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Article

Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice

by
Jingna Zhuang
†,
Yilu Fang
†,
Jinxi Zheng
†,
Yan Duan
,
Xuexue Liu
and
Zhaowen Mo
*
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Agriculture, South China Agricultural University, Guangzhou 510642, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agriculture 2025, 15(3), 335; https://doi.org/10.3390/agriculture15030335
Submission received: 21 December 2024 / Revised: 26 January 2025 / Accepted: 27 January 2025 / Published: 3 February 2025
(This article belongs to the Section Crop Production)
Browse Figures
Versions Notes

Abstract

:
Previous studies have shown that selenium (Se) can influence rice growth and yield. However, the Se effect on rice lodging remains unknown. This study aimed to investigate the impact of different Se treatments on seedling growth and stem sheath hardness in fragrant rice. A hydroponic experiment was conducted using two fragrant rice varieties, Yuxiangyouzhan and Xiangyaxiangzhan, as experimental materials. Two forms of selenium fertilizers (amino acid-chelated selenium and sodium selenite) were used. There were five foliar spraying selenium fertilizer treatments (CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; and T4: 8 μmol·L−1 sodium selenite), and the effects of the different selenium fertilizer treatments on seedling growth and stem sheath hardness in fragrant rice were studied. Significant Se treatment effects on root fresh weight, seedling dry weight, plant height, stem sheath length, number of leaves, chlorophyll content, stem sheath hardness, peroxidase activity in leaf and stem sheaths, and lignin content in the roots were detected. A significant Se treatment and variety interaction effect on the stem sheath hardness was observed. The different forms/levels of selenium fertilizer affected the seedling growth and the stem sheath hardness differed. The Se treatments improved seedling growth and significantly affected the dry weight, chlorophyll content, stem sheath hardness, and peroxidase activity in leaf and stem sheaths. Compared with the CK treatment, the Se treatments increased the total dry weight of seedlings in Xiangyaxiangzhan and Yuxiangyouzhan by the ranges of 25.43–52.77% and 18.97–30.09%, respectively. The T2–T4 treatments increased the stem sheath hardness values in Xiangyaxiangzhan and Yuxiangyouzhan by the ranges of 21.6–54.7% and 38.3–146.6%, respectively, as compared to the CK treatment. The Se treatments had a promoting effect on physiological indexes such as stem sheath length, lignin content in the stem sheath, and dry matter accumulation in different plant tissues, thereby increasing the total dry weight. The Se treatment had an inhibitory effect on chlorophyll b content and total chlorophyll content, whilst it increased the chlorophyll a content and chlorophyll a/b ratio, which in turn affected the photosynthesis of rice. Therefore, appropriate Se treatments (the application of 8 μmol·L−1 amino acid-chelated selenium, 4 μmol·L−1 sodium selenite, and 8 μmol·L−1 sodium selenite) could improve seedling growth and stem sheath hardness, which was related to the parameter changes, such as the dry weight, photosynthesis pigments, and peroxidase activity. These findings suggest that different Se fertilizers can positively regulate rice resistance to lodging and growth. This study can provide theoretical support for the application of selenium fertilizer.

