Drought-tolerant Maize Hybrids Research Articles

Approaches and progress in breeding drought-tolerant maize hybrids for tropical lowlands in west and central Africa.

Drought represents a significant production challenge to maize farmers in West and Central Africa, causing substantial economic losses. Breeders at the International Institute of Tropical Agriculture have therefore been developing drought-tolerant maize varieties to attain high grain yields in rainfed maize production zones. The present review provides a historical overview of the approaches used and progress made in developing drought-tolerant hybrids over the years. Breeders made a shift from a wide area testing approach, to the use of managed screening sites, to precisely control the intensity, and timing of drought stress for developing drought-tolerant maize varieties. These sites coupled with the use of molecular markers allowed choosing suitable donors with drought-adaptive alleles for integration into existing elite maize lines to generate new drought-tolerant inbred lines. These elite maize inbred lines have then been used to develop hybrids with enhanced tolerance to drought. Genetic gains estimates were made using performance data of drought-tolerant maize hybrids evaluated in regional trials for 11 years under managed drought stress, well-watered conditions, and across diverse rainfed environments. The results found significant linear annual yield gains of 32.72kg ha-1 under managed drought stress, 38.29kg ha-1 under well-watered conditions, and 66.57kg ha-1 across multiple rainfed field environments. Promising hybrids that deliver high grain yields were also identified for areas affected by drought and variable rainfed growing conditions. The significant genetic correlations found among the three growing conditions highlight the potential to exploit the available genetic resources and modern tools to further enhance tolerance to drought in hybrids.

AMMI an GGE biplot analysis of grain yield for drought-tolerant maize hybrid selection in Inner Mongolia

Due to the ongoing global warming, maize production worldwide is expected to be heavily inflicted by droughts. The grain yield of maize hybrids is an important factor in evaluating their suitability and stability. In this study, we utilized the AMMI model and GGE biplot to analyze grain yield of 20 hybrids from the three tested environments in Inner Mongolia in 2018 and 2019, aiming at selecting drought-tolerant maize hybrids. AMMI variance analysis revealed highly significant difference on main effects for genotype, environment, and their interaction. Furthermore, G11 (DK159) and G15 (JKY3308) exhibited favorable productivity and stability across all three test environments. Moreover, G10 (LH1) emerged as the most stable hybrid according to the AMMI analysis and the GGE biplot. Bayannur demonstrated the highest identification ability among the three tested sites. Our study provides accurate identification for drought-resilient maize hybrids in different rain-fed regions. These findings can contribute to the selection of appropriate hybrids that exhibit productivity, stability, and adaptability in drought-prone conditions.

Drought tolerant maize hybrids have higher yields and lower water use under drought conditions at a regional scale

Drought is an enduring abiotic constraint to stable and consistent maize productivity under climate change, especially for low rainfall regions with limited irrigation. One adaptation for severe drought is using drought-tolerant (DT) hybrids. Here, we characterize differences between conventional and DT hybrids in terms of yield and water-use efficiency under drought conditions at a regional scale of the Texas High Plains (THP). Using a validated version of APSIM-Maize, we simulated yields of conventional and DT hybrids across 11 water regimes and 25 counties in THP from 1984 to 2018. When irrigation amounts were constrained to 90%, 80%, 70%, 60% and 50% of total irrigation used for the baseline scenario (BS; a simulated scenario of conventional hybrid under full irrigation), DT hybrids showed lower yield penalties under drought stress relative to conventional hybrids. This improved total production by 19%, 24%, 26%, 26%, and 21% for each of the above irrigation levels. When the yield-target was set as 90%, 80%, 70%, and 60% of BS, total regional irrigation applied to DT hybrid could be saved more than that to the conventional hybrid, and therefore reduced more 17%, 16%, 15%, and 15% of BS irrigation, respectively. We showed that DT hybrids had greater yield gain and water savings through improved water productivity under deficit irrigation, highlighting the potential of deficit irrigation for increasing yield for the adoption of DT hybrid. Our quantitative evaluation of the yield advantage and water saving potential associated with DT hybrids also highlighted the regional benefits associated with adoption of drought adaptive hybrids.

