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Article

Hormone Metabolism and Substance Accumulation in Cucumber Plants: Downy Mildew Infection and Potassium Stress

by
Yafei Wang
1,*,
Qiang Shi
2,*,
Jiale Lin
1,
Xuanting Lu
1,
Bin Ye
1,
Huanxing Lv
1,
Xiaoxue Du
3 and
Tianhua Chen
4
1
School of Agricultural Engineering, Jiangsu University, Zhenjiang 212013, China
2
School of Science and Technology, Shanghai Open University, Shanghai 200433, China
3
School of Optoelectronic Engineering, Changzhou Institute of Technology, Changzhou 213032, China
4
College of Biological and Agricultural Engineering, Jilin University, Changchun 130022, China
*
Authors to whom correspondence should be addressed.
Agriculture 2025, 15(9), 994; https://doi.org/10.3390/agriculture15090994
Submission received: 8 April 2025 / Revised: 29 April 2025 / Accepted: 1 May 2025 / Published: 3 May 2025
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Abstract

:
In order to understand the effects of biotic stress and abiotic stress on hormone metabolism and substance accumulation in cucumber, two different infection levels of downy mildew were set, B0 (diseased) and B1 (disease-free), and T1 (K-50%: 50% of normal potassium application), T2 (K-100%: normal potassium application), and T3 (K-150%: 150% of normal potassium application). The results show that the hormone metabolism in the cucumber plants was measured on the 15th day after transplanting. Compared with the B1T2 treatment, the cane sugar contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 35.87%, 23.29%, 25.41%, 12.98%, and 6.05%; the soluble sugar contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 36.16%, 27.13%, 31.97%, 9.89%, and 7.84%; the hydrogen peroxide (H2O2) contents in the B0T1, B0T2, B0T3, and B1T1 treatments increased by 30.59%, 21.08%, 14.74%, and 9.2%; the catalase (CAT) contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 53.78%, 36.57%, 47.18%, 34.75%, and 16.39%; the superoxide dismutase (SOD) contents in the B0T1, B0T2, B0T3, and B1T1 treatments increased by 30.28%, 22.59%, 12.9%, and 13.17%; and the polyphenol oxidase (PPO) contents in the B0T1, B0T2, B0T3, and B1T1 treatments increased by 39.38%, 25.27%, 4.49%, and 23.05%, respectively. Compared with the B1T2 treatment, the malondialdehyde (MDA) contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments increased by 82.78%, 23.07%, 60.21%, 74.55%, and 25.12%. Compared with the B1T2 treatment, the hydrogen peroxide (H2O2), superoxide dismutase (SOD), and polyphenol oxidase (PPO) contents in the B1T3 treatment decreased by 16.11%, 4.36%, and 4.43%. On the 20th day after transplanting the cucumber plants, downy mildew infection and potassium stress had significant effects on the dry and fresh weights of the leaves, stems, and roots (p < 0.05). The B0T1 treatment had the greatest effect on the dry and fresh weights of the leaves, stems, and roots of the cucumber plants. The B1T3 treatment had the least effect on the dry and fresh weights of the leaves, stems, and roots of the cucumber plants. This research can provide a theoretical basis for the study and cultivation of cucumber stress resistance.

1. Introduction

The protected cultivation area in China is more than 4.2 million hectares, and it is widely distributed in China, ranking first in the world in total area [1,2]. It is the main support of China’s vegetable basket project and one of the important ways to increase farmers’ incomes [3,4]. Cucumber is deeply loved by consumers because of its rich taste and nutritional value, and the cucumber cultivation area accounts for the main part of the protected cultivation area in China [5,6]. Cucumber is inevitably exposed to abiotic stress (such as salt stress, drought stress, high-temperature stress, low-temperature stress, and UV-B stress) and biological stress (such as bacterial diseases and fungal diseases) during its growth [7,8,9]. Therefore, it is particularly important to understand its stress response and adaptation mechanism under different stresses and be effective in preventing greenhouse airborne diseases in time [10,11,12].
Cucumber downy mildew is caused by Pseudoperonospora cubensis infection. After the disease occurs, it mainly harms the leaves of cucumber plants, but also the stems and inflorescences of cucumber plants [1,4]. It can occur from the seedling stage to the growth stage of cucumbers, especially when cucumbers enter the harvest stage. After the disease occurs, most of the leaves of cucumber plants will die within one or two weeks, and the cucumber field will be yellow [13,14]. Cucumber downy mildew will increase year by year with the expansion of the cultivation area and the increase in the years of continuous cropping, which can seriously reduce production, with a yield loss of 20–50% or even no harvest [15,16].
Potassium fertilizer, as a major element for plant growth, is very important for plant growth and development. In the physiological and biochemical reaction network of plants, potassium participates in a variety of processes [17,18]. Potassium ions are needed as an auxiliary factor in enzyme activation to give full play to enzyme activity, thus promoting various chemical reactions to be carried out efficiently. Photosynthesis is the key pathway for plants to convert light energy into chemical energy, in which potassium affects the normal operation of photosynthetic institutions, and the absorption, transmission, and transformation of light energy are inseparable from the role of potassium [19,20]. Respiration is an important way for plants to obtain energy, and potassium also participates in it to ensure smooth respiration and metabolism. In carbohydrate metabolism, potassium plays an indispensable regulatory role in the synthesis, transportation, and transformation of carbohydrates. During the synthesis of proteins, potassium helps to maintain the charge balance in cells, promotes the transport and integration of amino acids, and provides a suitable environment for the synthesis of proteins [21,22]. At the same time, potassium plays a central role in maintaining the osmotic pressure of plant cells. By adjusting the concentration of potassium ions in cells, the normal swelling pressure of cells is ensured, and the morphological and functional stability of plant cells is ensured. In the process of regulating the opening and closing of stomata, the transmembrane transport of potassium ions promotes the guard cells to absorb or lose water, thus controlling the opening and closing of stomata, which is very important for gas exchange and water balance between plants and the external environment [23,24]. Moreover, an adequate potassium supply can significantly enhance the stress resistance of plants. Whether dealing with abiotic stresses, such as drought, flood, high temperature, and low temperature, or resisting biotic stresses, such as pests and diseases, potassium can help plants improve their self-defense ability [25,26].
However, there are relatively few studies on the effects of biotic and abiotic stresses on hormone metabolism and substance accumulation in cucumber plants, and a systematic understanding has not yet been formed [15,27]. Therefore, considering the effects of downy mildew infection and potassium stress on hormone metabolism and substance accumulation in cucumber plants can provide a theoretical basis for the research and cultivation of cucumber stress resistance.

