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Article

Effect of Ethephon on Sensitivity Difference of Lodging Resistance in Different Maize Inbred Lines

by
Siyao Liu
1,2,
Feng Guo
1,2,
Mengzhu Chai
1,
Shiwei Gu
1,
Dacheng Wang
1,
Zihao Wang
1,
Yidan Chen
1,
Tenglong Xie
1,
Deguang Yang
1 and
Qian Zhang
1,2,*
1
College of Agriculture, Northeast Agricultural University, Harbin 150030, China
2
National Key Laboratory of Smart Farm Technologies and Systems, Harbin 150030, China
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(5), 1248; https://doi.org/10.3390/agronomy15051248
Submission received: 16 April 2025 / Revised: 16 May 2025 / Accepted: 18 May 2025 / Published: 21 May 2025
(This article belongs to the Section Farming Sustainability)
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Versions Notes

Abstract

:
Lodging imposes substantial constraints on maize yield potential and agronomic efficiency, critically undermining productivity and resource optimization in cultivation systems. This study aimed to elucidate the mechanism whereby ethephon enhances lodging resistance and analyze the sensitivity differences to ethephon among distinct maize inbred lines. Through exogenous application of ethephon (200 and 400 mg/L, S1 and S2 treatments) to four classic maize inbred lines (Zheng58, Chang7-2, PH6WC, and PH4CV), we systematically evaluated its effects on plant morphology, stalk biomechanical properties, and lignin biosynthesis. Results demonstrated that ethephon optimized plant morphology through reductions in plant height, ear height, leaf area, leaf angle, and internode length. Significant augmentations in stalk bending resistance (a maximum increase of 52.61% in PH4CV) and puncture strength (most pronounced in Zheng58) were mechanistically associated with increased lignin content and enhanced activity of key biosynthetic enzymes [cinnamyl alcohol dehydrogenase (CAD), phenylalanine ammonia-lyase (PAL), and 4-coumarate-CoA ligase (4CL)], with PH6WC exhibiting the most robust enzymatic response. These findings underscored genotype-specific regulatory effects of ethephon, bridging the knowledge gap regarding its molecular–physiological interplay with maize genotypes. The study provides critical insights for precision breeding and optimization strategies employing plant growth regulators to improve maize lodging resistance.

1. Introduction

Maize (Zea mays L.) is a globally critical crop, serving as a staple food source, livestock feedstock, industrial raw material, and energy resource. According to United Nations projections, the world population will exceed 9 billion by 2050 [1], necessitating a doubling of maize production. However, during the grain-filling period, maize is susceptible to lodging due to intrinsic plant characteristics and environmental stressors, and every 1% increase in the rate of maize lodging reduces yields by about 108 kg/hm2 [2], with severe cases leading to total crop loss, which is detrimental to the stability and security of the global food supply. Lodging disrupts the vascular system of stalks, impairing upward transport of water and nutrients from roots. Concurrently, reduced leaf photosynthesis limits the translocation of photosynthetic products to ears, resulting in a bald tips length increase, decreased thousand-kernel weight, and reduced yield. Furthermore, lodging causes maize kernel protein and starch content to reduce, which affects its nutritional value and processing quality. It also leads to moldy kernels, compromising quality appearance. Lodged crops create micro-environments with poor air circulation, promoting pathogen proliferation and pest infestation. Mechanized harvesting becomes inefficient due to entangled plants, escalating production cost and economic losses [3]. Therefore, lodging has garnered significant global research attention, aiming to develop effective mitigation strategies.
Maize lodging is categorized into two types: root lodging, where roots lose grip on the soil, and stem lodging, characterized by stalk breakage due to insufficient stalk stiffness [4]. Stem lodging alone accounts for 5–20% of annual maize yield losses. Stalk strength, a critical agronomic trait influencing yield potential, has been extensively studied. Zhao et al. [5] demonstrated that plant height and ear height negatively correlate with lodging resistance, with shorter plants exhibiting enhanced stability. Ma et al. [6] concluded significant positive correlations between stem lodging incidence and basal internode diameter, whereas negative correlations were observed with the basal internode length and stem thickness coefficient. Robertson et al. [7] found that stalk rind penetration strength was significantly negatively correlated with the rate of lodging. Ghorbani et al. [8] discovered an inverse relationship between the lodging index and breaking force. Stalk strength is controlled by cell wall composition, particularly lignin and cellulose content [9]. As one of the major chemical constituents of the secondary cell wall, lignin enhances mechanical rigidity, improving stem bending resistance [10,11]. There are three key enzymes in the lignin synthesis pathway: cinnamyl alcohol dehydrogenase (CAD), phenylalanine ammonia-lyase (PAL), and 4-coumarate-CoA ligase (4CL). Elevated activities of these enzymes promote lignin accumulation [12], with lodging-resistant varieties exhibiting significantly higher lignin enzyme activity compared to lodging-prone genotypes [13].
Plant growth regulators (PGRs) are synthetic compounds that mimic natural phytohormones to optimize plant morphology, enhance stress resistance, and improve crop yield formation. The efficacy of PGRs has been validated in agricultural practices. Ethephon, an ethylene-releasing agent, induces ethylene biosynthesis and signaling, leading to suppressed internode elongation. This results in reduced plant height, ear height, and center-of-gravity height, increased dry weight per unit of internode, and increased stem strength [14,15]. Ethephon application also significantly influences growth characteristics and yield in maize. Scientific chemical regulation can improve lodging resistance in densely planted summer maize, facilitating a high and stable yield [16]. Ethephon and its compound-based PGR are widely used in densely planted maize to mitigate lodging risk and increase yield [17]. Spraying of EDAH (a formulation containing 27% ethephon and 3% DA-6) can effectively improve lodging resistance, as it optimizes canopy architecture and enhances yield potential in maize [18,19].
Previous studies have predominantly focused on ethephon’s generic effects on lodging resistance in maize hybrids, yet a systematic investigation into genetic disparities and molecular regulatory mechanisms within classical inbred lines is lacking. This study innovatively demonstrates sensitivity differences to ethephon across four representative maize inbred lines (Zheng58, Chang7-2, PH6WC, and PH4CV) through comparative analysis. The objectives of this study were twofold: (1) to elucidate the effects of ethephon on maize plant architecture, stem lodging resistance, and enzyme activities associated with lignin biosynthesis; (2) to analyze sensitivity differentials to ethephon among disparate maize inbred lines. These findings establish a theoretical foundation and technical framework for advancing lodging-resistant cultivar development, precision agronomic practices, and scientifically informed application of plant growth regulators.

