Osthole–pyrethrins combination loaded onto hollow microsphere silica nanoparticles inhibits Fusarium solani growth and controls root rot incidence in Cynanchum auriculatum

This study investigated the synergistic effects of compound bio-derived fungicide against Fusarium solani, the pathogen of root rot in Cynanchum auriculatum (CA), and the enhancement effect of loading these combinations through hollow microsphere silica nanoparticles (HMSNs). The mycelial growth rate method was used to evaluate the inhibition rates and EC₅₀ values of eight biogenic fungicides. Highly active fungicide were identified, and their co-toxicity coefficients (CTCs) and combined toxicity were determined. A pot experiment was conducted using HMSN-loaded fungicide combinations. Among the eight fungicides tested, F. solani showed greatest sensitivity to pyrethrins, eugenol, and osthole, with EC₅₀ values of 2.00, 9.49 and 10.90 mg/L, respectively. Of the 27 mixtures tested, the osthole–pyrethrins combination in 1:0.275 ratio exhibited the highest CTC (139.87) and the lowest EC₅₀ (4.00 mg/L), demonstrating a strong synergistic effect. The HMSN-loaded mixture (CS@HMSN) significantly inhibited F. solani growth at all tested concentrations. At 50 mg/L, CS@HMSN achieved the lowest disease incidence (12.50) and incidence rate (33.33 %) while also activating defense enzymes such as superoxide dismutase, catalase, and peroxidase. This alleviated the adverse effects of F. solani on CA and improved plant resilience. These findings suggest that 50 mg/L CS@HMSN is a promising fungicide formulation for the biological control of CA root rot, offering an effective alternative to chemical fungicides while enhancing sustainability in production systems.