Ensuring maize production in the main producing areas of the Yellow River, Huaihe River and Haihe River (the junction of North China, East China and Central China) is of great significance for stabilizing China's food security. In recent years, high temperature and lodging occurred frequently in maize production season in this region, which seriously affected maize yield. In order to improve maize yield, population plant type, comprehensive resistance and grain seed setting rate should be further optimized while increasing planting density. Plant growth regulators can affect plant growth and development, improve plant resilience, and play an important role in high and stable crop yield by regulating endogenous plant hormones (Zhao et al., 2006). In maize, high temperature stress caused damage to the microscopic morphology of pollen filaments, inhibited the development of male and female panicles, significantly reduced maize photosynthetic capacity, reduced the number of grains per spike and kernel weight, and significantly reduced grain yield (Gao et al., 2020). Plant growth regulator can promote the early growth and development of maize, facilitate the growth of root system and the accumulation of dry matter, improve the double ear rate, have obvious activation and regulation effects on the plant, and yield increase effect is obvious (Li, 2006). Other studies have shown that plant growth regulators can regulate leaf area index (LAI) and improve dry matter accumulation and mobility. Improve grain morphology, speed up grain metabolism, expand grain storage capacity; Improve water or nutrient use efficiency, reduce lodging rate, and then increase maize yield, affecting grain harvest (Qiao et al., 2013; Jiao et al., 2014; Li et al., 2016; Jiang et al., 2016; Liu et al., 2017; Zhang et al., 2019; Xu et al., 2019; Liu et al., 2020). Therefore, it is of great significance to study the yield effects of different plant growth regulators on different types of maize varieties to achieve high and stable yield.

This study took three maize varieties as the research object, research the corn growth period, plant type, group structure indicators, and other important agronomic traits and yield response to the two different growth regulators, aims to illustrate the different plant growth regulator on the different types of maize plant type, resistance and yield related traits, spraying on the different varieties of the best matching scheme is put forward, In this way, the plant type of maize population was optimized, the ability of maize to resist toppings and high temperature was improved, the seed setting rate of maize was further increased, and the water content of maize was reduced. Finally, the yield of maize was increased and the production risk was reduced, which provided a reference for the further realization of maize grain mechanized harvesting in this region.

1 Results and Analysis

1.1 Analysis of important phenotypic characters among maize varieties treated with different plant growth regulators

EXCEL 2016 software was used to conduct basic statistical analysis of all important phenotypic traits of maize varieties under different plant growth regulator treatment conditions, and the results are listed in Table 1 and Table 2 (the growth stage related traits that have little difference were not listed). As can be seen from Table 1, the application of "Baochai" can effectively reduce the plant height and ear height of different varieties, and the reduction amplitude of different varieties is different. Compared with the control, the plant height and ear position of Zhengdan 7137 are decreased by 6.7% and 22.1%, respectively. Zhengdan 7153 decreased by 8.9% and 19.1% respectively; Zhengdan 958 decreased by 0.5% and 8.0%, respectively. Compared with the control, the yield of Zhengdan 7137 and Zhengdan 958 was increased by 4.3 kg (30.1%) and 2.2 kg (21.6%), respectively. Application of Lingzhisu could increase the yield of Zhengdan 7137 and Zhengdan 958 plots by 1.7 kg (11.9%) and 3.8 kg (37.3%) respectively. Spraying plant growth regulator had little effect on grain water content at harvest stage. The yield of Zhengdan 7137 was higher than that of the other two varieties under the condition of "Baochai" treatment, while Zhengdan 7153 was higher under the control and "Lingzhisu" treatment, and Zhengdan 7137 was higher than Zhengdan 958. Under three treatment conditions, the grain water content of Zhengdan 7137 was lower than that of the other two varieties, and the grain water content of Zhengdan 958 was the highest.

Table1 The descriptive statistics for phenotypes traits in maize varieties under different treatment

Table 2  The descriptive statistics for ear yield traits in maize varieties under different treatment

According to the overall field performance, the new varieties Zhengdan 7137 and Zhengdan 7153 had higher plot yield and lower grain moisture content than the control Zhengdan 958, and had better production potential. The grain water content of Zhengdan 7137 was lower than that of the other two varieties, and under the condition of "Baochai", the yield of Zhengdan 7137 was outstanding, and it had better grain harvesting potential.