2. Materials and Methods

2.1. Plant Materials and Reagents

Four inbred lines, including Zheng58, Chang7-2, PH6WC and PH4CV, widely utilized in Chinese maize breeding programs, were selected for this study; these inbred lines serve as parental components of the commercial hybrids Zhengdan958 and Xianyu335, respectively. All materials were obtained from the Maize Research Institute, Heilongjiang Academy of Agricultural Sciences, China.
Reagents: Ethephon, supplied by the Crop Chemical Regulation Research Center of China Agricultural University, and other analytical-grade reagents were procured from commercial suppliers.

2.2. Experimental Design

This experiment was conducted from April to October 2016 at the Xiangyang Experimental Base of Northeast Agricultural University, located in Harbin City, Heilongjiang Province (45°45′31.27″ N, 126°53′56.37″ E, 145 m above sea level). The site experiences a temperate continental climate characterized by concurrent precipitation and thermal conditions during the growing season, with summer rainfall abundance and the annual rainfall of the annual precipitation ranging from 500 to 550 mm. The region has a frost-free period of approximately 140 days, with the mean annual temperature latitudinal gradient from north to south between −5 °C and 4 °C. The area receives 2460–2786 h of annual sunshine duration, has an active cumulative temperature of ≥10 °C exceeding 2700 °C, and sufficient solar radiation, with an average annual wind speed of 2–5 m/s. Figure 1 shows the 2016 meteorological data for Xiangyang Experimental Base in Harbin.
The experimental soil, classified as chernozem, exhibited the following properties: available nitrogen was 154.32 mg/kg, available phosphorus 69.50 mg/kg, available potassium 144.56 mg/kg, organic matter content 24.60 mg/kg, and pH 6.75.
In this experiment, ethephon was foliar-applied at the maize seventh-leaf stage (V7 growth stage) at concentrations of 200 mg/L (S1) and 400 mg/L (S2), while water served as the control (CK). The solution was uniformly sprayed at a rate of 450 L·hm−2 using a calibrated handheld sprayer. A randomized complete block design (RCBD) with three replicates was implemented, totaling 36 experimental plots (4 inbred lines × 3 treatments × 3 replicates). Each plot had an area of 32.5 m2 and consisted of 10 rows, each 5 m in length with 0.65 m row spacing. Sowing occurred on 26 April 2016, at the density of 60,000 plants·ha−1, following the application of basal fertilizer during plowing. Field management practices, including irrigation, weed control, and pest monitoring, adhered to standard agronomic protocols for maize production in the region.

2.3. Measurement Items and Methods

2.3.1. Maize Morphological Indicators

At the silking stage (R1 growth stage), five representative plants per plot were selected for morphological measurements:
Plant height: Distance from soil surface to the apex of the tassel. The unit is cm.
Ear height: Distance from soil surface to the node bearing the uppermost functional ear (defined as an ear with ≥10 fully developed kernels at maturity). The unit is cm.
Center of gravity height: Measured using the pivot balance method, representing the vertical distance from the stem base to the equilibrium point. The unit is cm.
Leaf area per plant: Calculated as = ∑ (leaf length × maximum leaf width × correction factor), where fully expanded leaves used a factor of 0.75 and partially expanded leaves 0.5. The unit is cm2.
Leaf angle: Angle between the leaf midrib and stem axis, measured with a protractor. The unit is °.

2.3.2. Stem Morphological Indicators

Internode length: Distance between two adjacent nodes (excluding leaf sheaths). The unit is cm.
Internode diameter: Mid-internode thickness measured with digital calipers The unit is mm.

