Silicon Nanoparticles and Methyl Jasmonate Enhance Productivity and Nutritional Quality of Vegetable Cluster Bean ( Cyamopsis tetragonoloba L.) Under Deficit Irrigation

ABSTRACT

Cluster bean ( Cyamopsis tetragonoloba L.) is usually grown for its high galactomannan content as an industrial crop. Young edible cluster bean pods are also eaten as a nutritious vegetable in many areas. There is little research on the effects of drought on pod yield or the nutritional content of edible cluster bean pods, even with the growing importance of producing vegetable cluster bean in dry and semiarid regions. In this study, the effect of silicon nanoparticles (Si NPs) and methyl jasmonate (MeJA) applied concurrently on the growth performance, pod productivity, and nutritional quality of vegetable cluster bean was evaluated at three irrigation rates. A three‐factor experiment was done in a completely randomized block design with three replications under field conditions, with three irrigation rates (100% field capacity, 50% field capacity, and 25% field capacity), three Si NP levels (0, 50, and 100 ppm), and three MeJA levels (0, 20, and 40 μmol L⁻¹). Drought stress (with irrigation at 25% FC) significantly reduced the growth of the plant, pod yield, crude protein, crude fat, fiber, dry weight, and mineral composition of the edible cluster bean pods. Pod weight reduction of approximately 50% occurred when they were irrigated at 25% FC, compared to pod yield from well‐watered plants. The addition of Si NPs and MeJA, when applied together, was able to reduce the adverse effects of low and moderate drought on pod yield and improve the productivity and nutritional quality of the edible cluster bean pods. The combined application of 100‐ppm Si‐NPs and 40‐μmol L⁻¹ MeJA was the most effective treatment for improving the productivity and nutritional quality of vegetable cluster bean under deficit irrigation. These findings suggest that this combination for cluster bean cultivation under moderate drought conditions after economic feasibility and field‐scale validation studies.

1. Introduction

Legumes provide the nutrient minerals, proteins, and vitamins for a bulky part of people, especially in developing countries (Sichkar 2025). Guar ( Cyamopsis tetragonoloba (L.) Taub.) is an annual grain legume crop that due to its strategic significance is recognized as one of the most sought‐after and promising crop plants in the world (Vishnyakova et al. 2023). Guar (also known as cluster beans) was cultivated in widespread regions, especially in arid and semiarid conditions of Africa, Middle East, West Asia, and the United States. Guar is characterized by a galactomannan compound that is extracted from the endosperm of the seed and is used specifically in the food and cosmetic industries (Chiofalo et al. 2018; Gautam et al. 2024; Gresta et al. 2018). Unripe fruits are also consumed as fresh vegetable, animal feed, and green fertilizer (Chiofalo et al. 2018; Singh and Bhagwati 2016). The guar green pods are sometimes sold as foodstuff especially in India and Pakistan and in some local markets of Atlanta and Georgia, USA (Morris and Wang 2017). Cluster beans have very high nutritional value and are rich in protein, fat, carbohydrates, vitamin A, vitamin C, calcium, and iron (Zanoni et al. 1980).

Previous studies confirmed that oxidative stress adversely affected growth, photosynthesis, and reproduction (Zulfiqar et al. 2024). Drought significantly weakens water and nutrient uptake and photosynthetic development, subsequently causing a cascade of physiological disturbances, ultimately reducing crop production (Gupta et al. 2022; Haghpanah et al. 2024). Drought significantly weakens the water and nutrient uptake and photosynthetic developments, subsequently causing a cascade of physiological disturbances, ultimately reducing crop production (El‐Saadony et al. 2024; Haghpanah et al. 2024; Keya et al. 2025; Khan et al. 2025). It also causes the creation of excessive reactive oxygen species, resulting in damage to vital molecules, i.e., nucleic acids, proteins, and lipids (Gupta et al. 2022; Khamis et al. 2025; Qiao et al. 2024). Likewise, drought lessens the cell osmotic stability in leaves through the accumulation of several compatible and noncompatible biological compounds (Haghpanah et al. 2024; Shaffique et al. 2024).

Phytohormones are vital regulators of plant growth and development, playing key roles in plant's life cycle, physiological processes, and response to various environmental stresses (EL Sabagh et al. 2022; Ma et al. 2024; Mahendhiran et al. 2024; Shafqat et al. 2024). Jasmonic acid (JA), a fatty acid–derived PGRs, stands out for their role in stress signaling and development (Ahmad et al. 2025; Ali and Baek 2020). JA stimulate flowering, fruit ripening, nutrient uptake, stomatal function, and stress responses by regulating gene expression and triggering protective mechanisms during environmental challenges (Ali and Baek 2020; El Nahhas et al. 2021). Also, JA improves antioxidant activity, increases levels of specific amino acids and sugars, and controls water loss by adjusting stomatal behavior (lateef et al. 2025; ShariffAl‐Sheikh et al. 2025). Furthermore, JA contributes in common signal transduction pathways of plants, including those of gene networks, regulatory proteins, enzymes, and protective compounds against abiotic stresses (Ali and Baek 2020). JA creates a complex regulatory network through interactions with plant hormones and transcription factors for specific gene expressions, which allows plants to adapt their metabolism and growth to challenging environmental conditions (Das et al. 2025; Gan et al. 2025; Thilakarathne et al. 2025).

Research has indicated that the use of silicon (Si) supplements can help with plant growth, increase the efficiency of photosynthesis, and support the plant's ability to deal with stressful situations. Si, when applied as a foliar spray or in nutrient solutions to crops grown hydroponically, has demonstrated an increase in photosystem efficiency and an increase in biomass produced by the crop plant (Shoukat et al. 2025). Si has lots of additional benefits, such as promoting root development, the amount of chlorophyll the plant can produce, how efficient a plant is at using water, and how efficient a plant is at producing antioxidant responses, which are all benefits of Si in the cultivation of a plant under drought conditions. Different types and forms of Si, including silicic acid, SiO₂, and Si nanoparticles (NPs), vary in their effectiveness in increasing plant resistance to stress, with the NP forms typically demonstrating the best results due to their larger surface area and ability to penetrate cells (Ashfaq et al. 2022).

Nanotechnology has allowed researchers to extend their developments into the area of agriculture and potentially aid in producing agricultural products under stress conditions (Singh et al. 2023; Singh et al. 2024; Singh et al. 2025). Under stressed conditions, nanonutrients can improve phytobiochemical processes, water‐use efficiency, nutrient uptake, and efficiency, resulting in improved photosynthesis and plant structure (Demeke et al. 2025; Pereira et al. 2024; Zargar et al. 2019). Si NPs are considered to be a compatible and nontoxic form of Si, making them a potentially effective method to increase the tolerance of plants to the toxic effects of stress during the growing process (Nedjimi 2025). Recently, advances in nanotechnology have provided new opportunities for improving crop tolerance to abiotic stresses. Silicon nanoparticles (Si‐NPs), owing to their high surface area and enhanced reactivity, have shown considerable potential to improve water relations, nutrient uptake, photosynthetic performance, and stress tolerance under drought conditions (Nedjimi 2025).

