Non-strigolactone natural products interfering with parasitic weed development

Covering: up to 2026Strigolactones dominate the research on parasitic plant germination. Nevertheless, other types of natural products have roles in stimulating or inhibiting the germination and subsequent growth of parasitic weeds, including synergistic interactions with other compounds released by host roots that mediate host recognition and chemotropism. This review focuses on the bioactive non-strigolactone compounds, classified as terpenes and terpenoids, aromatic metabolites, N-containing metabolites and miscellaneous structures. Terpenes and terpenoids are the most common germination stimulants (51.0% of the total, among which sesquiterpene lactones represent the most common structures), while aromatic (41.7%) and N-containing (36.5%) metabolites are the leading inhibitors of germination or seedling development. The clog P trends suggest that molecular lipophilicity alone does not allow distinguishing between stimulants or inhibitors, but the data showed that two main intervals are particularly enriched in bioactive structures: moderately lipophilic compounds (47%, with clog P values between 1.0 and 3.0) and hydrophilic molecules (24%, with clog P below 0). An evaluation of germination-induced specificity indicated that sesquiterpene lactones are the strongest elicitors for O. cumana, P. aegyptiaca and S. asiatica, karrikin₁ and different terpenoids for O. minor and S. hermonthica, and isothiocyanates for P. ramosa. Notably, several sesquiterpene lactones and isothiocyanates induced germination at concentrations comparable to those of natural strigolactones. Beyond germination, recent findings implicate non-strigolactone cues in haustorium initiation and host chemotropism, underscoring the complexity of chemical signaling in parasitic plant development. Overall, the evidence gathered herein shows that parasitic development is influenced by a wider chemical space than strigolactones alone, opening perspectives for eco-rational bioherbicide development and for understanding host-parasite communication.