Effects of Phloem-Feeding Pest, Dalbulus maidis on Morphological Expression of Drought-Tolerant Traits in Maize

Drought is amongst the most important stressors affecting maize production globally. Existing strategies to offset drought impacts are centered around the rapid development of drought-tolerant cultivars through plant breeding. However, under both current conditions and projected climate changes, additional stressors such as insect pests will co-occur. To determine the impact of combined insect and drought stress on drought tolerance in maize, we assessed the effects of Dalbulus maidis, drought, and both stresses combined in drought-tolerant maize hybrids. We measured several maize morphological growth traits (i.e., plant height, stem diameter, shoot weight, root weight, root length, and root-to-shoot ratio) at the end of a 28-day period of pulse-stress and no-stress control exposure. We found that seedling growth declined when both stressors co-occurred. Nevertheless, drought-tolerant maize hybrids remained strongly tolerant to drought regardless of D. maidis infestation. While our results showed that drought tolerance is maintained in drought-tolerant maize seedlings, future studies should address any effects on maize yield. Our study highlights the importance of testing the combined effects of drought and insect stressors to better predict insect–plant interactions in the context of plant breeding for drought-tolerant traits in a changing climate.

Assessing the Fodder Potentials of Drought-Tolerant Maize (Zea mays L.) Hybrids in West Africa

The study evaluated the fodder potential of 42 promising drought-tolerant (DT) three-way cross maize (Zea mays L.) hybrids, 11 commercial hybrid checks, and 1 local variety check under irrigation. Agronomic and laboratory trials were conducted to determine their morphological traits and fodder potential. Hierarchical cluster analysis (HCA) to group cultivars into clusters is based on quantity, quality, and the combination of both variables. Selection of potential food-feed cultivars was based on the quantity traits (grain and biomass yield) and quality traits crude protein (CP), in vitro organic matter digestibility (IVOMD), and metabolizable energy (ME). Variation was found for dry matter yield (DMY) at harvest as commercial hybrid recording the maximum DMY of 14.1 t ha−1 and the highest grain yield of 1.4 t ha−1 (P < 0.01), while local check produced a minimum grain yield of 0.54 t ha−1 (P < 0.01) with grain moisture content range between 8.4 and 11.6%. The maximum mean ash content was 5.8% for DT hybrids. Average CP was the highest in commercial hybrids with a value of 6.1%. The mean values for ME were similar (P > 0.01) in both commercial hybrids (7.2 MJ/kg DM) and DT hybrid (7.2 MJ/kg DM), while the highest ME (7.6 MJ/kg DM) was recorded for the local check. Ranking of the hybrids based on grain yield, DMY, CP, ME, and IVOMD showed that cluster subgroup A3 (M1124–24, M1527-7, 30F32, and M1427-6) and A4 (M1427-3, SC637, and M1627-11) exhibited the best potential traits and can therefore be recommended for commercial cultivation following adoption trials by farmers.

Response of Maize-Hybrids Phenology Under high Plant Population Density in parts of Northern Guinea Savanna of Nigeria