This research hypothesized that the application of both Si‐NPs and MeJA as a combined treatment would mitigate the negative effects of drought exposure on both plant growth and pod yield (PY) while also improving nutritional and quality traits associated with immature pods from vegetable cluster bean when grown under deficit‐irrigated conditions. Based on our literature survey, previous studies on guar ( C. tetragonoloba L.) have primarily focused on its industrial value as a legume crop cultivated for mature seeds, which are processed for guar gum production and widely used in the food, pharmaceutical, cosmetic, textile, paper, and oil industries. In contrast, information regarding vegetable cluster bean cultivated for consumption of immature edible pods remains extremely limited. Furthermore, no previous study has comprehensively evaluated the combined application of Si‐NPs and methyl jasmonate (MeJA) to improve the productivity and nutritional quality of immature edible pods under deficit irrigation. Therefore, this study addresses an important research gap by focusing on vegetable cluster bean as a fresh food crop rather than an industrial seed crop. Thus, the goal of the present study was to investigate the efficacy of Si‐NPs and MeJA on enhancing growth performance, pod production, mineral content, and nutritional value of vegetable cluster bean produced under varying irrigation levels.

2. Materials and Methods

2.1. Field Site Description, Plant Materials, and Research Design

This experiment was carried out in the research field of the Medicinal and Industrial Research Centre, Ardakan University, Iran, in 2024. The precipitation and temperature values during the experiment period are presented in Figure 1. A factorial experiment was carried out with a randomized complete block design (RCBD) and three replications. Seeds of cluster bean VG‐1142 were supplied from the Medicinal and Industrial Research Centre, Ardakan University, Iran. Each experimental plot was 2 × 3 m, with a spacing of 25 cm in rows and 40 cm apart per replication. Three irrigation regimes (100% FC [control], 50% FC, and 25% FC) were applied during growing seasons, and foliar spraying of Si‐NPs was applied at 0, 50, and 100 ppm, and methyl JA at 0, 20, and 40 μmol L⁻¹.

FIGURE 1.

The precipitation and temperature values during experiment period.

The experiment consisted of 27 treatment combinations (3 irrigation levels × 3 Si‐NP levels × 3 MeJA levels) arranged in a RCBD with three replicates, resulting in a total of 81 experimental units. All figures present the mean values of the three replicates for each treatment combination (n = 3).

Foliar sprays were applied four times: The first application at the early vegetative stage (20 days after sowing), then repeated each 15 days until onset of podding. Applications were made in the late afternoon at a rate of approximately 300 L ha⁻1 per application, equivalent to approximately 4 mL per plant, using a handheld sprayer calibrated for uniform leaf coverage (Rahimi‐Moghaddam et al. 2026). The silicon dioxide (SiO₂) NPs used in this study were purchased from NANOSHEL (Stock No. NS6130‐03–341). According to the manufacturer's specifications, the NPs had a purity of 99.9% and an average particle size (APS) of 15–20 nm. The chemical formula of the NPs was SiO₂, with a molecular weight of 60.08 g/mol. They were supplied as a white powder with a density of 2.4 g/cm³. The melting and boiling points were reported as 1610°C and 2230°C, respectively.

Water stress was applied during the experiment (2 months) using three gradient levels. Soil moisture content in each plot was measured daily by means of a time‐domain reflectometry sensor from a 20‐cm soil layer. The depth of water (d_iw) required to bring moisture content of soil back to the FC was assessed according to Equation (1) (Cuenca 1989).

$$d\mathit{iw}=\left(\mathit{PFC}-\mathit{Pi}\right).D.\mathit{Bd}$$ (1)

PFC and Pi are water content at FC and at the time before irrigation (in terms of weight percentage), respectively; Bd is bulk‐specific gravity in g cm⁻³, and D is effective root depth in cm. The total volume of irrigation water in the scale of plot area was determined after calculation of diw. Irrigation at each stage was performed when the soil's moisture content was not more than FC. The amount of irrigation water applied at each irrigation event was not fixed throughout the growing season. Instead, irrigation volume was calculated separately for each treatment according to the measured soil moisture content using Equation (1), with the objective of restoring soil moisture to the target field capacity (FC) assigned to each irrigation treatment (100%, 50%, or 25% FC). Consequently, the volume of water applied varied among irrigation events depending on soil moisture depletion and prevailing environmental conditions.

The experiment was conducted on sandy loam‐textured soil, and the main physicochemical characteristics of the soil are summarized in Table 1. Irrigation was performed immediately after planting, followed by subsequent irrigations every 10 days depending on evapotranspiration demands (Munir et al. 2025). Irrigation was supplied using a drip (trickle) irrigation system to ensure precise water application. Weed management was carried out manually throughout the growing season using hand hoeing.

TABLE 1.

The soil physical and chemical characteristics of the experimental field before planting.

Texture	Clay (%)	Silt (%)	Sand (%)	K (mg/kg)	P (mg/kg)	N (%)	O.C (%)	pH	EC (dS/m)
Sandy loam	38	32	30	287	7.8	0.19	0.98	7.2	1.85

The experiment was conducted during a single growing season (2024). Each treatment was replicated three times. Although the study was performed for one season, the experimental design and replication allowed reliable statistical evaluation of treatment effects.

2.2. Measurement of Morphological, Yield, and Yield Components Parameters

Morphological characteristics (plant height [PLH], stem diameter [SD], branch number [BN], pod length [PL], and leaf area [LA]) and yield‐related characteristics (pods per plant and PY per plant) were measured from five randomly selected plants of each plot during podding.

2.3. The Digestibility of Dry Matter (DDM)

The digestibility of dry matter was evaluated using a two‐step in vitro procedure (Tilley and Terry 1963). Initially, the samples were oven‐dried at 105°C until a constant weight was achieved, then ground, and sieved through a 1‐mm mesh. A 0.5‐g aliquot of the prepared sample was incubated anaerobically with a buffer solution and fresh rumen fluid at 39°C for 48 h to simulate microbial fermentation in the rumen. Following this, the gastric digestion phase was conducted by adding a pepsin‐containing hydrochloric acid solution and incubating the mixture for an additional 48 h under the same temperature conditions. After the completion of both incubation stages, the remaining residues were dried and weighed. The DMD was then calculated according to the standard formula (Equation 2).

$$\mathit{DMD}\left(\%\right)=\frac{\left(\mathit{\text{initial}}\mathit{dry}\mathit{\text{weight}}-\mathit{\text{residual}}\mathit{dry}\mathit{\text{weight}}\right)}{\left(\mathit{\text{initial}}\mathit{dry}\mathit{\text{weight}}\right)}\times 100$$ (2)

2.4. Crude Protein

The samples' crude protein content was evaluated through the micro Kjeldhal method (Stuart 1936). In this method, the crude protein content can be calculated by multiplying the nitrogen content by a factor of 6.25 (Dubetz and Welis 1968).