2.3.3. Measurement of Stem Strength

Rind penetration strength: At 5 days post-ethephon application, leaf sheaths were removed from the 2nd–5th basal internodes. Five stems per plot were sampled and analyzed using a ZQ-30A stalk strength tester equipped with a 0.01 cm2 probe. The probe was vertically inserted at a constant speed into the upper, middle, and lower regions of each internode. Maximum penetration force was recorded, with three replicates per internode. The unit is N. At 5 days post-ethephon application, the leaf sheath was removed at the fixed growth stage of 2–5 internodes, 5 plants from each plot were taken, and they were then brought back to the laboratory for measurement. The ZQ-30A stem strength tester was used to measure: a 0.01 cm2 measuring head was installed and was slowly inserted vertically in the direction of the stem at a constant speed in the upper, middle, and lower parts of each internode of the stem. The maximum value of penetration through the stem epidermis was read, and this was repeated 3 times to take the average value. The unit is N.
Breaking resistance strength: At 5 days post-ethephon application, leaf sheaths were removed from the 2nd–5th basal internodes. Internodes were horizontally placed on two supports (5 cm apart) of the tester. Force was applied at the midpoint until fracture; peak force indicated breaking resistance strength. The unit is N.

2.3.4. Measurement of Lignin Content and Related Enzyme Activities in Stalks

Lignin content was determined by the method of Bhaskara et al. [20], with three replications and samples required to be dried at high temperature after killing. PAL activity was determined by the method of Kovácik et al. [21]. CAD activity was determined by the method of Knobloch et al. [22]. 4CL activity was determined by the method of Morrison et al. [23].

2.3.5. Measurement of Lodging Resistance Index

Lodging Resistance Index (LRI) = 3rd internode resistance/height of center of gravity of the stem.

2.4. Data Analysis

The experimental data were analyzed using IBM SPSS Statistics version 27.00 data processing system for analysis of variance (ANOVA) and correlation analysis using Least Significant Difference method (LSD method), with the level of significance of difference defined as 0.05. Graphing was performed using Origin2021 software.

3. Results

3.1. Effect of Ethephon on Maize Plant Morphology

As shown in Figure 2, plant height, ear height, center of gravity height, and ear position coefficient of the four maize inbred lines decreased progressively with increasing ethephon concentrations. Compared to the control (CK), ethephon treatment significantly reduced plant heights by 16.75% in Zheng58, 7.17% in Chang7-2, and 12.29% in PH6WC (p < 0.05). Similarly, the center of gravity height decreased by 11.92% in Zheng58, 20.74% in PH6WC, and 12.88% in PH4CV (p < 0.05). Ethephon significantly reduced ear height and ear position coefficients across all four inbred lines (p < 0.05). Under ethephon treatment, specific reductions in the ear position coefficient were observed: Zheng58 (12.87%), Chang7-2 (9.08%), PH6WC (8.49%), and PH4CV (7.07%). Notably, Zheng58 showed the most sensitive response to ethephon on plant morphology. Compared to S1, the S2 treatment significantly reduced plant height, ear height, center of gravity height, and the ear position coefficient in Zheng58 and PH6WC (p < 0.05). Between S1 and S2 treatments, Chang7-2 and PH4CV showed no significant differences in center of gravity height, but the ear position coefficient was significantly altered (p < 0.05).
In Figure 3 and Figure 4, differential effects of ethephon on leaf area and leaf angle across different node positions are shown, with the strongest impact on ear leaves. Ethephon treatment significantly reduced ear-leaf area by 31.18%, 19.92%, 24.88%, and 13.84% compared to CK in Zheng58, Chang7-2, PH6WC, and PH4CV. Corresponding reductions in leaf angle were 34.98% (Zheng58), 21.40% (Chang7-2), 36.74% (PH6WC), and 16.50% (PH4CV). Leaf area and angle above the ear also declined progressively with higher ethephon concentrations. Zheng58 and PH6WC showed greater sensitivity to ethephon than Chang7-2 and PH4CV.

3.2. Effects of Ethephon on Maize Stalk Morphology and Biomechanical Properties

3.2.1. Internode Morphology

As shown in Figure 5, the four maize inbred lines exhibited differential responses in stem internode length and internode diameter to ethephon application.
In Figure 5A, the stem internode lengths of the 2nd to 5th in Zheng58 and PH6WC were significantly reduced (p < 0.05) after ethephon treatment, while no significant differences were observed in Chang7-2 and PH4CV. Genotypic sensitivity to ethephon varied, with internode shortening intensity decreasing in the following order: Zheng58 > PH6WC > Chang7-2 > PH4CV. Under the S1 treatment, the 3rd internode of PH6WC and the 4th internode of Zheng58 were the most responsive, with lengths reduced by 17.63% and 20.18%, respectively, versus CK. However, under the S2 treatment, the 4th internode of PH6WC and the 3rd internode of Zheng58 showed the highest sensitivity, with reductions of 34.87% and 48.23%, compared to CK. Compared to S1, the S2 treatment induced significant shortening of the most responsive internodes in Zheng58, PH6WC, Chang7-2, and PH4CV by 38.89%, 25.65%, 4.13%, and 2.89% (p < 0.05).
According to Figure 5B, under ethephon application, PH6WC and Zheng58 exhibited maximal sensitivity at the 4th internode, with internode diameters increasing by 34.37% and 16.42%. In Chang7-2, internode 5 was most responsive under both S1 and S2, with diameter increases of 13.84% (S1) and 21.02% (S2) (p < 0.05). For PH4CV, internode 3 under S1 and internode 4 under S2 were most sensitive, showing increases of 10.69% and 22.33%, respectively (p < 0.05).