1. Introduction

Rice is an important cereal crop and the development of rice production is essential for ensuring food security [1]. Fragrant rice is a particular type of cultivated rice with a high economic value but a low yield and susceptibility to lodging [2]. Lodging could result in low-yield and low-quality issues in rice production. The main type of rice lodging is stem lodging resulting from the weak stem [3]. Lodging rice can lead to significant yield losses and a substantial decline in quality and also causes a considerable increase in harvesting costs, ultimately leading to economic losses [4,5,6]. Therefore, increase the lodging resistance of rice is highly important for rice production.
Selenium (Se) is an essential trace element and is important for human health [7]. The production of selenium-rich grains is therefore popular because it provides a safer and more effective way to provide selenium for the body’s selenium needs [8,9,10]. Selenium benefits not only the human body but also rice growth, and a previous study indicated that moderate selenium supplementation can promote rice yields, increase the quality, regulate photosynthesis, and increase antioxidant capacity and resistance [8]. Therefore, research on the Se fertilization in rice has great practical value.
Research has indicated that the concentration of selenium fertilizer and the selenium fertilizer application method are two critical factors affecting plant growth characteristics and selenium enrichment performance. A previous study indicated that the application of low concentrations of selenium fertilizer promotes plant growth and development, increasing yield, quality, and antioxidant capacity [11]. Regarding the selenium fertilizer application method, studies have suggested that soil-based selenium fertilizers, foliar selenium sprays, and selenium seed priming are popular ways to increase selenium levels in plants [12]. Research has shown that the selenium enrichment effect in plants resulting from foliar spraying of selenium fertilizers is eight-times greater than that resulting from soil application and that foliar spraying of selenium fertilizers is also more environmentally friendly [13,14]. In addition, the form of selenium significantly impacts the effectiveness of selenium fertilizers [15]. Organic selenium has a low toxicity and high absorption efficiency whilst inorganic selenium has a specific physiological toxicity and a low absorption efficiency but good bioavailability [16]. Other studies have shown that sodium selenite has dual effects on the growth of rice seedlings under hydroponic conditions. At low concentrations, selenium treatment promoted rice seedling growth by increasing biomass, root length, and antioxidant capacity. On the contrary, high concentrations of sodium selenite can damage rice, resulting in lower chlorophyll content, reduced biomass, and stunted growth [17]. Therefore, the effects of selenium treatment on rice can be explored by designing different concentration gradients. A previous study suggested that selenium can increase the lignin content and cell wall thickness in plants at the cellular level and that the application of selenium may increase the resistance of plants to lodging [18]. A previous study indicated that the soil application of selenium fertilizer treatment increased plant height and increased the lodging index [19]. This result contradicts the conclusions of previous studies. Therefore, there are still debates about whether selenium is positively or negatively related to rice lodging.
It could be concluded that the concentration, application method, and form of selenium applied to the rice plant are important factors to regulate rice lodging. This study hypothesizes that foliar spraying selenium has benefits for rice lodging resistance, and that the different forms of selenium will show different effects on rice lodging resistance. Therefore, a hydroponic experiment was conducted by using two fragrant rice cultivars that were grown under different forms and levels of selenium fertilizer, and the seedling growth, stem sheath hardness, cellulose, and lignin synthesis were investigated. This study aimed to investigate the ability of different forms and levels of selenium fertilizers to positively regulate rice lodging resistance and provide theoretical support for applying selenium fertilizer and guaranteeing food security.

2. Materials and Methods

2.1. Experimental Description and Treatment

A pot experiment was conducted in October 2020 at the College of Agronomy, South China Agricultural University, Guangzhou, Guangdong Province, China. This experiment was conducted at room temperature and under natural conditions. The temperature ranged from 17 to 29 °C, with an average temperature of 24.15 °C. Humidity ranged from 52% to 81% and the average humidity was 66.86%. The fragrant rice seed varieties used in the experiment were Xiangyaxiangzhan and Yuxiangyouzhan, which were provided by the Rice Research Laboratory of South China Agricultural University. Xiangyaxiangzhan and Yuxiangyouzhan are popular high-quality fragrant rice varieties in South China. Xiangyaxiangzhan is a conventional indica rice variety. It is characterized by a poor agronomic performance, relatively low yield, and high degree of susceptibility to environmental conditions [20]. Yuxiangyouzhan is a super rice variety with great potential for high productivity and wide adaptability [21]. There are differences between the two rice varieties. Therefore, it is possible to explore the effects of selenium treatment on different rice varieties by using Xiangyaxiangzhan and Yuxiangyouzhan as experimental materials.
Two fragrant rice varieties (Xiangyaxiangzhan and Yuxiangyouzhan) were used as experimental materials. The two fragrant rice varieties were treated with two forms of selenium fertilizer: inorganic selenium (sodium selenite) and organic selenium (amino acid-chelated selenium). The selenium fertilizer treatments were applied through foliar spraying, and the five foliar spraying selenium fertilizer treatments were as follows: no selenium fertilizer treatment (CK); foliar spraying of 4 μmol·L−1 amino acid-chelated selenium (T1); foliar spraying of 8 μmol·L−1 amino acid-chelated selenium (T2); foliar spraying of 4 μmol·L−1 sodium selenite (T3); and foliar spraying of 8 μmol·L−1 sodium selenite (T4). Before sowing, the empty grains of Yuxiangyouzhan and Xiangyaxiangzhan were removed by water separation. Seedlings were raised in a substrate, and transplanting was conducted when the seedlings reached the three-leaf stage. The uniform growth seedlings were transplanted into a hydroponic container containing 15 L of culture medium. After three days, the first foliar spray was applied and selenium fertilizer was sprayed for a total of 4 sprays. The culture medium was changed every 7 days. The nutrient solution for the seedling growth in the pot was the Kimura B nutrient solution, and the pH value was adjusted to 4.7–4.9. The nutrient solution included the following: Stock 1 of 500 mL with KNO3 (9.25 g) and Ca(NO3)2·4H2O (43.16 g); Stock 2 of 500 mL with MgSO4·7H2O(67.50 g), K2SO4(7.95 g), and (NH4)2SO4 (24.1 g); Stock 3 of 500 mL with KH2PO4 (12.4 g); Stock 4 of 1000 mL with FeSO4·7H2O (5.57 g) and Na2EDTA (7.45 g); and Stock 5 of 500 mL with MnCl2·4H2O (0.9 g), ZnSO4·7H2O (0.11 g), CuSO4·5H2O (0.04g), H3BO3 (1.43 g), and (NH4)6Mo7O24·4H2O (0.09 g). The stock solution at 1:1000 ratio was the final nutrient solution for the seedling growth. Each hydroponic pot size was 65.0 cm × 41.0 cm × 15.5 cm, with three repetitions pots for each treatment. The seedlings in each pot were at a planting density of 2.0 cm × 2.0 cm.