2.5. Crude Fat

The Soxhlet system was used to calculate the crude fat content of dried samples (AOAC 1970). The dried sample powder (3000 mg) was extracted in three Soxhlet extractors using continuous petroleum ether at a flow rate of 2–3 drops per second, followed by sample drying at 95°C ± 4°C. The percentage of crude fat was calculated using Equation (3).

$$\mathit{\text{Crude}}\mathit{fat}\left(\%\right)=\frac{\left[\mathit{\text{Flask weight}}\mathit{wit}\mathit{fat}-\mathit{\text{Flask weight without}}\mathit{fat}\right]}{\mathit{\text{sample weight}}}\times 100$$ (3)

2.6. Crude Ash Content (CAC, %)

CAC of samples was determined by ashing the samples at 550°C for 8 h in an ash oven (AOAC 1990), and the values were expressed in percentage (AOAC No: 923.03).

2.7. Crude Fiber Determination

Crude fiber content of cluster bean pod samples was determined according to the standard method of AOAC International (AOAC Method 962.09). Dried samples were ground and passed through a 1‐mm sieve. Approximately 2 g of each sample was sequentially digested with 1.25% sulfuric acid and 1.25% sodium hydroxide for 30 min under boiling conditions. The residues were filtered, thoroughly washed with distilled water, ethanol, and acetone, and dried at 105°C to constant weight. The dried residues were then ashed at 550°C for 4 h. Crude fiber percentage was calculated from the weight loss after ashing relative to the initial sample weight (Equation 4).

$$\mathit{\text{Crude Fiber}}\left(\%\right)=\frac{W1-W2}{W\mathit{\text{sample}}}\times 100$$ (4)

2.8. Mineral Content

All immature pods were digested using the dry‐ash method in a muffle furnace at 500°C for 6 h (Miller 1988). Then, phosphorus (P), potassium (K), and calcium content (Ca) of pod tissues were measured, respectively, at wavelengths 470, 766.5, and 422.7 nm, using inductively coupled plasma optical emission spectrometry (ICP‐OES, Perkin Elmer Optima 2100 DV, Waltham, MA).

2.9. Data Analysis

Data were processed with IBM SPSS Software Ver.27 and Minitab software Ver. 20. The full factorial ANOVA was used to evaluate the effects of irrigation, Si NPs, and MeJA levels. Tukey's HSD test (α = 0.05) was employed for mean differentiation when ANOVA findings were significant, and principal component analysis (PCA), Pearson's correlation estimation, and regression analysis were done.

3. Results

A factorial ANOVA (Table 2) indicated there was a significant effect of irrigation regime (p ≤ 0.01) on all traits measured in this study (morphophysiological biochemistry, yield, and nutrient‐related traits). An irrigation regime was the primary factor that affected plant performance. Irrigation also significantly affected the following traits measured: height, number of branches, diameter of stems, area of leaves, number of pods per plant, length of pods, PY per plant (kg), crude protein, fat, fiber, ash, DM, and mineral content (P, K, and Ca). The application of Si NPs had a very significant effect on most of the traits measured, including vegetative growth, PY, crude protein, fiber, ash, DM, and phosphorus content, and therefore showed strong evidence that Si NPs can enhance the growth and productivity of cluster bean under varying irrigation regimes. MeJA, however, had relatively few main effects. MeJA significantly affected PLH, number of branches, pods per plant, PY per plant (kg), crude protein, and K and Ca content (p ≤ 0.05–0.01). Measurements of SD, however, number of leaves, % fat, fiber, property %, % ash, and % phosphorus were not significantly affected when treated with only MeJA.

TABLE 2.

The results of factorial ANOVA for morphophysiological, physio‐biochemical, yield, and nutrient contents of edible cluster bean plants under different irrigation, Si NPs, and MeJA levels.

Source	df	Plant height	Branch numbers	Stem diameter	Leaf area	Pod/plant
Irrigation (I)	2	5766.4**	1276.8**	35.93**	2955.4**	4809.0**
Si Np	2	2046.6**	271.4**	6.44**	939.9**	949.9**
MeJA	2	520.2**	20.3*	0.33 ns	46.99 ns	83.6**
I × Si Np	4	35.0 ns	40.11**	2.41**	100.80**	134.4**
I × MeJA	4	31.6 ns	3.11 ns	0.17 ns	74.36**	20.3 ns
Si Np × MeJA	4	45.5 ns	11.6*	0.27 ns	29.76 ns	30.9*
I × Si Np × MeJA	8	114.3**	9.6*	0.40 ns	55.68**	34.4**
Error	54	20.72	4.41	0.23	17.87	9.04
CV	—	5.14	9.12	6.44	3.77	3.91
Source	df	Pod length	Pod yield/plant	Pod crude protein	Fat	Fiber
Irrigation (I)	2	78.75**	17913.0**	68.92**	8.01**	41.96**
Si Np	2	17.21**	3538.4**	14.45**	0.46**	6.63**
MeJA	2	0.47 ns	311.4**	2.16**	0.12 ns	0.26 ns
I × Si Np	4	4.81**	500.5**	0.49*	0.07 ns	2.66**
I × MeJA	4	0.23 ns	75.5 ns	0.20 ns	0.18*	0.18 ns
Si Np × MeJA	4	0.43 ns	115.1*	0.23 ns	0.28**	0.02 ns
I × Si Np × MeJA	8	0.67*	128.1**	0.27 ns	0.27**	1.43**
Error	54	0.31	33.7	0.18	0.06	0.21
CV	—	7.49	3.91	3.63	12.36	6.29
Source	df	Ash	Dry matter	P content	K content	Ca content
Irrigation (I)	2	2.78**	205.57**	1404.93**	22741.8**	7787.42**
Si Np	2	0.76**	65.56**	226.39**	538.93 ns	3871.75**
MeJA	2	0.16 ns	1.67 ns	3.26 ns	2417.33**	284.79**
I × Si Np	4	0.23*	33.33**	79.91**	870.11**	549.29**
I × MeJA	4	0.23*	3.81 ns	6.48 ns	676.31*	107.55*
Si Np × MeJA	4	0.04 ns	3.32 ns	3.54 ns	1295.33**	224.16**
I × Si Np × MeJA	8	0.40**	12.53**	4.58 ns	417.01 ns	135.59**
Error	54	0.07	3.19	2.72	231.28	33.28
CV	—	7.46	4.91	4.95	4.28	21.11

Abbreviation: ns, nonsignificant.

^**Significant at the 0.05 level.

^*Significant at the 0.01 level.

Results from the interaction analyses showed that the response of edible cluster beans to the treatments used was dependent on the three‐way interaction of irrigation, Si NPs, and MeJA. The effects of the irrigation by Si NPs interaction (I × Si NPs) were significant (p ≤ 0.01) for most of the growth and productivity traits measured, including BN, SD, LA, number of pods per plant, length of pods, PY per plant, dry matter (DM), and nutrient content (i.e., fat, ash, K, and Ca). This indicates that Si NPs impacted how the plants responded to water availability via the irrigation treatment. The interaction between irrigation and MeJA demonstrated fewer significant effects; however, LA, fat, ash, and K and Ca were still significantly affected by this treatment combination. Similarly, there were significant effects of the Si NPs by MeJA interaction on BN, number of pods per plant, PY, fat, and K and Ca content. The three‐way interaction (I × Si NPs × MeJA) was shown to have significant effects on PLH, BN, LA, number of pods per plant, length of pods, PY per plant, fat, fiber, ash, DM, and Ca content (as shown in Table 2), indicating that the combined treatments altered the growth, yield, and quality of vegetable cluster beans.

