Identification of Allelochemicals in Ficus carica L. and Their Stimulatory Effects on Isatis indigotica Fort. Growth

Medicinal agroforestry system contributes to enhancing agricultural productivity. In this process, allelochemicals play a crucial role, and certain allelochemicals can even promote the growth of intercropped plants significantly. Previous studies by our group have shown that fig tree (Ficus carica L.) extract promotes woad (Isatis indigotica Fort.) growth significantly. However, the specific mechanism by which fig tree influences the growth of woad remains unclear. In this study, we demonstrated the growth-promoting effects of fig tree extract on woad through sterile seedling cultivation experiments and identified three allelochemicals—psoralen, bergapten, and umbelliferone. To further validate the growth-promoting activity of these compounds, a pot experiment was conducted by exogenously applying the three allelochemicals. The results revealed that all three allelochemicals derived from fig tree exhibited a property of concentration dependence on the growth of woad seedlings. Specifically, it shows an obvious promoting effect at the low concentration, while exhibiting inhibiting effects at high concentrations. Among them, the magnitude of the promoting effect, from strongest to weakest, was as follows: bergapten, psoralen, and umbelliferon. This study primarily aimed to elucidate the growth-promoting effect of woad induced by allelochemicals present in fig tree extracts and to clarify how these allelochemicals regulate woad growth.