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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Spanish maize (Zea mays L.) populations can be useful for enhancing adaptation and stress tolerance of commercial varieties. Two improved Spanish maize populations, one from the northwest and the other from the southeast of Spain, that represent an alternative heterotic pattern have been subjected to three cycles of fullsib reciprocal recurrent selection to increase the performance of the population cross. The objectives of this study were to evaluate the effect of selection on grain yield and on the correlated responses in the populations and their crosses and to investigate changes in heterosis and inbreeding depression during selection. Ten populations per se (S0), selfed (S1) and intercrossed were evaluated at six environments. Yield significantly increased with selection in the population cross (4.1% per cycle) and in the northwestern population (6.7% per cycle). Yield of the southeastern population did not change with selection. Correlated responses in other important agronomic traits were also in the desired direction. Mid-parent and high-parent heterosis increased significantly with selection (2 and 1.5%, respectively). The third cycle of selection of both populations is an interesting source for new inbred lines that could be the foundation for new adapted hybrids. The cross between the improved cycles could be useful for sustainable or organic agriculture as population hybrids, but more importantly, the reciprocal recurrent selection program can continue improving the population cross. [ABSTRACT FROM AUTHOR]

Breeding of maize (Zea mays L.) in the Atlantic coast of Europe has focused on developing hybrids to exploit heterosis between flint and dent germplasm. Flint X flint hybrids could have some advantages because of their earliness and early vigor that are important in short growing season areas. The objective of this work was to study the adaptation of a set of 10 flint varieties crossed to flint and dent testers and in a diallel design to check the feasibility of a breeding program to obtain flint hybrids well adapted to European Atlantic conditions. In the testcrosses, general combining ability (GCA) of the flint tester EP42 for kernel moisture at harvest and days to silking was lower than those of dent testers. Improvement of flint varieties for combining ability with inbred line EP42 could be done to obtain earlier flint X flint hybrids with a better dry-down rate than flint X dent hybrids. Diallel entries were analyzed following Analysis 11 of Gardner and Eberhart. Variety and heterosis effects were significant for all traits. Varieties Gallego and Norteño, besides having large variety effects, also showed intermediate variety heterosis for adaptive traits and they would be the best adapted varieties to include in breeding programs. The cross ‘Gallego X Basto/Enano levantino’ combined the best yield and good specific heterosis for adaptive traits. Thus, flint hybrids to be grown in short season areas could be obtained following this heterotic pattern. [ABSTRACT FROM AUTHOR]

Most maize (Zea mays L.) hybrids cultivated in Europe follow the heterotic pattern European flint × Corn Belt dent. However, at present, no commercial hybrids have been obtained from European flint inbreds exclusively. A flint × flint heterotic pattern could be an alternative to use in breeding programs to obtain early maturity, highyielding hybrids, potentially useful for producing high quality flours. The objective of this work was to search for heterotic patterns within flint germplasm adapted to temperate conditions. Ten open-pollinated flint maize cultivars were crossed in a diallel design without reciprocals and evaluated in four environments in northwestern Spain. Cultivar effects explained most of the sum of squares for traits analyzed, except for yield. Crosses yielded 30% more than parental cultivars. Yield of crosses ranged from 3.94 to 5.61 Mg ha[sup -1]. Midparent heterosis values ranged from 2.5 to 64.7%. The crosses 'Gallego' × 'Basto/Enano Levantino' and Basto/Enano Levantino × 'Longfellow' showed high heterosis and the best averages for grain yield. On the basis of these results, these crosses could be included in a recurrent reciprocal selection breeding program to increase heterosis among the cultivars and improve their hybrids. A cluster analysis made with midparent heterosis for grain yield as a measure of distance revealed that the flint germplasm probably had similar origins and were related to the 'Northern Flint' race. Some differences among these cultivars were detected. 'Norteño Largo' was closely related to Northern Flint, while Basto/Enano Levantino was different from the rest of the cultivars. It was concluded that the development of hybrids combining good yield and the typical agronomic characteristics of flint maize is feasible. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]