3.1. Growth Parameters

In general, the decrease in soil moisture loss due to drought conditions (from 100% of normal FC down to as low as 25% of FC) greatly reduced the overall growth parameters. This is indicative of the impact of drought‐related soil moisture stress on the growth of the vegetable cluster bean. Vegetable cluster bean grown under normal moisture conditions (100% of FC) reached their maximum growth parameters (i.e., PLH, number of branches, and diameters of stem), whereas at the same time, the vegetable cluster bean grown under severe drought stress (25% of FC) showed maximum suppression of growth parameters. In addition, the use of Si NPs and MeJA reduced the undesirable effects of drought stress on growth parameters in vegetable cluster bean regardless of the irrigation rate (i.e., irrigation rate ≤ 100% FC) of the plants.

Under each irrigation treatment, there was a positive effect on PLH (Figure 2a), regardless of the irrigation regime, with increasing concentrations of Si NPs. At 100% FC, the tallest plant (114 cm) was a guaranteed growth enhancer produced by treatment with a mix of 20 μmol L⁻¹ of the MeJA and 100 ppm of Si NPs, and the shortest plant was 90 cm tall (untreated). At 50% of FC with no nutrition or treatment, the untreated plant measured 75 cm. When treated with a combination of 40 μmol L⁻¹ of MeJA and 100 ppm of Si NPs, the plant measured 104 cm. At 25% of FC due to drought stress, the combination of 100 ppm of Si NPs and 40 μmol L⁻¹ of MeJA resulted in a height increase of 93 cm, and all the untreated controls resulted 62 cm or less, indicating that Si NPs and MeJA significantly reduced the drought‐induced reduction in growth. A similar trend was observed for BN per plant (Figure 2b). At 100% FC, BN increased from 23–28 branches plant⁻¹ in untreated or low‐input treatments to 36 branches plant⁻¹ under 100‐ppm Si NPs combined with 40‐μmol L⁻¹ MeJA. Under 50% FC, the maximum BN (25 branches plant⁻¹) was also observed at the highest combined treatment level. Severe drought stress reduced branching considerably; however, the application of Si NPs and MeJA partially restored branch formation, with the highest value (22 branches plant⁻¹) recorded under 100‐ppm Si NPs combined with either 20‐ or 40‐μmol L⁻¹ MeJA.

FIGURE 2.

The interaction effect of irrigation × Si NPs × MeJA levels for plant height (a), branch number (b), and stem diameter (c) in cluster bean (Tukey's HSD test, α = 0.05). Each treatment combination consisted of three biological replicates.

SD followed the same general pattern, decreasing under water‐deficit conditions and improving with Si NP and MeJA applications (Figure 2c). Under 100% FC, SD increased from 7.3 cm in untreated plants to 9.6 cm with 100‐ppm Si NPs combined with either 0‐ or 20‐μmol L⁻¹ MeJA. Under 50% FC, the maximum SD (7.5 cm) was achieved at 100‐ppm Si NPs regardless of MeJA level. Under severe drought stress, the highest SD (7.2 cm) was observed in plants treated with 0‐ppm Si NPs plus 40‐μmol L⁻¹ MeJA, whereas some reductions were noted at higher MeJA concentrations combined with Si NPs, suggesting that SD was less responsive to the combined treatments under severe stress conditions. Collectively, the results demonstrate that the combined application of Si NPs and MeJA effectively enhanced cluster bean growth and alleviated the negative impacts of drought stress, particularly at higher Si NP concentrations.

In general, decreasing soil moisture from 100% to 25% FC substantially reduced all measured yield‐related traits (LA, pod plant⁻¹, and PL), indicating the negative impact of drought stress on cluster bean development. However, the application of Si NPs and MeJA alleviated these adverse effects and improved plant performance under both normal and water‐deficit conditions.

Combined treatments had a significant effect on LA (Figure 3a). The LA for untreated plants increased from approximately 112 cm² plant⁻¹ under well‐irrigated (100% FC) conditions to a maximum of 136 cm² plant⁻¹ when 100‐ppm Si NPs were applied with 40‐μmol L⁻¹ MeJA. LA for plants under moderate drought stress (50% FC) was between 103 and 116 cm² plant⁻¹; the highest LA was typically achieved at the higher Si NP concentrations. There was a significant reduction in LA under severe drought stress (25% FC); however, leaf growth improved as a result of the application of Si NPs and MeJA, with the highest value (109 cm² plant⁻¹) being produced at 100‐ppm Si NPs in the absence of MeJA application. The results indicate that Si NPs were key in supporting leaf growth when exposed to drought stress.

FIGURE 3.

The interaction effect of irrigation × Si NPs × MeJA levels for leaf area (a), pod number per plant (b), and pod length (c) in edible cluster bean (Tukey's HSD test, α = 0.05). Each treatment combination consisted of three biological replicates.

Pod number per plant (PN) (Figure 3b) showed a similar trend as LA. At 100% FC, PN increased with increasing Si NP concentration and MeJA application, to a maximum of 107 pods plant⁻¹ when treating with 100‐ppm Si NPs and 40‐μmol L⁻¹ MeJA, as compared to 80 pods plant⁻¹ in untreated plants. PN was significantly diminished under moderate drought stress (50% FC), with a range of 64–75 pods plant⁻¹; however, higher concentrations of Si NPs helped to partially compensate for the drought‐induced reductions.

PL (Figure 3c) had significant impacts from different levels of irrigation and treatment combinations. The mean PL for treated plants at 100% FC increased from 7–8 to 11 cm for those treated with 100‐ppm Si NPs and either MeJA (0 or 40 μmol L⁻¹). With moderate drought stress, PLs were 6–8 cm, and the greatest lengths were typically found with the higher Si NP treatments. PLs were greatly decreased with severe drought stress, with values decreasing to approximately 5.4–7.4 cm. The highest mean PL (7.4 cm) resulted from the treatment of 100‐ppm Si NPs in conjunction with 40‐μmol L⁻¹ MeJA during the period of severe drought stress. Overall, the results suggest that Si NPs combined with MeJA, particularly when both were applied at higher dosages, are effective in reducing the negative impacts of drought stress on the growth and yield of edible cluster bean.

3.2. PY and Physio‐Biochemical Attributes

Combinatory applications of MeJA, Si NPs, and irrigation level greatly impacted harvest parameters of edible cluster bean. Irrigation regimes were positively correlated with both the yield and quality of yield attributes of vegetable cluster bean. Reduction from 100% FC to 25% FC produced significant reductions in both yield and quality parameters, thereby confirming the detrimental impact of drought on yields of edible cluster bean. Application of Si NPs and MeJA reduced damage caused by drought and improved both yield and biochemical composition of vegetable cluster bean grown under limited water availability.

