Effect of Plant Growth Regulators on Cotton Seedling Root Growth Parameters and Enzyme Activity

It is well known that the survival rate of cotton seedlings is low, and the growth and development status at this stage is crucial to improve productivity. Plant hormones are important factors that promote the growth and development of cotton seedlings. Growth regulators have the same function as plant hormones. The purpose of this research is to explore the effects of different concentrations of growth regulators on cotton root morphological parameters and enzyme activities, and to find suitable plant growth regulators and their optimal concentrations to improve the growth of the cotton seedling root system. Three cotton varieties, “Zhongmian 619” (Z619), “Xinluzao 27” (Z27), and “Xinluzao 39” (Z39), and three growth regulators, gibberellin (GA(3)), salicylic acid (SA), and paclobutrazol (PP(333)), at three concentrations were used in our experiment. In Z619 and Z27, 0.050 mg/L GA(3) significantly increased the total root length. Similarly, 0.010 mmol/L SA significantly increased the root growth parameters of Z619 and Z39. In Z619, 0.1 mg/L PP(333) significantly increased the total root length and total surface area and reduced the average root diameter. For all three cotton varieties, 0.050 mg/L GA(3) increased peroxidase (POD) activity in the roots. In Z27 and Z39, 0.80 mg/L GA(3) increased superoxide dismutase (SOD) activity in the roots. All SA concentrations increased SOD activity in roots of Z619 and Z27; 0.10 mg/L PP(333) significantly increased SOD and POD activities in the roots of Z619 and significantly increased SOD activity in Z27. Principal component analysis indicated that 0.10 mmol/L SA was the optimal treatment for promoting the development of the roots of Z619 and 0.050 mmol/L SA was the optimal treatment for promoting the development of the roots of Z27 and Z39.