Zhijun Wang, Yongmei Dong
ABSTRACT Mepiquat chloride (MC) is an inhibitory plant growth regulator (PGR), pivotal to optimizing cotton (Gossypium hirsutum L.) growth architecture, stress resilience, and yield-quality parameters. In this research, we conducted a randomized complete block (RCB) design, evaluating four diverse cotton genotypes (SD217, XLZ74, SD1068, and AY161) under field conditions, consisting of three replicates. The treatments included various concentrations of MC (40, 80, and 120 mg L-1) applied during three key growth periods: Squaring, flowering, and bolling stages. Our results indicated that the relationship between MC insensitivity and MC sensitivity was established by analysing the effects on photosynthetic characteristics, chlorophyll fluorescence, cotton yield, yield components, agronomic traits, and fibre quality. Across the four upland cotton materials, under MC treatments (40, 80, and 120 mg L-1), SPAD values were significantly enhanced by 7.11%-38.05%, transpiration rate, net photosynthesis rate (PN), stomatal conductance increase by 5.72%-35.03%, 25.56%-54.21% and 1.35%-61.58% respectively in most cases, seed index increased by 0.56%-10.16%, but Lint percent decreased by 0.44%-11.83% in most cases .Chlorophyll fluorescence parameters, including quantum efficiency of photosystem II, maximum photochemical efficiency of PSII, minimal and maximal chlorophyll fluorescence, and photochemical quenching coefficient (qP), also tended to increase in most treatments, whereas non-photochemical quenching coefficient decreased. In addition, MC treatment also improved fibre quality and single boll weight. These results collectively demonstrate that MC treatment enhances PN and reduces the non-photochemical quenching coefficient by increasing chlorophyll content, thereby improving cotton yield.