1 Introduction

Cucumber (Cucumis sativus) is an economic crop widely cultivated around the world. It is rich in nutrients and consumed by many people. It is one of the common vegetables in many regions and also very important in vegetable cultivation. However, cucumbers are very vulnerable to various diseases and pests during their growth, such as fungi, bacteria, viruses, and many other pests. These biological stresses can lead to a decrease in cucumber yield and a deterioration in quality, causing significant losses to agricultural production (Chen et al., 2020; Das et al., 2022; Meng et al., 2022).

To address these issues, cucumbers have evolved their own "immune system". It can identify external pathogens or pests and activate a series of defense responses to protect itself. Genes such as the WRKY transcription factor and CRK receptor kinase play very important roles in the defense response (Nanda et al., 2023). In addition, cucumbers can regulate signaling molecules in the body, such as reactive oxygen species (ROS), glutathione (GSH), and jasmonic acid (JA), to enhance their disease resistance (Chen et al., 2019; Tamandegani et al., 2021; Jia et al., 2023; 2024).

In recent years, scientists have also discovered that some external substances added, such as nano-selenium, oligosaccharides and beneficial microorganisms, can also help cucumbers enhance their immunity. These substances called biostimulants can induce cucumbers to initiate defense responses, thereby reducing diseases (Pring et al., 2024).

Systematically sorting out the coping mechanisms of cucumbers in the face of these biological stresses can help us understand more clearly how they prevent diseases. This knowledge can also provide a scientific basis for breeding disease-resistant varieties and developing green agricultural technologies.

2 Overview of Biotic Stresses in Cucumber

Cucumber (Cucumis sativus L.) is a vegetable crop widely cultivated all over the world. During its growth process, it is very vulnerable to various diseases and pests, such as fungi, bacteria, viruses, and insects, etc. These problems will seriously affect the yield and quality of cucumbers (Das et al., 2022).

2.1 Common pathogens and pests

2.1.1 Fungi: Podosphaera xanthii (powdery mildew), Fusarium oxysporum

Powdery mildew (Podosphaera xanthii) is a very common fungal disease of cucumbers. It will affect the normal growth of the plants and reduce the yield. Cucumber varieties that are resistant to this disease can activate cell wall and hormone-related genes in the early stage and quickly initiate the defense response (Meng et al., 2022).

Fusarium oxysporum is also very serious. Studies have found that some fungi, such as Trichoderma harzianum, can help enhance the disease resistance of the roots of cucumbers. It keeps the plant in a stable state by regulating the balance of reactive oxygen species (ROS) and reactive nitrogen species (RNS) (Chen et al., 2019).

2.1.2 Bacteria: Pseudomonas syringae, Erwinia tracheiphila

Pseudomonas syringae pv. lachrymans is the main cause of bacterial spot disease in cucumbers. If cucumbers are exposed to salt stress, the disease will become more severe. At this time, hormones such as salicylic acid and abscisic acid and the antioxidant system will be disrupted, and the disease resistance will also decline (Chojak-Koźniewska et al., 2017; 2018). Another type of bacteria, Erwinia tracheiphila, can cause wilting symptoms in cucumbers, ultimately affecting the yield and causing serious losses (Das et al., 2022).

2.1.3 Viruses: cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV)

Cucumber Mosaic virus (CMV) is a kind of virus with a wide range of transmission. It will significantly reduce the yield and quality of cucumbers. Some beneficial microorganisms, such as Trichoderma asperellum, can stimulate the plant's own resistance, activate JA, ET and SA signaling pathways, and enhance the defense against CMV (Tamandegani et al., 2021). ZYMV also frequently occurs in cucumber planting areas, which can affect the healthy growth of plants (Das et al., 2022).

2.1.4 Insects: Aphids, whiteflies, cucumber beetles

Aphids and whiteflies not only directly feed on cucumbers, but also bring viruses to plants, indirectly making the disease more severe (Das et al., 2022). The cucumber beetle mainly feeds on roots and stems, which can affect the normal development of plants.

2.2 Impact on yield and quality

2.2.1 Disease incidence and economic losses

After cucumbers encounter pests and diseases, the incidence of diseases will increase significantly. Very often, both output and commodity quality are greatly affected, and farmers suffer significant losses (Das et al., 2022). For example, during the outbreaks of powdery mildew and fusarium wilt, the output may drop by more than 30% (Chen et al., 2019; Meng et al., 2022).