Plant distribution in the field, as affected by plant density, has been one area that has received a great deal of attention over the last several decades. Population density, whether directly on the plant or indirectly on biotic factors associated with plant density is one of the most important factors in determining physiological attributes of a crop. Maize grain yield has a parabolic response to stand density that maximizes yield, which is widely known by the crop managers, physiologists and breeders; together with the concept that this optimum stand density varies with the environment. Development of breeding populations and hybrids with improved tolerance to high plant densities should be an important part of maize breeding programs. A field experiment was therefore conducted during 2015 and 2016 rainy season at Tudun Wada, Kano and Shika, Zaria in the Northern Guinea savanna of Nigeria in order to assess the phenological components of maize-hybrids at high plant population density. The experiment consisted of two plant populations of 53,333 plantha-1 and 88,888 plantsha-1 as main plot and eight recently developed drought–tolerant maize hybrids: M0826-7, M0926-8, M1026-10, M1026-13, M1124-4, M1124-10, M1227-12 and M1227-14 and two widely cultivated commercial hybrids as controls (Oba-98 and Oba super-1) as sub-plots laid out in a randomized split-plot design and replicated three times. Maize-hybrids responded to high plant population density in the two locations. Increasing plant population significantly decreased the phenology of maize-hybrids, which showed better adaptation of hybrids to high plant population density. Hybrids showed shorter days to maturity and shorter anthesis-silking interval. Maize-hybrids performed better at Zaria than at Tudun Wada because rainfall was higher and better distributed in this location. However recent hybrids were more tolerant to high plant population than the commercial hybrids, therefore the recently released maize-hybrids were more adapted to biotic stress.
 Keywords: Biotic stress, Growth, Phenology, Plant population density and Maize-hybrids

Varijabilnost i međuzavisnost osobina hibrida kukuruza različite dužine vegetacije

Maize is one of the most important field crops with broad genetic and phenotypic variations. It occupies an important place in agricultural production in the world as in Serbia. The main aim of maize breeding is to obtain new inbred lines, i.e. to identify new hybrid combinations that will surpass existing hybrids in terms of grain yield and other important traits. The aim of this study was to examine the phenotypic variability of 10 NS maize hybrids of different genetic bases and maturity groups in agroecological conditions in Rimski Šančevi, to consider the interdependence of grain yield and other tested traits using PCA and correlation analysis. The obtained results indicate a significant variation of all examined properties except for the ear length. The significance of the difference indicated by the F test was confirmed by the Duncan test. Correlation coefficients indicate a significant positive interdependence between the mass of 1000 grains and the ear length (r = 0.698). PCA analysis provided a more complex analysis of the interdependencies of the examined traits and grain yield. The highest yields were achieved by hybrids that simultaneously showed high values of several yield components. Yields ranged from 11,210 kg ha-1 in the G-10 hybrid (FAO 600), to 14,790 kg ha-1 in the G-3 hybrid (FAO 400). In this study, hybrids of earlier maturity achieved higher grain yields, mainly due to drought tolerance. Therefore, the goal is to create drought-tolerant maize hybrids that will successfully endure the negative consequences of global warming.

Maize Hybrid Response to Sustained Moderate Drought Stress Reveals Clues for Improved Management

Crop water productivity (CWP), irrigation water productivity (IWP), actual seasonal basal crop coefficient (Kab), and actual crop evapotranspiration (ETa) are essential parameters for accurate estimation of crop water requirement to prevent irrigation water waste. These parameters were evaluated by conducting three experiments using a drought-tolerant maize hybrid and a non-drought-tolerant (‘standard’) maize hybrid receiving 50, 100, and 150% of the recommended optimal nitrogen (N) fertilizer rate and grown under well-watered conditions, drought stress from the 14 leaf collar maize phenological stage (V14) to maize physiological maturity (R6), and drought stress from the blister maize phenological stage (R2) to R6. Across hybrids, ETa decreased with increased duration of drought stress. The drought-tolerant hybrid had 7 and 8% greater CWP and IWP, respectively, compared to the standard hybrid when drought stress began at V14. Mid-season Kab was 1.08, 0.89, and 0.73 under well-watered conditions and when drought stress began at R2 and V14, respectively. These results reveal that (i) maize achieved more effective physiological acclimation with earlier exposure to drought stress, (ii) grain yield of the drought-tolerant hybrid was unchanged by earlier, compared to later, onset of drought despite a 10% decrease in ETa, and (iii) two phases of acclimation were identified: Maize Kab declined upon exposure to drought but stabilized as the crop acclimated.