2.2. Sampling and Measurements

Sampling was carried out one week after treatment. Forty seedlings were sampled to measure the morphological indices. Eighteen seedlings were harvested for measurement of stem sheath hardness. Ninety rice seedlings were randomly selected from each treatment and separated into different plant parts, and then were dipped in liquid nitrogen immediately after sampling. The samples were then stored in a −80 °C refrigerator for later measurement of physiological indices.

2.2.1. Determination of Morphological Indices

Measurements of fresh weight, dry weight, and morphological indicators were carried out in six replicates. The plant height is each plant’s average length from the stem base’s lowest point to the leaf’s highest end. The root length is from the end of the root system to the bottom of the stem base. Leaf age is determined by the number of leaves that have emerged from the main stem and the length of leaves that have not fully emerged. A rough comparison was made with an adjacent leaf as a percentage of the extracted length. The roots, stems, and leaves were separated, and each part’s fresh weight was measured for all three plants. The sum represents the total fresh weight of the seedlings. Each part was dried in an oven at 80 °C until a constant weight was reached, after which the dry weight of each part and the total dry weight were measured.

2.2.2. Determination of Chlorophyll Content

Fresh leaf samples (0.100 g) were taken and macerated with 7.5 mL 95% ethanol and loaded into a 10 mL centrifuge tube. They were put in a dark place for 24 h and then centrifuged at 5000 rpm for 10 min at 4 °C. The absorbance of the supernatant was recorded at 665 nm, 649 nm, and 470 nm. The chlorophyll a content, chlorophyll b content, and total chlorophyll content were estimated [22].

2.2.3. Determination of Lignin and Cellulose Contents

To determine the cellulose and lignin contents in various parts of the rice seedlings, a lignin content detection kit and a cellulose content detection kit (Beijing Suolaibao Technology Co. Ltd., Beijing, China) were used [23].

2.2.4. Determination of Peroxidase (POD) Activity

To determine POD activity, the guaiac lignanol method was employed. The amounts of 100 μL of 0.3% H2O2, 285 μL of 0.2% guaiacol, and 300 μL of 0.05 mol·L−1 sodium phosphate buffer were mixed with 15 μL of crude enzyme extract. The absorbance value was recorded every 30 s at a wavelength of 470 nm, and the total measurement duration was 2 min. The POD activity was defined as U g−1·FW [24].

2.2.5. Determination of the Stem Sheath Hardness

A lodging resistance meter (YYD-1A lodging tester, Topyunong Science and Technology Co., Hangzhou, Zhejiang, China) was used to measure the stem sheath hardness of the rice seedlings [19,25]. The unit of stem sheath hardness is expressed in N.

2.3. Data Analysis

The data were recorded in Microsoft Excel 2019 and analyzed via Statistics version 8.0 for ANOVA and multiple comparisons. The means of each treatment were compared via the least significant difference (LSD) test at 5% probability. Pearson correlation analysis was performed on the data via IBM SPSS Statistics 21 software. Figures were created via Origin 2021.

3. Results

3.1. ANOVA Analysis

The variety significantly affected root fresh weight, total fresh weight, plant height, stem sheath length, leaf area per plant, stem sheath hardness, peroxidase activity in leaves, lignin content in leaves, and lignin content in roots (p < 0.05). The selenium treatment significantly affected root fresh weight, dry weight, plant height, stem sheath length content, number of leaves, total chlorophyll content, stem sheath hardness, peroxidase activity in leaves, peroxidase activity in the stem sheath, and lignin content in roots (p < 0.05). The interaction of variety and selenium treatment significantly affected leaf fresh weight, plant height, stem sheath length, number of leaves, total chlorophyll content, stem sheath hardness, peroxidase activity in the stem sheath, cellulose content in roots, and lignin content in leaves (p < 0.05) (Table 1).