2.2.2 Resistance breakdown and management challenges

Many pathogens mutate rapidly, and resistant varieties of cucumbers can easily "lose their effectiveness". This will increase the difficulty of disease prevention and control. To address this challenge, researchers are constantly screening for new resistance genes and also promoting the development of molecular breeding techniques. But so far, it is still not easy to obtain both broad-spectrum and durable resistance (Das et al., 2022).

3 Plant Immune System: General Mechanisms

The immune system of plants mainly consists of two layers of defense: one is called PAMP-triggered immunity (PTI), and the other is called effector triggered immunity (ETI). In addition, there are system-acquired resistance (SAR) and induced systemic resistance (ISR), which can play a defensive role throughout the entire plant.

3.1 Overview of PTI (PAMP-triggered immunity) and ETI (effector-triggered immunity)

PTI is an "early warning" mechanism that plants use to identify pathogens. There are some "sensor" proteins on the cell membranes of plants, such as LecRLK and CRK, which can recognize the molecular signals released by pathogens. This recognition initiates defenses, such as the release of reactive oxygen species (ROS) and the activation of some defense genes (Haider et al., 2021; Nanda et al., 2023).

ETI is a stronger form of immunity for plants. When the pathogen releases effector proteins into plant cells, the R genes within the cells (such as the NBS-LRR type) can recognize these proteins and then initiate a more intense response. This reaction may include rapid cell death (also known as allergic reaction HR), with the aim of preventing the spread of bacteria (Wang et al., 2021; Pagan and Garcia-Arenal, 2022; Li et al., 2024).

In cucumbers, some R genes (such as CSSGR, CsRSF1 and CsRSF2) can directly recognize pathogenic effectors, trigger cell death and defense gene expression, thereby enhancing resistance to diseases such as powdery mildew (Wang et al., 2021; Li et al., 2024) (Figure 1).

Figure 1 Identification of CsRSF1/CsRSF2-overexpressing cucumber plants (Adopted from Wang et al., 2021) Note: (A) Schematic of the CsRSF1/CsRSF2-GFP constructs. CsRSF1 and CsRSF2 were between 35S Pro and GFP protein, and chimeric PCR identifications of CsRSF1 and CsRSF2 genetically modified cucumber were successful. Vector, recombinant plasmid; plant, non-transgenic cucumber; GFP: 00, empty vector; GFP:CsRSF1, CsRSF1-transient overexpressing in cucumbers; GFP:CsRSF2, CsRSF2-transient overexpressing in cucumbers. (B) Luminescence signal identification for transient overexpressing cucumber cotyledons. Bar=10 µm. (C) CsRSF1/CsRSF2-overexpressing were identified in transgenic plants by qRT-PCR. Data are means±standard deviations (SD) from three independent experiments, and each column represents a sample containing three cucumber cotyledons from different plants. Expression analysis of candidate genes using the 2−ΔΔCt method. The asterisks indicated a significant difference (Student’s t-test, * p<0.05 or **p<0.01) (Adopted from Wang et al., 2021)

3.2 Role of PRRs and R genes in defense initiation

PRRs (such as LecRLK, CRK, etc.) are generally located on the cell membrane. They can recognize foreign molecules from pathogens. Once recognized, they will initiate the PTI response to help plants activate defense mechanisms, such as regulating the expression of some enzymes or signaling molecules (Haider et al., 2021; Nanda et al., 2023; Su et al., 2025).

The R gene mainly works inside the cell. They specifically recognize the effector proteins of the pathogen and trigger the ETI response. This is usually accompanied by enhanced expression of defense genes (such as PR1, PR5, etc.), and responses such as cell death may also occur (Wang et al., 2021; Li et al., 2024).

In cucumbers, the expression levels of PRRs such as LecRLK and CRK increase when fungi or bacteria invade. Meanwhile, some R genes are also activated, and their functions are closely related to the disease resistance of cucumbers (Haider et al., 2021; Wang et al., 2021; Nanda et al., 2023).

3.3 Systemic acquired resistance (SAR) and induced systemic resistance (ISR)

SAR is a "systemic" immune response. It is usually caused by local bacterial infection, but it makes the entire plant more resistant. SAR relies on the accumulation of some signaling molecules, such as salicylic acid (SA), pyrrolidine (Pip), and NHP. These substances can make defense genes more active and also increase the activity of defense enzymes (Nawrocka et al., 2017; Adam et al., 2018; Pazarlar et al., 2021). When Pip is sprayed externally, cucumbers produce SAR responses to multiple pathogens, which are manifested as increased SA, ROS generation and upregulation of defense genes (Pazarlar et al., 2021).

