold shed in Taigu District of Shanxi Province. The selected materials were healthy without pests and diseases and grew in a consistent manner. Girdling was carried out at the full-bloom stage of each variety. The tree growth, fruit soluble solids, titratable acid, yield per plant, fruit cracking rate and fruit shrinkage rate of the stripped and unstripped varieties were measured and compared. At the full- bloom stage, a secondary branch was left at the base of the trunk for girdling, and the girdling width was 1/6 of the trunk thickness. Each plant of each variety was repeated five times. The phloem was stripped to the xylem without damaging the xylem, and no girdling was set as the control group (CK). The fruit cracking rate is the number of cracking fruits per plant divided by the total number of fruits per plant, and the fruit shrinkage rate determination method is the same as the fruit cracking rate determination method. The measurement method of tree growth is to measure the growth and development index of the tree before the girdling, and to measure it again after the tree stopped growing. As for other fruit quality and traits, refer to the‘jujube germplasm resources description specifications and data standards’.【Results】Girdling significantly increased the single fruit weight of each variety. Among them, the increase efficacy of single fruit weight of different varieties was as follows: Lindong 2＞Beijingsuanzao＞ Liuyuexian＞Panzao＞Lengbaiyu＞Longpandongzao＞Yingqiuhong＞Zaohongmi, namely 10.66 g＞ 8.14 g＞6.39 g＞4.55 g＞3.6 g＞3.18 g＞2.16 g＞1.46 g. The longitudinal diameter of the fruit of Zaohongmi, Panzao, Lindong 2 and Lengbaiyu was significantly different from that of the fruit without girdling, and the longitudinal diameter of the fruit after girdling was larger than that of the fruit without girdling. The fruit transverse diameter showed that the fruit transverse diameter of flat jujube, Liuyuexian, Lindong 2, Beijingsuanzao and Lengbaiyu after girdling was larger than that of the fruit without girdling and the difference was significant. The fruit lateral diameter of Zaohongmi, Yingqiuhong, Panzao, Lindong 2, Beijingsuanzao and Lengbaiyu had significant difference before and after girdling. The fruit lateral diameter of Lindong 2 and Beijingsuanzao increased the most. Girdling increased the soluble solids content of fruits of all varieties except Lindong 2, and the increase effect of soluble solids content was 0.90%-5.65%. It had different effects on the change of titratable acid contents of different varieties. The titratable acid contents of Yingqiuhong, Longpandongzao, Beijingsuanzao and Lengbaiyu increased by 0.19%, 0.12%, 0.33% and 0.44%, respectively, after girdling, while the titratable acid contents of Zaohongmi, Panzao, Liuyuexian and Lindong 2 decreased by 0.07%, 0.02%, 0.21% and 0.36%, respectively. The fruit cracking rate of Zaohongmi was reduced by 15.02%, and the fruit shrinkage rates of Yingqiuhong, Lindong 2 and Longpandongzao were reduced by 26.19%, 13.15% and 9.94%, respectively, while the fruit shrinkage rates of Panzao, Liuyuexian and Lengbaiyuwere increased by 2.22% , 6.25% and 22.65%, respectively, compared with the control. Except for Lindong 2 and Longpandongzao, the inhibition effect of tree height growth of each variety was as follows: Lengbaiyu> Liuyuexian＞ Yingqiuhong＞Panzao＞Beijingsuanzao＞Zaohongmi, that is, 9.3 cm＞6.9 cm＞6.2 cm＞3.1 cm＞ 0.6 cm＞0.5 cm. Girdling could significantly increase the yield per plant of each variety by 384.42 g- 4 166.9 g. The effect of increasing yield was: Lengbaiyu＞Liuyuexian＞Beijingsuanzao＞Longpandongzao＞Lindong 2＞Panzao＞Yingqiuhong＞Zaohongmi, that is, 4 166.9 g＞3 835.4 g＞3 518.6 g＞ 2 401.1 g＞2 029.8 g＞1 693.7 g＞1 422.69 g＞384.42 g. The effects on the growth of stem diameter, crown width, secondary branch length and secondary branch diameter of different varieties were differ-ent. There was a significant positive correlation between single fruit weight and fruit longitudinal diameter, and a significant positive correlation between single fruit weight and fruit transverse diameter. The growth of secondary branch diameter was significantly and negatively correlated with soluble solids. The suitability degree of girdling for each variety was as follows: Lindong 2＞Lengbaiyu＞Panzao＞ Liuyuexian＞Beijingsuanzao＞Longpandongzao＞Zaohongmi＞Yingqiuhong. 【Conclusion】 Girdling helps to improve the yield per plant and single fruit weight of each variety, increase the soluble solids content of each variety except Lindong 2, and effectively inhibit the tree height growth of each variety, but has different effects on the cracking rate and shriveling rate of different varieties. And there are differences in the growth of stem diameter, crown width, secondary branch length and secondary branch diameter of different varieties. Lindong 2, Lengbaiyu, Panzao and Liuyuexian are more suitable for girdling, while Zaohongmi and Yingqiuhong are suitable for labor- saving cultivation varieties. No (less) girdling is the main measure of labor-saving cultivation, and the varieties with easy fruit setting can be reduced or exempted from girdling. The varieties that must be stripped should be stripped as reasonably as possible, which is labor-saving and effective.