DROUGHT STRESS IN Brassica napus: PHYSIOLOGICAL RESPONSES, MOLECULAR MECHANISMS, AND INTEGRATED MANAGEMENT STRATEGIES

INTRODUCTION

Susceptibility to a hostile environment, particularly water deficit stress, triggers a range of adaptive responses in plants, resulting in dynamic cellular reprogramming at the transcriptomic, epigenomic, proteomic, and metabolic levels. Together these changes enable plants to adjust and survive under adverse conditions. This process involves complex interactions among cellular components, beginning with stress perception and signaling and ultimately leading to the activations of stress responsive genes and corresponding phenotyping changes. Meanwhile, by 2050 the rising demands for the edible oils and renewable energy, is expected to significantly increase oil production requirements due to the continuous growth of the global population (Holechek et al., 2022). To meet this growing demand requires increased focus on oilseed crops such as B. napus a key member of the Brassicaceae family that originated from the natural hybridization of Brassica rapa L. (B. rapa) and Brassica oleracea L. (B. oleracea) (Lu et al., 2019). B. napus act an important role in the global vegetable oil market, contributing approximately 14.7% of total human consumption and ranking as the third most important source of vegetable oil (Figure 1a). In recent years, its cultivation has expanded significantly across major producing regions worldwide (Carré and Pouzet, 2014). It is a versatile crop whose yields range of products beyond its oil, including animal feed, bakery protein isolates, and protein-rich products for human consumption (Wang et al., 2023). Through the production of various bio-based compounds, B. napus has substantial industrial value, contributing to various non-food sectors such as cosmetics, printing inks, aviation de-icing agents, biodegradable greases, bio plastics, and industrial lubricants. (Raza, 2021). Moreover, B. napus is a key contributor to the feed industry, supplying protein-rich isolates for livestock, poultry, companion animals, and aquaculture (Wang et al., 2023).  Moreover, under climate change conditions, it is expected to intensify drought in many B. napus cultivation regions by increasing air temperatures, enhancing atmospheric evaporative demand, and changing rainfall patterns. These changes will make droughts happen more often, last longer and be more severe, and expose the crop often to water-scarce conditions under sensitive developmental stages (Figure 1d) (IPCC, 2021).

Figure 1. Global distribution and projections related to B. napus: (a) global production yield of B. napus; (b) cultivation patterns of spring-type vs winter-type B. napus; (c) top B. napus producing countries during the 2023/2024 season; and (d) projected future drought prone zones worldwide.

The winter-type B. napus is sown in the fall and harvested in the summer (primarily in Europe, China, and the United States). Spring-type B. napus is grown in the spring and harvested in summer, although in some regions it is sown in the fall and harvested in the spring. The regional distribution of cultivation patterns of spring-type vs winter-type B. napus is presented in Figure 1b (Wu et al., 2019; Zheng and Liu, 2022). From 2023 to 2024, the EU, Canada, China, India, and Japan (Figure 1c) (Ritchie et al., 2022) were among the leading global producers of  B. napus, accounting for nearly 77% of global production and harvested area. Winter B. napus is predominantly grown in temperate regions such as China, Germany, France, Poland, and England, along with selected areas of the United States, Australia, Canada, and Chile. In the face of climate change, characterized by more frequent and severe summer droughts, the cultivation of winter B. napus offers a viable adaptation strategy to improve cropping system resilience and reduce the impacts of abiotic stress. Importantly, winter types typically exhibit 20–30% higher yield potential than spring B. napus (Secchi et al., 2023).

B. napus hybrid cultivars exhibit greater drought tolerance than non-hybrid cultivars under certain drought conditions. This advantage is often associated with the heterosis, increased genetic diversity, and favorable trait combinations that contribute to improved photosynthetic activity, WUE, and yield-related performance. B. napus is vulnerable to abiotic stresses like limited water availability conditions and temperature stress, significantly affecting plant development and productivity. Limited water supply affects stomatal conductance, influencing crop yield (Jiao et al., 2023). Generally, the effects of drought decreased B. napus yield and oil quality. A substantial reduction (52%) in seed oil content was documented under drought stress in B. napus (Elferjani and Soolanayakanahally, 2018).

Drought stress considerably intensifies yield reductions (Zandalinas et al., 2018), negatively impacting the growth, development, and overall productivity of B. napus, thereby resulting in significant economic losses in crop production. The increasing severity of abiotic stresses associated with climate change presents major challenges to fulfilling the growing global demand for B. napus. The development and adaptation of drought-tolerant B. napus, combining knowledge from morphological, physiological, biochemical, and molecular levels, is necessary to maintain agricultural productivity under more changeable and drought-prone climatic circumstances. It also emphasizes current developments in transcriptional control, stress-responsive genes, and phytohormone signaling. Important agronomic techniques such as optimal sowing timing, exogenous application of osmolytes and plant growth regulators, balanced mineral nutrition, and the use of advantageous microbial inoculants to increase drought resistance in B. napus are also included in the review.

Furthermore, this investigation covers new biotechnology technologies that have received little focus in previous research, such as genetic breeding, QTL, mapping, and transgenic methods like CRSPR/Cas9 genome editing. By accepting these many different viewpoints, the study not only analyzes existing knowledge but also reveals significant information gaps and gives recommendations for future research. All things considered, it offers valuable advice for scientists, plant breeders, and lawmakers working to develop drought tolerance and assure sustainable oilseed production.

Data collection: In this present study, research publications regarding drought stress in B. napus were collected from the Web of Science Core Collection (WoSCC) and Scopus databases. A total of 1,545 records were first obtained from the publications from January 1, 1990, to December 31, 2025, based on the search terms given in Table 1. Furthermore, some other authoritative reports and online sources, such as crop production databases and the IPCC, were used only for background information, global production statistics, and climate-related context; these were not counted as peer-reviewed articles retrieved from the WoS or Scopus.

Table 1 Database search criteria for bibliometric analysis.

Only peer-reviewed English-language research articles and reviews were considered. Duplicate records were identified by comparing the peer-reviewed article titles, authors’ names, year of publication, and DOI; only one copy of each duplicated record was retained. Records were considered irrelevant and excluded if they were not related to B. napus. The remaining records were screened based on the title, abstract, and link to drought stress in B. napus. Only the peer-reviewed records linked to B. napus, drought stress, and its mitigation were included. Finally, 217 records, including peer-reviewed studies, books, and book chapter were selected for this review article. These included studies that explicitly summarized understanding the drought-induced effects, physiobiochemical responses, molecular mechanisms, agronomic management techniques, breeding approaches, genome-editing tools, and future research objectives in the B. napus.

Harmful effects of drought in B. napus: The development, yield, and general quality of B. napus are severely constrained by water deficit stress. However, the degree of its effects varies and is primarily determined by the plant's genotype, developmental stage, and the degree of stress. Essential physiological functions like photosynthesis, stomatal control, seed germination, and embryo development are all hampered by dryness, which eventually leads to poor seed quality and decreased yield  (Sehgal et al., 2018).

Effects on seed germination and plant development: A crop's germination is an important stage of development that shapes the plant's whole life cycle and establishes the groundwork for subsequent growth (Channaoui et al., 2017). However, adverse environmental conditions, particularly water stress, can impair seed germination and reduce successful stand establishment (de Figueiredo e Albuquerque and De Carvalho, 2003). Effective germination, along with vigorous seedling development, is essential for normal plant growth and optimal crop performance yield in B. napus (El-Badri et al., 2021). Under stress, the germination rate of B. napus is substantially decreased, adversely impacting seedling vigor and entire crop yield. During the early developmental stages, water deficit delays both germination and seedling growth by limiting water uptake, restricting storage reserve mobilization, and suppressing enzyme activity (Hussain et al., 2018).