ISR is another different form of immunity. It is mainly caused by some beneficial microorganisms, such as Trichoderma, PGPR, etc. ISR relies on signaling molecules such as jasmonic acid (JA) and ethylene (ET) to activate defense genes such as PR4, making cucumbers more resistant to soil-borne diseases and viruses (Nawrocka et al., 2017; Tamandegani et al., 2021; Samaras et al., 2022). The SAR and ISR reactions can occur simultaneously and cooperate with each other to enhance the overall disease resistance of cucumbers at multiple levels.

4 Cucumber Immune Responses to Biotic Stresses

4.1 Structural and chemical barriers

When cucumbers are attacked by bacteria, they will activate some "physical barriers" to prevent invasion, such as thickening the cell walls or forming more lignin and keratin layers on the surface. In addition to these structural protections, cucumbers also produce some special chemical substances, such as cucurbitacin and phenolic compounds. These substances have antibacterial effects and can help cucumbers resist the growth of pathogens. Studies have found that treatment methods such as nano-selenium or glutathione can significantly promote the generation of these substances, thereby enhancing the resistance of cucumbers to Botrytis cinerea (Jia et al., 2023; 2024). In addition, if DAMP/MAMP oligosaccharides are used to treat cucumber leaves, it can also thicken the leaves, promote the formation of callose, and enhance the physical defense effect (Pring et al., 2024).

4.2 Hormonal signaling pathways

The hormones of plants play a very important role in the immune response of cucumbers. Especially jasmonic acid (JA), which is the most crucial in combating fungal diseases. After pathogen infection or nano-selenium treatment, JA and its related genes synthesized (such as LOX, AOS1, AOC2) will be activated in large quantities, helping cucumbers produce more defense substances, such as bitter substances (Jia et al., 2023; 2024). Salicylic acid (SA) and abscisic acid (ABA), these two hormones, are also involved in regulating cucumbers' responses to bacteria and fungi. Under the "double attack" of salt and pathogens, these hormones interact with each other, thereby affecting the expression of defense genes such as PR1 (Chojak-Koźniewska et al., 2017; 2018). In addition to hormones, some proteins, such as heat shock proteins (HSPs), and the MAPK signaling pathway, are also activated when cucumbers are exposed to diseases like powdery mildew and participate in defense (Meng et al., 2022).

4.3 Reactive oxygen species (ROS) and hypersensitive response (HR)

When cucumbers are confronted with pathogenic bacteria, they rapidly release reactive oxygen species (ROS), which is one of their "emergency response" methods. Sometimes, local cell death (HR response) may also occur to prevent the pathogen from spreading further. This phenomenon may be caused by pathogen invasion or DAMP/MAMP oligosaccharide treatment, usually accompanied by the activation of MAPK signaling and callose deposition (Pring et al., 2024). Some beneficial microorganisms, such as Trichoderma harzianum or Pseudomonas fluorescens, can also help. They can regulate the balance of ROS and RNS in cucumber roots, enhance the activity of antioxidant enzymes, and reduce oxidative damage caused by pathogens (Chen et al., 2019; Tamandegani et al., 2021; Zhu et al., 2021).

4.4 Defense-related genes and transcription factors

Some transcription factors play an important role in the response of cucumbers to diseases. For instance, members of the WRKY and Dof families are the key "commanders" in regulating defense. Whole-genome analysis identified 61 WRKY genes, many of which were activated under stress such as powdery mildew and downy mildew, thereby regulating the expression of other defense genes (Chen et al., 2020; Meng et al., 2022). The CRK family (cysteine-rich receptor kinases) is also crucial. They are elevated in expression when cucumbers are exposed to fungal (such as Aspergillus) infections and are involved in signal transduction and defense responses (Nanda et al., 2023). There are also some typical defense genes, such as PR1 and defensin-like proteins, which are also abundantly expressed after pathogen infection or induction by beneficial microorganisms, helping to enhance the immunity of cucumbers (Tamandegani et al., 2021; Zhu et al., 2021).

