Performance of maize hybrids grown in a semi-arid region under rainfed and wastewater irrigation systemsABSTRACT
Considering the high importance of maize as a subsistence crop and the need for optimal use of water resources in semi-arid regions, this study aimed to evaluate the agronomic potential, heterosis, and heterobeltiosis within different genetic categories of maize hybrids grown in a semi-arid region in Sergipe, Brazil, under rainfed and wastewater irrigation systems. Ten maize genotypes, their 45 hybrid combinations, and five commercial genotypes as controls were evaluated based on plant height, ear height, and grain yield. Positive heterosis and heterobeltiosis were found under both growing environments for hybrids H1, H13, H16, H32, H35, H5, H8, and H9. Genotypes P2, P3, and P9 were identified as potential parents for the development of new hybrid maize varieties for growing in the semi-arid region of Sergipe. Better agronomic performance was found for the wastewater irrigation system, indicating an excellent strategy for maize production under semi-arid conditions. The hybrids formed by the combination of variety × intervarietal hybrid [F1 (P1 × P2), F1 (P1 × P5)], variety × single hybrid [F1 (P2 × P6), F1 (P2 × P9), F1 (P5 × P7), and F1 (P5 × P10)], intervarietal hybrid × single hybrid [F1 (P1 × P6) and F1 (P1 × P9)], and double hybrid [F1 (P1 × P10)] indicate promising hybrid candidates for maize crops in semi-arid regions.
Key words: Zea mays L.; hybrid varieties; heterosis
RESUMO
Devido à alta importância do milho como cultura de subsistência e do melhor uso dos recursos hídricos em região semiárida, este estudo teve como objetivo determinar o potencial agronômico, a heterose e a heterobeltiose em diferentes categorias genéticas de híbridos de milho na região semiárida, sob condições de cultivo em sequeiro e irrigação com águas residuais. Foram avaliados 10 genótipos de milho, e suas 45 combinações híbridas, além de cinco genótipos como testemunhas, em regime de sequeiro e sob irrigação com água residuária. Estimou-se a altura da planta, altura da espiga e a produtividade de grãos. Observou-se heterose e heterobeltiose positivas em ambos os ambientes para os híbridos H1, H13, H16, H32, H35, H5, H8 e H9. Os genótipos P2, P3 e P9 mostraram-se como potenciais genitores para criação de novas variedades híbridas de milho no semiárido sergipano. Observou-se maiores desempenhos em regime irrigado com água de reuso, apresentando-se como uma excelente estratégia para a produção de milho em região semiárida. Os híbridos formados pela combinação de variedade × híbrido intervarietal [F1(P1 × P2), F1(P1 × P5)], variedade × híbrido simples [F1(P2 × P6), F1(P2 × P9), F1(P5 × P7) e F1(P5 × P10)], híbrido intervarietal × híbrido simples [F1(P1 × P6) e F1(P1 × P9)] e híbrido duplo [F1(P1 × P10)] sinalizam novas opções de cultivo em região semiárida.
Palavras-chave: Zea mays L.; variedades híbridas; heterose
HIGHLIGHTS:
Positive heterosis was evident in the experiments, distinguishing the genetic classes evaluated.
The parent genotypes can be used to develop new maize populations suitable for cultivation in semiarid regions.
The use of wastewater for irrigation can improve the performance of maize hybrids.
Introduction
Maize (Zea mays L.) is a prominent crop in the world economy, ranking third in terms of cultivated area worldwide (Andrade et al., 2023). In Brazil, second-crop maize production has maintained an average production of 78 million Mg over the past five years (IBGE, 2023). However, despite technological advancements in the semi-arid region of the Northeast Brazil, challenges due to high temperatures, limited rainfall, and prolonged droughts, persist (Silva et al., 2023).
Efficient maize production in semi-arid regions, especially during drought periods, is only possible through irrigation, which is limited by low water availability, leading to the use of alternative sources, such as treated domestic effluents. These wastewaters benefit plant development, mainly due to their nitrogen contents. Additionally, the use of wastewater has positively impacted maize plant height throughout the growth cycle (Costa et al., 2009). Integrating wastewater into irrigation practices has allowed farmers in these regions to optimize farming methods, increase crop yields, and mitigate the impact of prolonged droughts, conserving precious water resources and promoting sustainable agriculture.
The application of wastewater for maize crops can contribute to soil fertilization, as wastewater may contain nutrients and organic matter, making it a potentially beneficial nutrient source for soil and plant growth (Silva, 2018; Marques et al., 2022). In this context, it is imperative to recognize the potential of wastewater use in semi-arid regions such as those in Sergipe, Brazil, to address pressing issues related to water scarcity.
