Abstract:

In order to investigate regulatory effects of cotton chemical capping agents in the Liaohe River Basin, a comparative experiment was conducted from 2019 to 2020 at the Liaoning Institute of Industrial Crops (Liaoyang, Liaoning). The study used chemical capping agent from China Agricultural University, composed of 25% Mepiquat chloride (1,1-dimethyl-piperidinium chloride, DPC) and auxiliary naphthenate, with two application timings (July 13^th and July 18^th) and three concentration levels (750, 1125 and 1500 mL/hm²). A total of six treatments were set up, using no-topping as control (CK). Hormone contents including indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellin (GA₃), and zeatin (ZR) were continuously measured in the main stem apex (0-5 cm) and sub-apex (5-10 cm). Plant growth parameters, including plant height (PH), number of fruit branches (NFB), average length of upper fruit branches (LFB), and average length of upper internodes (LUI) on the main stem, were also systematically observed and recorded. The variations in IAA and ABA contents were directly proportional to the concentration of the chemical agent, whereas changes in ZR content exhibited an inverse relationship. The fluctuation in GA₃ content was most pronounced at medium concentration. The variations in IAA, ABA and ZR contents of different dosages were more evident when treatment was applied on July 13^th, while no obvious differences were observed in GA₃ content between the two application timings. IAA content showed marked variation at the main stem apex, whereas ZR content varied more noticeably at the sub-apex; in contrast, ABA and GA₃ levels exhibited only slight differences between the two sampling sites. Chemical capping effectively inhibited plant growth. The inhibitory effects on NFB and LFB intensified with treatment concentration increasing. For the July 13^th application, the degree of inhibition on PH was positively correlated with treatment concentration, whereas for the July 18^th application, the suppression of both PH and LUI was more pronounced at medium treatment concentration. Following treatment with a chemical capping agent, the levels of IAA and GA₃ at the apical region of the main stem decreased significantly, whereas ABA content increased markedly, and ZR content remained relatively unchanged. Furthermore, the reductions in IAA and ABA levels were directly proportional to the concentration of the capping agent, with earlier application resulting in more pronounced effects. Notably, IAA content at the apex of the main stem and ZR content in the subapical exhibited significant changes. Plant development was inhibited after capping treatment, and this growth suppression was consistent with the observed hormonal fluctuations. In the future, combined with the yield and fiber quality indicators, the application parameters of chemical capping agent can be optimized, and a simplified cultivation technology system suitable for the cotton area of Liaohe River Basin can be established.

Key words: cotton, chemical capping, agent concentration, application timing, apical of main stem, endogenous hormone, plant development