Chemical topping with 1,1-dimethylpiperidinium chloride increases lint yield and defoliation of cotton by improving canopy development

Chemical topping with 1,1-dimethylpiperidinium chloride (DPC) has been considered a promising measure to inhibit apical dominance in cotton (Gossypium hirsutum L.). However, knowledge of the plant growth and canopy development of cotton under chemical topping with DPC remains limited, and the effect of this practice on lint yield and defoliation is unclear. A two-year (2019–2020) field experiment was conducted with two varieties, Xinluzao 60 (L60, DPC-insensitive) and Jinken1402 (JK1402, DPC-sensitive), and four topping methods, manual topping (MT), no topping (NT), DPC⁺ (fortified DPC) and DPC. We found that the lint yields of L60 and JK1402 treated with DPC were equivalent to those of L60 and JK1402 treated with DPC⁺ but were enhanced by 0.9–4.7% in L60 and 6.7–11.8% in JK1402 relative to those under MT and NT, with no significant difference in fiber quality. This was mainly due to the change in plant growth and canopy structure. In particular, compared with MT, application of DPC shortened the upper branches and extended the duration of the leaf area index peak. Moreover, in the late reproductive period, DPC application increased the number of upper leaves and reduced diffuse noninterceptance. Notably, the light transmittance rate (LLR) of JK1402 treated with DPC was higher than that of MT in the middle and lower parts of the canopy. Furthermore, there was positive correlation between LLR and defoliation rate. Therefore, chemical topping with DPC provided an effective alternative for manual topping.