In Sergipe, the smallest state in the Northeastern region of Brazil, the mean maize production in the 2022 crop season was 713,156.8 Mg. Notably, Sergipe achieved a maize grain yield of 4.6 Mg ha-1, closely following Piauí (4.7 Mg ha-1) (IBGE, 2023). This can be partially attributed to the utilization of advanced technologies, such as the VTPRO4® hybrid maize biotechnology, genetically modified varieties, and hybrid genotypes well-adapted to the winter window and tolerant to droughts (Pinto et al., 2023). However, small and medium-sized farmers still face challenges related to cultivation techniques and the need for genotypes suited to the demands of semi-arid regions (Silveira et al., 2021).
Several studies have addressed water scarcity and evaluated the use of wastewater as an alternative for growing crops under low-water availability conditions, mainly in semi-arid regions (Cavalcante et al., 2021; Albalasmeh et al., 2022; Zhao et al., 2022). The development of new genotypes adapted to local conditions, while using wastewater for irrigation, has shown promise for increasing grain yield and farmers’ income in semi-arid regions.
The pursuit of increased crop yields has intensified in recent years, highlighting the importance of information about hybrid vigor, or heterosis, in agriculture. Heterosis, especially in maize hybrid production, occurs when a hybrid’s performance exceeds the mean of its parents, which is a crucial phenomenon for increasing grain yields. In this context, heterobeltiosis is a determining factor for the selection of commercial maize hybrids, as it exploits genetic differences between parents to optimize production, highlighting the hybrid’s superiority over the mid-parent value (Lorencetti et al., 2006; Ferreira et al., 2009; Doná et al., 2011).
Therefore, the objective of this study was to evaluate the agronomic potential, heterosis, and heterobeltiosis within different genetic categories of maize hybrids grown in a semi-arid region in Sergipe, Brazil, under rainfed and wastewater irrigation systems.
Material and Methods
Two experiments were conducted in the 2022 crop season at two distinct locations in Sergipe, Brazil. The region is characterized by an As, tropical climate, according to the Köppen classification. The first experiment was conducted under irrigated conditions (February 4, 2022) at an experimental area within a wastewater treatment plant in the municipality of Nossa Senhora das Dores (10° 12’ 48.44” S, 37° 11’ 34” W, and altitude of 200 m). The second experiment was conducted under rainfed system (June 16, 2022) at an experimental farm of the Brazilian Agricultural Research Corporation (Embrapa Semi-Arid) in Nossa Senhora da Glória (10° 29’ 27” S, 37° 19’ 1.68” W, and altitude of 291 m).
A pollination field was established in 2021 to facilitate the crossing of 10 maize genotypes (Table 1) using the method 2 of Griffing (1956), which is based solely on hybrid and parental data, resulting in a total of n(n+1)/2 observations and 45 hybrids. These hybrids were classified into three distinct genetic categories: intervarietal hybrids (variety × variety), double hybrids (single hybrid × single hybrid), and topcrosses (variety × single hybrid, variety × intervarietal hybrid, and intervarietal hybrid × single hybrid).
Pollination plots consisted of two rows of male plants and four rows of female plants, each with a length of 4 m, spaced 0.8 m apart, with 0.2-m spacing between plants to facilitate efficient movement between plots during the manual pollination process.
Male maize rows were sown at two different times, with a 5-day interval between sowings, to enhance synchrony between male and female flowering. Before pollination, ears were covered prior to silk emergence to prevent contact with pollen (Forsthofer et al., 2004; Cargnelutti Filho & Guadagnin, 2011). The tassels of the male rows were enclosed in paper bags, and after 24 hours, the female ears were pollinated. During the harvest process, all pollinated ears were collected separately, tagged, and then shelled. The identification tags on the parental lines were carefully tracked. Seeds corresponding to a specific cross were stored in a cold chamber for subsequent assessments.
Plants were irrigated with wastewater from the sewage treatment plant using a drip irrigation system with drip tapes and a 0.2-m spacing between plants (Table 2).
Physicochemical characteristics of the treated wastewater used for irrigation of maize plants
Supplemental irrigation was applied on days without rain to meet the plants’ water needs, based on rainfall data collected using a rain gauge (Figure 1). The rainfed experiment was conducted without the use of wastewater irrigation throughout the maize growth cycle.