Efficiencies of Heterotic Grouping Methods for Classifying Early Maturing Maize Inbred Lines

The success of a hybrid breeding program is dependent on available heterotic patterns for exploitation of grain-yield heterosis. The efficiency of the assignment of germplasm lines into heterotic groups is a prerequisite for obtaining useful heterotic patterns among germplasm lines. A total of 256 maize hybrids, comprising 244 top crosses, six diallel cross hybrids, and six checks, were grown under Striga infestation, drought, and optimal conditions, from 2015 to 2017. The study determined the combining abilities of the parental inbreds, classified the inbreds into heterotic groups, and compared the efficiencies of the following four grouping methods for classifying the inbreds: specific combining ability (SCA) effect of grain yield; general combining ability (GCA) effects of multiple traits (HGCAMT); SCA and GCA (HSGCA) for yield; and single nucleotide polymorphism-based genetic distance (SNP-based genetic distance (GD)). Significant GCA and/or SCA mean squares were revealed for most measured traits in all test environments. Sums of squares (SS) due to GCA were higher than SCA SS for measured traits in all test environments. The HSGCA, SCA, and SNP-based GD methods identified four heterotic groups, whereas the HGCAMT identified three groups, in all environments. The additive gene effect was preponderant in the inheritance of most measured traits. The efficiencies of the grouping methods varied with the test environments. The HSGCA and SCA methods were the most efficient for grouping in all test conditions. For practical breeding purposes, the HGCAMT and HSGCA methods were recommended under Striga infestation and drought, respectively. The heterotic patterns, which were revealed in this study, were effective for planning hybridization schemes for developing high-yielding, Striga-tolerant/resistant, and drought-tolerant maize hybrids for stressful environments.

Stomatal closure response to soil drying at different vapor pressure deficit conditions in maize

A plant transpiration rate under progressive soil drying remains constant until a threshold fraction of transpirable soil water (FTSW) is reached, and subsequently decreases linearly. The sensitivity of this function and the involvement of abscisic acid (ABA) and aquaporins in such responses have not been compared at various levels of atmospheric evaporative demand conditions. This study was conducted in controlled environment chambers with a drought-tolerant maize hybrid imposing progressive drought stress under three levels of vapor pressure deficit (VPD- 1.2, 2.3, and 3.5 kPa). A shift in threshold-FTSW from 1.2 kPa (FTSW-0.42) VPD to 3.5 kPa(FTSW-0.51) VPD was observed, showing an effect of VPD on stomatal closure response under soil drought conditions. Foliar ABA showed a substantial rise approximately at the same time as of stomatal closure initiated (FTSW-threshold), indicating ABA involvement. As the drought progressed, an increase in plasma membrane intrinsic protein and a decrease in tonoplast intrinsic protein expression levels were observed. Overall, this study suggests the influence of evaporative demand on the initiation of stomatal closure of drought-tolerant maize subjected to soil drying. The sensitivity of stomatal closure was associated with foliar ABA under drought stress but not under high evaporative demand conditions, indicating alternative water conservative mechanisms.

Identification of superior drought tolerant maize hybrids based on combining ability and heterosis with Line × Tester mating design

Maize (Zea mays) is an important multipurpose cereal crop. Single-cross hybrids play a crucial role in maize cultivation in terms of acreage and production. The combining ability and heterosis are prime criteria for efficacious maize improvement and breeding. This study was focused to access the performances of hybrids, and to estimate heterosis and combining ability for grain yield and yield-related traits. The present study was conducted using 16 parents and 28 F1 cross combinations of maize hybrids during rabi 2019 to identify the best inbred lines and hybrid combinations. The overall study of gca effects suggested that the parents CBM-DL-448, CBM-DL- 435, CBM-DL- 360 and UMI1230 were found to be good general combiners for desirable yield-related traits. Among the hybrids, CBM-DL-360 × UMI 1200, CBM-DL-435 × UMI 1230, and CBM-DL-448 × UMI 1230 exhibited positive and significant sca effects and standard heterosis for single plant yield.