3.2. Fresh Weight

For Xiangyaxiangzhan, compared with the CK treatment the T2 and T4 treatment significantly increased the leaf fresh weights by 33.88% and 32.09%, respectively. The leaf fresh weight of Yuxiangyouzhan slightly decreased (Figure 1A). The fresh weight of the stem sheath of Xiangyaxiangzhan significantly increased by 37.51%, 39.66%, and 45.65% in T1, T2, and T4, respectively (Figure 1B). For Xiangyaxiangzhan, compared with the CK treatment the T4 treatment significantly increased the root fresh weights. The root fresh weight of Yuxiangyouzhan increased by 40.10% and 47.23% under the T3 and T4 treatments, respectively (Figure 1C). Compared with the CK treatment, the T1, T2, and T4 treatments increased the shoot fresh weights in Xiangyaxiangzhan by 30.49%, 37.12%, and 39.44%, respectively (Figure 1D). Compared with the CK treatment, the T2 and T4 treatments significantly increased the total fresh weight in Xiangyaxiangzhan by 36.31% and 44.87%, respectively (Figure 1E).

3.3. Dry Weight

Compared with the CK treatment, the Se treatment increased the leaf dry weight. The leaf dry weight of Yuxiangyouzhan significantly increased by 31.61% under the T1 treatment. The leaf dry weight of Xiangyaxiangzhan significantly increased under the T4 treatment (Figure 2A). Compared with the CK treatment, the T2 and T4 treatments significantly increased the stem sheath dry weight in Xiangyaxiangzhan by 43.94% and 70.38%, respectively (Figure 2B). Compared with the CK treatment, the root dry weights of Xiangyaxiangzhan and Yuxiangyouzhan significantly increased under the T4 treatment (Figure 2C). Compared with the CK treatment, the T2 and T4 treatments significantly increased the shoot dry weight in Xiangyaxiangzhan by 36.14% and 47.08%, respectively. The dry weight of the shoot of Yuxiangyouzhan significantly increased by 32.05% under the T1 treatment (Figure 2D). The total dry weight was improved under the Se treatments. For Xiangyaxiangzhan, compared with the CK treatment the T2 and T4 treatment significantly increased the total dry weight by 35.41% and 52.78%, respectively (Figure 2E).

3.4. Plant Height, Stem Length, Leaf Age, and Leaf Area of Rice Seedlings

For Xiangyaxiangzhan, compared with the CK treatment the Se application treatment slightly increased the plant height. The plant height of Yuxiangyouzhan increased significantly at the T4 treatment as compared to the CK treatment (Figure 3A). Compared with the CK treatment, the stem sheath length of Yuxiangyouzhan significantly increased under the T3 and T4 treatments, respectively (Figure 3B). Compared with the CK treatment, the T1, T3, and T4 treatments significantly increased the number of leaves in Xiangyaxiangzhan (Figure 3C). Compared with the CK treatment, the Se treatments did not lead to changes in the leaf area per plant (Figure 3D).

3.5. Chlorophyll Content in Rice Seedlings

Compared with the CK treatment, the Se treatments promoted the chlorophyll a content whilst they inhibited the chlorophyll b content and regulated the chlorophyll a/b ratio. For Xiangyaxiangzhan, compared with the CK treatment the T1, T2, T3, and T4 treatments significantly increased the chlorophyll a content. The chlorophyll a content in Yuxiangyouzhan significantly increased under the T1, T2, and T3 treatments (Figure 4A). Compared with the CK treatment, the Se treatments resulted in reductions in the chlorophyll b content (Figure 4B). Overall, the Se treatments inhibited the total chlorophyll content in Xiangyaxiangzhan and Yuxiangyouzhan (Figure 4C). Compared with the CK treatment, the T1 and T4 treatments increased the chlorophyll a/b ratio in Xiangyaxiangzhan by 111.05% and 198.13%, respectively. The chlorophyll a/b ratio of Yuxiangyouzhan significantly increased by 100.16% and 123.79% in the T2 and T3 treatments, respectively (Figure 4D).

3.6. Hardness of Rice Seedling Stem Sheaths

Compared with the CK treatment, the T2, T3, and T4 treatments significantly increased the stem sheath hardness in Xiangyaxiangzhan, by 38.31%, 84.86%, and 146.62%, respectively. The stem sheath hardness of Yuxiangyouzhan significantly increased by 38.77%, 21.57%, and 54.73% under the T2, T3, and T4 treatments, respectively (Figure 5).