These effects are linked with the reduction in water imbibition and hydrolysis in the seed, as well as the accumulation of ROS, oxidative damage, and the disruption of the hormone-related signaling. This led to a slowdown of embryonic axis growth, cell division, nutrient distribution, and seedling establishment (Channaoui et al., 2017; Xiong et al., 2018; Khan et al., 2019). Drought stress significantly affects B. napus plant morphology, including shoot length, by hindering water uptake and assimilate accumulation (Li et al., 2018a; Batool et al., 2023). A considerable decrease in stem length, leaf area, and photosynthetic pigments occurs under drought conditions in B. napus. Similarly, studies report a substantial reduction in root length due to lower cell expansion (Ashraf et al., 2013), degenerated enzyme structure, and reduced efficacy of enzymes and photosynthesis, resulting in a decrease in biomass (Wang et al., 2020). The flowering stage is the most drought sensitive phase for B. napus, and water deficit during this period has severe and often irreversible impacts on growth and yield. Drought stress reduces the number of flowers, increases pollen sterility, and limits successful fertilization, resulting in poor pod formation and reduced thousands-seed weight (Shafighi et al., 2021; El Idrissi et al., 2023). These effects cause a substantial decline in productivity, often greater than losses caused by stress at vegetative stages.

Physio-biochemical alterations during drought stress: Nutrient balance and its availability are crucial for optimal plant development and yield (Shang et al., 2019). Drought conditions decrease the absorption of nutrients such as (potassium (K⁺), calcium (Ca²⁺), nitrogen (N), and phosphorus (P), thus seriously affecting physiological mechanisms and reducing crop productivity (Ashraf et al., 2013). Under water limit conditions, nutrient uptake in plants declines due to several interconnections of physiological processes. When plant face drought stress, the transpiration rate decreases significantly, which is the main concern to the closure of stomata, which inhibits the conservation of water. This reduction in transpiration limit the movement of water and dissolved nutrients from the soil into the roots and subsequently to the rest of the plants (Gunes et al., 2006). Drought reduced both sulfur and N uptake in B. napus, but the tolerant cultivar ‘Saturnin’ maintained higher N acquisition thanks to more efficient nutrient transport systems. In less N efficient cultivars, nitrate transportation under water stress remarkably decreases due to lower N uptake (Lee et al., 2016).

Deficient water conditions frequently cause serious impairment and a significant decline in photosynthetic efficiency by damaging the photosynthetic apparatus (Majidi et al., 2015). The reduction in chlorophyll levels has been observed under drought stress. This decline is accompanied by a substantial decrease in anthocyanin content and carotenoids levels, as well as the synthesis of photosynthesis pigments (Majidi et al., 2015). Moreover, chlorophyll levels were lower in susceptible plants compared to tolerant ones due to higher photoinhibition (PS II) (Zhang et al., 2015). Rapid stomatal closure in response to water stress, which helps limit transpiration and sustain hydraulic function, also restricts CO₂ uptake, ultimately reducing assimilate accumulation in B. napus (Dikšaitytė et al., 2019). Furthermore, a 4% decrease in relative water content substantially lowered stomatal resistance (from 1.89 to 2.94 cm⁻¹) in plants (Ardestani and Rad, 2012). In B. napus, an 80% reduction in relative water content significantly impacts photosynthesis by impairing the plant's ability to maintain cellular functions and turgor pressure. The 50% reduction in photosynthesis is due to the drought stress effects on stomatal closure, reduced enzyme activity, and compromised metabolic processes. A substantial decrease in moisture content in studied varieties was documented under water deficiency in B. napus (Elferjani and Soolanayakanahally, 2018).

Effects on yield and quality: Plant developmental stages, from early to late growth, are severely influenced by water stress; however, the reproductive stage is highly sensitive (Ghobadi et al., 2006), leading to decrement in yield (Elferjani and Soolanayakanahally, 2018). The number of siliques and seeds is reduced by drought during floral development, affecting sink and source efficiency, thus reducing seed production (Shafighi et al., 2021; Batool et al., 2023). Water deficit conditions hinder pod development, photosynthetic efficiency, and seed oil quality, leading to fewer pods in B. napus. Water deficit conditions significantly decrease oil quality by altering lipid and protein concentrations, thus affecting product quality (Aslam et al., 2009). Likewise, water stress reduces linoleic acid and boosts glucosinolates in plants. In essence, water deficit conditions are detrimental to yield and its components possibly due to stress associated changes in metabolism and physio-chemical mechanisms, and subsequent adverse effects on reproductive organs, leading to lower B. napus. seed quality and yield. In conclusion, drought stress significantly affects plant development, ultimately impacting yield. A brief description of common effects is presented in Figure 2.

Figure 2. Physiological and morphological trait responses to water deficit stress in B. napus. LEA, late-embryogenesis abundant; WUE, water-use efficiency

Drought stress can affect the economic yield of B. napus. Short-term drought “stress” when applied before the end of flowering had the greatest effect on protein content and the longest lasting effects on B. napus seed (Secchi et al., 2023). When B. napus plants are exposed to long term drought stress it reduces seed yields and oil yield. Short-term drought stress reduced seed oil concentration, yield, and oil yield more than other crop growth phases, indeed it had a similar negative effect on seed quantity and weight during flowering stage (Sehgal et al., 2018). When the oil yield of B. napus decreases, the production of its derived products is reduced, leading to a shortage. This scarcity drives up the prices of these products, oil and related commodities. This condition increases the prices of B. napus. Therefore, the prices of oil and other things become higher.

Key points:

1. Drought stress in B. napus negatively affects germination, seedling vigor, flowering and fertilization by limiting water uptake, disrupting enzyme activity, and altering hormonal regulation.

2. Drought disrupts physiological processes, including reduced uptake of nutrients (N, P, K, Ca), decreased chlorophyll and carotenoid levels and impaired photosynthesis due to stomatal closure.

3. The high sensitivity of reproductive stages leads to fewer siliques, increased pollen sterility, poor fertilization and reduced thousands seed weight.

4. Drought reduces oil yield, alters fatty acid composition, and increases glucosinolate levels, resulting in significant economic losses.

Mechanisms of drought tolerance

Osmotic adjustment: Plants are organisms that are sessile in nature, yet they respond to challenging environmental circumstances, such as drought, via signaling pathways that allow for adaptation (Dai et al., 2020). Osmotic adjustment and suitable solutes assist plants deal with drought stress (Dustgeer et al., 2021) by preserving cellular structure, function, and turgor pressure (Blum, 2017). Numerous studies have shown that osmotic adjustment under stress circumstances is connected with long-term B. napus output (Niknam et al., 2003). Furthermore, accumulating solutes protect cell structures and maintain cellular activity (Slama et al., 2015).

