Comparative Metabolomics Reveals Family–Genus-Specific Chemical Signatures and Potential Recognition Mechanisms in Cynomorium songaricum–Host Interactions

Cynomorium songaricum is an important medicinal holoparasitic plant in the arid regions of northwestern China. Its extremely low seed germination rate relies on chemical signals released from the rhizosphere of specific host plants. This study aimed to elucidate the chemical basis of host recognition by C. songaricum by characterizing and comparing the rhizosphere volatile metabolomes of five host plant species. Gas chromatography–mass spectrometry (GC–MS) was used to analyze the rhizosphere volatiles of three Nitraria species (N. roborowskii, N. sibirica, N. tangutorum), Peganum multisectum, and Zygophyllum xanthoxylum. Multivariate statistical analyses, including PCA, HCA, and OPLS-DA, were employed to identify shared and differential metabolites. A total of 116 volatile compounds were identified. Alkanes were the predominant metabolite class (accounting for 46.27–76.47% in each host), and 11 C11–C16 alkanes were shared by all species. Notably, Z. xanthoxylon (belonging to a different family) exhibited a distinct metabolic profile, with a significantly higher proportion of benzene derivatives (35.82%) compared to the other hosts. PCA and cluster analysis revealed family/genus-specific clustering patterns, with Z. xanthoxylon forming a separate cluster. Several differential metabolites unique to Z. xanthoxylon possessed antimicrobial and stress-resistant activities. This study reveals the chemical signatures of C. songaricum host roots. The shared alkanes are proposed as potential background signals for general recognition, though this hypothetical role requires experimental validation. Family/genus-specific compounds might be involved in host selection. The unique chemical profile of Z. xanthoxylon suggests that C. songaricum may employ a flexible recognition strategy, enabling it to parasitize plants across different families. These findings provide fundamental data for understanding the chemical basis of host–parasite interactions in this species.