3.7. Lignin Content in Rice Seedlings

Compared with the CK treatment, the T4 treatment significantly decreased the leaf lignin content in Xiangyaxiangzhan, whilst the leaf lignin content in Yuxiangyouzhan significantly increased in the T3 treatment (Figure 6A). Compared with the CK treatment, the stem sheath lignin content in Xiangyaxiangzhan did not show significant changes, whilst the stem sheath lignin content in Yuxiangyouzhan significantly increased in the T3 and T4 treatments (Figure 6B). Compared with the CK treatment, the T2 treatment significantly decreased the root lignin content in Yuxiangyouzhan. No significant changes in the root lignin in Xiangyaxiangzhan were detected (Figure 6C).

3.8. Cellulose Content in Rice Seedlings

Compared with the CK treatment, the selenium treatments did not significantly affect the cellulose content in the leaves, stem sheath, and roots in Xiangyaxiangzhan and Yuxiangyouzhan, respectively. The cellulose content in the leaves of Yuxiangyouzhan at T1 was significantly higher than that of Xiangyaxiangzhan at T2. The cellulose content in the roots of Yuxiangyouzhan at T2 and T3 was significantly higher than that of Xiangyaxiangzhan at T3 (Figure 7).

3.9. POD Activity in Rice Seedlings

Compared with the CK treatment, the T4 treatment resulted in lower POD activity in leaves in Yuxiangyouzhan (Figure 8A). Compared with the CK treatment, the T1 and T2 treatments increased the stem sheath peroxidase activity by 7.71% and 15.68%, respectively. The stem peroxidase activity of Yuxiangyouzhan significantly increased by 43.63%, 30.25%, and 35.03% under the T1, T3, and T4 treatments, respectively (Figure 8B). For Xiangyaxiangzhan, compared with the CK treatment the T3 and T4 treatments increased the root peroxidase activity by 38.10% and 41.27%, respectively. No significant changes were detected in the root peroxidase activity in Yuxiangyouzhan (Figure 8C).

3.10. Correlation Analysis

To better understand the relationship between a better seedling growth and the stem sheath hardness with other investigated parameters, a correlation analysis was conducted. The results indicated that the total dry weight was positively related to the seedling fresh weight, dry weight, number of leaves, chlorophyll a content, chlorophyll a/b ratio, lignin content in the stem sheath, and peroxidase activity in roots, whilst it was negatively related to the chlorophyll b content, total chlorophyll content, cellulose content in the stem sheath, and peroxidase activity in leaves. The stem sheath hardness was positively related to the seedling fresh weight, dry weight, lignin content in the stem sheath, and peroxidase activity in roots, whilst it was negatively related to the lignin content in roots. Further, this result indicated the relationship between the better seedling growth and a good stem sheath hardness (Figure 9).