2. Materials and Methods

2.1. Study Site and Experimental Design

The experiment was carried out in the Venlo-type greenhouse of Jiangsu University. The experimental cucumber variety was “Jinyou No.1”, selected by the Tianjin Academy of Agricultural Sciences. The experiment started on 25 July 2024 and ended on 18 August 2024. On 29 July 2024, perlite was poured into a flowerpot with a volume of 10 L, and the dust in the perlite was rinsed with tap water. On 30 July 2024, the well-grown and similar cucumber seedlings with two leaves and one heart were taken out of the pot and transplanted. The greenhouse temperature range during the experiment was 16.83~36.47 °C. The temperature range during the day was 20.52~36.47 °C. The average temperature was 25.8 °C. The average relative humidity was 85.6% RH (23.7~95.6% RH). The experimental design consisted of 6 treatments, each of which was repeated 6 times. B0 (diseased) and B1 (disease-free), and T1 (K-50%: 50% of normal potassium application), T2 (K-100%: normal potassium application), and T3 (K-150%: 150% of normal potassium application). Therefore, the six test treatments were B0T1, B0T2, B0T3, B1T1, B1T2, and B1T3. Infected cucumber plants and uninfected cucumber plants were cultivated in different greenhouses. The plant spacing for cucumber cultivation was 50 cm, the row spacing was 32 cm, and the ridge spacing was 60 cm.
The trial treatment began on 6 August 2024. The prepared suspension of pathogenic bacterial spores was sprayed on the cucumber leaves with a spray bottle from 6:00 to 7:00 p.m. The control group was tested by spraying sterile water. The cucumber downy mildew disease degrees were classified according to GB/T179800.26-2000 [28]. In addition, during the experimental treatment period, 400 mL of a nutrient solution was poured into the experimental cucumber plant samples from 8:00 to 9:00 a.m. every day. The dosages of KNO3 and NaNO3 in the K-50% test treatment were 303 g and 255 g, respectively. The dosage of KNO3 in the K-100% and K-150% test treatments was 606 g. The dosage of KCl in the K-150% test treatment was 223 g. The usage of elements in other nutrient solutions is detailed in reference [15].

2.2. Experimental Data Acquisition

On the 15th day after transplanting, the hormone metabolism was determined (the disease degree of the cucumber plants was grade 3). The classification of disease severity was based on reference [28]. The content of malondialdehyde (MDA) in the cucumber leaves was determined by the TBA method. The superoxide dismutase (SOD) content in the cucumber leaves was determined by the cytochrome C reduction method. The content of hydrogen peroxide and catalase (CAT) in the cucumber leaves was determined by ammonium molybdate colorimetry. The activity of polyphenol oxidase (PPO) is often determined by spectrophotometry. The measuring principle is that the product formed by the oxidation of catechol, catalyzed by PPO, has a maximum light absorption peak at 420 nm. The soluble sugar content in the cucumber leaves was determined by anthrone colorimetry. Based on the color reaction of sucrose hydrolysate and resorcinol under acidic conditions, the sucrose content in the cucumber leaves was determined at a 480 nm wavelength [29]. The kits for the determination of the malondialdehyde (MDA), superoxide dismutase (SOD), hydrogen peroxide (H2O2), catalase (CAT), polyphenol oxidase (PPO), and soluble sugar contents in the cucumber leaves were purchased from the Chengjian Institute of Bioengineering. The determination kit for the sucrose content in the cucumber leaves was purchased from Beijing Suoleibao Technology Co., Ltd. The test equipment was a 721 Visible Spectrophotometer (Shanghai Youke Instrument Co., Ltd. Shanghai, China).
On the last day of the experiment, the leaves, stems, and roots of the cucumber plants were collected, and the fresh weights of the leaves and stems were measured by an electronic scale (accuracy: 0.01 g). In order to reduce the experimental error, before the measurement of the accumulation of fresh material at the roots, the excess water on the surfaces of the roots was absorbed with absorbent paper, weighed with a precision electronic scale (accuracy: 0.001 g), and then put into an envelope after measurement. After measuring the accumulation of fresh materials in the leaves, stems, and roots of the cucumber plants, they were placed in an oven, and the temperature of the oven was set at 105 °C and kept at a constant temperature for 15 min. Then, the temperature of the oven was set at 80 °C, and the leaves, stems, and roots of the cucumber plants continued to be dried and dried until their weight was constant [16]. At last, the dry weights of the cucumber leaves, stems, and roots were measured by a precision electronic scale (accuracy 0.001 g).

2.3. Statistical Analyses

The statistical analysis software SPSS_29.0.2.0 was used to analyze the data. ANOVA was used to analyze the statistical differences between the two groups. The minimum significant difference (LSD) test was used to determine the level of significance (p < 0.05).

3. Results

3.1. Hormone Metabolism

The effects of the different experimental treatments on hormone metabolism in the cucumber plants are shown in Table 1. Downy mildew infection and potassium stress had significant effects on the sucrose and soluble sugar contents in the cucumber leaves (p < 0.05). Compared with the B1T2 treatment, the cane sugar contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 35.87%, 23.29%, 25.41%, 12.98%, and 6.05%; the soluble sugar contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 36.16%, 27.13%, 31.97%, 9.89%, and 7.84%; the hydrogen peroxide (H2O2) contents in the B0T1, B0T2, B0T3, and B1T1 treatments increased by 30.59%, 21.08%, 14.74%, and 9.2%; the catalase (CAT) contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 53.78%, 36.57%, 47.18%, 34.75%, and 16.39%; the superoxide dismutase (SOD) contents in the B0T1, B0T2, B0T3, and B1T1 treatments increased by 30.28%, 22.59%, 12.9%, and 13.17%; the polyphenol oxidase (PPO) contents in the B0T1, B0T2, B0T3, and B1T1 treatments increased by 39.38%, 25.27%, 4.49%, and 23.05%; and the malondialdehyde (MDA) contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments increased by 82.78%, 23.07%, 60.21%, 74.55%, and 25.12%. Downy mildew infection and potassium stress had significant effects on the hydrogen peroxide (H2O2), catalase (CAT), superoxide dismutase (SOD), polyphenol oxidase (PPO), and malondialdehyde (MDA) contents in the cucumber leaves (p < 0.05). The hydrogen peroxide (H2O2) content in the cucumber leaves treated with B1T3 decreased by 16.11%. The superoxide dismutase (SOD) content in the cucumber leaves treated with B1T3 decreased by 4.36%. The levels of polyphenol oxidase (PPO) in the cucumber leaves treated with B1T3 decreased by 4.43%.