3.2.2. Physical Strength of Internodes

As illustrated in Figure 6, ethephon significantly enhanced the stalk rind penetration strength and breaking strength of internodes in different maize inbred lines, though the magnitude of these effects varied by inbred lines and internode position (p < 0.05).

3.3. The Effect of Ethephon on Lignin Content and Related Enzyme Activity in Maize Internodes

Based on the morphological variations (internode length, stem diameter) and mechanical variations (rind penetration strength) observed in the 3rd–5th internodes of stalks in inbred lines (Figure 5 and Figure 6), this study investigated ethephon-mediated regulation of lignin content and its three metabolic enzymes.
As shown in Figure 7A–C, ethephon differentially activated 4CL, CAD, and PAL activities, altering lignin precursor synthesis pathways across inbred lines. Genotype-specific spatial responses were evident: the 4CL activity of PH6WC and Zheng58 exhibited maximal sensitivity to ethephon in the 4th internode (59.67% and 60.36% increases vs. CK), while Chang7-2 peaked at the 5th internode (59.55% increases vs. CK). PH4CV showed treatment-dependent 4CL activation, with S1 and S2 elevating activity by 32.48% (4th) and 50.00% (5th), respectively. CAD activity was universally upregulated, with PH4CV, PH6WC, and Chang7-2 showing highest induction at the 4th internode (46.67–70.29% increases), contrasting Zheng58’s 5th internode sensitivity (24.57% increases vs. CK). Notably, PAL—the phenylpropanoid pathway rate-limiting enzyme—displayed consistent activation patterns, with the 4th internode achieving maximum enhancement (103.85–113.43% increases across inbred lines), implicating it as the ethylene signaling hub for lignin biosynthesis. These findings demonstrate ethephon’s spatiotemporal modulation of lignification enzymes, potentially directing internode-specific lignification trajectories.
As shown in Figure 7D, ethephon application significantly increased lignin content in maize stalks. PH4CV and Zheng58 displayed the most pronounced effect at the 5th internode, with lignin content increasing by 45.16% (PH4CV) and 20.78% (Zheng58) compared to CK. PH6WC exhibited significant differences across the 3rd to 5th internodes, with the 5th internode showing the largest increase (41.55%). In Chang7-2, the lignin content of 5th internode increased by 18.03% under S1 treatment, while that of 4th internode increased by 48.33% under S2 treatment.

3.4. The Effect of Ethephon on Lodging Resistance Index and Yield Components of Maize

According to Table 1, after being treated with ethephon, the LRI of Zheng58, Chang7-2, PH6WC, and PH4CV were significantly increased by 29.38%, 43.26%, 49.73%, and 58.14%, respectively, compared to CK. Among the 4 inbred lines, PH4CV exhibited the most significant increase in LRI, suggesting that it was the most sensitive to ethephon. Treatment with ethephon led to a significant reduction in the yield of the four maize inbred lines (p < 0.05). The crop yields of Zheng58, Chang7-2, PH6WC, and PH4CV showed a marked decline of 2.32%, 1.23%, 1.78%, and 1.67%, respectively, when the ethephon treatment was compared to CK. Ethephon has a significant impact on the number of grains per ear in maize yield components, but it has no significant effect on the thousand-grain weight.

3.5. Correlation Analysis of Various Agronomic Traits of Plants with Lodging Resistance Index and Yield

According to Table 2, the lodging resistance index exhibited a highly significant negative correlation (p < 0.01) with maize ear height and leaf angle, and it showed significant negative correlations (p < 0.05) with plant height, center of gravity height, and leaf area. The results showed that ethephon improved the lodging resistance index of maize on the one hand by reducing stem length and increasing lignin content and its related enzyme activity, and on the other hand by lowering ear height and leaf angle. The yield of maize is highly significantly negatively correlated (p < 0.01) with leaf angle and leaf area, and significantly negatively associated (p < 0.05) with ear height. The results indicate that foliar-applied ethephon can lead to a decrease in yield by affecting leaf area, leaf angle, and ultimately the number of grains per ear.