4. Discussion

Lodging is an important limiting factor in cereal crop production, as it restricts yield and quality by bending or breaking stems [26]. According to numerous studies, characteristics such as rice variety, plant height, stem length, and stem wall thickness are the main factors affecting rice lodging [27,28,29]. Studies have shown that the lodging index is related to the plant height and stem thickness, wall thickness, and cross-sectional area [30,31,32]. This study revealed that applying Se fertilizer resulted in changes in the height or stem length of rice seedlings, and the changes varied for the Se fertilizer forms and levels (Figure 3). This is consistent with the results of previous research [33].
According to previous research, the addition of selenium can promote lignin synthesis in rice suspension cells under cadmium stress [18] and in pepper plants under cadmium stress [34]. In the present study, selenium fertilizer application was found to have a contributory but not significant effect on the stem lignin content (Figure 6B). Studies have shown that selenium application can promote root biomass as well as the synthesis of cellulose and lignin [35,36]. As shown in Figure 1C and Figure 2C, selenium application increased fresh and dry root weights. This finding is consistent with previous research. As shown in Figure 7C, treatment with low concentrations of sodium selenite promoted the synthesis of root cellulose. All the treatments had an inhibitory effect on the root lignin content. A comparative analysis of the two studies revealed that the cause of the above situation mainly depends on the different doses of selenium received by the rice plants. The dose of fertilizer used in previous studies was lower than that used in this study. It can be concluded that applying selenium fertilizer can promote the synthesis of root cellulose and lignin in rice seedlings. According to previous studies, collapse can be divided into stem and root types [37]. Therefore, it is indicated that the application of selenium fertilizers at a right concentration can promote root growth, which ultimately improves the resistance of rice to lodging.
Previous research has shown that applying selenium fertilizer can increase POD activity in rice seedling stems [38]; this study detected similar results (Figure 8B). POD is an important antioxidant enzyme in plant cells with various biological functions, including antioxidant activity, stress resistance, cell signaling, and lignin biosynthesis [39,40]. This study showed that applying Se fertilizer increased stem POD activity and increased stem lignin and cellulose contents (Figure 6, Figure 7 and Figure 8). The stem structure is mainly composed of several vascular bundles, layers of thick-walled tissue cells, their degree of lignification, and the thickness of the cortical fiber tissue. When the vascular bundles of the stalks are thicker and more numerous, thick-walled tissues have more cell layers and greater lignification. The thicker the cortical fiber tissue is, the greater the resistance of the rice stalks to bending and falling [41]. Figure 5, Figure 6, Figure 7 and Figure 8 show that the application of selenium fertilizer promoted the activity of stem POD and increased the cellulose content, lignin content, and stem sheath hardness. These findings suggest that selenium fertilizer application can increase stem POD activity, promoting increased stem cellulose and lignin contents. Therefore, it can be preliminarily concluded that applying Se fertilizer can increase stem sheath hardness, resulting in a high lodging resistance in rice. The specific reasons and mechanisms still require further research.
Yuxiangyouzhan is a super rice variety suitable for broad regions in South China [42]. Xiangyaxiangzhan is a temperature-sensitive conventionally cultivated rice [43]. The two varieties are different rice varieties. Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8 show that plant height, stem length, fresh root weight, total fresh weight, stem sheath hardness, leaf lignin content, and leaf POD activity significantly differed among the varieties. Moreover, the lignin content in the roots and cellulose in the stems of the two rice varieties tended to increase or decrease under the same concentration gradient of Se fertilizer. On the basis of the different characteristics of the two rice varieties, it can be preliminarily concluded that the difference is due to the different sensitivities of the two rice varieties to selenium fertilizer. This finding is similar to a previous conclusion [44]. Overall, under selenium fertilizer the stem sheath hardness and stem lignin content parameters in Yuxiangyouzhan were greater than those in Xiangyaxiangzhan.
Selenium exists in various forms, such as inorganic, organic, and nanoselenium. Sodium selenite is a type of selenite selenium fertilizer, and amino acid-chelated selenium is organic selenium. According to previous research, plants are more likely to absorb selenite and selenate. However, inorganic selenium is usually not effectively utilized by the human body and can even have specific biotoxic effects. It can be converted into organic selenium through biochemical reactions within the plant [45]. An analysis of Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8 revealed that compared with amino acid-chelated selenium sodium selenite generally has a more substantial promoting effect on the stem, root dry matter, and stem sheath hardness of the two rice seedling varieties. These findings suggest that sodium selenite is more effective than amino acid-chelated selenium in enhancing the resistance of rice to lodging.
Previous studies indicated that Se fertilization promotes chlorophyll accumulation in rice [46,47]. In this study, the Se treatments increased the chlorophyll a content, inhibited the chlorophyll b content and the total chlorophyll content, and regulated the chlorophyll a/b ratio (Figure 4). According to previous research [48], chlorophyll a precedes chlorophyll b when chlorophyll synthesis begins. The conversion of chlorophyll results in the formation of chlorophyll b, the most crucial element in the formation of chlorophyll. The mechanism by which selenium affects the conversion of chlorophyll a to chlorophyll b still requires further research. Figure 4 also shows that the application of selenium fertilizer increased the value of the chlorophyll a/b ratio. According to previous research [49], a low chlorophyll a/b ratio benefits light energy absorption, whereas a high chlorophyll a/b ratio has a greater ability to resist photoinhibition. The chlorophyll a/b ratio was significantly and negatively correlated with the photosynthesis rate. The Se treatment affected the fresh/dry weight of the rice seedlings (Figure 1 and Figure 2). It can be concluded that optimizing the application of selenium fertilizer can promote plant growth to some degree.

