Host preference and performance shape infection patterns in the parasitic plant Cuscuta chilensis in the Chilean...

Host choice shapes infection patterns in parasitic plants, yet how host availability translates into realized host use in natural communities remains poorly understood. We investigated host use by the stem parasite Cuscuta chilensis in the Chilean Coastal Desert, examining how host detection, choice, and infection after contact contribute to field infection patterns and whether host use is associated with parasite performance.

We conducted field surveys to document host availability and infection prevalence. Germinated C. chilensis seedlings were used in laboratory and greenhouse experiments to assess host detection and choice, and in greenhouse and field experiments to evaluate infection success after contact. We also quantified flower production and realized germination of C. chilensis parasitizing different host species to assess the fitness consequences of host use.

Host detection differed among species, although discrimination was limited. In greenhouse choice assays, seedlings tended to select living hosts over the control but did not discriminate among host species. Seedlings successfully infected all host species tested in the greenhouse, whereas field infection success was highest on Heliotropium stenophyllum. Myrcianthes coquimbensis had the highest infection prevalence and supported the greatest flower production, whereas seeds produced by parasites growing on H. stenophyllum had the highest realized germination.

Host use by C. chilensis emerges from sequential processes of host encounter, detection, choice, and acceptance that do not consistently favor the same host species. The host associated with greatest flower production differed from that associated with highest realized germination. Thus, no single stage fully explains field host use, and the relationship between host use and performance depends on the fitness component considered.