Distribution of the water blade in the irrigated experiment in Nossa Senhora das Dores, Sergipe, Brazil
The soil for both experiments was conventionally tilled, following the recommendations for the use of soil amendments and fertilizers in the State of Sergipe (Sobral et al., 2007). Phosphorus and potassium fertilizers were applied at planting based on the soil chemical and fertility analysis (150 kg ha-1 of P and 0 kg ha-1 of K), consisting of 137.14 kg ha-1 of P and 68.57 kg ha-1 of K for the irrigated experimental area, and 68.57 kg ha-1 of P and 34.28 kg ha-1 of K for the rainfed experimental area. Nitrogen fertilizer was applied at 100 kg ha-1 as topdressing between V4 and V6 stages in both experiments.
The experiments were conducted in a randomized block design with 60 treatments, consisting of 45 intervarietal hybrids, ten parents, and five commercial genotypes as controls, each with two replications, forming 120 plots in each experiment (Table 1). The experimental plots consisted of two four-meter rows spaced 0.7 m apart, with 0.2-m spacing between plants, totaling a stand of 40 plants per plot and a population density of 71,428 plants ha-1.
Plant height (PH) and ear height (EH) were measured when experimental plots reached 50% male flowering. Five randomly selected plants in each plot were measured for PH from the ground level to the base of the tassel, whereas EH was measured from the ground level to point of insertion the prominent ear on the stalk. Grain yield (GY) was assessed after harvesting, drying, and shelling ears, and determining moisture content. GY was estimated using the Zuber method, with moisture content adjusted to 13% (Zuber, 1942; Schmildt et al., 2001).
Multivariate analysis of variance (MANOVA) using a randomized block design was employed to assess differences among genetic materials. Heterosis was estimated for all genotypes in hybrid combinations to determine the superiority of hybrids over the mid-parent value, and the complementarity of crosses in generating new genetic constitutions with crop potential. It was expressed as a percentage using Eq. 1.
where:
H - is the estimated heterosis value from the cross between two genotypes;
F1 - is the mean of the hybrid; and,
MPV - is the mean value (mid-parent value) of the two parents involved in the cross.
Heterobeltiosis determines the superiority of the hybrid over the better parent; it was estimated as a percentage using Eq. 2:
where:
HBP - is the heterobeltiosis value representing the superiority of a hybrid over the better parent;
F1 - is the mean of the hybrid; and,
MBP - is the mean of the better parent between the two parents involved in the cross.
The equations for heterosis and heterobeltiosis are adaptations based on the expressions described by Matzinger et al. (1962).
The Pillai trace test was used in MANOVA, a powerful statistical tool used for analyzing differences among groups when there are multiple dependent variables. The main objective is to determine significant differences among groups concerning a set of dependent variables simultaneously (Tabachnick et al., 2013). All statistical analyses were performed using R software (R Core Team, 2018) via RStudio.
Results and Discussion
Multivariate analysis of variance (MANOVA) for plant height, ear height, and grain yield showed variability among the evaluated maize genotypes (overall MANOVA) (Table 3). This variability may be attributed to differences between parents and controls (parental MANOVA), as no differences were found among intervarietal hybrids (hybrid MANOVA). This result is crucial for selecting the most promising parental genotypes for future breeding programs (Mukri et al., 2022).
Differences were found for both growing environments, allowing for the assessment of successful selection of productive parents with the potential to generate new populations under the evaluated conditions. Moreover, the importance of wastewater management in conserving water resources and promoting sustainable agricultural practices should be considered (Poustie et al., 2020; Kesari et al., 2021).
The means found for the genotypes evaluated in this study, as well as the overall mean for both irrigated and rainfed systems (Table 4) provide a general estimate of the difference between the irrigated and rainfed systems. The irrigated experiment using treated wastewater resulted in higher mean grain yields than the experiment under rainfed system, with 5632.13 kg ha-1 for genotype F1 (P5 × P7) and 5099.44 kg ha-1 for genotype (P3), respectively. These yields significantly exceeded the mean grain yield of 4847 kg ha-1 for Sergipe (2021/2022 crop season), where the experiments were conducted (CONAB, 2023).
These results can be attributed to the water availability provided by irrigation, which allowed for better plant growth and development, as evidenced by an average reduction of over 20 cm under rainfed system. These findings denote the importance of the nutrients present in wastewater used for irrigation, which not only improves maize grain yield but also enhances the adaptability of genotypes to irrigation practices, consequently contributing to sustainable water resource management and efficient agricultural production (Cakmakci & Sahin, 2021; Yerli et al., 2023).
