Orobanche cumana-Sunflower Interaction: Histological Dissection of Sunflower Parasitic Resistance Mechanisms

Background Orobanche cumana ( O. cumana ), a root parasitic plant, causes significant losses to crop like sunflowers. While breeding resistant varieties is a key solution, a standardized method for analyzing resistance mechanisms has been lacking due to the complex infection process. In this study, we established a method to analyze O. cumana resistance phenotypes using O. cumana and two sunflower ( Helianthus annuus ) lines with differing resistance levels, a susceptible cultivar LD5009 and a resistant cultivar JK103. Results Specifically, we combined statistical analysis and tissue sectioning to track the parasite infection process, through which seven distinct infection stages were clearly defined. Using this established method, we analyzed the O. cumana resistant line JK103. Results revealed that chemical signaling communication before physical infection remained unaffected. However, the parasite infection process was prolonged, with high mortality observed in the tubers. Furthermore, additional investigations showed that in JK103, parasite invasion induced lignin accumulation adjacent to parasite invading cells; the vascular bridge failed to develop properly. These observations most likely explain the prolonged infection duration and programmed cell death in the terminal haustorium of O. cumana infecting JK103. Conclusions This research provides a standardized screening strategy for breeding sunflower germplasm resistant to O. cumana , facilitates the exploration of parasite-host molecular interactions, and serves as a reference for similar systems (e.g. Striga parasitism on cereals).