3.2. Substance Accumulation

The effects of the different experimental treatments on substance accumulation in the cucumber plants are shown in Figure 1. The dry and fresh weights of the cucumber leaves, the dry and fresh stem weights, and the dry and fresh root weights were significantly affected by the different potassium treatments and downy mildew infection. Compared with the B1T2 treatment, the fresh leaf weight contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 58.13%, 25.39%, 41.29%, 15.49%, and 7.62%; the dry leaf weight contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 53.63%, 43.37%, 48.29%, 25.75%, and 25.48%; the fresh stem weight contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 57.19%, 18.2%, 32.75%, 13.59%, and 4.62%; the dry stem weight contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 27.52%, 13.74%, 15.54%, 10.85%, and 6.46%; the fresh root weight contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 40.06%, 22.18%, 27.94%, 32.96%, and 10.03%; and the dry root weight contents in the B0T1, B0T2, B0T3, B1T1, and B1T3 treatments decreased by 33.14%, 21.54%, 24.63%, 31.92%, and 18.83%.

4. Discussion

4.1. Cane Sugar and Soluble Sugar

Downy mildew destroys chloroplasts and other organelles in leaves and affects normal photosynthesis. Photosynthesis is the basis for the synthesis of sugar substances such as sucrose. A decrease in photosynthetic capacity leads to a decrease in the synthesis of photosynthetic products, and the synthesized amount of sucrose also decreases [30,31]. When cucumber plants resist downy mildew infection, they initiate a series of defense reactions, which require a lot of energy. Sucrose, as an important energy source, is decomposed and utilized in priority, resulting in a further reduction in its content in the plant. Sufficient potassium can promote photosynthesis in cucumber, improve photosynthetic efficiency, and provide more raw materials for sucrose synthesis. At the same time, potassium can also participate in the regulation of sugar metabolism in plants and promote the synthesis of sucrose [32,33]. Cucumber plant growth is inhibited, photosynthesis is weakened, and sucrose synthesis decreases when potassium is deficient. Moreover, potassium deficiency affects nutrient transport and distribution in the plant, resulting in the insufficient accumulation of sucrose in the leaves. Excessive potassium may inhibit the absorption and utilization of other elements (such as nitrogen, calcium, magnesium, etc.) by crops, resulting in element imbalance, affecting physiological metabolism in plants, and, thus, interfering with the synthesis, transportation, and metabolism of sucrose, and its content may also decrease [34,35,36].
The soluble sugar content in cucumbers usually changes after infection with downy mildew. On the one hand, due to the destruction of the chloroplast structure and function of leaves by bacteria, photosynthesis is affected, resulting in a decrease in the synthesis of photosynthetic products and a corresponding decrease in the synthesis of soluble sugars. On the other hand, in order to resist the infection of bacteria, plants start a series of defense reactions and consume a lot of energy and substances. Soluble sugar is consumed as an important energy source, and its accumulation in the plant decreases [37,38]. In addition, when the disease is severe, the leaves dry up and die, and photosynthesis cannot proceed normally, which further aggravates the reduction in the soluble sugar content. However, other studies have found that in the early stage of the disease, plants may regulate their metabolism to convert part of the sugars into soluble sugars so as to improve the osmotic pressure in cells and enhance the disease resistance of the plants. At this time, the content of soluble sugars may rise briefly, but it will eventually decline with the development of the disease [39,40]. An appropriate potassium supply can promote the synthesis and transportation of photosynthetic products, enabling the smooth accumulation of soluble sugar from leaves to fruits and other parts, thereby increasing the content of soluble sugar in cucumber fruits. At the same time, potassium can also participate in the regulation of sugar metabolism in plants, promote the synthesis of starch and other polysaccharides, and indirectly affect the content of soluble sugar [41,42]. When potassium is deficient, cucumber plant growth is inhibited, photosynthesis is weakened, sugar synthesis is reduced, and sugar transport and distribution are affected, resulting in an insufficient accumulation of soluble sugar in the leaves [43,44].

4.2. Hydrogen Peroxide (H2O2) and Catalase (CAT)

Downy mildew activates cucumber plants’ defense response, resulting in the production of reactive oxygen species (ROS) in large quantities, and the content of H2O2, as an important ROS, increases significantly [45]. When potassium is deficient, the growth and metabolism of cucumber plants are inhibited, the intracellular reoxidation–reduction balance is unbalanced, reactive oxygen species accumulate, and the content of H2O2 increases. Long-term potassium deficiency can lead to inadequate plant nutrition and impaired cell membrane structure and function, and can further aggravate the accumulation of H2O2 [46,47].
In the early stages of downy mildew infection, the activity of catalase (CAT) increases rapidly in order to remove excessive H2O2 and protect cells from oxidative damage. As the disease progresses, when the bacteria multiply and seriously damage the structure and function of plant cells, the synthesis and activity maintenance of catalase (CAT) may be affected, resulting in a decline in its activity [48]. An appropriate supply of potassium is helpful to maintain the activity of catalase (CAT) in cucumber plants so that the antioxidant system in the cells can effectively remove reactive oxygen species and keep a stable content of H2O2. When potassium is deficient, the early plants may increase the activity of catalase (CAT) by inducing the expression of the H2O2 gene so as to enhance the ability to remove reactive oxygen species. However, with the aggravation of potassium deficiency and the extension of time, due to poor plant growth, protein synthesis is blocked, and the synthesis and stability of catalase (CAT) are affected, and its activity will eventually decline [49]. When potassium is excessive, due to the imbalance of elements and physiological metabolism disorders in the plant body, the activity of catalase (CAT) may also be inhibited, affecting its ability to remove H2O2 and resulting in the accumulation of H2O2 [50,51].