4. Discussion

4.1. Key Characteristics of Lodging Resistance in Maize

Maize lodging, a complex phenomenon caused by the plant transitioning from upright to inverted under a combination of factors including external and internal, is influenced by multiple morphological and physiological traits. As a tall-stalked crop, plant height, ear height, and center of gravity height are critical morphological indicators linked to lodging risk. Studies [5,24] indicate that higher ear position and center of gravity height increase lodging susceptibility. Niu et al. [25] demonstrated that reducing plant height lowers the center of gravity and enhances lodging resistance. Plant height and ear height exhibit a significant positive correlation with lodging rate. Han et al. [26] proposed the ear position coefficient as a comprehensive metric for lodging resistance evaluation: lower values correlate with stronger resistance. In this study, Zheng58 and Chang7-2 exhibited lower plant morphological heights compared to PH6WC and PH4CV. Among the four maize inbred lines, Chang7-2 had the lowest plant height, whereas PH6WC had the highest plant height and center of gravity height; PH4CV displayed the highest ear height, while Zheng58 had the lowest. In commercial hybrids, the F1 generation Zhengdan958 has a lower plant height than Xianyu335.
Basal internode morphology strongly influences lodging resistance. Plants with elongated basal internodes exhibit higher ear position and center of gravity, elevating lodging risk; conversely, shorter and sturdier basal internodes enhance lodging resistance. Fuli et al. [27] proposed that the lodging resistance can be estimated via ear position coefficient and stem length-to-diameter ratio, with a lower coefficient and smaller ratio indicating stronger resistance. Compact maize varieties, characterized by reduced ear height, should maintain ear placement at 33% of total plant height. These genotypes are ideally suited to dense planting configurations while demonstrating robust lodging resistance. In contrast, flat-variety phenotypes exhibit elevated ear positioning, necessitating management at 50% of plant height to optimize cultivation outcomes. Our results showed the longest average internode length in PH6WC, followed by Zheng58, PH4CV, and Chang7-2. For stem diameter, Zheng58 ranked highest, followed by Chang7-2, PH4CV, and PH6WC. The proportions of the ear height to the total plant height of the four maize inbred lines in this study are Zheng58 (32–43%), Chang7-2 (33–44%), PH6WC (32–45%), and PH4CV (31–43%).
Lodging disrupts leaf distribution and canopy structure, reducing photosynthetic efficiency. The leaves at and above the ear position, the primary source organs of grain filling, directly influence light capture through their area and angle. Leaf area and leaf angle are key determinants of canopy light distribution and radiation use efficiency. With constant leaf area, erect leaves enhance photosynthetically active radiation penetration to the middle and lower canopy. A study on maize hybrids since the 1970s report reduced leaf angles and gradual lodging resistance improvements [28]. An ideal plant type features larger leaf spacing and smaller leaf angle above the ear, improving light penetration to the middle and lower canopy, thereby promoting growth and enhancing lodging resistance while reducing grain abortion [29]. In this study, for ear position and leaf area, Zheng58 was ranked the highest, followed by PH6WC, PH4CV, and Chang7-2; leaf angle at ear position followed PH4CV > PH6WC > Zheng58 > Chang7-2.
Stem mechanical properties are critical for lodging resistance [25,30]. Stem mechanical strength serves as a direct and quantifiable index for lodging resistance evaluation, and is widely applied in breeding programs [31]. Jampatong et al. [32] reported a significant negative correlation between stem puncture strength and field lodging rate. Chesang-Chumo et al. [33] established a close relationship between puncture strength and stem lodging, with a linear association to lodging rate. Gou et al. [34] demonstrated that bending force reliably reflects lodging resistance strength, providing a robust metric for stem evaluation. Our data indicate the highest stalk rind penetration strength in Zheng58 and the highest breaking resistance in PH4CV at the second internode, and the highest physical strength in PH6WC at the third internode; at the fourth and fifth internodes, Zheng58 had the highest puncture strength, while PH6WC showed superior bending resistance.
Lignin, a complex phenolic polymer and key structural carbohydrate in stems reinforces cell wall rigidity and stem mechanical strength. Wang et al. [35] identified a significant positive correlation between lignin content and basal internode mechanical strength, with higher lignin content enhancing lodging resistance. Wu et al. [36] observed reduced PAL and CAD activities in rice stalks, leading to decreased lignin content. Elevating lignin, cellulose, and hemicellulose content improves stalk strength [37]. In this study, lignin content in the third and fifth internodes ranked Zheng58 > PH6WC > Chang7-2 > PH4CV; in the fourth internode, the order was PH6WC > Zheng58 > Chang7-2 > PH4CV. Among the three internodes, 4CL activity was highest in PH4CV, while PAL and CAD activities were elevated in Zheng58 and PH6WC.