The root architecture of plants controls water and nutrient intake, which is critical for stress tolerance (Dai et al., 2020).  Root system architecture (RSA) plays a fundamental role in plant adaptation to drought stress because it determines the plant’s ability to explore soil for water and nutrients. RSA includes traits such as root depth, root length density, root angle, branching pattern, root diameter, and the development of lateral and fine roots. These traits collectively determine the efficiency of plant water uptake from the soil, particularly under water-limited conditions (Dai, 2013; Lynch, 2013). Deep and well-established root systems allow crop plants to cope with the stress conditions in better ways, as they can access deep water sources when surface water is scarce. Genotypes with the deeper penetration are more successful in maintaining water supply so that vital activities of the plants, such as transpiration and the photosynthesis, can continue even under the water stress. On the other hand, plants with shallower roots are unable to obtain deeper moisture and are more vulnerable to the effects of water deprivation (Uga et al., 2013). So, the root density and the surface area are the important factors in the drought tolerance in crop plants. Higher root surface area and the its density allow crop plants to get into more soil and to uptake the available water more effectively. Meanwhile, the development of fine roots hairs and the lateral branches increases the interaction between root and the soil, increasing the water as well as the available nutrient uptake during stress conditions (Comas et al., 2013). Another important trait is the plasticity of the root system, which is the capacity of the roots to change their shape under changing soil moisture. This allows roots to grow deeper or to the moist region of the soil and helps plants to keep their water uptake under changing environmental conditions. Furthermore, the changes in the root structure also help to enhance drought tolerance in plants. These modifications are the development of endodermal and exodermal obstacles and increased deposition of suberin and lignin that facilitate regulation of water and reduction of stress. A recent study reported that changes in the cortical tissue increase effective movement of the water and reduce the energy cost of soil investigation (Lynch, 2018). Moreover, recent studies highlight that auxin, abscisic acid (ABA), and cytokinins are responsible for regulating the root elongation, directional growth and the lateral root formation under the drought stress (Liu et al., 2015). Similarly, rhizosphere-associated activities and root soil interactions have been focused on more as the major determinants of water deficiency tolerance. Root exudates can stimulate microbial processes and improve the soil aggregation, which could lead to an increase in soil nutrient availability and water holding capacity (Vurukonda et al., 2016). Therefore, optimizing RSA traits through breeding and agronomic management is considered a promising strategy to improve crop resilience under drought-prone environments. Furthermore, several metabolites, such as proline, trehalose, and glycine betaine, operate as osmoregulatory chemicals and accumulate in B. napus during drought stress to reduce osmotic stress (Müller et al., 2012). In addition to RSA-mediated adaptation, osmotic adjustment is another major component of drought tolerance. Several metabolites, including proline, trehalose, and glycine betaine, function as compatible solutes and accumulate in B. napus under drought stress to reduce cellular osmotic damage (Müller et al., 2012). Under osmotic stress, the expression of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT) increases, whereas the expression or activity of proline dehydrogenase (ProDH) decreases, promoting proline accumulation. Proline acts as an osmotic material, increasing with P5CS synthesis or OAT expression and decreasing with reduced proline dehydrogenase expression (Xue et al., 2009). Additionally, B. napus plants increase trehalose (is an osmoregulatory compound that helps plants to maintain osmotic balance and protect against stresses) to enhance growth, photosynthesis, and the efficiency of antioxidative enzymes, while reducing reactive species and lipid peroxidation accumulation under drought conditions at the seedling stage (Shao et al., 2022). Similarly, tolerant cultivars exhibit high osmolyte levels, although this might be affected by physiological traits specific to particular tissues, species, and cultivars (Zhu et al., 2021a). Previous investigations have investigated the role of sugars in drought acclimation in B. napus, revealing that during first week of the period (0-6 days), sucrose and hexose accumulation were synchronized with the expression of HXK1 (hexokinase 1), along with the SA related genes and ABA synthesis. In the later period (6–14 days), hexose accumulation, sucrose loading, and degradation of starch were dominant with increased expression of starch degradation and ABA responsive genes highlighting the sugars’ role in drought acclimation in B. napus (Park et al., 2021). Nevertheless, additional findings are required to apprehend the complex interaction of osmoregulatory processes under drought conditions that are beneficial for progressing stress resilience in plants.

Hormone signaling:  Hormonal signaling is important in determining plant response as a result of adverse environmental challenges like heat and drought. Plants use different hormones, such as abscisic acid (ABA) and ethylene which can help to cope with adverse environmental conditions and help plants grow in difficult environments (EL Sabagh et al., 2022). Drought stress stimulates regulatory mechanisms that may operate via ABA-independent and dependent pathways. Subsequently, the downstream drought-responsive genes such as responsive to desiccation 20A, 29A, 29B, 22 (RD20A, RD29A, RD29B, RD22), Jasmonate ZIM-domain Proteins 1-12 (JAZ1-12), Nonexpresser of Pathogenesis-Related Genes 1 (NPR1), Early Responsive to Dehydration (ERD15), and Responsive to ABA 18 (RAB18) are activated (Lång and Palva, 1992; Kiyosue et al., 1994; Abe et al., 1997; Dong, 2004; Chini et al., 2007; Aubert et al., 2010; Bihmidine et al., 2013). Recent studies identified B. napus Calcium-Dependent Protein Kinase 5 (BnaCPK5) as a positive regulator of drought tolerance through phosphorylation of B. napus ABA-Responsive Element Binding Factor 3 (BnaABF3) and B. napus ABA-Responsive Element Binding Factor 4 (BnaABF4), which in turn enhance RD29B expression (Cheng et al., 2022). The concentration of ABA increases in response to drought conditions, promoting stomatal closure and thereby reducing water loss through transpiration. ABA also enhances a plant's tolerance to dehydration (Aslam et al., 2022).  Research in B. napus has shown that drought responsive genes regulate movement of ions such as K⁺, NO₃^-, Cl^-, and divalent malate, as well as key processes like stomatal regulation and water uptake by roots. Particularly, there is a close relationship between ABA and ROS: ABA causes ROS to build up, which helps to increase stress tolerance. Because of the interaction between ABA and ROS, plants are better able to control oxidative stress, which eventually increases their production and resilience in challenging environmental circumstances (Figure 3) (Liu et al., 2015).

Figure 3. The drought stress response in B. napus involves both ABA-dependent and ABA-independent signaling pathways in roots and leaves. In the ABA-dependent pathway, the regulatory network includes several transcription factor (TF) systems: AREB/ABF TFs interacting with ABRE elements, MYB/MYC TFs with MYBR/MYCR elements, and WRKY TFs binding to W-box (WRKYR) motifs. Meanwhile, the ABA-independent pathway is mediated by AP2/EREBP TFs targeting DRE/CRT elements, as well as NAC/ZFHD TFs associated with NACR/ZFHDR elements. As a result, various drought-responsive genes are activated, such as RD29B, RD20A, RD22, JA-inducible JAZ1–12, RAB18, NPR1, RD29A, and ERD1. These genes contribute to changes in ion exchange and osmotic potential, promoting stomatal closure in leaves and enhancing water uptake in roots.

Circulating hormone concentrations along with related signaling pathways for stress tolerance are influenced by several external circumstances (Bittner et al., 2022). By programmed cell death, ABA and ROS can hasten leaf senescence and harm root tips (Guo et al., 2017). Drought stress, on the other hand, raises ABA levels and the expression of associated genes including ABA Responsive Element Binding Protein 2 (AREB2) and Receptor-like Kinase 2.2 (RK2.2) (La et al., 2019a).  A comprehensive technique for promoting stress adaption is formed by the management of ROS, hormones like ABA, and osmolyte like proline (Osakabe et al., 2014). Moreover, during drought conditions, proline, ROS, Ca²⁺ signaling, and CPK5 gene expression are synergistically elevated (Lee et al., 2022). Different stress responsive genes are presented in Table 2.

Table 2. Key genes and their functions under drought stress in B. napus

Studies have shown that plant hormones synergistically contribute to plant stress tolerance, with SA, ABA, and Jasmonic acid (JA) recognized as substantial signaling regulators (La et al., 2019b). SA plays an imperative role in stress resilience  (Khan et al., 2021), while the antagonistic relationship between ABA and SA  regulates adaption processes (Muñoz-Espinoza et al., 2015). Additionally, JA contributes to regulating stomatal movement by maintaining stomatal aperture, while SA works to shield the photosynthetic apparatus and membrane structure during water deficiency in B. napus (Wenjing et al., 2020). Moreover, the correlation between SA and JA signaling processes shows transcriptional regulation related to stress tolerance (Batool et al., 2023).

In B. napus and other plants, ABA, brassino steroids (BRs), and auxin play an imperative role under stressful conditions where BRs signaling modulates tolerance mechanisms to abiotic stress, especially in drought (Shamloo-Dashtpagerdi et al., 2015) by adjusting stress-related transcription processes (Ye et al., 2017), triggering the antioxidative system (Tunc-Ozdemir and Jones, 2017), improving the accumulation of osmo-protectants (Fàbregas et al., 2018), and regulating different cellular mechanisms in B. napus upon drought exposure (Shamloo-Dashtpagerdi et al., 2015).