4.3. Superoxide Dismutase (SOD), Polyphenol Oxidase (PPO), and Malondialdehyde (MDA)

Downy mildew makes cucumber produce a lot of reactive oxygen species (ROS), which destroy the redox balance in cells. In order to remove excessive reactive oxygen species and protect cells from oxidative damage, cucumber plants activate the antioxidant defense system, in which SOD is one of the key antioxidant enzymes [52]. It is able to convert superoxide anions into hydrogen peroxide, which is then further broken down into water and oxygen by catalase (CAT), thereby reducing the damage by oxidative stress to cells. In the early stage of downy mildew infection, the activity of SOD in cucumber leaves usually increases significantly to enhance the antioxidant capacity of the plant and resist the invasion of pathogens [32]. However, with the development of the disease, SOD activity may decline when the stress of the plant exceeds its own regulatory ability, which may be due to the proliferation and infection of bacteria that lead to serious damage to the structure and function of plant cells, affecting the synthesis or maintenance of SOD activity [45].
In the case of sufficient potassium, the SOD activity in cucumber roots and leaves can be maintained at a high level because potassium can be used as an activator of SOD to promote its activity [46]. At the same time, potassium can also participate in regulating the osmotic pressure and ion balance in plant cells, stabilize the structure of cell membranes, reduce the production of reactive oxygen species, and indirectly protect the activity of antioxidant enzymes, such as SOD. When potassium stress occurs, whether it is insufficient or excessive potassium, it has an adverse effect on the growth and metabolism of cucumber [48]. When potassium is deficient, cucumber plant growth is inhibited, photosynthesis is weakened, the intracellular redox balance is unbalanced, and reactive oxygen species accumulate, which induce an increase in SOD activity to remove the excessive reactive oxygen species. However, long-term potassium deficiency will lead to plant nutrient deficiency and reduce SOD activity. Excessive potassium may inhibit the absorption and utilization of other elements (such as calcium, magnesium, etc.) by crops, leading to element imbalance, which, in turn, affects the physiological metabolism of plants, and the activity of SOD is also inhibited to some extent [53].
In the early stage of plant disease, the defense mechanism is activated, and PPO activity increases. It can work with peroxidase (POD) to oxidize polyphenols in plants into toxic ketones, thus inhibiting the growth and reproduction of pathogens. At the same time, it also participates in the synthesis of lignin, enhances the mechanical strength of host cells, and limits the uptake of nutrients by pathogens. However, with the development of the disease, when the bacteria proliferate and seriously damage the structure and function of plant cells, the synthesis and activity maintenance of PPO may be affected, resulting in a decline in its activity [54]. An appropriate potassium supply is helpful to maintain the normal physiological function of cucumber plants and keep PPO activity at a relatively stable level. When potassium is deficient, the growth and metabolism of cucumber are affected, the intracellular redox balance is unbalanced, and reactive oxygen species accumulate, which may induce an increase in PPO activity to enhance the plant’s defense ability. However, long-term potassium deficiency will lead to plant nutrient deficiency, affect the synthesis and stability of PPO, and, eventually, reduce its activity, which, in turn, will affect the physiological metabolism of the plants, and PPO activity may also be inhibited to a certain extent [50].
Downy mildew destroys the normal physiological function of plant cells and leads to the accumulation of reactive oxygen species (ROS) in cells. These reactive oxygen species can trigger membrane lipid peroxidation and increase the content of malondialdehyde (MDA). Under the condition of sufficient potassium, cucumber plants can maintain a good growth state, the stability of the cell membranes is high, and the antioxidant system in the cells can effectively remove reactive oxygen species, so the content of MDA is at a low level. When potassium is deficient, the growth and metabolism of cucumber plants are inhibited, photosynthesis is weakened, the intracellular redox balance is unbalanced, reactive oxygen species accumulate, membrane lipid peroxidation is enhanced, and the MDA content is increased [55]. Long-term potassium deficiency leads to plant nutrient deficiency, impaired cell membrane structure and function, and the further intensification of MDA accumulation [56].

4.4. Substance Accumulation

As the leaves gradually dry out, the dry matter accumulation is also affected, and the dry weight is reduced [15,57]. When the disease is severe, a large number of leaves wither and die, and the dry and fresh weights of the whole leaves are significantly reduced. Although downy mildew is less harmful to stems than leaves, it can affect the vascular bundle system of stems and hinder the transport of water and nutrients. This results in inhibited stem growth and a slow gain in fresh weight. At the same time, due to the lack of a nutrient supply, the accumulation of dry matter in the stems is also reduced, and the dry weight is relatively low compared with normal plants. Downy mildew mainly affects the above-ground part, but lesions in the above-ground part can affect the root system. On the one hand, the photosynthesis in leaves is weakened, the delivery of photosynthetic products to the roots is reduced, growth is inhibited, and the increase in fresh and dry weights is restricted. On the other hand, overall physiological and metabolic disorders in plants may affect the ability of roots to absorb water and nutrients, further leading to poor root development and a decrease in dry and fresh root weights [58,59].
When potassium is deficient, cucumber leaves grow slowly, the leaf area is small, the color is pale, and the edges are yellow. This is because potassium participates in the processes of photosynthesis and carbohydrate metabolism and transportation, and potassium deficiency leads to poor transport of photosynthetic products, reduced accumulation in leaves, and reduced fresh and dry weights of leaves [16,60]. An appropriate amount of potassium contributes to the robust growth of stems, promotes the synthesis of cellulose and lignin, makes stems tough, enhances lodging resistance, and increases the fresh and dry weights of stems. When potassium is deficient, the stems are thin, growth is slow, the fresh weight increase is not obvious, and the dry weight is lower than the normal level due to the decrease in cellulose and lignin synthesis. Excessive potassium may destroy the ion balance in the plant, affect the normal physiological function of the stems, and negatively affect the dry and fresh weights of the stems [61]. A proper amount of potassium can promote the growth and vitality of roots and develop roots, and the fresh and dry weights of the roots are higher. When potassium deficiency occurs, root growth is inhibited, root elongation and lateral root development are hindered, root vitality is decreased, and the ability to absorb water and nutrients is weakened, resulting in a decrease in the fresh and dry root weights. Excessive potassium may cause ionic toxicity to roots, affect the normal physiological function of root cells, inhibit root growth, and affect their dry and fresh weights [62,63].

5. Conclusions

In order to understand the effects of biotic stress and abiotic stress on hormone metabolism and substance accumulation in cucumber, two different infection levels of downy mildew were set, B0 (diseased) and B1 (disease-free), and T1 (K-50%: 50% of normal potassium application), T2 (K-100%: normal potassium application), and T3 (K-150%: 150% of normal potassium application). The results show that on the 15th day after transplanting, the hormone metabolism in cucumber plants was measured (the incidence of the cucumber plants was grade 3). Downy mildew infection and potassium stress had significant effects on the cane sugar, soluble sugar, hydrogen peroxide (H2O2), catalase (CAT), polyphenol oxidase (PPO), malondialdehyde (MDA), and superoxide dismutase (SOD) contents in the cucumber leaves (p < 0.05). On the 20th day after transplanting the cucumber plants (the disease degree of the cucumber plants was grade 7), downy mildew infection and potassium stress had significant effects on the dry and fresh weights of the leaves, stems, and roots (p < 0.05). This study can provide a theoretical basis for cucumber stress resistance cultivation in greenhouses.

Author Contributions

Conceptualization, Y.W. and Q.S.; methodology, Y.W., Q.S. and T.C.; software, Y.W., Q.S. and X.D.; validation, Y.W., Q.S., X.D. and T.C.; formal analysis, Y.W.; investigation, Y.W. and Q.S.; resources, Y.W. and Q.S.; data curation, Y.W., Q.S., J.L., X.L., B.Y., H.L., X.D. and T.C.; writing—original draft preparation, Y.W., Q.S., J.L., X.L., B.Y., H.L., X.D. and T.C.; writing—review and editing, Y.W., Q.S., J.L., X.L., B.Y., H.L., X.D. and T.C.; visualization, Y.W., Q.S., X.D. and T.C.; supervision, Y.W.; project administration, Y.W. and Q.S.; funding acquisition, Y.W. and Q.S. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by the National Natural Science Foundation of China (grant no. 32201686) and the Shanghai Oriental Talent Program Youth Project (QNJY2024095).