4.2. Effects of Ethephon on Lodging Traits of Maize

Physical and chemical regulation can not only promote the growth and development of plants, improving the morphological characteristics, but can also increase the accumulation of dry matter, enhance lodging resistance, and improve the yield and quality of maize. Li et al. [38] found that the plant height of Zhengdan958 and Dongnong254 treated with ethephon decreased. Molla et al. [39] found that the plant height of maize decreased significantly after ethephon application. Zhang et al. [14] found that ethephon regulated the growth of maize by regulating the expression of genes resulting in the reduction in plant height and ear height. The results of this experiment are consistent with previous studies: ethephon treatment reduced plant height, ear height, center of gravity height, and the ear position coefficient with increasing ethephon concentrations. Zheng58 and PH6WC exhibited this more significantly than Chang7-2 and PH4CV.
Plant morphology can be modified by plant growth regulators (PGRs), which effectively shape the canopy structure, optimize the environment of the maize population, enhance ventilation and light transmission, and improve photosynthetically active radiation (PAR) utilization. Geng et al. [16] found that ethephon reduced the leaf area index (LAI) and increased canopy light transmittance while elevating SPAD values, thereby improving the photosynthetic capacity of the leaves and favoring the accumulation of stalk material and strength. Gong et al. [3] reported that EDAH treatment significantly reduced corn leaf area. Jade Gold (containing ethephon as the primary component) was able to effectively reduce the leaf area of the ear and the upper part of the ear by 13% and 27%, respectively, facilitating the penetration of light into the ear and enhancing the PAR utilization. Huang [40] proposed that chemical control agents applied treated at high density could reduce leaf angle and leaf area, shorten basal internode length, increase upper internodes above panicles length, and improve mid-to-upper canopy structure, enhancing ventilation and light transmission at the base. Our results showed that ethephon application significantly reduced maize leaf area and leaf angle, with the most pronounced effects on the ear leaf. This may occur as ethephon disrupts endogenous hormones via ethylene release, inhibiting cell elongation and leaf expansion, thereby optimizing light interception at the ear layer. Additionally, ethephon may induce wax synthesis-related regulating genes through ethylene response factors, enhancing leaf surface wax hydrophobicity and altering leaf angle via cell wall ductility. Ahmad et al. [41] found that the exogenous application of uniconazole significantly improved the lignin content, activities of lignin-related enzymes, and internode diameter, as well as reducing the plant and ear height in maize. The results suggested that uniconazole significantly alleviated lodging stress by enhancing lignin metabolism and optimizing the culm morphological characteristics. Our study found that ethephon shortened internode length and increased stem diameter, likely due to ethylene-induced inhibition of internode elongation and microtubule reorganization in elongating cells, promoting radial thickening. Furthermore, shorter internodes reduce source–sink distance, weaken stem storage capacity, and alleviate the competition between stem growth and ear development, thereby increasing yield. Zhao et al. [42] reported that exogenous ethephon reduced internode elongation, weakened stem storage capacity, and mitigated stem-ear competition, strengthening puncture strength and bending resistance while reducing lodging risk. Zhang et al. [14] found that ethephon elevated ethylene accumulation in stems, suppressed auxin and gibberellin concentrations, and upregulated secondary cell wall genes, leading to shorter internodes, thicker stems, and enhanced bending resistance. Xu et al. [43] suggested that EDAH increases vascular bundle number and stem mechanical strength. The improved physical strength of basal internodes after ethephon treatment correlated with their reduced length enhanced internode compactness from shortening.
Ethephon enhances stem mechanical strength by thickening sclerenchyma and parenchyma cell walls, expanding vascular bundle area, and stimulating lignin accumulation, which improves the stem elasticity and lodging resistance. Our results showed that ethephon increased stem lignin content and lignin-related enzyme activities (PAL, CAD, and 4CL), aligning with previous studies. For example, Fan et al. [44] reported that DTB spraying elevated cellulose, hemicellulose, and lignin content, boosted CAD and 4CL activities, and enhanced stem bending resistance to reduce lodging. Chai et al. [15] found that ethephon treatment upregulated lignin content and related enzyme activities (PAL, CAD, and 4CL). Similarly, spring maize studies confirmed a positive correlation; there was a significant positive correlation between lignin content and these enzyme activities [45].
In summary, ethephon application increased maize stalk lignin content, enhanced stem strength, inhibited auxin transport and internode elongation, promoted dwarfing, and reduced plant height, ear height, and center of gravity height, establishing a compact plant architecture conducive to lodging-resistant maize populations.

4.3. Influence of Variety Difference

Genetic background-driven sensitivity to ethephon varies among maize varieties, potentially mediated by molecular-level gene expression differences. For example, studies on cut roses [46] and goldfish flower [47] have demonstrated species-specific ethylene responses. Wei et al. [48] reported that Nongda108 and Ludan981 hybrids exhibited differential responses to ethephon, indicating that parental line sensitivity determines hybrid performance. As parental lines of Zhengdan958, Zheng58 and Chang7-2 contribute to the high-yielding, lodging-resistant traits. Similarly, PH6WC and PH4CV constitute Xianyu335, a widely adopted cultivar in Northeast China’s spring maize belt and the Huang-Huai-Hai summer maize region due to its rapid grain dehydration and high yield. Consistent with these genetic differences, increasing ethephon concentrations progressively reduced upper ear-leaf area and leaf angle, with maximal effects observed at the ear leaf. Zheng58 and PH6WC showed greater responsiveness compared to Chang7-2 and PH4CV. Internode-specific responses were observed: internodes 3–5 exhibited heightened ethephon sensitivity with increasing ethephon concentrations, Zheng58 displayed maximal sensitivity in internode length and puncture strength, PH6WC responded most strongly in internode diameter, while PH4CV responded most strongly in flexural strength. Varietal differences in lignin content and lignin-related enzyme activities to ethephon were pronounced, with the fourth internode showing the strongest effects. Among the lines, PH6WC has emerged as the most ethephon-sensitive genotype.
Our findings demonstrate that the hormone maintains environmental stability under non-stress conditions. Across diverse environments including multi-year trials, open field or screen house, the effects of this hormone exhibited minimal variability, with no statistically significant intervarietal disparities observed [14]. Notably, even under abiotic stressors (cold exposure in seedling-stage or precipitation extremes in grain-filling period), environmental variability failed to induce measurable alterations in genotypic sensitivity to hormonal regulation [49].