The study of regulatory pathways showed that exposure to drought improved the expression of ABA1 ortholog, which indicates ABA synthesis and BRs signaling were activated by its binding to a membrane receptor kinase, displaying the antagonistic relationship between ABA and BRs signal transduction under stress. Furthermore, the CBL-interacting protein kinase 6 (CIPK6) gene was up-regulated and correlated with Ca²⁺-dependent ABA signaling activation under drought conditions. It was also associated with auxin transport, leading to stress tolerance by adjusting root architecture (Shamloo-Dashtpagerdi et al., 2015). B. napus A-genome chromosome 6 Repressor of Gibberellin Signaling (BnaA6.RGA) positively regulates drought tolerance by enhancing ABA sensitivity and stomatal closure, thereby reducing water loss under water deficit conditions (Wu et al., 2020). Moreover, DELLA proteins, which reduce GA, require further research and can be exploited in stress tolerance related developmental programs.

In summary, drought stress poses a major constraint to the growth, physiology, and productivity of B. napus. The plant tackles a water deficit through osmotic adjustment, root system architecture improvement, and hormonal signaling (ABA and SA), alongside stress-responsive genes and antioxidant defenses that preserve cellular stability. These integrated responses strengthen drought tolerance, and more profound insights into them will guide breeding and advanced molecular strategies for resilient cultivars.

Molecular mechanisms: Free radicles excessively accumulate in different cells as a result of the cell dehydration response, causing alterations in redox mechanisms leading to protein degradation (Zhang et al., 2019a). In B. napus, guard cell conductivity was regulated by 65 redox responsive proteins (ABA treatment), including SNRK2 kinase and 3-isopropylmalate dehydrogenase, demonstrating that ABA signaling is controlled by thiol-based redox reactions (Zhu et al., 2014). In B. napus, guard cell conductivity was regulated by 65 redox responsive proteins (ABA treatment), including SNRK2 kinase and 3-isopropylmalate dehydrogenase, demonstrating that ABA signaling is controlled by thiol-based redox reactions (Zhu et al., 2014).

A previous study indicated that the Late Embryogenesis Abundant 3 (LEA3) and Vicinal Oxygen Chelate (VOC) proteins are involved in drought response, with LEA3 proteins helping to protect cellular structure during dehydration, and VOC domain containing proteins contributing to detoxification; may also be linked to lipid accumulation (Liang et al., 2019). Furthermore, transcriptomic analyses under drought conditions identified 169 differentially expressed genes (DEGs) in B. napus (Wang et al., 2017) and important regulatory pathways have been examined under external climatic factors. The gene MYC2 TFs (Myelocytomatosis oncogene transcription function) were found to regulate stomatal conductance under drought stress (Wenjing et al., 2020). Furthermore, functional studies of different drought related proteins demonstrated that vesicular transportation processes, ion mobilization, and stress signaling are vital processes for early drought stress response. Conversely, proteins involved in photosynthetic, metabolic processes, translation and transcriptional mechanisms were significantly altered under stress conditions, indicating their role in drought response, which means that these proteins play a crucial role in the plant’s adaptive mechanism to cope with drought stress, the change in these proteins reflect the plant physiological adjustment necessary for maintaining homoeostasis and functionally under water limit conditions (Luo et al., 2015).

ROS homeostasis under drought: Drought stress, triggers multiple physiological disruptions in plants, primarily through the overproduction of ROS such as superoxide radicals (O₂^-), hydroxyl radicals (•OH), and hydrogen peroxide (H₂O₂). ABA mediated stomatal closure under water deficit conditions limits CO₂ assimilation, disturbs electron transport, and promotes the peroxidation of protein, nucleic acid, photosynthetic pigments, and lipids (Kheradmand et al., 2014). In B. napus sever ROS induced lipid peroxidation and H₂O₂ accumulation have been associated with reduced yield and increased osmotic stress (Shahzad et al., 2022).

To mitigate ROS toxicity, B. napus has developed a dynamic antioxidant defense system that efficiently scavenges free radicals and helps the plant cope with stress conditions (Batool et al., 2023). A detailed illustration is presented in Figure 4 (Laxa et al., 2019).  Antioxidants play an important role in reducing the effects of oxidative stress by directly or indirectly scavenging ROS and controlling their synthesis (Carocho and Ferreira, 2013). The plant antioxidant defense system consists of two main components: low-molecular-weight non enzymatic antioxidants and specialized antioxidant enzymes (Hasanuzzaman et al., 2019). Non enzymatic antioxidants like ascorbate (AsA), phenolic compounds (PhOH), glutathione (GSH), flavonoids, α-tocopherol, alkaloids, and non-protein amino acids work together with enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), peroxidases (POX), monodehydroascorbate reductase (MDHAR), ascorbate peroxidase (APX), and dehydroascorbate reductase (DHAR). These components work together to keep ROS levels balanced and prevent oxidative damage (Figure 4) (Laxa et al., 2019).  B. napus plants use SOD to convert superoxide radicals (O₂⁻) into hydrogen peroxide (H₂O₂) as their first defense against stress (Nouairi et al., 2009). The generated H₂O₂ is detoxified through several enzymatic and non-enzymatic pathways. It can be converted into water by catalase (CAT), ascorbate peroxidase (APX), or glutathione peroxidase (GPX), or processed via the ascorbate–glutathione (AsA–GSH) cycle. With the coordinated actions of four essential enzymes APX, DHAR, MDHAR, and glutathione reductase (GR) as well as non-enzymatic antioxidants including glutathione (GSH) and ascorbate (AsA), this cycle plays a crucial role in preserving cellular redox equilibrium and detoxifying H₂O₂ (Fotopoulos et al., 2010; Hasanuzzaman et al., 2019). Additionally, GST and GPX help control ROS by detoxifying H₂O₂ and xenobiotics, improving cellular resilience. The most prevalent soluble antioxidants among nonenzymatic antioxidants in higher plants are AsA and GSH, which work as electron donors to directly scavenge ROS via the AsA-GSH cycle (Hasanuzzaman et al., 2019). By squelching hydroxyl radicals (OH), superoxide (O₂⁻), and peroxyl radicals (ROO), other antioxidants like beta-carotene also contribute significantly to the reduction of total ROS levels. Furthermore, ROS like hydrogen peroxide and superoxide radicals accumulate in plant cells under adverse environmental conditions. These ROS have the capability to damage the cell, proteins, lipids, and nucleic acids. It affects the growth stages and productivity. However, B. napus has several mechanisms, such as several antioxidant enzymes like superoxide dismutase, catalase, and peroxidases which can help it to improve its resistance (Batool et al., 2023). Beside this it also has some non-enzymatic antioxidants like ascorbate and glutathione which can help to minimize this drought stress. These components work together to neutralize ROS, thus protecting cellular integrity and function (Rudenko et al., 2023). Antioxidant enzymes can also play an important role in improving seed yield, oil yield, growth, and stability (Naheed et al., 2021). A previous study showed that antioxidant defensing systems help the B. napus to cope with adverse environmental conditions for sustainable agricultural practices under drought and heat stress (Iqbal et al., 2010). The association of antioxidative enzymatic activities and gene expression patterns has a substantial role in the antioxidative system during drought in B. napus. Moreover, antioxidative enzyme related genes such as Cu/Zn/MnSOD, glutathione reductase (GR), (APX), and GPX were found to be improved in stress-tolerant plants of B. napus to encounter drought stress conditions (Hosseini et al., 2015; Xia et al., 2016). In B. napus BnCAT was activated and highly correlated with cell structures, contributing to stress-related antioxidative processes under drought conditions (Raza et al., 2021). The higher relative transcription ratio of CAT2, gPOD, and cytosolic APX, suggests that enzymatic activity and gene expression are directly related to defending cells under water deficit conditions (Hosseini et al., 2015). To sum up, maintaining high concentrations of enzymatic and non-enzymatic antioxidants is critical to improving B. napus plants' resistance to drought. However, addressing several metabolic pathways is also necessary to increase drought tolerance. In addition to taking into consideration the time and location of signaling events associated with drought stress adaptation, these pathways must be carefully selected to prevent interfering with important developmental processes.

