Chlorine dioxide enhanced cuttage efficiency in chrysanthemum via accumulating tryptophan and derived auxin

The development of new techniques for the effective use of smaller cuttings for cuttage to eliminate the need for exogenous plant growth regulators is expected to enhance the production of chrysanthemum, an important ornamental, edible, and medicinal plant. This study aimed to explore the effect of chlorine dioxide (ClO₂) at promoting cuttage in three varieties of chrysanthemum. Irrigation with 0.005—0.01 mg·L⁻¹ ClO₂ remarkably promoted rooting, as exhibited by their increased biomass, root number, root length, chlorophyll content, and activities of antioxidant enzymes and tryptophan synthase (P < 0.05). A targeted metabolic analysis indicated that the contents of both tryptophan and its derivative indole-3-acetic acid were enhanced significantly under treatment with 0.005 and 0.01 mg·L⁻¹ ClO₂. A total of 584 differentially expressed genes were detected between the CK and 0.01 mg·L⁻¹ ClO₂ treatment as shown by a transcriptomic analysis, which are primarily associated with tryptophan, fatty acid and carbon metabolism. An elemental analysis suggested that treatment with 0.01 mg·L⁻¹ ClO₂ disrupts the imbalance of chemical elements in chrysanthemum cuttings. These results guide the conclusion that suitable concentrations of ClO₂ act as growth stimulants that can improve the cuttage efficiency in chrysanthemum.