<i>Penicillium restrictum</i> Reshapes Root Exudates and Inhibits <i>Peucedanum praeruptorum</i> Bolting Through Field Inoculation and Co‐Cultivation

ABSTRACT Early bolting significantly restricts the harvest and therapeutic use of Peucedanum praeruptorum materials. Although some endophytes have been isolated from the roots of P . praeruptorum , their effects on host growth and responsive mechanisms remain unknown. Through field inoculation and co‐cultivation of endophytes with tissue culture seedlings, this study demonstrated that Penicillium restrictum reduced the bolting rate of P . praeruptorum while increasing the accumulation of coumarins. Field inoculation with a low concentration of P . restrictum reduced the bolting rate to &lt; 20%. P . restrictum gradually colonised and invaded the roots and stems into tissue‐cultured P . praeruptorum seedlings over a period of 30 consecutive days. Scanning electron microscopy (SEM) analysis revealed that during co‐cultivation, P . restrictum hyphae penetrated the root cork layer of tissue culture seedlings and commenced colonisation on Day 7. The levels of eight major coumarins in P . praeruptorum were determined before and after bolting, following inoculation with both P . restrictum and mixed strains at three different concentrations. Before bolting, the levels of some coumarins in flowers and xanthotoxin in leaves were higher in the control group than in the treatment group. Distinct colouration and fluorescence were observed in the cork layer and phloem of P . restrictum ‐infected roots. Coumarin was primarily distributed within the secretory channel, while the fluorescent signal weakened after bolting. Non‐targeted metabolomics technology indicated that the coumarins changed significantly after co‐cultivation. Our findings indicate the potential effect of co‐cultivation with P . restrictum to inhibit P . praeruptorum bolting.