PY per plant (Figure 4a) was influenced by both irrigation levels and treatment interactions. PY was increased with higher concentration of Si NP and application rate of MeJA under adequate irrigated growing conditions (100% FC) to a maximum of 207 g plant⁻¹ with the combination of 100‐ppm Si NP + 40‐μmol L⁻¹ MeJA and minimum harvest of 154 g plant⁻¹, where no treatments were applied. Under moderate drought stress (50% FC), growth of plants declined significantly by 124–145 g plant⁻¹ (drought); however, the application of both Si NPs and MeJA partially offset yield reductions due to drought. Under severe drought stress (25% FC), the lowest PY (116 g plant⁻¹) was recorded in plants receiving 0‐ppm Si‐NPs combined with 20‐μmol L⁻¹ MeJA. In contrast, the highest PY (142 g plant⁻¹) was achieved in two treatment combinations: 50‐ppm Si‐NPs + 40‐μmol L⁻¹ MeJA and 100‐ppm Si‐NPs + 40‐μmol L⁻¹ MeJA (Figure 4a). The interaction between irrigation, Si NP, and MeJA was not significant for crude protein content (Figure 4b). Under 100% FC, crude protein increased from approximately 12.1%–12.8% in untreated plants to a maximum of 14.5% with 100‐ppm Si NPs combined with 40‐μmol L⁻¹ MeJA. Moderate drought stress reduced crude protein content to 10.4%–13.1%, whereas severe stress further reduced values to 9.4%–10.9%. Despite these reductions, the application of Si NPs and MeJA improved protein accumulation under stress conditions, with the highest protein contents generally observed at 100‐ppm Si NPs combined with 40‐μmol L⁻¹ MeJA. These findings suggest that Si NPs and MeJA enhanced nitrogen metabolism and maintained seed quality under drought stress.

FIGURE 4.

The interaction effect of irrigation × Si NPs × MeJA levels for pod yield (a), pod crude protein number (b), and fat content (c) in edible cluster bean (Tukey's HSD test, α = 0.05). Each treatment combination consisted of three biological replicates.

Fat content was also significantly affected by irrigation and treatment interactions (Figure 4c). Under well‐watered conditions, fat content ranged from 2.2% to 2.9%, with the highest value recorded at 100‐ppm Si NPs combined with 40‐μmol L⁻¹ MeJA. Moderate drought stress reduced fat accumulation in response to several treatments, although the application of 100‐ppm Si NPs together with 40‐μmol L⁻¹ MeJA increased fat content to 2.6%, compared with only 1.5%–1.7% in some untreated or low‐input treatments. Severe drought stress markedly decreased fat content, with values ranging from 1.3% to 1.7%. Nevertheless, plants treated with higher Si NP concentrations maintained relatively greater fat content than untreated plants.

Overall, the results indicate that the combined application of Si NPs and MeJA effectively mitigated drought‐induced reductions in edible cluster bean yield and quality attributes, particularly when higher Si NP concentrations (100 ppm) were used.

The mean comparison analysis demonstrated that irrigation level, Si NPs, and MeJA significantly influenced the physio‐biochemical traits and nutrient composition of vegetable cluster bean (Figure 5). In general, severe drought stress (25% FC) markedly reduced fiber content, DM accumulation, and mineral concentrations compared with well‐watered plants (100% FC), whereas ash content tended to increase under water‐deficit conditions. The highest fiber content values were mainly recorded under well‐watered conditions combined with Si NP application. Specifically, plants treated with 100‐ppm Si NPs and 20‐μmol L⁻¹ MeJA at 100% FC produced the highest fiber content (9.60%), followed closely by treatments receiving 100‐ppm Si NPs with either 0‐ or 40‐μmol L⁻¹ MeJA. In contrast, the lowest fiber content (5.30%) was observed under severe drought stress (25% FC) with 50‐ppm Si NPs and 20‐μmol L⁻¹ MeJA, indicating that drought substantially reduced fiber accumulation (Figure 5a). Ash content exhibited a different trend, increasing under severe water‐deficit conditions (Figure 5b). The maximum ash content (4.57%) was recorded at 25% FC with 50‐ppm Si NPs and no MeJA application, whereas the minimum value (2.80%) occurred under 100% FC with 100‐ppm Si NPs combined with 40‐μmol L⁻¹ MeJA. DM accumulation (Figure 5c) was greatest under favorable irrigation conditions and higher Si NP concentrations. The highest DM percentage (44.63%) was achieved under 100% FC with 100‐ppm Si NPs plus 20‐μmol L⁻¹ MeJA, followed by 43.67% under the same Si NP concentration with 40‐μmol L⁻¹ MeJA. Conversely, the lowest DM content (32.13%) was recorded under severe drought stress at 25% FC without Si NP application but with 20‐μmol L⁻¹ MeJA (Figure 5c).

FIGURE 5.

The interaction effect of irrigation × Si NPs × MeJA levels for fiber content (a), ash content (b), and dry matter of edible cluster bean pods (c) (Tukey's HSD test, α = 0.05). Each treatment combination consisted of three biological replicates.

3.3. Nutrients Content

Under well‐watered conditions (Table 3), Si NP application majorly improved the phosphorus accumulation rate. The maximum phosphorus level (45.47%) occurred at 100% FC, when 100‐ppm Si NPs and 40‐μmol L MeJA were used. The minimum phosphorus level (24.03%) occurred at 50% FC, when 50‐ppm Si NPs and 40‐μmol L MeJA were combined. The concentration of potassium also differed significantly in response to different treatments. The maximal potassium concentration (425‐mg potassium/100‐g dry wt) occurred at 100% FC, when 100‐ppm Si NPs and 40 μmol L were used. The minimal level of potassium (304‐mg potassium/100‐g dry wt) was displayed during times of severe drought stress, when 100‐ppm Si NP was used alone and no MeJA was used. Similar to phosphorus and potassium, calcium concentration followed the same trend; maximum calcium concentration (115.33‐mg Ca/100‐g dry wt) occurred at 100% FC when combined with 100‐ppm Si NP and 20‐μmol/L MeJA. Minimum calcium levels (52.33‐mg Ca/100‐g dry wt) were similarly observed under conditions of severe drought stress and low levels of Si NP. The data confirmed that drought stress negatively impacted biochemical composition and minerals nutrition of edible cluster bean; however, the application of Si NP and MeJA, especially at high concentrations of Si NP, alleviated the negative effects of drought stress and improved quality traits of the vegetable cluster bean under both optimal and stress conditions.

TABLE 3.

The mean comparison of physio‐biochemical variables and nutrient content of vegetable cluster bean under different irrigation, Si NPs, and MeJA levels.

