Cotton harvest aids promote the translocation of bur-stored photoassimilates to enhance single boll weight

The application of harvest aids is an important prerequisite for realizing cotton mechanical harvesting. It is necessary to clarify the impact of harvest aid application on photoassimilate translocation and partitioning in the cotton boll–leaf system to reduce the negative impacts of harvest aids on seed cotton yield. The objective of this study was to determine the effects of harvest aids on photoassimilate repartitioning in the cotton boll–leaf system and its relationship with boll weight formation in the late growth stage of cotton. The leaf photosynthetic rate decreased sharply 1 d after applying harvest aids, and was only 0.91–6.30 μmol m−2 s−1 3 d after spraying. In addition, the synthesis and transport of leaf photosynthates were rapidly restricted. The contribution rate of leaf photosynthates to boll weight under ethephon application was 0.52–1.97%, showing a positive contribution. The application of harvest aids significantly reduced the single boll weight by 0.21–0.58 g, and the fiber weight per boll and the cottonseed weight per boll were 1.59–1.81 g and 2.19–2.60 g, respectively. About 0.09–0.15 g of photoassimilates in the bur were repartitioned after harvest aid application, and the contribution to the boll weight was 4.47–10.33%. The probability of increasing the boll weight by increasing the photoassimilate translocation rate in the bur was 33.8–46.1%. When the bur weight decreased by 0.10 g, the boll weight increased by 0.01–0.40 g. Therefore, improving the photoassimilate translocation rate in burs is a crucial approach to enhancing the single boll weight under harvest aid application.