Developing high-yielding Striga-resistant maize in sub-Saharan Africa.

Abstract Striga hermonthica is a major stress of maize in sub-Saharan Africa (SSA). The International Institute of Tropical Agriculture (IITA), in collaboration with national scientists, have used team approach to investigate how best to solve the problem. Emphasis was on (i) establishing a reliable infestation technique for selecting resistant/tolerant genotypes, (ii) availability of appropriate germplasm and good sources of Striga resistance, (iii) use of appropriate breeding methods for incorporating resistance genes into adapted germplasm, and (iv) extensive multilocational evaluation to identify genotypes with stable performance. Host plant resistance, with additive-dominance model, has been the major control option for S. hermonthica infestation on maize. Recurrent selection, followed by hybridization of inbred lines developed from its products, have been used to identify high-yielding, stable hybrids for commercialization in SSA. In a study involving early-maturing tropical maize inbred lines, 24 single nucleotide polymorphism (SNP) markers significantly associated with grain yield, Striga damage, ears per plant, and ear aspect under Striga infestation were detected. In a quantitative trait loci (QTL) mapping study involving extra-early white BC1S1 families obtained from TZEEI 29 (Striga-resistant) and TZEEI 23 (Striga susceptible) inbreds, 14 QTLs were identified for Striga resistance/tolerance traits. In a second QTL study involving the extra-early yellow F2:3 families derived from the Striga-resistant parent (TZEEI 79) and the susceptible parent (TZdEEI 11), 12 QTL were identified for 4 Striga resistance/tolerance traits. QTL identified in the studies would be invaluable for rapid introgression of Striga resistance genes into maize genotypes using marker-assisted selection approaches after validation of QTL in inbreds.