Data Availability Statement

The data are contained within this article.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Wang, Y.; Shi, Q.; Xu, G.; Yang, N.; Chen, T.; Taha, M.F.; Mao, H. Transmission Route of Airborne Fungal Spores for Cucumber Downy Mildew. Horticulturae 2025, 11, 336. [Google Scholar] [CrossRef]
  2. Zhang, C.; Li, X.Y.; Yan, H.F.; Ullah, I.; Zuo, Z.Y.; Li, L.L.; Yu, J.J. Effects of irrigation quantity and biochar on soil physical properties, growth characteristics, yield and quality of greenhouse tomato. Agric. Water Manag. 2020, 241, 106263. [Google Scholar] [CrossRef]
  3. Pan, L.X.; Zhou, C.G.; Jing, J.; Zhuang, M.; Zhang, J.C.; Wang, K.; Zhang, H.Y. Metabolomics analysis of cucumber fruit in response to foliar fertilizer and pesticides using UHPLC-Q-Orbitrap-HRMS. Food Chem. 2022, 369, 130960. [Google Scholar] [CrossRef]
  4. Wang, Y.F.; Li, T.Z.; Chen, T.H.; Zhang, X.D.; Taha, M.F.; Yang, N.; Mao, H.P.; Shi, Q. Cucumber Downy Mildew Disease Prediction Using a CNN-LSTM Approach. Agriculture-basel. Agriculture 2024, 14, 1155. [Google Scholar] [CrossRef]
  5. Shi, J.Y.; Wang, Y.Y.; Li, Z.H.; Huang, X.W.; Shen, T.T.; Zou, X.B. Simultaneous and nondestructive diagnostics of nitrogen/magnesium/potassium-deficient cucumber leaf based on chlorophyll density distribution features. Biosyst. Eng. 2021, 212, 458–467. [Google Scholar] [CrossRef]
  6. Yan, H.F.; Acquah, S.J.; Zhang, J.Y.; Wang, G.Q.; Zhang, C.; Darko, R.O. Overview of modelling techniques for greenhouse microclimate environment and evapotranspiration. Int. J. Agric. Biol. Eng. 2021, 14, 1–8. [Google Scholar] [CrossRef]
  7. Xu, Y.H.; Ma, Y.; Luz, C.M.; Angel, S.M.M.; Wang, Q.J. Compost biochemical quality mediates nitrogen leaching loss in a greenhouse soil under vegetable cultivation. Geoderma 2020, 358, 113984. [Google Scholar] [CrossRef]
  8. Rasool, G.; Guo, X.P.; Wang, Z.C.; Hassan, M.; Aleem, M.; Javed, Q.; Chen, S. Effect of Buried Straw Layer Coupled with Fertigation on Florescence and Yield Parameters of Chinese Cabbage Under Greenhouse Environment. J. Soil Sci. Plant Nutr. 2020, 20, 598–609. [Google Scholar] [CrossRef]
  9. Zhu, W.D.; Sun, J.; Wang, S.M.; Shen, J.F.; Yang, K.F.; Zhou, X. Identifying Field Crop Diseases Using Transformer-Embedded Convolutional Neural Network. Agriculture 2022, 12, 1083. [Google Scholar] [CrossRef]
  10. Zhu, J.; Sun, L.; Ju, F.; Wang, Z.; Xiong, C.; Yu, H.; Yu, K.; Huo, Y.; Khattak, W.A.; Hu, W.; et al. Potassium Application Increases Cotton (Gossypium hirsutum L.) Fiber Length by Improving K+/Na+ Homeostasis and Potassium Transport Capacity in the Boll-Leaf System under Moderate Salinity. Agronomy 2020, 12, 2962. [Google Scholar] [CrossRef]
  11. Li, M.Q.; Li, J.Y.; Wei, X.H.; Zhu, W.J. Early diagnosis and monitoring of nitrogen nutrition stress in tomato leaves using electrical impedance spectroscopy. Int. J. Agric. Biol. Eng. 2017, 10, 194–205. [Google Scholar] [CrossRef]
  12. Mustapha, A.T.; Zhou, C.S.; Amanor-Atiemoh, R.; Ali, T.A.A.; Wahia, H.; Ma, H.L.; Sun, Y.H. Efficacy of dual-frequency ultrasound and sanitizers washing treatments on quality retention of cherry tomato. Innov. Food Sci. Emerg. Technol. 2022, 62, 102348. [Google Scholar] [CrossRef]
  13. Shi, Y.; Yang, Q.Y.; Zhao, Q.H.; Dhanasekaran, S.; Ahima, J.; Zhang, X.Y.; Zhou, S.Q.; Droby, S.; Zhang, H.Y. Aureobasidium pullulans S-2 reduced the disease incidence of tomato by influencing the postharvest microbiome during storage. Postharvest Biol. Technol. 2022, 185, 111809. [Google Scholar] [CrossRef]
  14. Raynaldo, F.A.; Dhanasekaran, S.; Ngea, G.L.N.; Yang, Q.Y.; Zhang, X.Y.; Zhang, H.Y. Investigating the biocontrol potentiality of Wickerhamomyces anomalus against postharvest gray mold decay in cherry tomatoes. Sci. Hortic. 2021, 285, 110137. [Google Scholar] [CrossRef]
  15. Mao, H.P.; Wang, Y.F.; Yang, N.; Liu, Y.; Zhang, X.D. Effects of nutrient solution irrigation quantity and powdery mildew infection on the growth and physiological parameters of greenhouse cucumbers. Int. J. Agric. Biol. Eng. 2022, 15, 68–74. [Google Scholar] [CrossRef]
  16. Wang, Y.F.; Ma, G.X.; Du, X.X.; Liu, Y.; Wang, B.; Xu, G.L.; Mao, H.P. Effects of Nutrient Solution Irrigation Quantity and Downy Mildew Infection on Growth and Physiological Traits of Greenhouse Cucumber. Agronomy 2020, 10, 1921. [Google Scholar] [CrossRef]
  17. Li, C.; Zeng, Q.P.; Han, Y.Z.; Zhou, X.F.; Xu, H.W. Effects of Bacillus subtilis on Cucumber Seedling Growth and Photosynthetic System under Different Potassium Ion Levels. Biology 2024, 13, 348. [Google Scholar] [CrossRef]
  18. Dabu, X.; Li, S.; Cai, Z.; Ge, T.; Hai, M. The effect of potassium on photosynthetic acclimation in cucumber during CO2 enrichment. Photosynthetica 2019, 57, 640–645. [Google Scholar] [CrossRef]
  19. Mao, H.P.; Liu, Y.; Wang, Y.F.; Ma, G.X.; Wang, B.; Du, X.X.; Shi, Q.; Ni, J.H. Response of growth, photosynthesis, dry matter partition and roots to combined nitrogen-potassium stress in cucumber. Qual. Assur. Saf. Crop. Foods 2022, 14, 45–53. [Google Scholar] [CrossRef]