5 Genomics and Transcriptomics of Cucumber Defense

5.1 Insights from recent RNA-seq studies

In recent years, RNA-seq technology has been widely used in the research of the disease resistance mechanism of cucumbers. By analyzing the transcriptomes of disease-resistant and susceptible strains after infection, scientists discovered that cucumbers can quickly activate multiple signaling pathways during early defense, such as cell wall modification, hormone delivery, and MAPK signaling, etc. (Zheng et al., 2020; Meng et al., 2022). RNA-seq also discovered some key transcription factors, such as WRKY, NAC and TCP, which play important roles in plant defense responses.

5.2 Identification of differentially expressed genes under pathogen challenge

Many studies have identified a large number of genes with significant changes in expression levels under pathogen infection through RNA-seq, namely differentially expressed genes (DEGs). For instance, when infected with powdery mildew, the number of DEGs in the resistant strains is much higher than that in the susceptible strains, indicating that the resistant varieties can activate the defense mechanism more quickly and over a wider range (Zheng et al., 2020; Meng et al., 2022). The functions involved in these differentially expressed genes include cell wall metabolism, hormone signaling, pathogen recognition, and synthesis of various defense proteins (Chen et al., 2020; Zheng et al., 2020). Furthermore, some gene families, such as DREB, WRKY, LecRLK and CRK, have significant expression changes under various disease stresses (Haider et al., 2021; Wang et al., 2022; Nanda et al., 2023).

5.3 Functional annotation of immune-related genes

By combining genomic and transcriptomic data, researchers conducted a systematic analysis of the immune-related genes in cucumbers. It was found that several transcription factor families such as WRKY, DREB, VQ, BBX and MLP play important roles in regulating the disease resistance response (Chen et al., 2020; Shan et al., 2021; Wang et al., 2022; Zhu et al., 2022). In addition to these transcription factors, some receptor kinases, such as LecRLK, CRK and TRM, have also been confirmed to be involved in pathogen recognition and signaling (Haider et al., 2021; Nanda et al., 2023; Zhao et al., 2024). Through gene knockout or overexpression experiments, genes such as CsMLP1 and CsMLP5 have been confirmed to positively or negatively regulate the disease resistance of cucumbers (Kang et al., 2023).

5.4 Genome-wide association studies (GWAS) for resistance loci

With the development of high-density molecular markers and whole-genome sequencing technology, GWAS has become an effective method for finding disease-resistant loci. GWAS can be used to quickly identify QTL or candidate genes related to disease resistance traits, which helps to accelerate the breeding of disease-resistant varieties (Das et al., 2022). Pan-genome analysis also shows that there are many differences and variations in disease-resistant genes among different cucumber varieties. This information provides rich genetic resources for future breeding work (Wang et al., 2022; Zhao et al., 2024; Xu et al., 2025).

6 Breeding and Biotechnology for Enhanced Immunity

6.1 Classical breeding and marker-assisted selection

In the past, to enhance the disease resistance of cucumbers, people mainly adopted traditional breeding methods. This is usually achieved by screening and hybridizing disease-resistant varieties. Although this method takes a long time, it has always been the foundation of breeding work. In recent years, with the development of genomic research, molecular marker-assisted selection (MAS) has been of great help. This method can identify genes related to disease resistance more quickly. By using high-density genetic mapping and whole-genome sequencing, researchers can more quickly locate and clone molecular markers or candidate genes related to diseases, thereby significantly improving the efficiency of resistance improvement against powdery mildew, downy mildew, fusarium wilt, etc. (Das et al., 2022; He et al., 2022).

6.2 Transgenic approaches and genome editing

In addition to traditional breeding, there are now new technologies that can enhance the disease resistance of cucumbers. For instance, genetically modified technology is one of them. Scientists once introduced the chitinase gene of rice into cucumbers. As a result, these cucumber plants showed stronger resistance to Botrytis cinerea. Moreover, this resistance can be passed on to the next generation, providing new materials for breeding disease-resistant varieties (Tabei et al., 1998). In recent years, there have also been significant breakthroughs in gene editing technology. Especially the CRISPR/Cas9 system has begun to play a role in disease-resistant breeding of cucumbers. By knocking out the eIF4E gene, researchers have cultivated a new cucumber strain that is resistant to multiple viruses, such as cucumber vein yellow virus and Mosaic virus. This method does not require the introduction of exogenous genes, so it does not fall under the traditional sense of genetic modification and can reduce disputes. Moreover, it does not affect the growth of cucumbers, has stable resistance, and has a very good application prospect (Chandrasekaran et al., 2016).