Under the conditions of the same variety and different plant growth regulators, most of the phenotypic traits (ear length, ear diameter, kernel weight, seed yield, 100 grain weight, etc.) of the fruit ear did not change much (Table 2). Under the condition of "Lingzhisu", only the kernels per row and row number were higher than those in the other two treatments. However, under the same plant growth regulator treatment, the phenotypic characters of ear differed greatly among different varieties. The number of grains per row and the number of rows per ear of Zhengdan 7153 under the three treatment conditions was much higher than that of the other two varieties, but the final grain weight per ear of Zhengdan 7153 was higher than that of the other two varieties, showing better yield performance. For seed yield, Zhengdan 7137 and Zhengdan 7153 were higher than Zhengdan 958. After air drying, the grain moisture content of Zhengdan 7137 was much lower than that of the other two varieties.

1.2 Correlation analysis of important traits of maize varieties treated with different plant growth regulators

SPSS 20 was used to analyze the correlation of important traits of the three varieties under different plant growth regulator treatment conditions (Table 3). Lodging rate was positively correlated with plant height (r=0.47), and negatively correlated with grain moisture content (r=-0.42). Some yield traits such as ear length, ear diameter, row number, number of grains per ear and 100 kernels weight were significantly or extremely significantly positively correlated (r=0.41-0.88), but there was no significant correlation between the same plant type and physiological traits, which were not listed in the table.

Except for ear weight, plant height was significantly or extremely significantly correlated with all other traits, and negatively correlated with diffuse none-interceptance (DIFN), (mean leaf angle, MTA) (MTA), grain moisture content and cob diameter at harvest stage, and positively correlated with ear height, SPAD value, leaf area index, plot yield and seed rate. However, ear height was only negatively correlated with intercept-free scattering, and positively correlated with plant height and spike weight. The results showed that the more compact the plant type (the larger the mean leaf angle), the lower the plant height, the higher the grain water content, and the lower the yield and seed yield (Table 3).

Table 3  Correlation coefficients among important traits in maize varieties under different treatment Note: * and ** indicates significant at the 0.05 and 0.01 probability level

In terms of population structure index, SPAD value was significantly positively correlated with plant height, plot yield and seed rate, and negatively correlated with grain moisture content and cob diameter at suitable harvest stage. Leaf area index was positively correlated with plant height and ear height, and negatively correlated with diffuse none-interceptance, mean leaf angle and grain water content at harvest stage, but had no significant correlation with yield traits. There was no intercept scattering between mean leaf inclination and other traits except ear height. The results showed that only the physiological index SPAD value was positively correlated with yield, but all the population structure indexes were significantly correlated with grain water content at the suitable harvest stage. The cultivars with low chlorophyll content (SPAD value), few leaves (leaf area index), compact plant type (mean leaf angle) and strong canopy light absorption ability (No interception and scattering) had significantly higher moisture content at harvest stage.

Among the yield traits, plot yield was positively correlated with plant height, SPAD, ear weight and seed rate, and negatively correlated with grain moisture content at harvest stage. Except for ear height and ear weight, grain water content at the suitable harvest stage had significant or extremely significant correlation with all other traits. The grain water content was negatively correlated with plant height, SPAD value, leaf area index, plot yield and seed rate, and positively correlated with diffuse none-interceptance, mean leaf angle and cob diameter. Ear weight was positively correlated only with ear height and plot yield. Seed yield was positively correlated with plant height, SPAD value and plot yield, and negatively correlated with grain water content and axis diameter at suitable harvest stage. The Results showed that the grain yield, seed yield and grain water content were significantly affected by the character of cob. The coarser the grain yield and seed yield were lower, and the grain water content was higher, which seriously affected the grain harvesting.

1.3 Two-way analysis of variance and multiple comparisons among maize varieties under different plant growth regulator treatment conditions

The SAS 9.0 PROC GLM program was used to analyze all 22 important phenotypic traits under different plant growth modulation treatments and among different cultivars. The results showed that the overall variance of 13 characters reached significant or extremely significant level, including plant height, ear height, SPAD value, leaf area index, diffuse none-interceptance, lodging rate, plot yield, grain moisture content at harvest stage, the kernels per row, row number, cob diameter, seed rate and grain water content after air drying. Further, multiple comparisons of phenotypic traits with significant differences between different plant growth regulators and different varieties were conducted (Table 4; Table 5), focusing on traits (Figure 1; Figure 2).