Drought (% FC)	Si NP (ppm)	MeJA (μmol L−1)	P (% DW)	K (mg/100 g DW)	Ca (mg/100 g DW)
100	0	0	38.50 ± 1.00 bcd	371.67 ± 27.54 ab	70.00 ± 13.23 e‐i
100	0	20	37.10 ± 1.13 c‐f	386.67 ± 22.55 b‐i	66.67 ± 7.64 f‐i
100	0	40	37.50 ± 1.00 cde	360.00 ± 18.03 e‐j	78.33 ± 2.89 d‐h
100	50	0	39.17 ± 2.08 bc	330.33 ± 31.63 ab	72.33 ± 11.02 d‐h
100	50	20	42.83 ± 2.52 ab	391.67 ± 16.07 abc	90.67 ± 5.13 bcd
100	50	40	42.87 ± 0.55 ab	383.33 ± 12.58 b‐g	110.00 ± 5.00 a
100	100	0	45.27 ± 0.67 a	365.33 ± 12.86 abc	106.67 ± 10.41ab
100	100	20	45.33 ± 0.72 a	383.33 ± 25.17 b‐g	115.33 ± 4.16 a
100	100	40	45.47 ± 1.17 a	425.00 ± 5.00 a	103.33 ± 7.64 abc
50	0	0	33.50 ± 1.00 def	356.67 ± 6.11 b‐i	52.33 ± 2.52 i
50	0	20	34.17 ± 3.21 c‐g	360.33 ± 5.51 b‐h	53.00 ± 3.61 i
50	0	40	31.13 ± 1.48 ghi	358.33 ± 7.64 b‐i	62.33 ± 2.52 ghi
50	50	0	27.20 ± 1.04 h‐k	357.33 ± 2.52 b‐i	66.00 ± 1.73 f‐i
50	50	20	24.77 ± 1.52 jk	358.67 ± 10.20 b‐i	68.33 ± 7.64 e‐i
50	50	40	24.03 ± 0.50 k	380.00 ± 5.00 a‐d	68.33 ± 10.41 e‐i
50	100	0	32.80 ± 0.61 efg	371.67 ± 18.93 b‐f	86.67 ± 2.89 cde
50	100	20	31.83 ± 1.24 gh	370.00 ± 17.32 b‐f	82.00 ± 3.46 def
50	100	40	32.47 ± 0.95 efg	378.33 ± 11.55 a‐e	80.67 ± 5.13 d‐g
25	0	0	27.07 ± 1.63 h‐k	325.00 ± 5.00 f‐j	52.67 ± 2.52 i
25	0	20	29.33 ± 3.61 g‐j	324.67 ± 5.03 f‐j	52.33 ± 2.52 i
25	0	40	26.20 ± 0.62 ijk	316.67 ± 7.64 hij	61.00 ± 3.61 hi
25	50	0	24.57 ± 1.10 jk	320.33 ± 4.51 g‐j	52.33 ± 2.52 i
25	50	20	25.60 ± 1.01 jk	331.67 ± 15.28 d‐j	52.33 ± 2.08 i
25	50	40	25.80 ± 1.00 jk	337.00 ± 20.79 c‐j	53.00 ± 2.65 i
25	100	0	31.27 ± 4.00 ghi	304.33 ± 13.43 j	62.33 ± 2.52 ghi
25	100	20	32.20 ± 0.61 fgh	311.67 ± 18.93 ij	63.33 ± 1.53 ghi
25	100	40	31.5 ± 015 gh	330.00 ± 5.00 e‐j	62.33 ± 2.52 ghi

Note: Common letters indicate no significant difference. Mean ± SD, HSD Tukey's test, α = 0.05. Each treatment combination consisted of three biological replicates.

3.4. Correlation Estimation

The Pearson's correlation analysis (Figure 6) revealed predominantly strong positive associations among the evaluated morphological, nutritional, and mineral parameters, indicating a high degree of interdependence among the studied traits. PLH exhibited very strong positive correlations with PN and PY (r = 0.923 each), pod crude protein (PCP) (r = 0.921), PL (r = 0.902), BN (r = 0.896), and Ca content (r = 0.895), suggesting that increases in PLH were closely associated with improvements in PN, PY, pod cluster per plant, PL, BN, and calcium accumulation. Similarly, BN was strongly correlated with PL (r = 0.919), crude protein (r = 0.915), PN and PY (r = 0.906 each), indicating that plants with greater branching capacity tended to produce higher pod development and yield attributes. SD and LA also showed strong positive relationships with most agronomic traits, particularly between SD and LA (r = 0.884), and with Ca (r = 0.885 and 0.878, respectively), demonstrating that SD and LA contributed substantially to overall plant vigor and mineral accumulation.

FIGURE 6.

The person's correlation matrix for yield‐related traits, morphophysiological, physio‐biochemical, and mineral parameters of vegetable cluster bean cultivated under different irrigation, Si NPs, and MeJA levels. Dry matter (DM), plant height (PLH), pod number plant⁻¹ (PN), pod yield (PY), pod crude protein (PCP), pod length (PL), branch number (BN), stem diameter (SD), and leaf area (LA).

Among yield‐related parameters, PN and PY were perfectly correlated (r = 1.000), confirming that PN directly determined PY in the studied material. PCP displayed exceptionally high positive correlations with Ca (r = 0.937), PL (r = 0.926), PLH (r = 0.921), and BN (r = 0.915), indicating that pod cluster formation was a central trait linked to both vegetative growth and nutrient status. Fat and fiber contents also showed significant positive associations with most morphological and yield traits, particularly between fiber and PY (r = 0.894), crude protein (r = 0.885), and PLH (r = 0.862), suggesting that improved plant growth and pod development were accompanied by enhanced nutritional quality. Likewise, fat content correlated strongly with crude protein content (r = 0.868) and PL (r = 0.861), indicating coordinated enhancement of biochemical composition and productivity.

In contrast, ash content demonstrated consistent negative correlations with nearly all studied traits, including crude protein (r = −0.711), PLH (r = −0.706), PN and PY (r = −0.689 each), and Ca content of pod (r = −0.665), implying that increased ash accumulation may be associated with reduced growth performance and yield potential. Dry matter (DM) showed moderate to strong positive correlations with LA (r = 0.783), protein content of pod (r = 0.793), Ca (r = 0.795), and K content (r = 0.721), reflecting the importance of biomass accumulation in nutrient uptake and growth performance. Phosphorus (P) was positively associated with PL (r = 0.868), BN (r = 0.831), and fiber (r = 0.807), whereas potassium (K) exhibited substantial correlations with protein content (r = 0.789), LA (r = 0.767), and Ca content (r = 0.738). Calcium emerged as one of the most integrative mineral parameters, maintaining strong positive relationships with almost all morphological and yield variables, especially crude protein (r = 0.937), PLH (r = 0.895), SD (r = 0.885), and PL (r = 0.873). Overall, the correlation matrix indicates that vegetative growth traits, yield components, and nutritional quality parameters were highly synchronized, whereas ash content showed an antagonistic relationship with most productive traits.