Comparison of Lysimeter-Derived Crop Coefficients for Legacy and Modern Drought-Tolerant Maize Hybrids in the Texas High Plains

HighlightsDaily maximum crop coefficient (Kc) values were similar for legacy hybrids and a modern drought-tolerant (DT) hybrid.Later planting dates for a DT hybrid resulted in average season lengths ~25 days shorter than those of legacy hybrids.Results illustrated the effects of environment, planting date, interannual variation in temperature, and the importance of climate-specific Kc functions.DT hybrids may be more effective at reproductive growth during periods of heat stress in semi-arid environments, although additional data are needed to support this conclusion.Abstract. Corn (Zea mays L.) is a major irrigated crop grown in the Southern High Plains including the Texas Panhandle. Irrigation from the Ogallala Aquifer is required to sustain profitable corn production in the region by supplementing inadequate and erratic rainfall. Effective irrigation scheduling works to extend limited groundwater resources by avoiding water losses associated with runoff and/or percolation below the root zone. The use of crop coefficient (Kc) and reference evapotranspiration (ETo) values to estimate daily crop water use (ETc) remains an effective scheduling tool that can complement other irrigation scheduling approaches. Both Food and Agriculture Organization (FAO-56) piecewise and curvilinear Kc values for corn are found in the literature. However, advances in corn genetics have led to questions about the applicability of Kc values developed using legacy corn hybrids to irrigation of modern drought-tolerant (DT) hybrids. Lysimeter-derived Kc values for legacy corn hybrids grown in large weighing lysimeter fields at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, were compared with those derived from a modern DT corn hybrid recently grown in the same fields. Results indicated that although midseason daily Kc values were similar for all hybrids, average season length was ~25 days shorter for the modern DT hybrid, characterized by a shortened initial growth period followed by more rapid increase of Kc during the development period. However, plots of Kc over thermal time illustrated that the differences in season length were likely attributable to later planting dates associated with the DT corn hybrids. Average seasonal water use was 730 and 811 mm for the legacy and modern DT hybrids, respectively (three years each), with corresponding average yields of 1.2 and 1.4 kg ha-1. Results suggest that published Kc and Kcb values developed with legacy corn hybrids remain largely applicable to modern DT corn hybrids when used with accurate estimates of effective canopy-based growth stages and climate-specific Kc functions. Keywords: Crop coefficients, Drought-tolerant, Evapotranspiration, Maize, Weighing lysimeters.

Evaluation of Drought Tolerant Top Cross and Three-Way Cross Maize Hybrids for Grain Yield and Related Traits in Three Agro-Ecological Zones of Southwest Nigeria

Superiority of hybrid maize cannot be overemphasized. Different types of hybrids are developed by plant breeders to improve productivity and multi-locational evaluation of these hybrids prior to release is necessary to select the best. The objectives of this study were to identify maize hybrids with superior agronomic potentials and compare the performance of top-cross and three-way cross hybrid maize varieties for grain yield and related traits under rain-fed condition in three different locations (Abeokuta, Ibadan and Akure) of Southwest Nigeria. The study consisted of ten hybrids each of top-cross and three-way cross hybrid varieties, tested with two checks. At each location, the experiment was laid out in randomised complete block design with three replications. The results showed that effects of locations, genotypes and genotype x location interactions were highly significant (p<0.01) for all the traits evaluated. Significant differences were also revealed between the top-cross and three-way cross hybrids for all the traits evaluated except days to 50% tasseling, ear diameter and 100-grain weight. The top-cross hybrids were superior over the three-way cross hybrids for grain yield by 5.25%. The hybrids ‘M0926-7’, ‘M0926-8’, ‘M1026-11’, ‘M1026-3’, ‘M1226-2’ (top-cross hybrids), ‘M1124-24’, ‘M1124-27’, ‘M1124-31’, ‘M1227-6’ and ‘M1227-7’ (three-way cross hybrids) showed highest stable yields across the three locations. Hybrids ‘M0926-7’ (top-cross hybrid) and ‘M1124-24’ (three-way cross hybrid) that expressed early flowering with higher grain yield are recommended for drought stress prone areas because of their abilities to tolerate drought through escape.