5. Conclusions

This study demonstrates that ethephon enhances lodging resistance by optimizing plant architecture and augmenting stem mechanical strength. Zheng58 and PH6WC exhibited heightened responsiveness to ethephon compared to Chang7-2 and PH4CV. These findings establish a foundational framework for breeding lodging-resistant hybrids and tailoring plant growth regulator formulations, thereby enhancing maize production efficiency and supporting the “store grain in technology” strategy. However, the mechanistic link between ethylene signaling and genotype-specific lignin metabolic regulation remains unresolved. Subsequent studies should prioritize expanded genetic screening to identify common or genotype-specific ethylene-responsive gene alleles, complemented by transcriptomics or metabolomics analyses. This integrative approach will clarify genotype-dependent interactions between ethephon and lignin biosynthesis, advancing sustainable, intensive maize production.

Author Contributions

S.L.: Writing—original draft; Data curation; Investigation. F.G. and M.C.: Data curation; Investigation. S.G.: Formal analysis; Software; Visualization. D.W., Z.W. and Y.C.: Formal analysis; Software; Validation. T.X. and D.Y.: Writing—review and editing. Q.Z.: Funding acquisition; Writing—review and editing; Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Heilongjiang Provincial Natural Science Foundation Project (LH2024C002); the National Natural Science Foundation of China (31501251); Key R&D projects of Heilongjiang Program Province in 2023 (JD2023GJ01-11).

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to laboratory confidentiality agreement policies.

