Analysis of the Factors Affecting Germination of Cnidium monnieri Seeds and Its Endogenous Inhibitory Substances

<i>Cnidium monnieri</i> is a valuable functional plant with significant potential for green pest control. However, its large-scale application is limited by its low and uneven seed germination in fields. To determine the factors that affect the germination of <i>C. monnieri</i> seeds, we examined its seed viability, germination percentage and germination speed index (GSI) after seed-coat treatments, water permeability, and the types and activity of endogenous inhibitory substances in <i>C. monnieri</i> seeds. The results indicated that the seed viability of <i>C. monnieri</i> is 95%, but the germination percentage was relatively low (12.60%). Seed coat removal significantly enhanced both the germination percentage and the GSI, but had no significant effect on water absorption rate. Moreover, ethyl acetate extracts completely inhibited the seed germination of the control non-dormant <i>Brassica rapa</i> subsp. rapa, while diethyl ether extracts showed moderate suppression, and petroleum ether extracts exhibited the weakest effect. And the three endogenous inhibitory substances, i.e., dibutyl phthalate, 2,6-di-tert-butylphenol, and 2,4-di-tert-butylphenol significantly reduced the seed germination, seedling height and root length of <i>B. rapa</i>, indicating their high inhibitory efficiency on seed germination. Our study demonstrates that the mechanical barrier of the seed coat and the presence of potent endogenous germination inhibitory substances are the key factors influencing the germination of <i>C. monnieri</i> seeds. These findings provide a theoretical basis for promoting seed germination of <i>C. monnieri</i>, which enhance its application value as functional plant for green pest control.