3.5. PCA

PCA revealed substantial associations among the studied morphophysiological, yield, biochemical, and nutrient traits of vegetable cluster bean under different irrigation, Si NP, and MeJA treatments (Table 4). The first principal component (PC1) showed positive loadings for almost all measured variables, indicating that this axis primarily represented overall plant performance and productivity. The positive contributions to PC1 were observed for BN (0.276), PCP (0.276), PL (0.274), PN (0.271), PY (0.271), SD (0.269), fiber content (0.268), calcium content (0.266), PLH (0.265), and LA (0.265). These positive loadings suggest that improved vegetative growth was closely associated with enhanced yield, quality traits, and nutrient accumulation. In contrast, ash content exhibited a negative loading on PC1 (−0.197), indicating an inverse relationship with the majority of growth and productivity traits.

TABLE 4.

The values of eigenvalue, variance proportion, cumulative, and the share of variable for PC1 and PC2.

Variables	PC1	PC2	Variable	PC1	PC2
PLH	0.265	0.036	Fat	0.248	0.209
BN	0.276	−0.172	Fiber	0.268	−0.122
SD	0.269	−0.211	Ash	−0.197	−0.607
LA	0.265	−0.003	DM	0.237	0.291
PN	0.271	−0.165	P	0.255	−0.303
PL	0.274	−0.216	K	0.221	0.439
PY	0.271	−0.165	Ca	0.266	−0.085
PCP	0.276	0.143
Eigenvalue	12.237	0.760	Eigenvalue	12.237	0.760
Proportion of V (%)	0.816	0.051	Proportion of V (%)	0.816	0.051
Cumulative V (%)	0.816	0.866	Cumulative V (%)	0.816	0.866

Abbreviations: BN, branch number; DM, dry matter; LA, leaf area; PCP, pod crude protein; PL, pod length; PLH, plant height; PN, pod number plant⁻¹; PY, pod yield; SD, stem diameter.

The biplot of PCA (Figure 7) demonstrated substantial variation among the studied treatments (T1–T27) and clearly illustrated the relationships between morphological, yield, nutritional, and mineral traits. The first two principal components explained a major proportion of the total variability, with PC1 accounting for 82% of the variance (eigenvalue = 12.3) and PC2 contributing an additional 5% (eigenvalue = 0.76), together explaining 87% of the cumulative variation. This high cumulative variance indicates that the first two components adequately summarized the multidimensional dataset and effectively discriminated among the treatments and measured traits.

FIGURE 7.

The PCA graph for yield‐related traits, morphophysiological, physio‐biochemical, and mineral parameters of vegetable cluster bean cultivated under different irrigation, Si NPs, and MeJA levels. Dry matter (DM), plant height (PLH), pod number plant⁻¹ (PN), pod yield (PY), pod crude protein (PCP), pod length (PL), branch number (BN), stem diameter (SD), and leaf area (LA). T1–T27: (% FC + Si NP ppm + MeJa μmol/L): T1:100 + 0 + 0, T2: 100 + 0 + 20, T3: 100 + 0 + 40, T4: 100 + 50 + 0, T5:100 + 50 + 20, T6: 100 + 50 + 40, T7:100 + 100 + 0, T8:100 + 100 + 20, T9: 100 + 100 + 40, T10:50 + 0 + 0, T11: 50 + 0 + 20, T12: 50 + 0 + 40, T13: 50 + 50 + 0, T14:50 + 50 + 20, T15: 50 + 50 + 40, T16 = 50 + 100 + 0, T17: 50 + 100 + 20, T18: 50 + 100 + 40, T19: 25 + 0 + 0, T20: 25 + 0 + 20, T21: 25 + 0 + 40, T22: 25 + 50 + 0, T23: 25 + 50 + 20, T24: 25 + 50 + 40, T25: 25 + 100 + 0, T26: 25 + 100 + 20, T27: 25 + 100 + 40.

The PCA loading vectors revealed that most agronomic and nutritional traits, including PLH, PN, PY, PCP, PL, BN, SD, LA, fat, fiber, P, K, Ca, and DM were positively associated with PC1 and clustered closely together. The narrow angles among these vectors indicate strong positive correlations among these variables, which is consistent with the Pearson's correlation analysis. Traits such as PN, PY, fiber, PL, and SD were grouped tightly, suggesting that these characteristics contributed jointly to yield performance and nutritional quality. Similarly, PCP, LA, Ca, fat, and DM were strongly aligned in the positive direction of PC1, indicating their important contribution to plant vigor and productivity. In contrast, ash content was positioned separately on the negative side of PC1, opposite to the cluster of yield and growth traits, confirming its negative association with most productive parameters.

Biologically, the PCA indicates that treatments receiving the combined application of Si‐NPs and MeJA under well‐watered and moderate deficit irrigation conditions were associated with improved growth, PY, nutritional quality, and mineral accumulation. In contrast, plants exposed to severe drought (25% FC), particularly without Si‐NPs and MeJA application, were positioned opposite to these traits, indicating that water deficit adversely affected overall plant performance. Therefore, the separation of treatments along the principal components reflects differences in agronomic performance and nutritional quality rather than only statistical variation. Overall, the PCA biplot demonstrated that yield‐related traits, vegetative growth parameters, nutritional quality indices, and mineral contents were strongly interconnected and contributed collectively to treatment differentiation. The clear separation of superior treatments (T6–T9) from poorer‐performing treatments (T25–T27) suggests substantial genetic variability among the studied materials and highlights the usefulness of PCA as an effective multivariate tool for identifying superior treatments with desirable agronomic and nutritional characteristics.

3.6. Regression

The regression analysis revealed a strong and significant positive relationship between PY and PLH (R ² = 75.62%, adjusted R ² = 74.65%; p < 0.01). The regression equation (Y = 23.48 + 1.409×) indicates that PY increased by approximately 1.41 g for every unit increase in PLH. The relatively high coefficient of determination suggests that PLH explained a substantial proportion of the variation in PY of edible cluster bean. This finding demonstrates that taller plants tended to produce higher PYs, highlighting PLH as an important determinant of productivity and overall plant vigor (Figure 8a). A highly significant positive association was observed between PY and SD, with an R ² value of 79.34% and adjusted R ² of 78.51% (p < 0.01). The regression equation (Y = 3.37 + 19.47×) showed that PY increased by approximately 19.47 g with each unit increase in SD. The strong linear relationship indicates that thicker stems contributed substantially to improved yield performance, possibly due to enhanced assimilate transport, structural strength, and nutrient translocation capacity within the plant (Figure 8b). The regression model demonstrated a strong positive relationship between PY and LA, explaining 79.34% of the total variability in yield (adjusted R ² = 78.51%; p < 0.01). According to the regression equation (Y = −78.82 + 2.025×), PY increased by approximately 2.03 g for each unit increase in LA. The positive slope indicates that plants with larger photosynthetic surface areas were able to accumulate more assimilates, thereby enhancing pod development and final yield production (Figure 8c). PY exhibited the strongest positive association with PL among the evaluated traits, with an R ² value of 84.24% and adjusted R ² of 83.61% (p < 0.01). The regression equation (Y = 48.34 + 13.46×) revealed that an increase in PL substantially enhanced PY, contributing approximately 13.46 g per unit increase in PL. The high coefficient of determination indicates that PL was one of the most influential yield‐contributing characters and could serve as a reliable selection criterion for improving productivity (Figure 8d). Furthermore, a significant positive linear relationship was identified between PY and PCP content (R ² = 78.8%, adjusted R ² = 77.9%; p < 0.01). The regression equation (Y = −21.49 + 14.52×) suggests that PY increased by approximately 14.52 g with each percentage increase in crude protein content. This strong relationship indicates that higher‐yielding plants also tended to possess improved nutritional quality, reflecting a positive association between productivity and protein accumulation (Figure 8e). Finally, the regression analysis also showed a significant positive relationship between PY and phosphorus content, with an R ² value of 76.58% and adjusted R ² of 75.64% (p < 0.01). The regression equation (Y = 43.59 + 3.144×) indicates that PY increased by approximately 3.14 g for every unit increase in phosphorus concentration. The positive correlation emphasizes the importance of phosphorus in promoting reproductive development, energy transfer, and overall yield enhancement in the edible cluster bean (Figure 8f). The regression relationships should be interpreted in the context of the biological dependence among yield components. Traits such as PN and average pod weight directly contribute to PY and therefore naturally exhibited strong positive associations with total pod production. Likewise, improvements in vegetative growth and nutritional status are expected to enhance assimilate production and partitioning towards reproductive organs, ultimately contributing to higher PY. Accordingly, the regression analysis should be interpreted as reflecting biologically meaningful associations rather than direct cause‐and‐effect relationships.