Figure 4. Overview of the plant antioxidant defense system highlighting the types of antioxidants and the integrated roles of enzymatic and nonenzymatic mechanisms. APX, ascorbate peroxidase; CAT, catalase; AsA, ascorbate; DHA, dehydroascorbate; GPX, glutathione peroxidase; DHAR, dehydroascorbate reductase; GSH, reduced glutathione; GR, glutathione reductase; GSSG, oxidized glutathione; H₂O₂, hydrogen peroxide; OH·,   hydroxyl radicle; GST, glutathione S-transferase; MDHAR, monodehydroascorbate reductase; MDHA, monodehydroascorbate; NADPH, nicotinamide adenine dinucleotide phosphate; O₂⁻, superoxide anion; POX, peroxidases; PRX, peroxiredoxins; SOD, superoxide dismutase; TRX, thioredoxin; PPO, Polyphenol oxidase.

In B. napus plants, at the molecular level ROS homeostasis is tightly integrated with endogenous hormonal and transcriptional signaling networks. ABA and JA were increased under water scarcity conditions, associated with ROS and proline synthesis along with a reduction in potential [NAD(P)H/NAD(P)⁺ and GSH/GSSG] (Batool et al., 2023). Drought induced ROS production through the ABA signaling pathway is related to proline increment together with high cytosolic Ca²⁺ ion level and CPK5 expression in B. napus, indicating hormonal signal transduction interaction under stressful conditions. Several TFs, including NAM/ATAF1-2/CUC2 (NAC), myeloblastosis (MYB), and AP2/ERF responsive element binding proteins (AP2-EREB) regulate the target genes whose expression is affected by the activity of the TFs. Proline significantly contributes to stress tolerance at the transcriptional level in B. napus by regulating the genes responsible for its synthesis and decreasing the expression of genes involved in its degradation under stress conditions (Wang et al., 2019). Stomatal closure reduces the transpiration rate, which improves the water-use efficiency (WUE) , indicating a tolerance response in B. napus (Wu et al., 2020). Numerous adaptive responses to drought stress are shown in the schematic illustration (Figure 5) (La et al., 2019a; Wu et al., 2019; Zhang et al., 2019a). In conclusion, under water deprivation, several molecular mechanisms are induced, repressed, and interconnected; in addition, various alterations in gene expression occur, enabling plant subsistence under severe drought stress. Likewise, B. napus plants activate genes related to stress adaptation to ensure normal reproductive development. However, researchers do not fully understand stress sensors and regulators at the molecular level in response to drought stress, which is not well understood.

Figure 5. Proposed cellular events and signaling interactions in B. napus against drought stress. As a result of drought stress, plants accumulate reactive oxygen species (ROS) and trigger signaling cascades, likely through hormonal and Ca⁺² signaling. These reactions trigger the production of certain protein kinases, which trigger additional downstream reactions, which includes changes in the degree of expression of genes. Additionally, these signaling actions alter the metabolism of plants, resulting in the stimulation and production of antioxidants and organic solutes as well as stomatal closure during severe drought stress.

Key points:

1. B. napus adapts to drought by accumulating solutes such as proline, trehalose, and glycine betaine to protect membranes, maintain cell turgor, and stabilize enzymes.

2. ABA promotes stomatal closure, activates drought responsive genes, and interacts with other hormones such as JA, SA, BRs and ROS to coordinate stress responses.

3. In response to water scarcity, B. napus activate essential transcription factors (NAC, MYB, AP2/ERF), stress responsive genes (RD29, P5CS, CPK5), and proteins involved in ion transport vesicular trafficking.

4. ROS homeostasis is maintained by enzymatic antioxidants (SOD, CAT, APX), non-enzymatic antioxidants (ascorbate, glutathione), and hormonal and redox signaling pathways.

Management of drought stress

Agronomic practices:  Environmental stresses can be mitigated either through genetic improvement or the application of effective agronomic practices that enhance plants adaptation to adverse conditions. Developing tolerance to abiotic stress requires both the breeding of resilient cultivars and the implementation of optimized management strategies (Mariani and Ferrante, 2017). Recent studies emphasize the role of agronomic interventions, including optimized sowing time, method, and depth, as well as modification in plant density, tillage practices, irrigation scheduling, and nutrient management (Mubeen et al., 2021; Yonas et al., 2023). These measures can significantly support crop development and maintain yield under stress conditions (Iqbal et al., 2021). Among the different agronomic practices, the way of sowing plays a particularly important role because it directly affects seedling establishment, nutrient availability, and water uptake (Shabani et al., 2013; Hassan et al., 2019a). Sustainable practices such as furrow sowing, drill sowing, and bed planting are often recommended to improve crop performance in water-limited conditions (Aiken et al., 2015; Zawar et al., 2024; Zawar et al., 2025b). Traditional broadcasting tends to result in less uniform seed dispersion and thus increases plant competition for water, light, nutrients, and space. Irregular plant spacing can have a drastic effect on crop establishment and ultimately limit crop plant yield potential (Mwale et al., 2003). Drill sowing has been shown to be more effective than broadcasting methods in B. napus to enhance WUE, seedling establishment, and yield (Aiken et al., 2015). Similarly, furrow sowing in B. napus and its relative species has been demonstrated to improve its growth and yield over ridge sowing and also conserve the soil moisture and improve WUE by reducing soil evaporation (Shabani et al., 2013). This method helps to conserve moisture and alleviate the effects of drought stress (Buttar et al., 2006). Selecting an appropriate sowing method is therefore essential for improving WUE under drought-prone conditions. Integrating low-cost field phenotyping tools with suitable sowing strategies and modern phenotyping technologies can enhance the performance of B. napus under water-limited conditions. This can be achieved through carefully designed experiments and the application of targeted agronomic practices. In addition, the identification of key drought-resilient traits and the integration of diverse datasets using advanced analytical and predictive models’ approaches are essential.