Although shorter plants have an advantage in reaching physiological maturity more rapidly than taller plants (Cruz, 2005), mitigating the adverse effects of prolonged droughts, this characteristic results in lower dry matter accumulation and, consequently, reduced grain yield. In this context, the search for dual-purpose maize genotypes is a priority for many growers in semi-arid regions, particularly those in Sergipe due to the strong influence of livestock farming in these areas, which demands higher silage production (Paula, 2021).
The means for plant and ear heights and grain yield provide a comprehensive overview of the parents, hybrids, and controls (Table 4). The parents tended to outperform the hybrids in grain yield in both growing environments. Furthermore, the control genotypes resulted in higher grain yields than the parents and their hybrids under both growing environments. The inclusion of high-performing commercial hybrids as controls is crucial for performance comparison. Despite including non-commercial parents in their composition, the analysis showed that some parents (P7, P8, and P9) outperformed some control genotypes, emphasizing the importance of identifying the most promising parents for selection purposes. This provides valuable information for the development of high-performing maize hybrids (Yerli et al., 2023).
The selection of maize genotypes in Sergipe, as well as in other parts of the Brazilian Northeast region, considers the region’s specific climate and soil conditions. Frequently used genotypes, such as KWS 9960 VIP3, KWS 9555 VIP3, and KWS 9822 VIP3, are hybrids adapted to semi-arid environments, exhibiting good drought tolerance and ensuring high grain yields, even when grown under irrigation (KWS, 2021). Regarding plant height, the parental genotypes showed higher means than the controls and hybrids in both environments, highlighting the potential benefits of using treated wastewater for irrigation.
The availability of wastewater for irrigation can contribute to improvements in plant growth and development, resulting in increased plant height and grain yield (Yerli et al., 2023). Moreover, wastewater can serve as a sustainable solution to mitigate the challenges posed by water scarcity, ensuring a reliable water supply for crops in regions prone to drought conditions (Ungureanu et al., 2020). Therefore, the integration of wastewater management into agricultural practices can promote resilient agricultural systems and contribute to their sustainability in water-limited regions (Cakmakci & Sahin, 2021).
The results indicate that hybrids exhibited reduced ear height under rainfed system, with lower means compared to the controls, which performed better under irrigation. This highlights the effect of genetic diversity, as commercial hybrids were more stable in ear height, a crucial trait considered in their selection and market release (Ortez et al., 2023).
These findings indicate the significance of genetic diversity for the adaptation to diverse growing conditions and the development of high-performing genotypes. Additionally, irrigation with treated wastewater remains essential for enhancing the adaptability and resilience of maize hybrids, particularly when grown in water-limited environments.
Considering the hybrids evaluated in the irrigation experiment, 17 exhibited positive heterosis for grain yield, exceeding the mean of their parents (Table 5). These promising hybrids were: H1, H12, H13, H14, H15, H16, H2, H26, H32, H33, H35, H37, H4, H44, H5, H8, and H9, resulting from the crosses F1 (P1 × P2), F1 (P2 × P10), F1 (P2 × P5), F1 (P2 × P6), F1 (P2 × P7), F1 (P2 × P8), F1 (P2 × P9), F1 (P1 × P3), F1 (P4 × P6), F1 (P5 × P7), F1 (P5 × P8), F1 (P5 × P10), F1 (P6 × P8), F1 (P1 × P6), F1 (P1 × P9), and F1 (P1 × P10). The genotype F1 (P5 × P7) stood out for showing a higher mean grain yield (5632.13 kg ha-1) than that of Sergipe in the 2021/2022 crop season (4847 kg ha-1) (CONAB, 2023).
Values of heterosis and heterobeltiosis of intervarietal maize hybrids grown under wastewater irrigation and rainfed systems
Seven of these promising hybrids exhibited positive heterobeltiosis (H1, H26, H32, H35, H37, H44, and H9), standing out as successful crosses in the formation of new hybrids for growth in semi-arid regions. These results highlight the excellent complementarity of the parents (P2, P6, P7, P8, and P10) in these crosses, indicating an effective strategy for obtaining hybrids with high yield potential under semi-arid conditions.
Despite the decreased grain yields under rainfed due to irregular rainfall (Santos et al., 2023), twelve hybrids exhibited positive heterosis, corresponding to the following crosses: F1 (P1 × P2), F1 (P2 × P6), F1 (P2 × P9), F1 (P2 × P10), F1 (P5 × P7), F1 (P5 × P9), F1 (P5 × P10), F1 (P1 × P5), F1 (P8 × P9), F1 (P1 × P6), F1 (P1 × P9), and F1 (P1 × P10). Moreover, the crosses F1 (P1 × P2), F1 (P2 × P6), F1 (P2 × P10), F1 (P × P9), and F1 (P8 × P9) in heterobeltiosis due to parents P2, P6, P10, P9, and P8, which had excellent performance.