Studies have found that biostimulants like nano-selenium can also enhance the disease resistance of cucumbers. They can activate jasmonic acid signals and promote the synthesis of defense substances such as cucurbitacin, thereby enhancing cucumbers' resistance to diseases such as gray mold. This also provides a new idea for disease-resistant breeding (Jia et al., 2023; Jia et al., 2024).

7 Case Study: Cucumber Response to Pseudoperonospora cubensis (Downy Mildew)

7.1 Pathogen overview

Pseudoperonospora cubensis is the main pathogen causing downy mildew in cucumbers. It is a specialized parasitic oomycetes. This pathogen is present in cucumber growing areas all over the world and is one of the persistent and difficult problems affecting yields. It mainly infects plants of the Cucurbitaceae family, causing angular yellow spots on cucumber leaves and a layer of gray mold to grow on the back of the leaves. If the infection is severe, the plants will die prematurely and the yield will also decrease significantly (Figure 2)  (Chen et al., 2020; Sun et al., 2022). Different "types" of pseudooil mold strains may occur in different regions. There are genetic differences among them, and their pathogenicity also varies (Roman et al., 2022).

Figure 2 Infection cycle of Pseudoperonospora cubensis (Adopted from Sun et al., 2022)

7.2 Immune response in resistant vs susceptible lines

Different varieties of cucumbers respond differently to downy mildew. Resistant varieties, such as PI 197088 and PI 330628, develop fewer and smaller disease spots on their leaves after being infected, and the spores produced by the pathogen are also fewer. These resistant varieties will accumulate more lignin and callose at the lesion site, acting as a "thickening wall" to prevent the further spread of the pathogen (Chen et al., 2020; Pazarlar et al., 2020).

Proteomic and transcriptomic studies have found that resistant varieties activate many defense pathways after pathogen infection. For example, the expressions of related genes such as terpene synthesis, chitinase, peroxidase, PR protein, and heat shock protein are significantly increased (Luan et al., 2019; Zhang et al., 2019). Furthermore, the activity of antioxidant enzymes (such as superoxide dismutase and peroxidase) in resistant varieties is enhanced, which can help eliminate reactive oxygen species and reduce damage to cells. Hormone-related signaling pathways such as salicylic acid and jasmonic acid were also activated, helping plants develop systemic resistance (Pazarlar et al., 2020).

However, the susceptible varieties are different. They have a weak response to pathogens, less expression of defense genes, and weak cellular protective ability, so the disease develops faster and more severely (Adhikari et al., 2012; Zhang et al., 2019).

7.3 Implications for breeding programs

A thorough understanding of the mechanism by which cucumbers resist downy mildew is very helpful for disease-resistant breeding. Studies show that downy mildew resistance is not controlled by a single gene, but by the combined action of multiple genes. Therefore, when utilizing resistant resources, attention should be paid to the complementarity among different genotypes (Chen et al., 2020; Pitchaimuthu et al., 2024).

Proteomic and transcriptomic studies have identified some potential disease-resistant genes and regulatory pathways, which are all potential targets for future molecular marker selection and genetic engineering breeding (Jin and Wu, 2015; Luan et al., 2019; Zhang et al., 2019).

In actual breeding, cucumber strains with strong resistance can be used as parents. Combined with molecular marker screening and phenotypic observation, new cucumber varieties with both high yield and disease resistance can be bred relatively effectively (Chen et al., 2020; Pitchaimuthu et al., 2024). Inducers such as salicylic acid and chitosan, as well as biological control methods using beneficial microorganisms, have also provided new ideas for the green prevention and control of downy mildew (Sun et al., 2022).

8 Challenges and Future Directions

8.1 Emerging pathogens and resistance erosion

Cucumbers are prone to infection by some novel pathogens during their growth process, such as downy mildew, powdery mildew and gray mold. These germs are becoming increasingly common. The efficacy of the disease-resistant genes used in the past began to deteriorate over time, and resistance was gradually lost (Luan et al., 2019; Jia et al., 2023; Li et al., 2024). Pathogens change rapidly and have high genetic diversity, which makes it more difficult for traditional breeding methods to deal with these diseases (Das et al., 2022). Coupled with environmental stress such as salt stress, the immune system of cucumbers becomes weaker and diseases are more likely to occur (Chojak-Koźniewska et al., 2018).