5. Conclusions

In summary, the application of selenium fertilizer affected rice growth and physiological indicators. These indicators differ in terms of the interaction between varieties and treatments, such as the regulation of peroxidase activity by foliar spraying of selenium fertilizer. A significant increase in stem sheath hardness was found in rice. After amino acid-chelated selenium and sodium selenite treatment at 8 μmol·L−1, the sheath hardness values of the Yuxiangyouzhan and Xiangyaxiangzhan terpenes significantly increased, by 38.8% and 38.3% and by 54.7% and 146.6%, respectively. Moreover, applying an appropriate concentration of Se fertilizer also promotes indicators such as stem cellulose, root cellulose, and lignin. However, foliar spraying of selenium fertilizer can somewhat inhibit photosynthesis in rice. Therefore, exploring new ways to reduce the negative impacts of selenium fertilizer application is possible. Furthermore, this study did not measure the levels of antioxidant enzymes such as superoxide dismutase and catalase. Future research can explore these antioxidant enzymes in greater depth. Overall, appropriate selenium fertilizer treatment can increase the resistance of rice to lodging. This is due to effects on stem sheath hardness, stem lignin content, root lignin content, etc., which regulate the distribution of dry matter accumulation.

Author Contributions

Conceptualization, Z.M.; methodology, J.Z. (Jingna Zhuang) and Y.D.; formal analysis, J.Z. (Jingna Zhuang), Y.F., J.Z. (Jinxi Zheng) and Y.D.; investigation, Y.D.; data curation, J.Z. (Jingna Zhuang), Y.F., J.Z. (Jinxi Zheng) and Y.D.; writing—original draft preparation, J.Z. (Jingna Zhuang), Y.F. and J.Z. (Jinxi Zheng); writing—review and editing, J.Z. (Jingna Zhuang), Y.F., J.Z. (Jinxi Zheng), Y.D., X.L. and Z.M.; supervision, Z.M.; project administration, Z.M. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the Agricultural Disaster Monitoring Survey of Main Crops in Guangdong (152406016) and the Maturity of Rice Seedling Raising and High-yield Cultivation Technology in South China (152402042).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We gratefully acknowledge the Agricultural Disaster Monitoring Survey of Main Crops in Guangdong and the Maturity of Rice Seedling Raising and High-yield Cultivation Technology in South China.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Effect of selenium application on the fresh weight of fragrant rice. Leaf fresh weight (A), stem sheath fresh weight (B), root fresh weight (C), shoot fresh weight (D), and total fresh weight (E). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 1. Effect of selenium application on the fresh weight of fragrant rice. Leaf fresh weight (A), stem sheath fresh weight (B), root fresh weight (C), shoot fresh weight (D), and total fresh weight (E). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 2. Effects of selenium application on the dry weight of fragrant rice. Leaf dry weight (A), stem sheath dry weight (B), root dry weight (C), shoot dry weight (D), and total dry weight (E). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 2. Effects of selenium application on the dry weight of fragrant rice. Leaf dry weight (A), stem sheath dry weight (B), root dry weight (C), shoot dry weight (D), and total dry weight (E). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 3. Effects of Se application on the morphological indices of fragrant rice. Plant height (A), stem sheath length (B), number of leaves (C), and leaf area per plant (D). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 3. Effects of Se application on the morphological indices of fragrant rice. Plant height (A), stem sheath length (B), number of leaves (C), and leaf area per plant (D). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 4. Effect of selenium application on the chlorophyll content in fragrant rice. Chlorophyll a content (A), chlorophyll b content (B), total chlorophyll content (C), and chlorophyll a/b ratio (D). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 4. Effect of selenium application on the chlorophyll content in fragrant rice. Chlorophyll a content (A), chlorophyll b content (B), total chlorophyll content (C), and chlorophyll a/b ratio (D). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 5. Effects of selenium application on the stem sheath hardness of fragrant rice. Stem sheath hardness. CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 5. Effects of selenium application on the stem sheath hardness of fragrant rice. Stem sheath hardness. CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 6. Effect of selenium application on lignin in fragrant rice. Lignin content in leaves (A), lignin content in stem sheaths (B), and lignin content in roots (C). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 6. Effect of selenium application on lignin in fragrant rice. Lignin content in leaves (A), lignin content in stem sheaths (B), and lignin content in roots (C). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 7. Effect of selenium regulation on cellulose in fragrant rice. Cellulose content in leaves (A), cellulose content in stem sheaths (B), and cellulose content in roots (C). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 7. Effect of selenium regulation on cellulose in fragrant rice. Cellulose content in leaves (A), cellulose content in stem sheaths (B), and cellulose content in roots (C). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 8. Effect of selenium regulation on POD activity in fragrant rice. POD activity in leaves (A), POD activity in the stem sheath (B), and POD activity in roots (C). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