Role of exogenous osmolyte: Osmolytes are osmo-protective compounds that support plants in adapting to osmotic stress and scavenging ROS under adverse conditions (Hassan et al., 2019b). The exogenous application of glutathione has been shown to significantly increase leaf and pod weights as well as seed yield in drought-stressed B. napus (Mehanna et al., 2013). Similarly, applying poly-γ-glutamic acid (γ-PGA) under drought conditions improved chlorophyll content, relative water content (RWC), seedling growth, proline accumulation, and antioxidant activity, while reducing malondialdehyde (MDA) levels in B. napus cultivars (Xu et al., 2020). Glycine betaine (GB), when applied externally, enhanced drought tolerance in B. napus by increasing chlorophyll levels, seed yield, carbohydrate and proline contents, antioxidant activities, and root length, while decreasing MDA and hydrogen peroxide (H₂O₂) levels (Dawood and Sadak, 2014). Furthermore, exogenous application of ascorbic acid (ASA) or salicylic acid (SA) has been found to improve B. napus productivity by mitigating drought stress through enhanced antioxidative defense (Sabagh et al., 2019). JA, when applied externally, also boosted sugar accumulation in various crops, including B. napus (Sharma et al., 2019). Plant growth regulators (PGRs) are organic substances used in small quantities to influence plant physiological functions, thereby promoting growth and stress resilience. SA, a key PGR, enhances antioxidant activity, cellular homeostasis, and photosynthetic performance in B. napus (Tirani et al., 2013; Ahmadi et al., 2015; Brito et al., 2019). It also increases glutathione levels, helping to scavenge ROS and improve cellular signaling (Herrera-Vásquez et al., 2015). SA treatment has been shown to enhance ROS scavenging, promote proline accumulation, and upregulate proline biosynthesis genes such as Δ1-pyrroline-5-carboxylate synthetase 1,2 (P5CS1), (P5CS2), and Δ1-pyrroline-5-reductase (P5CR) (La et al., 2019b). Moreover, it limits the production of 1-aminocyclopropane-1-carboxylic acid (ACC), thereby improving drought tolerance in B. napus (Nazar et al., 2011). PGRs also facilitate the accumulation of organic solutes like proline, contributing to the stabilization of leaf RWC, and exhibit more antagonistic behavior than ABA under stress conditions (Muñoz-Espinoza et al., 2015). In addition, they can enhance water availability and maintain photosynthetic activity and stomatal conductance, thereby improving photosynthetic efficiency (Willenborg et al., 2004). ASA plays a crucial role in ROS detoxification by reducing oxidative damage from superoxide and free radicals, promoting enzymatic antioxidant activity, and alleviating osmotic stress (Shafiq et al., 2014; Ahmadi et al., 2015). In summary, the exogenous application of osmolytes and plant growth, this approach shows strong potential for improving drought tolerance in B. napus. ABA is a crucial hormone in drought signaling, particularly in regulating osmotic adjustment under water scarcity situations. Its interactions with SA and JA have been identified to be highly complex and dynamic. Drought-related stress has been found in recent study to increase the levels of ABA and JA, resulting in higher ABA/SA and ABA+JA ratios. On the other hand, salicylic prior treatment has been demonstrated to prevent oxidative damage, increase gas exchange, and strengthen the antioxidant defense system, support osmotic balance, and maintain physiological and biochemical stability, allowing plants to withstand drought stress more successfully (Jogawat et al., 2021; Iqbal et al., 2022). Nonetheless, other investigations demonstrate that SA may inhibit ABA signaling by reducing ABA-dependent molecular responses (Jogawat et al., 2021). These different outcomes are most likely influenced by plant genotypes, the severity of drought stress, and developmental stage, all of which affect hormone regulation. More study should be performed to clarify these complicated hormonal relationships using integrated multi-omics methodologies such as transcriptomic, metabolomics, and complete hormone profiling across distinct cultivars.

Function of mineral nutrient: Mineral nutrition (Mn) plays a fundamental role in crop productivity, and poor Mn management can reduce soil fertility and significantly limited yield potential. Therefore, maintaining a balanced nutrient supply is essential for improving plant performance and enhancing tolerance to environmental stress (Hansel et al., 2017). N is one of the essential nutrients and is particularly important in alleviating abiotic stress (Waraich et al., 2011). N helps in the production of NO, which is a key signaling molecule involved in protecting plants from oxidative stress by scavenging ROS. Adequate N supply in B. napus has also been linked to greater proline accumulation, which helps to reduce the negative effects of drought stress (Albert et al., 2012). K⁺ is also an important nutrient in drought tolerance (Umair et al., 2017). K⁺ deficiency inhibits protein synthesis and constrains the accumulation of amino acids and amides (Fageria, 2016). It also encourages root growth and development by enhancing stress tolerance (Egilla et al., 2001), and a recent study reported that it also helps to improve the growth of root hairs, ultimately the root surface area, thereby improving water and nutrient uptake under drought conditions (Römheld and Kirkby, 2010). In addition, K⁺ enhances proline accumulation for osmotic adjustment and controls the stomatal activity, photosynthesis, and assimilate distribution, which are all important for sustaining growth and yield under stress (Zörb et al., 2014). Relative water content was enhanced with adequate K⁺ supply due to better WUE in B. napus (Ali et al., 2014). The supply of Ca²⁺ also contributes considerably to drought tolerance. It helps stabilize cellular membranes, protect against oxidative damage, maintain hormonal balance as well as preserve photosynthesis activity under stress conditions. Furthermore, it functions as an important signaling molecule and strengthens antioxidants (Rezayian et al., 2018). In sum, balanced nutrient management is crucial for sustaining plant growth and productivity under drought stress. Combining nutrient optimization with advanced phenotyping approaches may further support the development of drought tolerate B. napus cultivars. Recent research in shogun metagenomics has also revealed important drought-induced changes in the rhizosphere microbiomes of B. napus. Under water deficit conditions, microbes communicate that plant hormones such as  auxin and cytokinin’s become more abundant, helping plants improve their stress tolerance (Lu et al., 2025). Moreover, genes involved in nutrient cycling, particularly those associated with nitrogen transformation such as ammonia oxidation and nitrate reduction, show increased activity, suggesting an adaptive mechanism that helps sustain nutrient availability under water stress conditions (Ait-El-Mokhtar et al., 2023). All of our data reveal that drought-induced changes in the rhizosphere microbiome play a dual function by boosting nutrient absorption and stimulating hormone-mediated stress responses, eventually enhancing plant survival under drought stress.

Function of seed priming: Seed priming has been suggested to be a successful strategy for improving germination, enhancing solute accumulation, and reducing oxidative damage, all of which result in increased drought tolerance. This approach boosts faster and more uniform seed germination, improves seedling establishment, increases WUE, and contributes to better yield performance in B. napus under stress circumstances (Khan et al., 2020). In particular, hormonal priming has been reported to increase soluble sugar and protein contents, as well as antioxidant activity, thereby helping plants maintain growth and development under unfavorable environmental conditions (Khanum et al., 2019). Nutrient-based priming also plays an important role. For instance, priming with KH₂PO₄ has been reported to improve plant growth, yield components, oil content, and silique formation (Sarma et al., 2014). Similarly, KNO₃ priming enhances the accumulation of proline and soluble sugars while strengthening antioxidant defense systems, thereby reducing drought-induced damage (Yan, 2015). Ca²⁺ priming also contributes to stress tolerance by increasing soluble sugar and proline contents, improving stomatal conductance, reducing transpiration losses, and supporting photosynthetic activity (Xiang et al., 2008). In addition, seed priming with melatonin and gibberellic acid (GA₃) has been shown to increase endogenous proline levels and enhance drought tolerance in B. napus (Khan et al., 2020), whereas ZnSO₄ priming improves the activity of antioxidative enzymes (Aboutalebian and Nazari, 2017). Overall, seed priming strengthens osmotic adjustment, improves photosynthetic efficiency, and enhances antioxidant capacity, enabling plants to better withstand drought stress. Overall, seed priming improves osmotic adjustment, photosynthetic efficiency, and antioxidant capacity, enabling plants to better withstand drought stress (El-Badri et al., 2021). Research in other crops, such as maize, has also demonstrated the potential of silicon (Si) priming to improve water uptake, stimulate root and shoot growth, and increase biomass accumulation under drought conditions (Zawar et al., 2025a). In conclusion, seed priming provides plants greater defensive mechanisms to withstand drought stress in addition to improving germination and early seedling growth. Merging priming techniques with modern research techniques could improve our comprehension of B. napus stress responses and aid in the breeding of cultivars that are more resilient.