8.2 Need for multi-omics integration (proteomics, metabolomics, epigenomics)

Although there are currently many studies on the transcriptome and metabolome, which help us understand some of the response mechanisms of cucumbers in the face of diseases, these are still only local. Data from other aspects such as proteome and epigenome have not been well integrated (Jia et al., 2023; 2024). Analyzing data from different omics together can help us gain a more comprehensive understanding of how immune signals are transmitted, how metabolic processes change, and how these affect the disease resistance of cucumbers. This is important for identifying new disease-resistant genes and clarifying the overall mechanism (Das et al., 2022).

8.3 Gaps in understanding cucumber immune signaling specificity

So far, we still don't have a very good understanding of the immune signaling pathways of cucumbers. Although studies have shown that some families of transcription factors, such as WRKY, DREB, BBX, and LecRLK, can participate in responses to different stresses, it is still unclear which signals they are responsible for and how they cooperate with each other when facing different pathogens or environmental stresses (Wen et al., 2016; Luan et al., 2019; Wang et al., 2022; Zhu et al., 2022). The molecular mechanisms of important responses such as how the R gene recognizes pathogenic effector proteins and how programmed cell death occurs also require further study (Li et al., 2024).

8.4 Opportunities for precision breeding and synthetic biology

Nowadays, with the continuous development of technologies such as whole-genome sequencing, molecular marker screening, and gene editing, we can adopt more "precise" methods for breeding. This has greatly improved the efficiency of disease-resistant breeding of cucumbers. Synthetic biology has also brought new opportunities. For example, multiple disease-resistant gene modules can be combined to design new immune receptors and regulatory factors. In this way, the limitation of "one gene against one disease" in the past can be broken through, and efforts can be made to achieve long-lasting and broad-spectrum disease resistance (Das et al., 2022). Some new biostimulants, such as nano-selenium, DAMP/MAMP oligosaccharides, etc., have also been proven to enhance the immunity of cucumbers, providing new solutions for green disease control (Jia et al., 2023; 2024; Pring et al., 2024).

9 Conclusion

In recent years, scientists have made many new discoveries in the research on the immune response of cucumbers (Cucumis sativus L.) when facing diseases. Studies have shown that transcription factor families like WRKY and the CRK receptor kinase family play a significant role in cucumbers' combat against pathogens such as powdery mildew, gray mold, and stem base rot. These genes are turned on or off at different stages to regulate the defense responses of plants. In addition, some externally added biostimulants, such as nano-selenium, glutathione, oligosaccharide combinations, as well as beneficial microorganisms like Trichoderma and Pseudomonas fluorescens, can also help cucumbers become more "disease-resistant". They can activate jasmonic acid (JA) -related signals, promote the synthesis of defense substances (such as cucurbitacin and phenolic acids), and also regulate reactive oxygen species (ROS) levels and the antioxidant system, enhancing the immunity of cucumbers in multiple aspects.

Cucumber varieties with strong resistance can usually respond quickly when pathogens first invade, activate multiple signaling pathways, and mobilize many defensive-related genes, thus having a stronger overall defense capability. However, if only one resistance mechanism is relied upon, it is very difficult to deal with the complex and changeable pathogenic bacteria. Therefore, current research is more inclined towards a "combination punch". That is to say, by integrating molecular breeding, genomics, transcriptomics, metabolomics and other technical means, along with the use of exogenous stimulants, a more comprehensive analysis of the immune system of cucumbers can be conducted to identify the truly important disease-resistant genes and regulatory factors. At the same time, the rational combination of inducers and beneficial bacteria can also activate multiple defense pathways simultaneously, enhance the crop's own resistance, and reduce the use of pesticides, making it more environmentally friendly and sustainable.

Understanding the immune mechanism of cucumbers is of great help for breeding and prevention and control. In the future, by using precise technologies such as molecular markers and gene editing, along with the application of biostimulants in the field, it is highly likely that we will breed new cucumber varieties that are resistant to multiple diseases and can maintain disease resistance continuously. This not only can increase output and quality, but also is expected to promote the development of facility agriculture towards a greener and more sustainable direction.

Acknowledgments

The author would like to express the gratitude to the two anonymous peer studyers for their critical assessment and constructive suggestions on the manuscript.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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