Effects of different training methods on the growth and flowering of young Huangguan pear trees with a bibaum system

【Objective】Huangguan pear is one of the main cultivars in China. The Bibaum system is one of the preferred tree shapes for future mechanized and simplified production in orchards. The training method during the young tree stage is crucial for achieving early flowering and early fruiting. Therefore, this study aimed to explore the suitable training method for Huangguan pear with a Bibaum system, providing theoretical support for achieving early and high-yield fruiting and simplified cultivation. 【Methods】Two- year- old Huangguan pear trees with a Bibaum system were used for the experiment. There were three types of branch qualities left on a single-leader: 6, 8, and 10. For each branch quantity, three training methods were set: (1) Chemical shoot control: spraying 450 mg · L- 1 prohexadione-calcium when the new shoots reached 20 cm, spraying once every 15 days, and spraying three times in a row. (2) Pinching: pinching the new shoot tip for the first time when the new shoots reached 20 cm, and then repeating the pinching process every 20 cm growth, pinching three times in a row. (3) Branch bending: bending the branches to open an angle of 80° when the new shoots reached 20 cm. A natural growth (Control, CK) was set as the control, with each treatment combination repeated three times on each individual tree. The length and thickness of the new shoots, gap fraction, openness, leaf area index, light interception rate, chlorophyll and carotenoid contents, net photosynthetic rate, maximum photochemical efficiency, and flowering rate were measured for each treatment.【Results】The results showed that different branch quantities left and shaping methods had significant effects on shoot growth, canopy characteristics, photosynthetic physiology, and flowering rate. 58 days after petal fall, in terms of new shoot growth, all training methods significantly inhibited the length of new shoots compared to the CK: when the single-leader branch quantity was 10, branch bending had a prominent effect on controlling growth, reducing it by 17.24% compared to the CK; when the single-leader branch quantity was 6 and 8, prohexadione-calcium had the best effect on controlling growth, reducing it by 26.06% and 22.60% compared to the CK, respectively. In terms of new shoot thickness, when the single-leader branch quantity was 8 and 10, branch bending effectively promoted the growth of new shoot thickness; when the single- leader branch quantity was 6, all three treatments had no significant effect on new shoot thickness, with pinching having the most significant inhibitory effect. In terms of canopy characteristics, the trends in gap fraction and openness were basically consistent: when the single- leader branch quantity was 10, the gap fraction and openness of both branch bending and pinching were significantly higher than those of CK; when the single-leader branch quantity was 8, the gap fraction and openness of all three treatments were significantly greater than those of CK; when the single- leader branch quantity was 6, the gap fraction and openness of all three treatments were significantly lower than those of CK. The light interception rate had a similar trend to the leaf area index but was opposite to the gap fraction and openness: under all three treatments with different amounts of branches left, the light interception rate of branch bending was significantly higher than that of CK; when the single-leader branch quantity was 10, the leaf area index of prohexadione-calcium spraying was significantly higher than that of CK, while pinching and branch bending were significantly lower than CK; when the single-leader branch quantity was 8, both prohexadione-calcium spraying and pinching had no significant effect on the light interception rate and leaf area index; when the single-leader branch quantity was 6, the light interception rate of prohexadione-calcium spraying and pinching was significantly lower than that of CK, but the leaf area index was significantly higher than that of CK. Among the photosynthetic physiological indicators, chlorophyll contents varied depending on the treatment and amount of branches left: when the single-leader branch quantity was 8 and 10, the chlorophyll content with prohexadionecalcium spraying and branch bending treatments was significantly higher than that of CK, by 40.56% and 13.95%, as well as 15.85% and 20.54%, respectively; when the single-leader branch quantity was 6, all three treatments had no significant effect on chlorophyll content. The net photosynthetic rate of all three treatments was significantly higher than that of CK, with branch bending showing the most significant increase. All three treatments had no significant effect on the maximum photochemical efficiency. In terms of flowering rate, the flowering situation under different training methods was consistent regardless of the amount of branches left: branch bending had the highest flowering rate, followed by prohexadione-calcium spraying, and pinching had the lowest, with both branch bending and prohexadione-calcium spraying showing higher flowering rates than CK.【Conclusion】The comprehensive evaluation results obtained through the entropy method indicate that when the single-leader branch quantity is 10,the tree treated with branch bending exhibits good growth control, a reasonable canopy structure, high photosynthetic efficiency, and high leaf quality, with the highest flowering rate. It ranks first in the comprehensive evaluation. However, considering the economic efficiency and operational feasibility of the technology, spraying 450 mg ·L-1 prohexadione-calcium can be promoted as a simplified training method for young Huangguan pear trees with a Bibaum system when the single-leader branch quantity is 10.