Figure 8. Effect of selenium regulation on POD activity in fragrant rice. POD activity in leaves (A), POD activity in the stem sheath (B), and POD activity in roots (C). CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; T4: 8 μmol·L−1 sodium selenite. Lowercase letters represent significant differences between treatments (LSD test, p < 0.05).
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Figure 9. Correlation analysis between the investigated parameters. V1, Leaf fresh weight; V2, Stem sheath fresh weight; V3, Root fresh weight; V4, Shoot fresh weight; V5, Total fresh weight; V6, Leaf dry weight; V7, Stem sheath dry weight; V8, Root dry weight; V9, Shoot dry weight; V10, Total dry weight; V11, Plant height; V12, Stem sheath length; V13, Number of leaves; V14, Leaf area per plant; V15, Chlorophyll a content; V16, Chlorophyll b content; V17, Total chlorophyll content; V18, Chlorophyll a/b ratio; V19, Stem sheath hardness; V20, Lignin content in leaf; V21, Lignin content in stem sheath; V22, Lignin content in root; V23, Cellulose content in leaf; V24, Cellulose content in stem sheath; V25, Cellulose content in root; V26, Peroxidase activity in leaf; V27, Peroxidase activity in stem sheath; V28, Peroxidase activity in root. * represents significant differences at p < 0.05. Red indicates a positive correlation, and blue indicates a negative correlation. The deeper the color, the greater the correlation.
Figure 9. Correlation analysis between the investigated parameters. V1, Leaf fresh weight; V2, Stem sheath fresh weight; V3, Root fresh weight; V4, Shoot fresh weight; V5, Total fresh weight; V6, Leaf dry weight; V7, Stem sheath dry weight; V8, Root dry weight; V9, Shoot dry weight; V10, Total dry weight; V11, Plant height; V12, Stem sheath length; V13, Number of leaves; V14, Leaf area per plant; V15, Chlorophyll a content; V16, Chlorophyll b content; V17, Total chlorophyll content; V18, Chlorophyll a/b ratio; V19, Stem sheath hardness; V20, Lignin content in leaf; V21, Lignin content in stem sheath; V22, Lignin content in root; V23, Cellulose content in leaf; V24, Cellulose content in stem sheath; V25, Cellulose content in root; V26, Peroxidase activity in leaf; V27, Peroxidase activity in stem sheath; V28, Peroxidase activity in root. * represents significant differences at p < 0.05. Red indicates a positive correlation, and blue indicates a negative correlation. The deeper the color, the greater the correlation.
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Table 1. Analysis of variance (ANOVA) of the investigated parameters.
Table 1. Analysis of variance (ANOVA) of the investigated parameters.
ParameterVariety (V)Treatment (T)V × T
Leaf fresh weightnsns*
Stem sheath fresh weightnsnsns
Root fresh weight***ns
Shoot fresh weightnsnsns
Total fresh weight*nsns
Leaf dry weightns*ns
Stem sheath dry weightns*ns
Root dry weightns*ns
Shoot dry weightns*ns
Total dry weightns*ns
Plant height***
Stem sheath length***
Number of leavesns**
Leaf area per plant*nsns
Chlorophyll a contentns***
Chlorophyll b contentns***
Total chlorophyll contentns***
Chlorophyll a/b rations**
Stem sheath hardness******
Peroxidase activity in leaf***ns
Peroxidase activity in stem sheathns****
Peroxidase activity in rootnsnsns
Cellulose content in leafnsnsns
Cellulose content in stem sheathnsnsns
Cellulose content in rootnsns**
Lignin content in leaf**ns**
Lignin content in stem sheathnsnsns
Lignin content in root***ns
*, significant at p < 0.05; **, significant at p < 0.01; ns, nonsignificant at the p > 0.05 level.
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MDPI and ACS Style

Zhuang, J.; Fang, Y.; Zheng, J.; Duan, Y.; Liu, X.; Mo, Z. Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice. Agriculture 2025, 15, 335. https://doi.org/10.3390/agriculture15030335

AMA Style

Zhuang J, Fang Y, Zheng J, Duan Y, Liu X, Mo Z. Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice. Agriculture. 2025; 15(3):335. https://doi.org/10.3390/agriculture15030335

Chicago/Turabian Style

Zhuang, Jingna, Yilu Fang, Jinxi Zheng, Yan Duan, Xuexue Liu, and Zhaowen Mo. 2025. "Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice" Agriculture 15, no. 3: 335. https://doi.org/10.3390/agriculture15030335

APA Style

Zhuang, J., Fang, Y., Zheng, J., Duan, Y., Liu, X., & Mo, Z. (2025). Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice. Agriculture, 15(3), 335. https://doi.org/10.3390/agriculture15030335

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