Impact of naphthalene acetic acid and Piriformospora indica on WOX gene expression and rooting in woody ornamentals

• NAA enhances root growth, laying the basis for Pi colonization. • NAA and Pi work together to induce WOX gene expression. • NAA+Pi significantly improved the rooting rate and survival rate of cuttings. Cutting propagation is a crucial technique for woody ornamental plant reproduction. While the plant growth regulator naphthaleneacetic acid (NAA) and the beneficial fungus Piriformospora indica ( Pi ) are vital for adventitious root formation and cutting survival, the underlying mechanisms of their synergistic effects remain unclear. This study investigated the impact of NAA and Pi on rooting in cuttings of three distinct woody ornamentals: Rhododendron simsii, Jasminum sambac , and Rosa chinensis . Three treatments were applied: control group (CK, direct cutting), Pi inoculation ( Pi ), and NAA soaking followed by Pi inoculation (NAA+ Pi ). The results demonstrated that compared to CK, NAA+ Pi significantly increased rooting rate (1.9 %-85.0 %) and survival rate (10.5 %-36.6 %), improved chlorophyll and free amino acid content, and enhanced plant height and fresh weight. Notably, NAA+ Pi dramatically upregulated the expression of the key root development gene WOX4 by 2.6–4.0 fold, indicating a synergistic activation of WOX4 gene expression. The increased free amino acid content in the NAA+ Pi treatment suggests enhanced secondary metabolism, providing essential resources for WOX expression and root development. All species demonstrated notable improvement, despite the fact that R. chinensis saw the most noticeable impacts. This underscores the considerable potential of using both NAA and Pi together to maximize the proliferation of woody ornamental cuttings. This research offers new insights for improving cutting propagation techniques.