Early-maturing provitamin A (PVA) quality protein maize (QPM) hybrids with combined drought and low soil nitrogen (low-N) tolerance are needed to address malnutrition and food security problems in sub-Saharan Africa (SSA). The current study's objectives were to (i) examine combining ability of selected early maturing PVA-QPM inbreds for grain yield and other agronomic traits under drought, low-N, optimal environments and across environments, (ii) determine gene action conditioning PVA accumulation under optimal environments, (iii) classify inbreds into heterotic groups and identify testers and (iv) assess yield and stability of hybrids across environments. Ninety-six hybrids generated from 24 inbred lines using the North Carolina Design II together with four commercial hybrid controls were evaluated under drought, low-N and optimal environments in Nigeria in 2016 and 2017. Fifty-four selected hybrids were assayed for PVA carotenoid and tryptophan content. Additive genetic effects were greater than non-additive effects for grain yield and most agronomic traits under each and across environments. The gene action conditioning accumulation of PVA carotenoids under optimal growing conditions followed a pattern similar to that of grain yield and other yield-related traits. The inbred lines were categorized into four heterotic groups consistent with the pedigree records and with TZEIORQ 29 identified as the best male and female tester for heterotic group IV. No tester was found for the other groups. Hybrid TZEIORQ 24 × TZEIORQ 41 was the highest yielding and most stable across environments and should be further tested for consistent performance for commercialization in SSA.

The number of drought and low‐N tolerant hybrids with elevated levels of provitamin A (PVA) in sub‐Saharan Africa could increase when PVA genes are optimized and validated for developed drought and low‐N tolerant inbred lines. This study aimed to (a) determine the levels of drought and low‐N tolerance, and PVA concentrations in early maturing PVA‐quality protein maize (QPM) inbred lines, and (b) identify lines harbouring the crtRB1 and LcyE genes as sources of favourable alleles of PVA. Seventy early maturing PVA‐QPM inbreds were evaluated under drought, low‐N and optimal environments in Nigeria for two years. The inbreds were assayed for PVA levels and the presence of PVA genes using allele‐specific PCR markers. Moderate range of PVA contents was observed for the inbreds. Nonetheless, TZEIORQ 55 combined high PVA concentration with drought and low‐N tolerance. The crtRB1‐3′TE primer and the KASP SNP (snpZM0015) consistently identified nine inbreds including TZEIORQ 55 harbouring the favourable alleles of the crtRB1 gene. These inbreds could serve as donor parents of the favourable crtRB1‐3′TE allele for PVA breeding in maize.

Drought and Striga are principal constraints to maize (Zea mays L.) production in sub‐Saharan Africa. An early yellow maize population, TZE‐Y Pop DT STR, which had undergone five cycles of selection for resistance to Striga, followed by three cycles of improvement for drought tolerance, was investigated for yield gains, changes in genetic variance, and interrelationships among traits under drought stress and optimum environments. Two hundred and forty S1 lines comprising 60 each from the base population and subsequent populations from three selection cycles improved for grain yield and drought tolerance were assessed under drought and optimal environments in Nigeria from 2010 to 2012. Genetic improvements in grain yield of 423 and 518 kg ha−1 cycle−1 were achieved under drought stress and optimal environments. Predicted improvements in selection for yield were 348 and 377 kg ha−1 cycle−1 under drought stress and optimum environments, respectively. The highest yield observed in C3 was accompanied by reduced days to silking and anthesis–silking interval, improved plant aspect and ear aspect, and increased plant height and ears per plant across research environments, as well as improved stay‐green characteristic under drought. The level of genetic variability for yield and a few other traits were maintained under drought and optimal environments in the population. The presence of residual genetic variability for yield and other assayed traits in C3 indicated that progress could be made from future selection in the population depending on the ability of breeders to identify outstanding genotypes and the precision level of experimentation. Substantial improvement has been made in yield and drought tolerance in C3 of the population.