Table 4  Comparison of phenotypic traits with significant difference under different treatment Note: Different lowercase letters indicate significant differences at the 0.05 probability level

Table 5   Comparison of phenotypic traits with significant difference under different varieties Note: Different lowercase letters indicate significant differences at the 0.05 probability level

Figure 1 Comparison of t some significant traits under different treatments Note: Different lowercase letters indicate significant differences at the 0.05 probability level

Figure 2  Comparison of t some significant traits under different varieties Note: Different lowercase letters indicate significant differences at the 0.05 probability level

For the four traits of plant height, ear height, leaf area index and row number (Table 4; Figure 1), both "Lingzhisu" and control treatment conditions were significantly higher than "Baochai" treatment; The diffuse none-interceptance was significantly higher in the "Baochai" treatment than in the other two treatments. For ear diameter and seed rate, "Lingzhisu" treatment was the highest, significantly higher than the control and "Baochai" treatment. the results showed that the application of plant growth regulator "Baochai" could significantly reduce plant height and ear height, optimize plant type, and increase light transmittance. The application of plant growth regulator "Lingzhisu" can significantly increase the seed yield and harvest index of the varieties, and has better economic benefits.

There were significant differences in plant type, yield and grain moisture content among different varieties (Table 5; Figure 2). The height of Zhengdan 7137 was the highest, which was significantly higher than that of Zhengdan 7153 and Zhengdan 958, which was the lowest, but there was no significant difference among the ear heights of three varieties. The leaf area index of Zhengdan 7137 was significantly higher than that of the other two cultivars, and the diffuse none-interceptance was significantly lower than that of the other two cultivars. The results showed that the plants of Zhengdan 7137 were taller and thicker, and the light transmittance was lower. In terms of yield and grain water content in the suitable harvest period, the yield of Zhengdan 7137 and Zhengdan 7153 plots was significantly higher than that of Zhengdan 958, while the grain water content of Zhengdan 7153 plots was significantly lower than that of Zhengdan 958, which was the lowest. the results of ear traits showed that there were significant differences among the three varieties, among which the seed rate of Zhengdan 7137 and Zhengdan 7153 were significantly higher than that of Zhengdan 958, and the grain water content of Zhengdan 7137 was also the lowest, significantly lower than that of the other two varieties.

2 Discussion

Many scholars study, through the application of plant growth regulator can effectively adjust the corn varieties of plant type, (plant height, stem, root, etc.), which affects some of its physiological indicators and population structure, improve the comprehensive resistance (resistance, resistance to high temperature, etc.), photosynthetic efficiency, water and nutrient use efficiency, grain endosperm and the development of starch, etc. (Zhao et al., 2013; Jiao et al., 2014; Fan et al., 2017; Liu et al., 2018; Gong et al., 2019; Liu et al., 2020), and finally achieve increased production and efficiency.

In order to further clarify the effects of different plant growth regulators on important agronomic traits and yield of different types of maize varieties, two plant growth regulators with different effects were used to analyze the important phenotypic traits of three maize varieties, such as growth period, plant type, main population structure indexes, final yield and grain moisture content. The results showed that the application of two different plant growth regulators had different effects on important agronomic traits and yield of maize varieties. Among them, "BAochai" had the effect of reducing plant height, increasing population light transmittance, optimizing plant type and increasing resistance. "Ganoderma lucidum" has the effect of increasing the resistance to high temperature, improving the ear firmness and seed rate, and further increasing the yield.

Compared with plant growth regulators, the differences among maize varieties contributed more to the effects of agronomic and yield traits. There were significant differences in important agronomic traits and yield-related traits among the three different maize varieties, especially in yield and grain water content, the yield of the newly selected varieties Zhengdan 7137 and Zhengdan 7153 was better, which was significantly higher than that of the control Zhengdan 958. And the grain water content of Zhengdan 958 was significantly lower than that of the control, while Zhengdan 7137 had the lowest grain water content, which was significantly lower than that of the other two varieties, which had better grain harvesting potential.

However, due to its own characteristics such as tall plants, high ear height and large yield of ear, Zhengdan 7137 shows a certain lodging rate and has potential production risks. the results of this study showed that the population plant type of zhengdan 7137 could be adjusted by spraying the special plant growth regulator "Baochai" (reducing plant height, ear position, etc.), so as to reduce lodging rate, and the stability of Zhengdan 7137 could be improved by reducing population density and other supporting cultivation and management measures, so as to achieve grain harvest. for the new variety Zhengdan 7153, the plant growth regulator "Lingzhisu" can be sprayed to improve its high temperature resistance, ear fruiting and seed yield, and finally achieve yield increase.