  20. Alotaibi, M.M.; El Nagy, M.M.M.; Almuziny, M.; Alsubeie, M.S.; Abo-Zeid, A.A.I.; Alzuaibr, F.M.; Alasmari, A.; Albalawi, B.F.; Abd-Elwahed, A.H.M.; Ismail, K.A.; et al. The Effect of Foliar Application with Naphthalene Acetic Acid and Potassium Nitrate on the Growth, Sex Ratio, and Productivity of Cucumbers (Cucumis sativas L.) under High Temperatures in Semi-Arid Areas. Agronomy 2024, 14, 1202. [Google Scholar] [CrossRef]
  21. Li, N.; Wang, X.X.; Xue, Z.J.; Li, Q.Y. Water and potassium utilization efficiency and yield and quality of cucumber (Cucumis sativus L.). Sci. Hortic. 2024, 330, 113025. [Google Scholar] [CrossRef]
  22. Lee, N.R.; Kim, Y.X.; Lee, Y.; Lee, C.; Song, Y.; Park, H.; Lee, C.H.; Lee, Y. Metabolomics Reveals the Effects of Nitrogen/Phosphorus/Potassium (NPK) Fertilizer Levels on Cucumber Fruit Raised in Different Nutrient Soils. Metabolites 2024, 14, 102. [Google Scholar] [CrossRef]
  23. Shi, Q.; You, L.; Wang, Y.; Du, X.; Chen, T. Effects of Downy Mildew Infection and Potassium on Growth and Physiological Traits of Greenhouse Cucumber. Agronomy 2025, 15, 1017. [Google Scholar] [CrossRef]
  24. Zhu, Z.X.; Li, D.; Wang, P.; Li, J.H.; Lu, X.C. Transcriptome and ionome analysis of nitrogen, phosphorus and potassium interactions in sorghum seedlings. Theor. Exp. Plant Physiol. 2020, 32, 271–285. [Google Scholar] [CrossRef]
  25. Sarah, M.M.D.; Prado, R.D.; de Souza, J.P.; Teixeira, G.C.M.; Duarte, J.C.D.; de Medeiros, R.L.S. Silicon supplied via foliar application and root to attenuate potassium deficiency in common bean plants. Sci. Rep. 2021, 11, 19690. [Google Scholar] [CrossRef]
  26. Thornburg, T.E.; Liu, J.; Li, Q.; Xue, H.Y.; Wang, G.; Li, L.J.; Fontana, J.E.; Davis, K.E.; Liu, W.Y.; Zhang, B.H.; et al. Potassium Deficiency Significantly Affected Plant Growth and Development as Well as microRNA-Mediated Mechanism in Wheat (Triticum aestivum L.). Front. Plant Sci. 2020, 11, 1219. [Google Scholar] [CrossRef]
  27. Gao, H.Y.; Gong, L.Y.; Ni, J.H.; Li, Q.L. Metabolomics Analysis of Lettuce (Lactuca sativa L.) Affected by Low Potassium Supply. Agriculture 2022, 12, 1153. [Google Scholar] [CrossRef]
  28. GB/T 17980.26-2000; Pesticide--Guidelines for the Field Efficacy Trials(I)--Fungicides Against Downy Mildew of Cucumber. The State Bureau of Quality and Technical Supervision: Beijing, China, 2000.
  29. Chai, W.C.; Yan, S.J. Effects of drought stress on growth and physiological indicators of grafted cucumber seedlings. North. Hortic. 2024, 7, 10–17. [Google Scholar] [CrossRef]
  30. Boussadia, O.; Steppe, K.; Zgallai, H.; El Hadj, S.B.; Braham, M.; Lemeur, R.; Van Labeke, M.C. Effects of nitrogen deficiency on leaf photosynthesis, carbohydrate status and biomass production in two olive cultivars ’Meski’ and ’Koroneiki’. Sci. Hortic. 2010, 123, 336–342. [Google Scholar] [CrossRef]
  31. Rasool, G.; Guo, X.P.; Wang, Z.C.; Ali, M.U.; Chen, S.; Zhang, S.X.; Wu, Q.; Ullah, M.S. Coupling fertigation and buried straw layer improves fertilizer use efficiency, fruit yield, and quality of greenhouse tomato. Agric. Water Manag. 2020, 239, 106239. [Google Scholar] [CrossRef]
  32. Shao, C.H.; Qiu, C.F.; Qian, Y.F.; Liu, G.R. Nitrate deficiency decreased photosynthesis and oxidation-reduction processes, but increased cellular transport, lignin biosynthesis and flavonoid metabolism revealed by RNA-Seq in Oryza sativa leaves. PLoS ONE 2020, 15, e0235975. [Google Scholar] [CrossRef] [PubMed]
  33. Wu, Y.; Zhu, J.; Li, Y.; Li, M. Effect of high-voltage electrostatic field on inorganic nitrogen uptake by cucumber plants. Trans. ASABE 2016, 59, 25–29. [Google Scholar]
  34. Sung, J.; Lee, S.; Lee, Y.; Ha, S.; Song, B.; Kim, T.; Waters, B.M.; Krishnan, H.B. Metabolomic profiling from leaves and roots of tomato (Solanum lycopersicum L.) plants grown under nitrogen, phosphorus or potassium-deficient condition. Plant Sci. 2015, 241, 55–64. [Google Scholar] [CrossRef]
  35. Song, H.F.; Cai, Z.; Liao, J.; Zhang, S. Phosphoproteomic and Metabolomic Analyses Reveal Sexually Differential Regulatory Mechanisms in Poplar to Nitrogen Deficiency. J. Proteome Res. 2020, 19, 1073–1084. [Google Scholar] [CrossRef] [PubMed]
  36. Abubaker, B.A.; Yan, H.F.; Hong, L.; You, W.Y.; Elshaikh, N.A.; Hussei, G.; Pandab, S.; Hassan, S. Enhancement of Depleted Loam Soil as Well as Cucumber Productivity Utilizing Biochar Under Water Stress. Commun. Soil Sci. Plant Anal. 2019, 50, 49–64. [Google Scholar] [CrossRef]
  37. Cui, J.; Lamade, E.; Tcherkez, G. Potassium deficiency reconfigures sugar export and induces catecholamine accumulation in oil palm leaves. Plant Sci. 2020, 300, 110628. [Google Scholar] [CrossRef]
  38. Yan, H.F.; Deng, S.S.; Zhang, C.; Wang, G.Q.; Zhao, S.; Li, M.; Liang, S.W.; Jiang, J.H.; Zhou, Y.D. Determination of energy partition of a cucumber grown Venlo-type greenhouse in southeast China. Agric. Water Manag. 2023, 276, 108047. [Google Scholar] [CrossRef]
