Xenognosin production and tolerance to Striga asiatica infection of high-yielding maize cultivars

Ten cultivars of maize, a number of which are high yielding in the presence of the weed Striga asiatica in sub-Saharan Africa, were tested for resistance and tolerance to this root hemiparasite. Observed in rhizotrons, Striga asiatica attached and developed on roots of all cultivars, indicating that none exhibited a true resistance mechanism. However, root exudates from two cultivars, IWD STR Co and Zea diploperennis BC4C2, stimulated relatively little germination of S. asiatica, indicating low xenognosin production, with few parasites attaching and no significant decrease in host height or biomass apparent after 55 days of infection. Cultivar 98 Syn WEC also exhibited no significant differences in height and biomass on infection despite high xenognosin production and a lack of resistance to parasite attachment and development, indicating the operation of a tolerance mechanism. Cross-breeding of these low xenognosin-producing maize cultivars and Striga-tolerant lines could produce cultivars that perform exceptionally well on Striga-infested soils. This study highlights the need for cereal breeders to distinguish between the different mechanisms underpinning host performance in the presence of Striga.