In recent years, as the main maize producing areas of the Yellow River, Huaihe River and Haihe River with "yield two crops a year", there are many urgent production problems to be solved, which mainly include poor high temperature grain yield, inverted inverted, unsuitable mechanized harvest grain, etc., which seriously limit corn production in this region. How to better coordinate the relationship among key traits such as yield, resistance and grain yield is an important way to solve the problem. However, there are often significant negative correlations among these important traits, and it is difficult to realize the coordination among them only by the improvement of varieties. therefore, it is of great significance to explore better methods of supporting cultivation and management so as to give full play to the potential of new varieties for high yield and stable yield, and realize the grain harvest as soon as possible.

This study found that through the promotion and utilization of new varieties, combined with the application of special plant growth regulator, the comprehensive resistance (high temperature resistance, lodging resistance, etc.) of maize varieties can be effectively improved, and the seed rate can be increased, so as to achieve high and stable yield, and achieve cost-saving and efficiency.

3 Materials and Methods

3.1 Test materials

Three Zhengdan series maize varieties were tested, including Zhengdan 958 (Control), two newly selected varieties Zhengdan 7137 (Xianyu 335 type variety) and Zhengdan 7153 (Zhengdan 958 type variety).

The two corn growth regulators were selected as the corn chemical control agent "Baochai" from Henan Zhongzhizhou Plant Protection Co., LTD. And the cell energy factor "Ganoderma" from Langfang Weijin Agricultural Science and Technology Co., LTD. Among them, "BAochai" contains polypeptide polymer chelating zinc, boron and other components, which can increase the number of root layers, shorten the length of stem basal internodes, optimize the population structure and other functions. "Ganoderma essence" contains a variety of amino acids, peptides and polysaccharides, which can improve photosynthetic efficiency, increase plant resistance, and increase grain yield and quality.

3.2 Experimental Design

The experiment was carried out in the second experimental base of Henan Academy of Agricultural Sciences (Xinxiang, Yuanyang) in the summer of 2019, and the seeds were sown on June 16. A randomized block design was used, and each variety was set up with 3 treatments (including blank control, sprayed with "Baochai" and sprayed with "Lingzhisu"), with 3 replicates per treatment, a total of 27 plots. Each plot was planted with 8 rows, 10 m long, 60 cm row spacing, 22 cm plant spacing, and a density of 75 000 plants /hm². The experimental field management was the same as the local field production. Harvest all plots at the appropriate harvest period and measure yield per ear.

At the jointing stage (8-leaf stage) of maize, dilute with water to an appropriate concentration according to the experimental design and application instructions of growth regulator, and spray plant growth regulator evenly on the leaf surface of all maize varieties, paying close attention to the cover during spraying.

3.3 Measurement items and methods

(1) Investigation of growth stage: tasseling stage, silking stage, powder dispersing stage, physiological maturity stage;

(2) Plant type survey: plant height, ear height;

(3) Determination of population structure index: SPAD value was determined by SPAD-502 plus; At the silking stage, leaf area index (LAI), mean tilt angle of the leaves (MTA) and diffuse none-interceptance (DIFN) were measured at the ear level layer between rows using LAI-2200 canopy analyzer.

(4) Suitable harvest period (the same period): investigate lodging rate; Plot yield and grain moisture content 1 were measured by using Wintersteiger plot harvester (Austria).

(5) Indoor seed test (after natural air drying): 10 representative fruit ears were kept in each plot, and ear length, ear diameter, the kernels per row, row number, cob diameter, ear weight, kernel weight, seed rate, 100 kernels weight and grain moisture content 2 were examined (determined by Japanese KETT grain water meter).

3.4 Data Analysis

EXCEL 2016 was used to sort out the data, and basic analysis of the average value and standard deviation of each phenotypic trait was carried out. SPSS 20 software was used for correlation analysis of each phenotypic trait. SAS 9.0 software was used to analyze the variance and multiple comparisons of phenotypic traits among different growth regulators and different varieties.

Authors’ contributions

WLF and LHY were the experimental designers and executors of this study. WLF completed the data analysis and wrote the first draft of the paper. MJ, WH, CYY, LJJ, JTJ and YJW participated in the experimental design and the analysis of experimental results. LHY was the architect and the person in charge of the project. He supervised the experimental design, data analysis, paper writing and revision. All authors read and approved the final manuscript.

Acknowledgments

This project was co-funded by the National Key Research and Development Program (2017YFD0101201) and the Fiscal Budget Project of Henan Province (2020CY01).