  39. Sun, Y.M.; Huang, X.L.; Zhang, T.; Yang, Y.H.; Cheng, X.F.; Xu, X.Y.; Yuan, H.Y. Potassium deficiency inhibits steviol glycosides synthesis by limiting leaf sugar metabolism in stevia (Stevia rebaudiana Bertoni) plants. J. Integr. Agric. 2021, 20, 2932–2943. [Google Scholar] [CrossRef]
  40. Ali, A.B.; Elshaikh, N.A.; Hussien, G.; Abdallah, F.E.; Hassan, S. Biochar Addition For Enhanced Cucumber Fruit Quality Under Deficit Irrigation. Biosci. J. 2020, 36, 1930–1937. [Google Scholar] [CrossRef]
  41. Sung, J.; Sonn, Y.; Lee, Y.; Kang, S.; Ha, S.; Krishnan, H.B.; Oh, T.K. Compositional changes of selected amino acids, organic acids, and soluble sugars in the xylem sap of N, P, or K-deficient tomato plants. J. Plant Nutr. Soil Sci. 2015, 178, 792–797. [Google Scholar] [CrossRef]
  42. Rasool, G.; Guo, X.P.; Wang, Z.C.; Chen, S.; Hamoud, Y.A.; Javed, Q. Response of Fertigation Under Buried Straw Layer on Growth, Yield, and Water-fertilizer Productivity of Chinese Cabbage Under Greenhouse Conditions. Commun. Soil Sci. Plant Anal. 2019, 50, 1030–1043. [Google Scholar] [CrossRef]
  43. Okazaki, K.; Tanahashi, T.; Kato, Y.; Suzuki, I.; Tanaka, F.; Ohwaki, Y. Metabolic indices related to leaf marginal necrosis associated with potassium deficiency in tomato using GC/MS metabolite profiling. J. Biosci. Bioeng. 2020, 130, 520–524. [Google Scholar] [CrossRef]
  44. Yan, H.F.; Zhang, C.; Gerrits, M.C.; Acquah, S.J.; Zhang, H.N.; Wu, H.M.; Zhao, B.S.; Huang, S.; Fu, H.W. Parametrization of aerodynamic and canopy resistances for modeling evapotranspiration of greenhouse cucumber. Agric. For. Meteorol. 2018, 262, 370–378. [Google Scholar] [CrossRef]
  45. Chen, Z.P.; Li, H.P.; Yang, T.Y.; Chen, T.T.; Dong, C.X.; Gu, Q.; Cheng, X.M. Transcriptome analysis provides insights into the molecular bases in response to different nitrogen forms-induced oxidative stress in tea plant roots (Camellia sinensis). Funct. Plant Biol. 2020, 47, 1073–1082. [Google Scholar] [CrossRef] [PubMed]
  46. Tewari, R.K.; Kumar, P.; Tewari, N.; Srivastava, S.; Sharma, P.N. Macronutrient deficiencies and differential antioxidant responses—Influence on the activity and expression of superoxide dismutase in maize. Plant Sci. 2004, 166, 687–694. [Google Scholar] [CrossRef]
  47. Matic, M.; Vukovic, R.; Vrandecic, K.; Camagajevac, I.S.; Cosic, J.; Vukovic, A.; Sabljic, K.; Sabo, N.; Dvojkovic, K.; Novoselovic, D. Oxidative Status and Antioxidative Response to Fusarium Attack and Different Nitrogen Levels in Winter Wheat Varieties. Plants 2021, 10, 611. [Google Scholar] [CrossRef] [PubMed]
  48. Zhu, B.; Xu, Q.W.; Zou, Y.G.; Ma, S.M.; Zhang, X.D.; Xie, X.Y.; Wang, L.C. Effect of potassium deficiency on growth, antioxidants, ionome and metabolism in rapeseed under drought stress. Plant Growth Regul. 2020, 90, 455–466. [Google Scholar] [CrossRef]
  49. Liu, Y.; Yin, Q.; Dai, B.J.; Wang, K.L.; Lu, L.; Qaseem, M.F.; Wang, J.X.; Li, H.L.; Wu, A.M. The key physiology and molecular responses to potassium deficiency in Neolamarckia cadamba. Ind. Crop. Prod. 2021, 162, 113260. [Google Scholar] [CrossRef]
  50. Waqas, M.; Chen, Y.N.; Iqbal, H.; Shareef, M.; Rehman, H.U.; Bilal, H.M. Synergistic consequences of salinity and potassium deficiency in quinoa: Linking with stomatal patterning, ionic relations and oxidative metabolism. Plant Physiol. Biochem. 2021, 159, 17–27. [Google Scholar] [CrossRef]
  51. Mustapha, A.T.; Zhou, C.S. Novel assisted/unassisted ultrasound treatment: Effect on respiration rate, ethylene production, enzymes activity, volatile composition, and odor of cherry tomato. LWT 2021, 149, 111779. [Google Scholar] [CrossRef]
  52. Sun, T.T.; Zhang, J.K.; Zhang, Q.; Li, X.L.; Li, M.J.; Yang, Y.Z.; Zhou, J.; Wei, Q.P.; Zhou, B.B. Integrative physiological, transcriptome, and metabolome analysis reveals the effects of nitrogen sufficiency and deficiency conditions in apple leaves and roots. Environ. Exp. Bot. 2021, 192, 104633. [Google Scholar] [CrossRef]
  53. Maswada, H.F.; Abd El-Razek, U.A.; El-Sheshtawy, A.N.A.; Mazrou, Y.S.A. Effect of Azolla filiculoides on Growth, Physiological and Yield Attributes of Maize Grown under Water and Nitrogen Deficiencies. J. Plant Growth Regul. 2021, 40, 558–573. [Google Scholar] [CrossRef]
  54. Helena Ramirez-Solet, C.; Magnitskiy, S.; Melo Martinez, S.E.; Alvarez-Florez, F.; Marina Melgarejo, L. Photosynthesis, biochemical activity, and leaf anatomy of tree tomato (Solanum betaceum Cav.) plants under potassium deficiency. J. Appl. Bot. Food Qual. 2021, 94, 75–81. [Google Scholar] [CrossRef]
  55. Pi, Z.; Stevanato, P.; Yv, L.H.; Geng, G.; Guo, X.L.; Yang, Y.; Peng, C.X.; Kong, X.S. Effects of potassium deficiency and replacement of potassium by sodium on sugar beet plants. Russ. J. Plant Physiol. 2014, 61, 224–230. [Google Scholar] [CrossRef]
  56. Liaqat, S.; Umar, S.; Saffeullah, P.; Iqbal, N.; Siddiqi, T.O.; Khan, M.I.R. Protective Effect of 24-Epibrassinolide on Barley Plants Growing Under Combined Stress of Salinity and Potassium Deficiency. J. Plant Growth Regul. 2020, 39, 1543–1558. [Google Scholar] [CrossRef]