Physiological Evaluations of Maize Hybrids under Low Nitrogen

A field experiment was conducted during 2014 and 2016 rainy season at Tudun Wada, Kano and Shika, Zaria in the Northern Guinea Savanna of Nigeria in order to study the physiological responses of maize hybrids under low nitrogen. The experiment consisted of two nitrogen levels 0 and 120 N kg ha−1 as main plot and 8 drought-tolerant maize hybrids and 2 controls as subplot laid out in a randomized split plot design and replicated three times. Physiological parameters of hybrids were significantly affected by low nitrogen at both locations. Interaction between hybrids and nitrogen was significantly affected at both locations. Based on these results, application of nitrogen significantly increased the physiological growth indices of maize hybrids. The extent of increment in physiological reactions was additionally higher in Zaria in view of higher soil natural carbon and nitrogen and higher precipitation was better dispersed at this area. However recent hybrids were more tolerant to nitrogen stress and out-yielded the older hybrids. Therefore the recently released hybrids were more adapted to abiotic stresses.

Grain Yield, Crop and Basal Evapotranspiration, Production Functions, and Water Productivity Response of Drought-tolerant and Non-drought-tolerant Maize Hybrids under Different Irrigation Levels, Population Densities, and Environments: Part II. In South-c

Abstract. Information and data on newer drought-tolerant maize hybrid response to water in different climates are extremely scarce. This research quantified the performance of non-drought-tolerant (NDT) (H1) and drought-tolerant (DT) (H2, H3, and H4) maize ( L.) hybrids response to grain yield, crop evapotranspiration (ETc), basal evapotranspiration (ETb), ETc-yield production functions (ETYPF), and crop water use efficiency (CWUE) at three irrigation levels and two plant population densities (PPDs) at two locations (transition zone between sub-humid and semi-arid climates at Clay Center (SCAL), Nebraska, in 2010 and 2012; and in a sub-humid climate at Concord (HAL), Nebraska, in 2010, 2011, and 2012). Irrigation treatments were: fully irrigated (FIT), early cutoff (ECOT) (i.e., no irrigation after blister stage), and rainfed (RFT) under two PPDs of 59,300 plants ha-1 (low PPD), and 84,000 plants ha-1 (high PPD). Generally, DT hybrids performed superior to NDT hybrid consistently at both locations, treatments, and years. DT H3 and DT H4 had highest grain yield consistently at SCAL and HAL, respectively. DT H3 and H4 hybrids’ productivity was not only superior in the RFT, but also in FIT. The highest yield of 16.3, and 15.3 Mg ha-1 were achieved by DT H3 (high PPD) and DT H2 (high PPD), respectively, associated with 471 and 590 mm of ETc in the FIT in 2012 at SCAL, and HAL, respectively. In most cases, all hybrids had highest grain yield under low PPD than high PPD at the RFT. All hybrids exhibited a linear yield response to increasing ETc in all years at both locations with positive slopes in all cases. The individual ETYPF response for individual hybrids had inter-annual variation in slopes between the hybrids and for the same hybrids between the years and location for both low and high PPDs. The ETYPF slopes ranged from 0.004 to 0.102 Mg ha-1 mm-,1 including all treatments (i.e., irrigation and PPDs) at SCAL for 2010 and 2012; and they ranged from 0.008 to 0.057 Mg ha-1 mm-1 including all treatments at HAL for 2010, 2011, and 2012. The ETb values exhibited inter-annual variation for the same hybrid between the irrigation levels, PPDs, and locations and they also exhibited an inner-annual variation between the hybrids and treatments in a given year with DT hybrids having consistently lower ETb values than the NDT hybrid. The greatest CWUE values were found in DT hybrids consistently at both locations. The DT hybrids can significantly increase yield productivity as well as crop water productivity per unit of ETc with respect to conventional hybrids not only in dry conditions, but also in average or above average years in terms of precipitation. Keywords: Basal evapotranspiration, Crop evapotranspiration, Drought-tolerance, Efficiency, Maize, Production functions.

