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Wheat (Triticum aestivum) Is Susceptible to the Parasitic Angiosperm Striga hermonthica, a Major Cereal Pathogen in Africa

Striga hermonthica is a parasitic weed endemic to sub-Saharan Africa. It most commonly parasitizes sorghum, maize, pearl millet, and upland rice, lowering yields and affecting the welfare of over 100 million people, principally subsistence farmers. Cereal crops with complete resistance to this pathogen have not been reported. In southern and eastern Africa, where Striga spp. are endemic, 5.6 million ha of wheat are cultivated annually. Despite this, there are only isolated field reports of wheat infected with Striga spp. It is not clear whether this is due to resistance in this cereal or to environmental factors. In this article, we examined the ability of root exudates from five cultivars of wheat (Chablis, Cadenza, Hereward, Riband, and Brigadier) to trigger germination of S. hermonthica seed. A study of the development of S. hermonthica on two cultivars of wheat (Hereward and Chablis) and on a range of ancestral relatives of wheat (Triticum and Aegilops spp.) then was conducted. Last, the effect of Striga spp. on host growth and yield was examined using wheat cv. Chablis and compared with that of a highly susceptible sorghum cultivar (CSH-1). Wheat was able to support the germination, attachment, and subsequent development of Striga spp. All wheat cultivars and ancestral species of modern wheat (Triticum and Aegilops spp.) were susceptible to S. hermonthica. In addition, in wheat, infection severely lowered plant height (-24%) and biomass accumulation (-33%); a small parasite biomass elicited a large host response. In conclusion, wheat is highly susceptible to S. hermonthica and, in light of global climate change, this may have implications for wheat-producing areas of Africa.