Variation in Responses of Sunflower Cultivars to the Parasitic Weed Broomrape

Development of four Orobanche species, O. cumana, O. aegyptiaca, O. ramosa, and O. cernua, was compared on resistant and susceptible sunflower cultivars. Sunflower plants were infected by O. cumana, O. aegyptiaca, and O. ramosa, but not by O. cernua, in field and greenhouse studies. However, cultivating the hosts and parasites in a polyethylene bag system allowed the observation that sunflower induced O. cernua seed germination. This difference demonstrates that O. cernua is unique from the other three species. O. cumana, O. aegyptiaca, and O. ramosa attached to and developed tubercles on the susceptible sunflower 'Adi.' On the resistant 'Ambar' sunflower, a greater percentage of tubercles were degenerated or dead than on the susceptible cultivar. Thus, resistance of Ambar appears to manifest during tubercle development. Seed production of Adi sunflower was greatly reduced with infection by O. cumona.