Acknowledgments

The authors sincerely thank the support from Maize Research Institute Heilongjiang Academy of Agricultural Sciences and Crop Chemical Regulation Research Center of China Agricultural University for giving four maize inbred line seeds and ethephon, respectively.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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Agronomy 15 01248 g001
Figure 1. Precipitation and average temperature of maize growing season in 2016.
Figure 1. Precipitation and average temperature of maize growing season in 2016.
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Figure 2. Effect of different concentrations of ethephon on height and ear position coefficient of maize. The capital letters represent the four inbred lines, respectively; (A): Zheng58, (B): Chang7-2, (C): PH6WC, (D): PH4CV; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05). CK: Blank control, S1: Ethephon concentration of 200 mg/L, S2: Ethephon concentration of 400 mg/L; The bar charts represent the different height values corresponding to each of the four inbred lines under different ethephon treatments, while the line graphs represent the ear position coefficient values of the four inbred lines under different ethephon treatments.
Figure 2. Effect of different concentrations of ethephon on height and ear position coefficient of maize. The capital letters represent the four inbred lines, respectively; (A): Zheng58, (B): Chang7-2, (C): PH6WC, (D): PH4CV; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05). CK: Blank control, S1: Ethephon concentration of 200 mg/L, S2: Ethephon concentration of 400 mg/L; The bar charts represent the different height values corresponding to each of the four inbred lines under different ethephon treatments, while the line graphs represent the ear position coefficient values of the four inbred lines under different ethephon treatments.
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Figure 3. Effect of different concentrations of ethephon on leaf area of maize. The capital letters represent the four inbred lines, respectively; (A): Zheng58, (B): Chang7-2, (C): PH6WC, (D): PH4CV.
Figure 3. Effect of different concentrations of ethephon on leaf area of maize. The capital letters represent the four inbred lines, respectively; (A): Zheng58, (B): Chang7-2, (C): PH6WC, (D): PH4CV.
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Figure 4. Effect of different concentrations of ethephon on leaf angle of maize. The capital letters represent the four inbred lines, respectively; (A): Zheng58, (B): Chang7-2, (C): PH6WC, (D): PH4CV.
Figure 4. Effect of different concentrations of ethephon on leaf angle of maize. The capital letters represent the four inbred lines, respectively; (A): Zheng58, (B): Chang7-2, (C): PH6WC, (D): PH4CV.
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Figure 5. Effects of different concentrations of ethephon on stem internode length and internode diameter of maize. The capital letters represent respectively; (A): Internode length, (B): Internode diameter; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
Figure 5. Effects of different concentrations of ethephon on stem internode length and internode diameter of maize. The capital letters represent respectively; (A): Internode length, (B): Internode diameter; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
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Figure 6. Effects of different concentrations of ethephon on stalk rind penetration strength and breaking resistance strength of maize. The capital letters represent respectively; (A): Stalk rind penetration strength, (B): Breaking resistant strength; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
Figure 6. Effects of different concentrations of ethephon on stalk rind penetration strength and breaking resistance strength of maize. The capital letters represent respectively; (A): Stalk rind penetration strength, (B): Breaking resistant strength; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
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Figure 7. Effects of different concentrations of ethephon on lignin content and enzyme activities of 4CL, PAL, and CAD in maize stem. The capital letters represent respectively; (A): 4CL activity, (B): CAD activity, (C): PAL activity, (D): Lignin content; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
Figure 7. Effects of different concentrations of ethephon on lignin content and enzyme activities of 4CL, PAL, and CAD in maize stem. The capital letters represent respectively; (A): 4CL activity, (B): CAD activity, (C): PAL activity, (D): Lignin content; different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
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Table 1. Effect of different concentrations of ethephon on lodging resistance index and grain yield of maize.
Table 1. Effect of different concentrations of ethephon on lodging resistance index and grain yield of maize.
CultivarTreatmentLRI (%)Grains per Ear1000-Grain Weight (g)Yield (kg/hm2)
Zheng58CK8.51 ± 0.44 c624.8 ± 4.02 a350.59 ± 0.57 a9092.84 ± 54.88 a
S110.34 ± 0.32 b614.3 ± 6.14 b350.25 ± 0.31 a8935.75 ± 67.31 b
S211.68 ± 0.58 a599.3 ± 8.19 c350.33 ± 0.44 a8828.81 ± 38.12 c
Chang7-2CK6.75 ± 0.55 c608.0 ± 10.18 a340.72 ± 0.68 a8838.81 ± 20.87 a
S18.37 ± 0.71 b587.6 ± 4.62 b340.56 ± 0.33 a8773.83 ± 40.94 b
S210.97 ± 1.26 a579.3 ± 2.31 c340.27 ± 0.41 a8686.50 ± 32.65 c
PH6WCCK7.31 ± 0.49 c617.0 ± 2.86 a350.72 ± 0.43 a9082.96 ± 40.26 a
S19.44 ± 1.47 b610.3 ± 5.23 ab350.54 ± 0.29 a8974.36 ± 38.79 b
S212.45 ± 1.38 a602.3 ± 3.01 b350.42 ± 0.14 a8869.11 ± 30.64 c
PH4CVCK6.21 ± 0.64 c605.0 ± 5.70 a340.34 ± 0.26 a8863.02 ± 42.06 a
S18.21 ± 1.22 b599.6 ± 9.48 ab340.27 ± 0.15 a8780.33 ± 30.17 b
S211.43 ± 0.86 a582.3 ± 8.95 b340.28 ± 0.27 a8650.49 ± 60.35 c
Different lowercase letters (a, b, c) indicate statistically significant differences between groups (p < 0.05).
Table 2. Correlation coefficients between plant morphology index and lodging index and yield.
Table 2. Correlation coefficients between plant morphology index and lodging index and yield.
TreatmentIndicatorsPlant HeightEar HeightHeight of Gravity
Center		Leaf AngleLeaf Area
CKLRI−0.84 *−0.93 **−0.76 *−0.93 **−0.81 *
Yield−0.64 ns−0.78 *−0.69 ns−0.89 **−0.98 **
S1LRI−0.79 *−0.98 **−0.88 *−0.91 **−0.76 *
Yield−0.71 ns−0.76 *−0.66−0.92 **−0.94 **
S2LRI−0.80 *−0.96 **−0.85 *−0.89 **−0.83 *
Yield−0.73 ns−0.71 ns−0.57 ns−0.95 **−0.95 **
In this table, ns indicates p > 0.05, * indicates 0.01 < p < 0.05, ** indicates p < 0.01.
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Liu, S.; Guo, F.; Chai, M.; Gu, S.; Wang, D.; Wang, Z.; Chen, Y.; Xie, T.; Yang, D.; Zhang, Q. Effect of Ethephon on Sensitivity Difference of Lodging Resistance in Different Maize Inbred Lines. Agronomy 2025, 15, 1248. https://doi.org/10.3390/agronomy15051248

AMA Style

Liu S, Guo F, Chai M, Gu S, Wang D, Wang Z, Chen Y, Xie T, Yang D, Zhang Q. Effect of Ethephon on Sensitivity Difference of Lodging Resistance in Different Maize Inbred Lines. Agronomy. 2025; 15(5):1248. https://doi.org/10.3390/agronomy15051248

Chicago/Turabian Style

Liu, Siyao, Feng Guo, Mengzhu Chai, Shiwei Gu, Dacheng Wang, Zihao Wang, Yidan Chen, Tenglong Xie, Deguang Yang, and Qian Zhang. 2025. "Effect of Ethephon on Sensitivity Difference of Lodging Resistance in Different Maize Inbred Lines" Agronomy 15, no. 5: 1248. https://doi.org/10.3390/agronomy15051248

APA Style

Liu, S., Guo, F., Chai, M., Gu, S., Wang, D., Wang, Z., Chen, Y., Xie, T., Yang, D., & Zhang, Q. (2025). Effect of Ethephon on Sensitivity Difference of Lodging Resistance in Different Maize Inbred Lines. Agronomy, 15(5), 1248. https://doi.org/10.3390/agronomy15051248

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