Maize (Zea mays L.) hybrids resistant to Striga hermonthica (Del) Benth and tolerant to drought are vital to the sustainability of productivity of the maize‐based farming systems of West and Central Africa (WCA). Thirty‐six diallel crosses derived from nine early maturing white maize inbreds were evaluated under drought, well‐watered, striga‐infested, and striga‐free conditions at five locations in Nigeria between 2007 and 2009. The objective was to examine the combining ability, performance and stability of the inbreds, and to identify the heterotic groups. Additive and nonadditive gene actions were important in the control of the inheritance of drought tolerance and striga resistance in the inbreds. General combining ability (GCA) mean squares of grain yield and other traits were larger than those of specific combining ability (SCA), indicating that additive gene action was more important in the inheritance of drought tolerance. The GCA mean squares for striga damage rating at 8 and 10 weeks after planting (WAP) were about six and five times greater than those of the SCA, indicating that additive gene action played a major role in the inheritance of the striga traits. The GGE biplot analysis revealed that TZEI 4 and TZEI 5 were the most promising inbreds in yield performance and stability across the test environments. Two heterotic groups were identified; [TZEI 7, TZEI 19, TZEI 2, TZEI 4] and [TZEI 5, TZEI 3]. Tester TZEI 3 was the closest to the ideal tester. Entry TZEI 7 had the highest GCA effects and TZEI 2 the lowest.

Appropriate testers are needed as well as information on heterotic patterns of tropical lowland early‐maturing germplasm. Diallel crosses involving nine tropical early maturing maize (Zea mays L.) inbreds were evaluated at five locations in Nigeria from 2007 to 2009 under drought stress, when Striga infested, and in optimal growing conditions to examine the combining abilities and heterotic patterns and identify appropriate testers. Results revealed that TZEI 17 was the closest to the ideal tester and may be considered as the best under drought stress, TZEI 23 and TZEI 9 under artificial Striga infestation, and TZEI 13 across growing conditions. No appropriate tester was identified for the optimal growing conditions. Inbreds were placed in three contrasting tester groups under drought stress, and four groups each were placed under Striga infestation and optimal growing conditions and across research environments. Hybrids between inbreds in contrasting tester groups of each research environment are expected to show heterosis. TZEI 23 × TZEI 13 had a superior performance under all research conditions, suggesting that it has a broad adaptation. Classification of inbreds into distinct tester groups was not possible for 33% of the inbreds under drought stress and for 22% when Striga infested, under optimal growing conditions, and across the test environments.

Striga, drought, and low soil fertility constrain maize (Zea mays L.) productivity in West and Central Africa (WCA). Two Striga‐resistant extra‐early populations, TZEE‐W Pop STR (white) and TZEE‐Y Pop STR (yellow) were improved by four cycles of S1 recurrent selection, and the products were evaluated in field trials in Nigeria from 2005 to 2007. The objective was to assess progress in improvements for grain yield, Striga resistance, and other traits when Striga‐free, Striga‐infested, and under low‐ and high‐N management. Under Striga infestation, yield gain from C0 to C4 was 136 kg ha−1 for the yellow population and 71 kg ha−1 cycle−1 for the white. The yield gain in advanced cycles of selection in the yellow population was associated with decreases in Striga emergence at 8 and 10 wk after planting (WAP) and Striga damage at 8 WAP, while that of the white was accompanied by increased days to silking (DS) and ears per plant (EPP) as well as a decrease in Striga emergence at 8 WAP. Under Striga‐free conditions, yield gain from C0 to C4 was 164 kg ha−1 cycle−1 for the white and 221 kg ha−1 cycle−1 for the yellow. The yield gain in advanced cycles of selection was more pronounced under high‐N (157 kg ha−1 cycle−1) than low‐N conditions (144 kg ha−1 cycle−1) in the yellow, and higher under low N than high‐N conditions in the white. Selection in the yellow was accompanied by increased days to anthesis (DA) and DS, plant and ear heights under low N and increased DS under high N. In the white, selection induced increased DA, ear height, and decreased anthesis–silking interval (ASI).

Maize (Zea mays L.) production in west and central Africa (WCA) is constrained by the parasitic weed Striga hermonthica (Del.) Benth and recurrent drought. Two early maize populations, TZE‐W Pop DT STR C0 (white) and TZE‐Y Pop DT STR C0 (yellow), developed from diverse genetic backgrounds, were subjected to three cycles of S1 recurrent selection under artificial Striga infestation. Inbreds and synthetic cultivars were developed from the different cycles of selection. The populations (C0), derived cultivars, and check cultivars were evaluated in 2002 and 2003 under Striga‐infested and Striga‐free environments in WCA. The objective was to assess the performance of the derived cultivars from the different cycles of selection. Under Striga infestation, ACR 94 TZE Comp5‐Y and ACR 94 TZE Comp5‐W, which were not from the selection program, were the highest‐yielding group (2158 and 2124 kg ha−1, respectively). The second group comprised six products of the selection program, with grain yield ranging from 1806 to 1954 kg ha−1 The third group, with grain yield of 1498 to 1759 kg ha−1 contained mostly Striga‐susceptible cultivars and the C0 of the selection program. Under Striga‐free conditions, the performance of several cultivars from the selection program was equal to or better than ACR 94 TZE Comp5‐Y and ACR 94 TZE Comp5‐W. The genotype plus genotype × environment interaction biplot analysis demonstrated that EV DT‐Y 2000 STR C1 and TZE‐W Pop DT STR C3 from the selection program, along with ACR 94 TZE Comp5‐W, had stable grain yield under Striga‐infested and noninfested conditions.

A breeding programme for resistance to Striga hermonthica in maize (Zea mays) was initiated in Côte d'Ivoire in 1994. Two extra-early populations, white (TZEE-W Pop STR) and yellow (TZEE-Y Pop STR), were formed from diallel crosses of the best adapted extra-early maturing maize germplasm in the West and Central African subregion. In an effort to improve the populations for Striga resistance, TZEE-W Pop was crossed to inbred 1368 STR (Tzi 3 STR), and TZEE-Y Pop to 9450 STR (Tzi 25 STR). The resulting F 1 populations were carried through two backcross (BC) generations. S 1 lines were developed from the BC 2 and subjected to two cycles of random mating to generate TZEE-W Pop STR C 0 and TZEE-Y Pop STR C 0 . These two populations were subjected to three cycles of S 1 recurrent selection under artificial Striga infestation and several experimental varieties were extracted from the different cycles of the selection programme. The original populations (C 0 ), improved populations, and experimental varieties were evaluated in two experiments under Striga-infested and Striga-free conditions. The primary objective was to determine the effectiveness of S 1 recurrent selection in developing Striga-resistant extra-early maize varieties. Results of the performance tests showed that the populations were good sources of Striga-resistant varieties with high-yield potential under both Striga-infested and Striga-free conditions. The results have also confirmed the effectiveness of inbreeding, selection and hybridization, as well as the backcross breeding methods, as tools for the development of extra-early populations, synthetic varieties and inbred lines.