| Cowpea, Vigna unguiculata [L.] Walp., is an important grain legume grown for its protein in the tropical and subtropical regions, primarily Africa. Although, it is an extremely resilient crop, cowpea faces severe biotic and abiotic production constraints including insect pests, diseases, nematodes, low soil fertility, heat, drought and parasitic weeds. The parasitic weed, Striga gesnerioides [Wild.] Vatke is one of the most important limitations to cowpea production. Host plant resistance is the only practical control method. Five virulence genotypes (races) of S. gesnerioides have been identified in different regions of Africa. Several host resistance genes have also been identified that are effective against specific races of S. gesnerioides. The rapid spread of this parasitic weed suggests the urgency for the development of cowpea varieties with multiple resistance genes. A recently identified cowpea breeding line, IT93K-693-2, has resistance to all known races. An F2 population developed from the cross between IT93K-693-2 and the susceptible variety IAR1696 was characterized for resistance against race 3 of S. gesnerioides for genetic analysis and molecular mapping. IT93K-693-2 has a single dominant gene for resistance. Four Amplified Fragment Length Polymorphism (AFLP) markers, designated E-ACT/M-CTC115, E-ACT/M-CAC115 , E-ACA/M-CAG120 and E-AAG/E-CTA190, were identified and mapped, respectively 3.2, 4.8, 13.5 and 23.0 cM from resistance gene Rsg1-3. The AFLP fragment from marker combination E-ACT/M-CAC which is linked in coupling with Rsg1-3 was cloned, sequenced, and converted into a Sequence Characterized Amplified Region (SCAR) codominant marker to enhance its usefulness in breeding programs. There is an urgent need to develop additional DNA markers in cowpea to enhance pyramiding of resistance genes. |
