A Phosphate-Solubilizing Endophytic Fungus Talaromyces lentulus PF12-1 Promotes Growth and Resveratrol Accumulation in Polygonum cuspidatum

Background and Aims Plant growth-promoting endophytic fungi enhance plant productivity and secondary metabolite accumulation. However, their potential in Polygonum cuspidatum Sieb. et Zucc. remains largely unexplored. We isolated endophytic fungi from this plant and evaluated their capacity to promote host growth and bioactive compound biosynthesis. Methods Fungi were isolated from P. cuspidatum and screened for phosphate-solubilizing activity. The selected strain was identified via morphology and multi-gene phylogeny, with its phosphate-solubilizing and IAA-producing activities quantified in vitro. Pot experiments were conducted on P. cuspidatum seedlings with hyphal inoculation. Growth, secondary metabolites (HPLC), and resveratrol biosynthetic gene expression (qPCR) were evaluated. Results Isolate PF12-1 ( Talaromyces lentulus X.Z. Jiang & L. Wang) solubilized 594.65 µg mL⁻¹ tricalcium phosphate and 619.00 µg mL⁻¹ calcium phytate, and produced 13.43 µg mL⁻¹ IAA. Inoculation significantly ( P  < 0.05) increased plant height (32.16%), root length (22.41%), shoot dry weight (23.66%), and root dry weight (41.38%), and promoted root development, as reflected by increases in root volume (199.82%), projected area (133.55%), and branch number (76.26%). Inoculation also increased resveratrol content by 20.0% and upregulated resveratrol biosynthetic genes. Conclusion Talaromyces lentulus X.Z. Jiang & L. Wang PF12-1 shows promising growth-promoting and resveratrol-enhancing effects on P. cuspidatum seedlings in pots, suggesting potential for field evaluation as a biofertilizer.