Role of plant growth-promoting bacteria: Plant growth-promoting bacteria (PGPB), often present as endophytes, play an important role in helping plants cope with drought stress (Marasco et al., 2012). A range of PGPB strains have been reported to improve drought tolerance in crops such as wheat (Gontia-Mishra et al., 2016), maize (Vardharajula et al., 2011), beans (Sarma and Saikia, 2014), and B. napus (Saeed et al., 2016b). In addition, inoculation with Glomus-associated PGPB has been shown to enhance plant growth and drought tolerance under arid conditions (Yonas and Zawar, 2024). The beneficial effects of PGPB are largely associated with improved water and nutrient uptake, better regulation of plant hormones, and enhanced photosynthetic performance and antioxidant activity (Naveed et al., 2014).  For instance, PGPB inoculation has been reported to reduce drought-induced damage and promote growth in Glycyrrhiza uralensis. In particular, Bacillus pumilus improves drought tolerance by protecting the photosynthetic system and increasing chlorophyll content and RWC. (Zhang et al., 2019b). Seed treatment with Azospirillum has been shown to reduce the effects of drought by promoting root growth, increasing chlorophyll content, improving plant water status, and enhancing antioxidant activity. These beneficial changes ultimately result in a higher number of seeds per pod, increased seed weight, and improved yield under drought conditions compared with non-inoculated plants (Saeed et al., 2016a; Batool et al., 2023). In general, microbial applications such as bacterial and fungal inoculants can enhance drought tolerance by increasing photosynthetic efficiency resource intake and improving the antioxidant defense. Future drought problems in B. napus will require an integrated approach by combining the developed drought-tolerant cultivars with the most efficient agronomic management techniques. This study aims at the agronomic and economic feasibility of different practices such as microbial inoculation, foliar application of plant growth regulators, and seed priming by assessing their cost per hectare with the respective yield benefits to assess the practical applicability of these techniques (Table 3). Moreover, a comparison of the drought performance of B. napus compared to other oilseed crops can help in identifying the most effective management practices and important traits for future crop improvement programs. The structural traits of B. napus are generally less robust (e.g., shallower root system, moderate WUE) than those of Helianthus annuus L. (sunflower), which has deeper roots, higher WUE, and robustness in yield stability under drought conditions (Ashraf and Siddiqi, 2024). However, the biochemical response of B. napus was often superior relative to Glycine max L. (soybean) with higher induction of proline, antioxidant, enzyme activity, and endogenous hormonal regulation (ABA, JA, SA) under drought conditions (Ayyaz et al., 2021).

Table 3. Comparative cost and yield benefit of seed priming PGR foliar spray and microbial inoculation based on field studies in B. napus.

Integration of modern phenotyping technologies for drought management: Recent developments in high-throughput phenotyping technologies have greatly improved the capacity to monitor crop performance under drought stress. Advanced tools such as unmanned-aerial-vehicles (UAVs), remote sensing platforms, and the multispectral imaging can provide rapid and non-destructive assessment of crop physiological traits over large field areas, providing valuable insights into plant responses to water deficit conditions (Araus and Cairns, 2014; Yang et al., 2017). UAV-based phenotyping systems can obtain high-resolution imagery that gives detailed information on canopy temperature, vegetation indices, such as the normalized-difference-vegetation-index (NDVI), chlorophyll content, and plant water status. These parameters are widely used as indicators of plant health and stress tolerance and assist in identifying drought-tolerant genotypes while facilitating real-time monitoring of crop stress under field conditions (Zarco-Tejada et al., 2012; Tattaris et al., 2016). By capturing fluctuations in canopy temperatures and spectral reflectance associated with water scarcity, satellite-based remote sensing and thermal imaging provide valuable tools for early detection of drought stress. By maximizing water use and monitoring stress before visible signs appear, these methods also aid precision irrigation (Yang et al., 2017; Araus et al., 2018). The efficiency of screening a large number of genotypes for resilience to drought has increased with the adoption of contemporary phenotyping tools in crop breeding. High-throughput phenotyping techniques make it feasible to determine significant traits that are directly related to drought resilience in crops, including B. napus, such as canopy temperature depression, biomass accumulation, and photosynthetic performance (Araus et al., 2018). Additionally, applying machine learning techniques with remote sensing data may enhance crop decisions for management and strengthen drought forecasting. These advancements provide significant potential to boost drought resistance and promote sustainable B. napus production in water-constrained situations (Li et al., 2014a; Yang et al., 2017).

Breeding approaches

QTL and candidate gene identification: Genomic tools need to be used with conventional breeding techniques in order to effectively breed B. napus for resistance to drought. To figure out genomic regions correlated with drought-related traits like seed yield, root architecture, and WUE, techniques like quantitative trait loci (QTL) mapping, marker-assisted selection (MAS), and genome-wide association studies (GWAS) have been extensively employed (Raman et al., 2019). By controlling hormonal pathways and stress-responsive systems, numerous other potential genes, including BnNAC485, BnSIP1-1, and BnABI5, have been shown to enhance stress tolerance (Luo et al., 2017). The discovery of drought-responsive loci has been reinforced by developments in high-density SNP arrays and genome sequencing (Fletcher et al., 2015; Clarke et al., 2016). Nevertheless, the consistency of marker-assisted selection under different field conditions might be restricted since drought tolerance is a complex quantitative trait influenced by considerable genotype × environment interactions. The B. napus genome’s polyploidy further complicates the identification of potential genes and marker–trait correlations. In order to overcome these obstacles and create stable drought-tolerant cultivars, MAS must be integrated with genomic selection, high-throughput phenotyping, and multi-environment trials. Emerging approaches such as speed breeding and UAV-based phenotyping also provide promising opportunities to accelerate the development of drought-resilient B. napus cultivars under variable environmental conditions.

Drought stress is a multifaceted problem in plant biology, mainly because of the complexity of the linked signaling pathways. Development and use of drought-tolerant cultivars have thus become a major objective of crop improvement programs. Nevertheless, progress is improving; drought tolerance in B. napus and its relative species by genetic means has been limited. Breeding approaches such as marker-assisted selection and transgenic approaches are still very common in B. napus, but both have limitations (Chang et al., 2021). The transfer of novel cytoplasmic backgrounds from tropical germplasm into B. napus has shown promise to express beneficial traits like improved tolerance to drought stress, as well as its photosynthetic efficiency (Choudhary et al., 2000). Moreover, selection under stress conditions has been shown to be effective to identify genotypes with enhanced adaptation and performance. In particular, it has been reported that simultaneous selection of traits such as yield and yield parameters under drought is 20% more efficient than direct selection under stress. Moreover, combined selection for flowering time and yield has been shown to enhance B. napus yield by an additional 16% (Richards and Thurling, 1979). A vital genetic material for the development of future cultivars is the wild relative of B. napus, which often exhibit remarkable resistance to drought. Transgenic B. napus-expressing genes like B. napus NAC transcription factor 485 (BnNAC485), B. napus SHAQKYF-type Interacting Protein 1-1 (BnSIP1-1), and B. napus ABA-Insensitive 5 (BnABI5) demonstrates enhanced resilience to abiotic stress (Luo et al., 2017). Backcrossing has resulted in diploid BC1 plants from intergeneric crossings, such as those between B. oleracea and M. arvensis, while BC2 monosomic lines preserve M. arvensis chromosomes for breeding purposes (Bang et al., 2007). Stomatal sensitivity to ABA increases and transpiration under dehydration diminishes via inhibiting farnesyl-transferase (FTA), a negative regulator of ABA (Wang et al., 2005). RD29A: anti-transgenic B. napus at flowering, the AtFTB construct demonstrated exceptional drought tolerance, with harvest indices that were on par with well-irrigated plants under mild stress. Transgenic methods provide focused answers, but natural selection is unable to swiftly produce drought-resistant plants. Innovative methods like high-density SNP arrays have augmented traditional QTL identification, which depends on the labor-intensive genotyping of large populations (Clarke et al., 2016) and sequencing (Fletcher et al., 2016). In B. napus, 31 QTLs for drought tolerance and 19 for drought resistance coefficients (DRC) have been mapped (Li et al., 2014b). Marker-assisted breeding, using recombinant inbred lines or double haploid populations, alongside association mapping for precise QTL localization (Qu et al., 2017), has advanced trait selection. A brief summary of QTL recent studies on drought related traits in B. napus is mentioned in Table 4. Efforts to diversify B. napus genetics include resynthesizing hybrids from B. oleracea and B. rapa (Wu et al., 2014) and introgression wild traits via hybrid bridges (Enjalbert et al., 2013).  In B. napus, genome-wide association studies (GWAS) have found SNPs connected to oil quality, seed weight, and drought tolerance (Raman et al., 2019). The mapped B. napus genome enables high-density polymorphism screening at a reasonable cost, which helps identify genes associated with drought responses, such as SCO1 and ATE1 (Hatzig et al., 2015). Study showed that, 314 drought-responsive SNPs were found in B. napus that demonstrating the value of genomic techniques in creating drought-tolerant recombinants.  In conclusion, integrating transgenic modification with cutting-edge genomic approaches (GWAS, SNP markers) allows an exact approach to engineer drought tolerance in B. napus, addressing limitations associated with conventional breeding and accelerating the development of climate-resilient cultivars. Furthermore, although there no published speed-breeding trials specifically under drought in B. napus, indoor phenotyping platforms have been successfully applied for multiple generations and traits screening in B. napus (Ćeran et al., 2024). These platforms, when paired with high-throughput phenotyping, such as UAV thermal imaging and hyperspectral tools. Which helps early and non-invasive detection of drought stress traits such as canopy temperature depressions and spectral stress signatures in B. napus (Chen et al., 2019). Together, this suggests that controlled environment speed breeding coupled with drone-based phenotyping could significantly accelerate drought tolerance selection cycles in B. napus.