  57. Abd El-Mageed, T.A.; Semida, W.M.; Taha, R.S.; Rady, M.M. Effect of summer-fall deficit irrigation on morpho-physiological, anatomical responses, fruit yield and water use efficiency of cucumber under salt affected soil. Sci. Hortic. 2018, 237, 148–155. [Google Scholar] [CrossRef]
  58. Yan, H.F.; Ma, J.M.; Zhang, J.Y.; Wang, G.Q.; Zhang, C.; Akhlaq, M.; Huang, S.; Yu, J.J. Effects of film mulching on the physiological and morphological parameters and yield of cucumber under insufficient drip irrigation. Irrig. Drain. 2022, 71, 897–911. [Google Scholar] [CrossRef]
  59. Anderson, N.O.; Annis, J.; Buchholz, M.; Cutting, J.; Heuring, E.; Jankila, E.; McCrumb, M.; Nelson, N.; Pehoski, M.; Piepho, K.; et al. Undergraduate Sustainable Learning: Effects of Sustainable Soilless Media on Production and Sensory Evaluation of Cucumbers, Basil, Parsley, and Lettuce. Sustainability 2011, 3, 1381–1398. [Google Scholar] [CrossRef]
  60. Yan, H.F.; Acquah, S.J.; Zhang, C.; Wang, G.Q.; Huang, S.; Zhang, H.N.; Zhao, B.S.; Wu, H.M. Energy partitioning of greenhouse cucumber based on the application of Penman-Monteith and Bulk Transfer models. Agric. Water Manag. 2019, 217, 201–211. [Google Scholar] [CrossRef]
  61. Anders, A.; Choszcz, D.; Markowski, P.; Lipinski, A.J.; Kaliniewicz, Z.; Slesicka, E. Numerical Modeling of the Shape of Agricultural Products on the Example of Cucumber Fruits. Sustainability 2019, 11, 2798. [Google Scholar] [CrossRef]
  62. Huang, S.; Yan, H.F.; Zhang, C.; Wang, G.Q.; Acquah, S.J.; Yu, J.J.; Li, L.L.; Mam, J.M.; Darko, R.O. Modeling evapotranspiration for cucumber plants based on the Shuttleworth-Wallace model in a Venlo-type greenhouse. Agric. Water Manag. 2020, 228, 105861. [Google Scholar] [CrossRef]
  63. Takahashi, H.; Pradal, C. Root phenotyping: Important and minimum information required for root modeling in crop plants. Breed. Sci. 2021, 71, 109–116. [Google Scholar] [CrossRef] [PubMed]
Agriculture 15 00994 g001aAgriculture 15 00994 g001b
Figure 1. Effects of downy mildew infection and potassium stress on substance accumulation in cucumber plants. Note: Error bars indicate standard deviations, with different lowercase letters between treatments indicating significant differences at p < 0.05. (a) Weight of fresh leaves; (b) weight of dry leaves; (c) weight of fresh stems; (d) weight of dry stems; (e) weight of fresh roots; (f) weight of dry roots.
Figure 1. Effects of downy mildew infection and potassium stress on substance accumulation in cucumber plants. Note: Error bars indicate standard deviations, with different lowercase letters between treatments indicating significant differences at p < 0.05. (a) Weight of fresh leaves; (b) weight of dry leaves; (c) weight of fresh stems; (d) weight of dry stems; (e) weight of fresh roots; (f) weight of dry roots.
Agriculture 15 00994 g001aAgriculture 15 00994 g001b
Table 1. Effects of different experimental treatments on metabolic data of cucumber plants.
Table 1. Effects of different experimental treatments on metabolic data of cucumber plants.
TreatmentMeasurement Index
Cane Sugar
(mg/gFW)		Soluble Sugar
(μg/gFW)		H2O2
(mmol/gprot)		CAT
(U/mgprot)		SOD
(U/gFW)		PPO
(U/gFW)		MDA
(nmol/mgprot)
B0T12.27 ± 0.24f2794.81 ± 32.02f4.31 ± 0.67a7.26 ± 0.43e686.54 ± 13.91a109.59 ± 5.39a1.45 ± 0.21a
B0T22.73 ± 0.23d3190.36 ± 70.26d3.99 ± 0.35b9.97 ± 0.32c646.06 ± 13.11b98.47 ± 7.73b0.97 ± 0.13d
B0T32.65 ± 0.21e2978.24 ± 52.5e3.78 ± 0.46c8.31 ± 0.19d595.43 ± 20.63c82.15 ± 6.19c1.27 ± 0.11c
B1T13.09 ± 0.14c3507.15 ± 44.92c3.6 ± 0.43c10.25 ± 0.13c596.4 ± 12.14c96.75 ± 4.41b1.38 ± 0.16b
B1T23.55 ± 0.24a4377.81 ± 61.19a3.29 ± 0.36d15.72 ± 0.23a526.97 ± 20.03d78.62 ± 5.2c0.79 ± 0.13e
B1T33.34 ± 0.28b4034.57 ± 53.34b3.76 ± 0.23e13.14 ± 0.38b503.86 ± 18.94e75.13 ± 4.39d0.99 ± 0.15d
Note: Different lowercase letters between treatments indicating significant differences at p < 0.05.
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Wang, Y.; Shi, Q.; Lin, J.; Lu, X.; Ye, B.; Lv, H.; Du, X.; Chen, T. Hormone Metabolism and Substance Accumulation in Cucumber Plants: Downy Mildew Infection and Potassium Stress. Agriculture 2025, 15, 994. https://doi.org/10.3390/agriculture15090994

AMA Style

Wang Y, Shi Q, Lin J, Lu X, Ye B, Lv H, Du X, Chen T. Hormone Metabolism and Substance Accumulation in Cucumber Plants: Downy Mildew Infection and Potassium Stress. Agriculture. 2025; 15(9):994. https://doi.org/10.3390/agriculture15090994

Chicago/Turabian Style

Wang, Yafei, Qiang Shi, Jiale Lin, Xuanting Lu, Bin Ye, Huanxing Lv, Xiaoxue Du, and Tianhua Chen. 2025. "Hormone Metabolism and Substance Accumulation in Cucumber Plants: Downy Mildew Infection and Potassium Stress" Agriculture 15, no. 9: 994. https://doi.org/10.3390/agriculture15090994

APA Style

Wang, Y., Shi, Q., Lin, J., Lu, X., Ye, B., Lv, H., Du, X., & Chen, T. (2025). Hormone Metabolism and Substance Accumulation in Cucumber Plants: Downy Mildew Infection and Potassium Stress. Agriculture, 15(9), 994. https://doi.org/10.3390/agriculture15090994

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