These results indicate the ability of the selected hybrids to overcome challenges posed by the rainfed system, highlighting their potential for developing genotypes adapted to water deficit conditions. Such information is significantly important for research and the development of genetic improvement strategies focused on obtaining high-yielding maize hybrids for growing in water-limited regions, as shown in the experiment conducted under rainfed system.
Some of the hybrids that stood out in the heterosis analysis coincide in both experiments (H1, H13, H16, H32, H35, H4, H5, H8, and H9), especially those with P2, P9, and P10 as parents. Genotype P10 was the most prominent as a superior parent in six hybrids that exhibited positive heterosis, however, P2 and P9 also showed significant responsiveness in the segregation of desirable genes.
Some hybrids with genotype P2 (variety) as a parent did not exhibit positive heterobeltiosis; however, their results contribute valuable information for the development of new breeding program strategies (Begna, 2021; Ene et al., 2023). This result may be attributed to their lower grain yields compared to the commercial hybrids evaluated in the present study. Moreover, this population tends to demonstrate a predominant tendency towards taller plant characteristics.
Thus, carefully evaluating and considering the parents in hybrid formation is essential, as each genotype contributes uniquely to expressing desirable traits. Additionally, the genetic nuances of parents P2, P9, and P10 stood out, indicating their potential for obtaining hybrids with superior performance and adaptability to specific growing conditions. These results provide valuable insights for the development of efficient genetic improvement strategies aimed at producing high-yielding maize hybrids with nutritional quality in regions with similar characteristics to the study area.
The hybrids that exhibited positive heterosis in both experiments (H1, H13, H16, H32, H35, H4, H5, H8, and H9) revealed the potential of parent P1. However, the reliability of this result is limited due to the low grain yield of P1, which may have affected the heterosis calculations. However, parents P2, P5, P9, and P10 stood out as superior and responsive, contributing to the increased grain yield found for progeny of P1. These results indicate the potential of these parents to be used as recurrent parents in the incorporation of promising genes for the development of more productive maize genotypes. The information provided is valuable for breeding programs focused on obtaining maize genotypes with higher grain yield and agronomic performance for semi-arid regions.
In summary, the significant advantage of topcross hybrids compared to those necessitating more sophisticated breeding technologies (which can elevate seed acquisition costs) is evident. Specific genetic combinations are crucial for the generation of high-performance hybrids, highlighting the beneficial interactions between parent plants. The positive heterosis found in the present study indicates that the synergistic effects of genetic dominance are resulting in a more favorable phenotypic expression compared to the parental lines. Specifically, in the growing environment supplemented with treated wastewater irrigation, the hybrids demonstrated significantly superior performance than those grown under rainfed system. This further highlights the significant contribution of wastewater irrigation to increases in grain yield and adaptability of these maize hybrids, particularly in water-scarce regions such as the semi-arid region of Sergipe.
Conclusions
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Topcross maize hybrids formed by the following combinations stood out among the evaluated genetic categories for exhibiting positive heterosis in both experiments (rainfed and wastewater irrigation systems): variety × intervarietal hybrid [F1 (P1 × P2), F1 (P1 × P5)], variety × single hybrid [F1 (P2 × P6), F1 (P2 × P9), F1 (P5 × P7), and F1 (P5 × P10)], intervarietal hybrid × single hybrid [F1 (P1 × P6) and F1 (P1 × P9)], and F1 double hybrid [F1 (P1 × P10)].
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The heterosis analysis showed that parents P2, P3, and P9 have the potential to synthesize new maize populations suitable for growing in a semi-arid climate.
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Parents P2, P5, P9, and P10 demonstrated superior performance in their progeny in both experiments, even when crossed with the least productive parent (P1).
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The use of wastewater for irrigation can significantly improve the performance of identified hybrid combinations, mainly in water-scarce environments. This approach is promising for sustainable agriculture in semi-arid regions.
Acknowledgments
The authors would like to thank the Federal University of Sergipe (UFS), the Brazilian Agricultural Research Corporation (EMBRAPA), the Semi-Arid Plant Breeding Study Group (GEMS), the Brazilian National Semi-Arid Institute (INSA), and the Brazilian Ministry of Regional Integration and Development (MIDR).
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No supplementary materials are available.
VE - Emergence; V4 - Four fully expanded leaves; V5 - Five fully expanded leaves; V10 - Ten fully expanded leaves; VT - Vegetative stage; R1 - Silking; R2 - Blister; R5 - Dent formation on kernel