References

Fan H.C., Gu W.R., Yu J.P., Wang Y.L., Meng Y., Zhang L.G., Li J., and Wei S., 2017, Mechanism of lodging resistance of maize improved by plant growth regulator, Jiangsu Nongye Xuebao (Jiangsu Journal of Agricultural Sciences), 33(2): 253-262.

Gao Y.B., Zhang H., Shan J., Xue Y.F., Qian X., Dai H.C., Liu K.C., and Li Z.X., 2020, Effects of pre-silking high temperature stress on yield and ear development characteristics of different heat-resistant summer maize cultivars, Scientia Agricultura Sinica, 53(19): 3954-3963.

Gong L., Li Z.B., Zeng E., Cheng F.X., Deng L.S., Zhang C.L., Hu K.W., and Tu P.F., 2019, Effects of liquid fertilizers with plant growth regulators on nutrient absorption and fertilizer using efficiency of sweet corn, Guangdong Nongye Kexue (Guangdong Agricultural Sciences), 46(11): 54-61.

Jiang Q., Li L., Wu R.J., and Zhang F.L., 2016, Effects of plant growth regulators on stalk redundancy and yield formation of summer maize, Huabei Nongxuebao (ACTA Agriculturae Boreali-Sinica), 31: 276-281.

Jiao L., Dong Z.Q., Gao J., Chen C.X., Lu L., Dong X.R., Li G.Y., and Xu Y.L., 2014, Effect of plant growth regulators on canopy structure in spring maize under different plant densities, Yumi Kexue (Journal of Maize Sciences), 22(6): 51-58.

Li D., Zhao J.J., Zheng D.F., Feng N.J., Liu W.B., Zhang H.P., Xu Y.H., Wang C., Yu Q., and Liang X.Y., 2016, Effects of chemical regulation on development process of grains and yield of spring maize, Yumi Kexue (Journal of Maize Sciences), 24 (6): 47-54。

Li Y.J., 2006, Effects of plant growth regulators on maize yield, Yumi Kexue (Journal of Maize Sciences), 14(1): 132-133.

Liu J., Sun B., Zhang W.Q., Feng X.X., Zhang J.Y., Ning D.F., Qin A.Z., Liu Z.D., Qiao M., Shen H.L., and Xu Y., 2020, Effects of chemical regulating on grain harvest quality and water use efficiency in summer maize, Zuowu Zazhi (Crops), (3): 161-168.

Liu W.B., Feng N.J., Zhang P.P., Li D., Zhang H.P., He T.M., Zhao J.J., Xu Y.H., Wang C., 2017, Effects of ethephon and kinetin on lodging-resistance and yield of maize, Zhongguo Shengtau Nongye Xuebao (Chinese Journal of Eco-Agriculture), 25(9): 1326-1334.

Liu X.Q., Zhan Y.T., Wang Y., Wang P., Yin S.K., Han C.X., and Dong X.H., 2018, Effect of some plant growth regulators used by stages treatments on endosperm cell and starch granule in maize endosperm development, Huabei Nongxuebao (ACTA Agriculturae Boreali-Sinica), 33(6):137-144.

Qiao J.F., Liu J.B., Huang L., Xia L.K., Zhu W.H., and Li C., 2013, Effect of different growth regulators on grain yield of maize in shading condition at flowering stage, Henan Nongye Kexue (Journal of Henan agricultural sciences), 42(12): 24.

Xu T.J., Lü T.F., Chen C.Y., Liu Y.E., Zhang Y.T., Liu X.Z., Zhao J.R., and Wang R.H., 2019, Effects of plant density and plant growth regulator on stalk traits of maize and their regulation, Zhongguo Nongye Kexue (Scientia Agricultura Sinic), 52(4): 629-638.

Zhang W.Q., Zhao B., Qin A.Z., Ning D.F., Sun B., Ding P.F., Liu J., Zang H.T., Liu Z.D., and Xiao J.F., 2019, Regulation of water use efficiency of summer maize by plant growth regulator in well-irrigation area of Huang-Huai-Hai river, Ganhan Diqu Nongye Yanjiu (Agricultural Research in the Arid Areas), 37(6): 43-48.

Zhao C.L., Wang X.P., Dong P.F., and Liu T.X., 2013, Effects of chemical regulators on lodging, senescence, grain yield and quality of maize under stress environment, Henan Nongye Kexue (ournal of Henan Agricultural Sciences), 42(5): 41-44.

Zhao M, Zhou S.X., and Cui Y.H., 2006, Research and application of plant growth regulators on maize (Zea mays L.) in China, Journal of Maize Sciences, 14(1): 127-131.