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Breeding cowpea varieties for resistance to Striga gesnerioides and Alectra vogelii
Two parasitic flowering plants, Striga gesnerioides (Wild.) Vatke and Alectra vogelii (Benth.), cause substantial yield reduction in cowpea in the dry savannas of sub-Saharan Africa. Alectra is more prevalent in the northern Guinea savanna and southern Sudan savanna of West Africa, as well as in East and southern Africa whereas Striga is mostly found in West and Central Africa. However, both are fast spreading beyond these limits. Collaborative studies with national and regional programs have revealed the presence of five strains of S. gesnerioides of which strain 1 is presently found in Burkina Faso, strain 2 in Mali, strain 3 in Nigeria and Niger, strain 4 in Benin Republic, and strain 5 in Cameroon. A local landrace, B 301 from Botswana, confers complete resistance to Striga and Alectra in Burkina Faso, Cameroon, Mali, Niger, and Nigeria. However, it has moderate levels of resistance to the strain from Benin Republic. Other lines such as IT81D-994, IT89KD-288, 58-57, and Gorom local confer complete resistance to strains from Benin Republic and Burkina Faso. Therefore, crosses were made among the selected complementary parents and a number of new varieties have been developed with combined resistance to Alectra as well as all the five strains of Striga. Most of these lines also serve as a false host for S. hermonthica reducing its seed bank in the soil when grown as an intercrop or in rotation with cereals.