Performance Assessment of Drought Tolerant Maize Hybrids under Combined Drought and Heat Stress.

Drought and high temperature are two major factors limiting maize productivity in sub-Saharan Africa. An increase in temperature above 30 °C reduces yield by 1% under optimal rain-fed condition and by 1.7% under drought stress (DS) and up to 40% under combined drought and heat stress (DSHTS). Approaches that improve performance under the two stresses are essential to sustain productivity. The objectives of this study were to (i) assess the extent of variation in tolerance to DSHTS from among the existing best drought tolerant (DT) hybrids; (ii) examine the response patterns of the hybrids to DSHTS; (iii) identify traits that contributed to better performance under DSHTS; and (iv) select the best hybrids with tolerance to DSHTS stress. We evaluated 40 DT hybrids under DSHTS, DS, and well-watered (WW) conditions for three years. Highly significant (p < 0.001) differences were found among hybrids for grain yield and other traits. Moderately to low repeatability values were detected for grain yield under DS (0.63) and under DSHTS (0.48). Grain yield under DS was not correlated with grain yield under DSHTS (r = 0.29; p = 0.06), but it was correlated with grain yield under WW (r = 0.74; p < 0.001). Grain yield was strongly correlated with ears per plant, ear and pant aspects, days to anthesis and silking under both DS and DSHTS. Tassel blast accounted for 28% of the yield reduction under DSHTS. The top five DT hybrids produced 9 to 26% more grain yields than the best commercial hybrid. Three hybrids produced high grain yields under DTHTS and DS as well as under WW. These hybrids will be tested further in collaboration with partners for possible release.

Effect of exogenous nitric oxide on sulfur and nitrate assimilation pathway enzymes in maize (Zea mays L.) under drought stress

The present study aimed at investigating the effects of foliar applied nitric oxide (as SNP [sodium nitroprusside]) on sulfur (glutathione reductase, guaiacol peroxidase, and glutathione S-transferase) and nitrate assimilation (nitrite and nitrate reductase) pathway enzymes in maize (Zea mays L.) exposed to water deficit conditions. The seedlings of a drought tolerant (NK8711) and sensitive (P1574) maize hybrid were applied with various SNP doses (0, 50, 100, 150, and 200 µM) under normal and drought stress conditions. Foliar spray of 100 µM markedly improved water status and chlorophyll contents and alleviated drought-induced oxidative damages through increased antioxidant (catalase, ascorbate peroxidase, and superoxide dismutase) activities in both maize hybrids. Moreover, exogenous SNP supply increased nitrite and nitrate reductase activities and upregulated glutathione reductase, glutathione S-transferase, and guaiacol peroxidase compared to no SNP supply. Interestingly, the negative effects of excess NO generation at high SNP doses (150, 200 µM) were more pronounced in P1574 than NK8711 leading to lower biomass accumulation in drought-sensitive hybrid.