Table 4. Summary of QTL and GWAS studies in B. napus under controlled conditions.

Advances in drought tolerant in B. napus: Despite the potential of transgenic approaches to enhance drought tolerance, several regulatory, ecological, and socio-economic challenges limit their large-scale deployment. The commercialization of genetically modified crops requires extensive biosafety assessments, regulatory approvals, and environmental risk evaluations, which can be costly and time-consuming (Qaim, 2020). Concerns regarding gene flow to wild relatives, potential impacts on non-target organisms, and public acceptance also remain important issues in many agricultural regions (Ellstrand et al., 2013). Moreover, drought tolerance is a complex quantitative trait controlled by multiple genes and regulatory networks, which limits the effectiveness of single-gene transgenic approaches (Blum, 2017). Gene stacking, which integrates multiple stress-responsive genes within a single genetic variation, has emerged as an effective approach to enhance drought tolerance as a way to mitigate these challenges. This approach can improve plant performance in water-limited environments by combining genes related to osmotic adjustment, antioxidant defense, and hormone regulation (Mittler and Blumwald, 2010). A realistic methodology for developing drought-resistant B. napus cultivars while taking environmental and regulatory factors into account is provided by the combination of cutting-edge genomic technologies and multi-gene engineering.

Although the complex nature of plant stress-response networks typically limits its application, genetic transformation is nevertheless an important tool for enhancing tolerance to environmental challenges. More efficient crop improvement is now feasible because of recent developments in gene-editing technologies, which enable precise change of target genes through activation or repression (Sedeek et al., 2019). High-throughput DNA and SNP-based markers have improved allelic association studies, functional analysis, and gene discovery in B. napus (Afzal et al., 2018). Moreover, RNA sequencing has been developed as a reliable method to evaluate stress responses in genotypes at a higher resolution than traditional methods such as QTL mapping, GWAS, and microarray analysis (Schmidt and Bancroft, 2011). Several dehydrin (DHN) genes, including Bn115, COR25, ERD10, ERD15, and BnDHN1 have been reported as drought-responsive markers in B. napus and are useful targets for crop plants improved through breeding initiative programs (Chikkaputtaiah et al., 2017). Similarly, the expression of genes encoding G-protein subunits e.g., BnGG2, BnGA1, and BnGB1, is upregulated under water deficit, probably via ABA-dependent signaling pathways (Lohani et al., 2020). In addition to that, genetic engineering techniques have also been used to modulate major stress-related hormones such as cytokinin, ethylene, and brassinosteroids which further contribute to improved drought tolerance in B. napus (Sahni et al., 2016). Innovative techniques like the in vivo site-specific assembly (MISSA) method enable the integration of multiple genes, such as Nine-cis-epoxycarotenoid dioxygenase 3 (NCED3), ABA Receptor (ABAR), C-repeat Binding Factor 3 (CBF3), Low Expression of Osmotic Stress 5 (LOS5), and Inducer of CBF Expression 1 (ICE1), into a single transformation vector (pABA-oriT). Transgenic B. napus expressing NCED3 demonstrated superior growth under stress compared to wild-type plants (Wang et al., 2018). In B. napus, genome-wide analysis of methyltransferase and demethylase gene families e.g., B. napus Domains Rearranged Methyltransferases (BnaDRMs) and B. napus Repressor of Silencing 1-like proteins (BnaROS1s) revealed conserved clades responsive to drought stress (Fan et al., 2020; Talarico et al., 2024). Additionally, methylation profiling studies under PEG-induced osmotic stress (or analogous dehydration treatments) identified dynamic changes in gene-body methylation of stress related loci, some correlating with transcriptional activation of ABA or ROS related pathways implying potential mechanisms for stress memory and transgenerational adaptation (Yuan et al., 2019; Rao et al., 2024). In summary, biotechnological approaches including gene editing, marker-assisted breeding and multi-gene engineering hold promise for developing drought-tolerant B. napus cultivars. Expanding genomic datasets will further facilitate comparative studies, unearthing novel stress-resilient traits in Brassica species and accelerating precision breeding efforts. 

Key points:

1. Optimal management of sowing time, irrigation, and nutrient supply improves WUE and crop yield under drought conditions.

2. The application of exogenous osmolyte, such as glycine betaine and proline, along with growth regulators including ABA, SA, and JA, enhances antioxidant defense and supports osmotic adjustment

3. Balanced nutrient management (N, K, and Ca), combined with seed priming and microbial inoculation, and improves stress tolerance by promoting water uptake, photosynthesis, and ROS scavenging.

4. A mixed approach combining agronomic, biochemical, and microbiological strategies is essential to sustain B. napus productivity under drought stress.

Conclusion: B. napus is negatively impacted by drought stress in a number of ways, such as decreased germination, photosynthetic efficiency, restricted nutrient uptake, and disturbed cellular integrity. However, B. napus has built-in adaptive mechanisms such osmotic adjustment, antioxidant defense system activation, and hormone-mediated signaling pathways that let plants survive in water-limited environments and partially mitigate drought-induced damage. Key drought-responsive genes, transcription factors, and signaling pathways that control stress tolerance in B. napus have been uncovered by recent developments in molecular biology and genomics. These findings present novel prospects for enhancement of crops through genome editing technologies, transgenic approaches, and marker-assisted selection. At the same time enhanced fertilizer management, priming of seeds, and the exogenous use of osmolyte and plant growth regulators are examples of optimal agronomic approaches that provide useful methods to increase drought resilience. Future studies should concentrate on integrated strategies that integrate physiological, biochemical, and molecular insights to ensure sustainable cultivation of B. napus under rising climate variability. In the end, these tactics will improve our knowledge of drought tolerance mechanisms and make it easier to create cultivars that are resistant to climate change, which will increase the security of food and oil around the world.

For gene-edited crops to be accepted while maintaining adherence to biosafety regulations, socioeconomic and regulatory frameworks are equally crucial (Rozas et al., 2022; Vora et al., 2023). By reducing production uncertainty, risk mitigation strategies like crop insurance and drought early warning systems might motivate farmers to use stress-tolerant cultivars (van Ginkel and Biradar, 2021; Tang et al., 2024). Additionally, improved selection choices and more effective use of agricultural resources can be supported by artificial intelligence and machine learning-based predictions of drought-prone regions and trait performance (Oyarzabal et al., 2025).Institutional support through subsidies, public-private partnerships, and extension programs will encourage wider adoption of drought tolerant B. napus, aligning innovations and climate adaption objectives.

Acknowledgements: Authors are highly acknowledged to Maria Batool MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China for her linguistic check to improve the manuscript.

Author’s contributions: MWY, conceived, designed, and wrote the main draft. MWY, SZ, MA, KM, JSD, AG, and HY analyses, write, and revise the manuscript.

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