Drought is one of the most detrimental abiotic stresses hampering seed germination, development, and productivity. Maize is more sensitive to drought than other cereals, especially at seedling stage. Our objective was to study genetic regulation of drought tolerance at germination and during seedling growth in maize. We evaluated 420 RIL with their parents from a multi-parent advanced generation inter-cross (MAGIC) population with PEG-induced drought at germination and seedling establishment. A genome-wide association study (GWAS) was carried out to identify genomic regions associated with drought tolerance. GWAS identified 28 and 16 SNPs significantly associated with germination and seedling traits under stress and well-watered conditions, respectively. Among the SNPs detected, two SNPs had significant associations with several traits with high positive correlations, suggesting a pleiotropic genetic control. Other SNPs were located in regions that harbored major QTLs in previous studies, and co-located with QTLs for cold tolerance previously published for this MAGIC population. The genomic regions comprised several candidate genes related to stresses and plant development. These included numerous drought-responsive genes and transcription factors implicated in germination, seedling traits, and drought tolerance. The current analyses provide information and tools for subsequent studies and breeding programs for improving drought tolerance.

Drought is the main constraint to maize production in the Mediterranean area. This is the first report of breeding temperate maize populations from the Algerian desert. The objective of this study was to evaluate response to selection for reduced anthesis-silking interval (ASI) in Algerian maize under drought and control conditions. Three cycles of selection for reduced ASI were carried out in four populations under control and drought conditions, and the breeding program was evaluated under both conditions. Selection under drought was more efficient than under control conditions, particularly for the LOM and TAO populations. Selection for low ASI reduced ASI and days per cycle for BTM and IGS, respectively, under drought conditions. Selection for ASI reduced anthesis in BTM, when selected under drought and evaluated under control conditions. Significant yield increase was observed for BTM under optimal conditions. Significant genetic gain for yield was observed for the population LOM under drought. Therefore, the improved Algerian populations BTM and TAO could be a novel source for reducing ASI and for earlier flowering time as a mechanism for avoiding drought. Furthermore, we propose these populations as sources to develop tolerant inbred lines and to find quantitative trait loci for drought tolerance.

Increasing drought incidence and infertile soils require the improvement of maize for nitrogen use efficiency (NUE) under drought conditions. The objectives were to assess tolerance and genetic effects of Algerian populations under no-nitrogen and water stress. We evaluated a diallel among six Algerian maize populations under no-nitrogen vs. 120 kg/ha N fertilization and drought vs. control. Variability was significant among populations and their crosses for NUE under drought. Additive genetic effects could be capitalized using the populations BAH and MST, with high grain nitrogen utilization efficiency (NUtE). The most promising crosses were SHH × AOR with no-nitrogen supply under both water regimes for NUtE, AOR × IGS, under water stress for partial factor productivity (PFP), and well-watered conditions with nitrogen supply for protein content; AOR × IZM for agronomic nitrogen use efficiency (AE) under water stress; and AOR × BAH for grain nutrient utilization efficiency (NUtE) under well-watered conditions with nitrogen. These parents could be promising for developing drought-tolerant or/and low nitrogen hybrids to improve these traits. Maximum heterosis could be exploited using those populations and crosses. Reciprocal recurrent selection could be used to take advantage of additive and non-additive gene effects found based on estimations of genetic parameters.

Drought and low nitrogen are major stresses for maize (Zea mays L.), and maize populations from the Sahara Desert are potential sources of stress tolerance. The objectives were to assess the tolerance and varietal and heterosis effects of Algerian populations under no-nitrogen fertilization and water stress. A diallel among six Algerian maize population was evaluated under drought (300 mm irrigation) vs. control (600 mm) and no-nitrogen fertilization vs. 120 kh ha⁻¹ N fertilization. Genotypes showed significant differences and genetic effects for water- and nitrogen-stress tolerance. We propose a reciprocal recurrent selection to take advantage of additive and non-additive effects, using AOR and IGS, since they showed good performance in optimum and stress conditions, for improving yield heterosis for AOR × IGS. Negative effects are not expected on plant height, anthesis–silking interval or early vigor. These populations and BAH could be sources of inbred lines tolerant to drought and no-nitrogen fertilization. There was no relationship between origin and genetic group and stress tolerance per se or as parents of tolerant crosses. These populations and crosses could be used as base material among Algerian populations, for breeding programs focusing on tolerance to water or nitrogen stress.

Delayed senescence could contribute to maintain yield under water stress and low nitrogen stress. Landraces from arid areas can provide favorable alleles for stay green under stress. The objectives of this study were to estimate varietal and heterosis effects of Algerian Saharan populations and their crosses for stay-green under water stress and no-nitrogen fertilization and to identify the most promising populations as sources of stay-green under stress. Six Algerian maize populations were evaluated in a diallel under water stress (300 mm irrigation) versus control (600 mm) and no-nitrogen fertilization versus 120 kg/ha N fertilization. Both varietal and specific heterosis were involved in delayed senescence under stress. Breeding programs could capitalize additive components by using the populations IZM or IGS with favorable varietal effects for delayed senescence under nitrogen stress, or dominance effects by using the population AOR with favorable heterotic effects for plant color under water and nitrogen stresses. Based on specific heterosis, under water stress conditions with no-nitrogen supply, the most promising cross was AOR × IZM for delayed senescence, while IZM × BAH (with no-nitrogen supply), and SHH × BAH (with nitrogen fertilizer), will allow a longer maintenance of the plant coloration. We suggest reciprocal recurrent selection with these populations for developing drought-tolerant and low nitrogen hybrids to improve stay-green.