Effects of branch bending angle on leaf nutrition, flower formation and nut quality of Qianhe 7 walnut

Abstract: 【Objective】The study aimed to explore the effects of branch bending angle on physiological growth, flower and fruit setting and fruit quality of Juglans sigillata Dode in order to provide scientific basis for high-quality and high-yield cultivation of Qianhe 7.【Methods】In 2017, the high-quality and late fruiting walnut Qianhe 7 was used as the test material, and the branches with natural growth and opening angle between 30°-35° were used as the control (CK). Except for the central trunk, the other branches were bended to 60°, 90° and 110° respectively. In November 2018, the branch lengths of each treatments, were measure and the branches were divided into 3 groups, that is, long branch (> 30 cm),medium branch (15-30 cm) and short branch (<15 cm). In the middle of April 2018, the number of fe- male flower buds and male flower buds on walnut trees were investigated and the ratio of the male flow-er buds to the female flower buds was calculated. The number and type of branches after branch pend-ing, the number of flowers and fruit setting were counted, and the fruit setting rates were calculated. On August 24, 2018, the photosynthetic characteristics of the leaves in the inner, middle and outer parts of trees were measured by portable Li-6400 photosynthetic apparatus and the contents of chlorophyll a, band carotenoid were determined by spectrophotometry. The contents of N in the leaves were determined by Kjeldahl method, P, K, Ca, Mg, Fe, Mn and Cu in the leaves were determined by vanadium molybde-num yellow colorimetry, and the contents of Zn in the leaves were determined by atomic absorption spectrophotometry. The crude fat content of walnut nut was determined according to GB 5009.6—2016,and the protein content was determined according to GB 5009.5—2016.【Results】Only the number of the medium and the long branches increased significantly when the branches were bended at 60° in pre-vious year. The total number of branches, the number of short branches and the number of medium and long branches of Qianhe 7 increased significantly when the branches were bended at 90°in previous year. The total number of branches, short branches and medium-length branches of Qianhe 7 was signif-icantly increased by 36.8%, 64.0% and 81.0% respectively compared with the control; When the bend-ing angle reached 110° at the same time, the number of short branches and medium long branches re-mained at a high level. When the bending angle was 90°, the number of female flowers, fruit setting and fruit setting rate of Qianhe 7 were significantly increased by 206.6% , 231.1% and 14.1% compared with the control. When the bending angle was 110°. The fruit setting rate of Qianhe 7 also increased; the bending angle at 60° and 110° did not make significant difference in the number of female flowers and fruit setting. The net photosynthetic rate, stomatal conductance, transpiration rate, chlorophyll- a content, chlorophyll-b content and carotenoid content in the inner, middle and peripheral of the trees reached the maximum value when the bending angle was 90°. When the bending angles were 90° and 110° the intercellular CO2 concentration of middle and peripheral leaves were reduced and the contents of P, Ca, Mg and Fe in the leaves were increased compared with the control. The content of the N ele- ment in the leaves was the highest when the bending angle was 110°. The content of the K element on the branches with the bending angle at 90° was significantly lower than those of the control, and the treatments of bending angles at 60° and 110°. The content of Zn increased with the increase of branch angle. However, the content of Mn in leaves decreased with the increase of branch angle. The content of the Cu in the leaves was no effected by the bending angle. In the case of not significantly changing the vertical diameter, cross-diameter, fruit index, shell thickness and kernel yield of Qianhe 7, branch bend-ing could promote the accumulation of its kernel weight, protein content and crude fat content. The bending angle at 90° significantly increased the single fruit weight of Qianhe 7 by 6.0% compared with the control.【Conclusion】Branch bending of Qianhe 7 walnut at 90° could increase the number of short branches and medium short branches, and effectively improve the photosynthetic conditions, increase the nutrient content of the leaves, greatly improve the number of female flowers, fruit setting and fruit setting rate, and improve the quality of the nuts. It is suggested that the branch bending at 90° would be an effective way in increasing the production and quality of the nuts of Qianhe 7 walnut.