Effects of Water Deficit in Flowering and Boll-setting Period on Boll Development and Yield in Different Fruit Branches

【Objective】 The changes of boll size (diameter, length, volume), dry weight of each component (boll shell, fiber, seed) and yield of fruit branches of different parts during flowering and boll-setting period were studied, and the relationship between water deficit treatment and boll index was also studied, so as to provide a reference for drip irrigation when water supply was insufficient in flowering and boll-setting period of machine harvesting. 【Methods】 Taking Xinluzao 50 and Xinluzao 73 as materials, 3 drip irrigation quantities were set in flowering and boll-setting period: 2,450 m³/hm² (CK), 2,050 m³/hm² (D₁) and 1 650 m³/hm² (D₂). Cotton bolls from the 2nd, 5th and 7th fruit branches were taken every 7 days from 17 days after flowering, and the size and dry weight of each component were determined for a total of 5 times. 【Results】 The length, diameter and volume of boll of fruit branches in different parts of the two varieties reached their maximum at 24 d after flowering. The boll diameters of middle and upper fruit branches of Xinluzao 50 decreased by 2.92% - 4% and 2.21% - 5.35%, respectively, on 45 days after flowering, D₁ and D₂. Xinluzao 73 decreased by 2.66% - 6.38% and 2.77% - 8.69%, respectively. The dry weight of each component of boll of the two varieties was cotton seed > fiber > boll shell, and boll shell, cotton fiber and seed weight reached the maximum at 24, 38 and 38 days after flowering, respectively. On the 45th day after flowering, the cotton seed weight of the middle and upper fruit branches of the two varieties treated with D₁ and D₂ was significantly different from that of the control group. The cotton seed weight of the middle and upper fruit branches of the two varieties decreased by 8.9% - 20.71% and 11.53% - 20.73%, respectively. Xinluzao 73 decreased by 8.96% - 16.24% and 10.21% - 17.06%, respectively. There was a significant positive correlation between seed yield and seed weight per plant. The yield of seed cotton on the lower, middle and upper branches of Xinluzao 50 decreased by 12.5%, 13.48% and 15.67%, respectively. Xinluzao 73 fell by 12.69%, 11.9% and 18.21%, respectively. 【Conclusion】 Boll diameter of middle and upper fruit branches is an important factor affecting boll dry weight. The water deficit was unfavorable to the development of cotton fiber and seed, and affected the seed of middle and upper fruit branches greatly. D₁ processing and control branch into different parts of bell number and seed cotton yield difference was not significant, therefore, 2,050 m³/hm² (D₁) can be used as a response to water supply shortage reference drip irrigation during flowering and boll-setting period.