Shoot and root traits in drought tolerant maize (Zea mays L.) hybrids

This study aimed to investigate the differences in shoot and root traits, and water use and water use efficiency (WUE) in drought tolerant (DT) maize (Zea mays L.) hybrids under full and deficit irrigated conditions. A two-year greenhouse study was conducted with four hybrids (one conventional hybrid, 33D53AM, two commercial DT hybrids, P1151AM, N75H, and an experimental hybrid, ExpHB) grown under two water regimes (I100 and I50, referring to 100 and 50% of evapotranspiration requirements). Under water stress, the hybids P1151AM, N75, and ExpHB showed more drought tolerance and had either greater shoot dry weight or less dry weight reduction than the conventional hybrid (33D53AM). However, these three hybrids responded to water stress using different mechanisms. Compared with the conventional hybrid, the two commercial DT hybrids (P1151AM and N75H) had a smaller leaf area, shoot dry weight, and root system per plant. As a result, these hybrids used less water but had a higher WUE compared with the conventional hybrid. In contrast, the experimental hybrid (ExpHB) produced more shoot biomass by silking stage at both irrigation levels than all other hybrids, but it had relatively lower WUE. The hybrids demonstrated different drought response mechanisms that may require different irrigation management strategies. More investigation and validation are needed under field conditions and in different soil types.

Yield and water use of drought-tolerant maize hybrids in a semiarid environment

Water shortage has been a challenge to sustainability of maize (Zea mays L.) production in many irrigated agriculture regions. Adoption of drought-tolerant (DT) hybrids could be a management strategy for maize production under water-limited conditions. The objective of this study was to investigate the differences in soil profile water extraction patterns at vegetative and grain filling stages, dynamics of evapotranspiration (ET), yield, and water use efficiency (WUE) in maize hybrids differing in drought tolerance characteristics in a semiarid environment. Field experiments were conducted in 2014 and 2015 in two conventional (33D53AM and N74R) and two DT hybrids (P1151AM and N75H). The hybrids were grown under two water regimes (I100 and I50, referring to meet 100% and 50% of ET requirement, respectively). Comparing the well-watered plants at I100, water stress at I50 reduced seasonal ET by 22–41%, grain yield by 30–48% and yield components by 6–41%; however, water stress only reduced WUE by 8%. Although the DT hybrids did not always provide yield benefit, the Pioneer AQUAmax® hybrid P1151AM had about 30% greater grain yield and WUE than the conventional hybrid 33D53AM. Regardless of year, water regime and hybrid, greater maize yield was related to greater biomass at maturity, harvest index, kernel weight and kernel number. Under water-limited conditions, two DT hybrids consistently had 3–6% lower seasonal ET than the two conventional hybrids. Compared with the conventional hybrids, the two DT hybrids extracted less soil water along the profile at vegetative stage. However, there were no significant differences in soil water extraction among hybrids during the reproductive stage. The results of this study demonstrated that effective use of soil water during grain filling is important for maintaining high yield under water limited conditions.

Agronomic performance of drought-tolerant maize hybrids in diverse environments of lowland tropics

ABSTRACTAssessment of maize (Zea mays L.) hybrids for adaptation to diverse environments is crucial for sustainability of maize production and productivity in sub-Saharan Africa. A total of 110 hybrids derived from 10 elite drought-tolerant maize inbreds and 11 checks were evaluated at three locations for 2 years in Nigeria to identify high-yielding and stable hybrids using different stability approaches. Mean squares were significant for genotypes (G), environments (E) and genotype x environment interaction (GEI) for grain yield and most other traits. The test environments contributed 83.7% to the total variation in grain yield, whereas G accounted for 5.0% and GEI 11.3%. The repeatability of traits ranged from 0.22 to 0.66. Grain yield of hybrids ranged from 2.1 t ha−1 for TZEI 17 × TZEI 16 to 4.1 t ha−1 for TZEI 129 × TZEI 16, with mean yield of 3.1 t ha−1. The results of additive main effect and multiplicative interaction (AMMI) analysis and rank summation index were found to be consistent, as both methods identified TZEI 129 × TZEI 16 and (TZEI 17 × TZEI 16) × TZEI 157 as high-yielding and consistent-performing across test environments. The outstanding hybrids should be further tested on-farm to facilitate the registration and commercialization in Nigeria.