FIGURE 8.

The linear regression between pod yield (dependent variable) and different yield‐related traits (predictors), including plant height (a), stem diameter (b), leaf area (c), pod length (d), and crude protein content of pods (e) and phosphorous content of pods (f) of vegetable cluster bean cultivated under different irrigation, Si NPs, and MeJA levels.

4. Discussion

This study addresses the fact that immature edible cluster bean pods are considered a fresh vegetable product rather than being seen only as a potential industrial seed crop. Research to date on edible cluster bean has focused on aspects related to seed yield, gum production, or industrial application use. Very little research has addressed the nutritional value or quality of edible cluster bean pods when subjected to environmental conditions that reduce water availability. Immature edible cluster bean pods can be used as a vegetable in many arid and semiarid regions; therefore, maintaining vitamin and mineral content from immature edible cluster bean pods under limited water content is critical for food security and horticultural production systems.

The interaction of irrigation, Si NPs, and MeJA pointedly affected growth parameters, including PLH, BN, LA, pods per plant, PL, PY per plant, and pod quality, including fat content, fiber, ash, and pod DM. Drought stress adversely affected edible cluster bean growth and yield. Under severe drought, the PY and quality meaningfully were reduced. Under severe stress conditions, the highest yield (142 g plant⁻¹) was obtained with either 50‐ or 100‐ppm Si NPs combined with 40‐μmol L⁻¹ MeJA (although it was significantly lower than the amount under normal irrigation conditions), indicating the positive role of these treatments in sustaining productivity under limited water availability. Present results demonstrate that the combined application of Si NPs and MeJA effectively enhanced edible cluster bean growth and alleviated the negative impacts of drought stress, particularly at higher Si NP concentrations. Furthermore, shortage irrigation adversely affected cluster bean biochemical composition (fat and crude protein) and mineral nutrition (P, K, and Ca), whereas the application of Si NPs and MeJA, particularly at higher Si NP concentrations (100 ppm), mitigated these negative effects and improved plant quality traits under both optimal and stress conditions. The enhancement of crude protein, fiber, mineral composition, and pod DM observed in the present study is particularly important for vegetable cluster bean production because these quality attributes directly influence nutritional value and consumer acceptance of fresh pods. Unlike industrial cluster bean production systems that primarily target seed gum yield, vegetable cluster bean cultivation requires the preservation of edible pod quality under environmental stress conditions. Therefore, the positive effects of Si NPs and MeJA on pod nutritional characteristics may contribute to the development of sustainable vegetable production systems in drought‐prone regions.

Long exposure to dehydration triggers drought avoidance in plants, which relies on maintaining the water potential (Ψw) of tissues at the physiologically acceptable level by increasing water uptake or limiting water loss (Kooyers 2015). During drought stress, the stomata closure is triggered by abscisic acid (ABA), and transpiration is decreased, resulting in the reduction of plant water losses during transpiration and gas exchange in photosynthesis and respiration (Muhammad Aslam et al. 2022; Vishnyakova et al. 2023). Hormone profiling shows that JA levels improved quickly in a transient manner within mere hours of drought stress, and then ABA concentration augmented slowly thereafter (Urano et al. 2017). Previous studies have suggested that MeJA may interact with ABA signaling pathways to regulate stomatal conductance under water‐deficit conditions (Osmolovskaya et al. 2018). Previous studies suggest that jasmonates may participate in signaling pathways involving stress‐responsive genes, regulatory proteins, and signaling intermediates during drought stress (Khan et al. 2024). The WRKY transcription factor has been shown to play a role in the regulatory network associated with jasmonate‐induced signaling in response to osmotic stress (Tayyab et al. 2020). Recently, direct evidence for the role of JAs in drought has emerged in Arabidopsis by overexpression of a JA signaling repressor gene, AtJAZ7. Furthermore, overexpression of the TIFY transcription factor, ZmJAZ13, has shown drought tolerance through control of redox balance, defense metabolites, and photosynthesis (Zhang et al. 2025). MeJA has been reported to improve drought tolerance by modulating internal signaling pathways and physiological responses involved in stress adaptation. Previous studies indicate that MeJA may cooperate with other plant hormones to enhance cellular defense mechanisms during drought stress. Previous reports have suggested that JA may enhance Rubisco activity, CO₂ assimilation, and photosynthetic performance under drought conditions (Askari‐Khorasgani and Pessarakli 2019; Begum et al. 2019; Liu et al. 2012; Skowron and Trojak 2021; Tanveer et al. 2019; Waheed et al. 2022). Previous studies have reported that JA may improve membrane stability, plant water status, nutrient uptake, and antioxidant defense under drought stress, although these physiological traits were not directly evaluated in the present study.

Our study revealed that applications of Si NPs significantly improved the growth and yield of vegetable cluster bean under normal and water deficiency conditions. Si NPs significantly increased cluster bean growth under different irrigation regimes. This efficiency under different drought conditions suggests that Si NPs may have a comprehensive role in improving plant growth beyond stress reduction, as also reported for banana plants (Mahmoud et al. 2020). The stronger response to Si‐NPs may also reflect the structural role of Si in improving water retention, membrane stability, and nutrient uptake, whereas exogenous MeJA primarily acts as a signaling molecule whose effectiveness depends on endogenous hormone status and stress severity. The most notable effects were observed at 100‐ppm Si NPs concentration, alone or in combination with 40‐μmol L⁻¹ MeJA, which led to substantial enhancements in vegetative traits, PY, protein, fat, and pod fiber. These results are consistent with the previous findings, which demonstrated that Si‐NPs applications could modulate plant stress responses and promote growth (Rastogi et al. 2019; Zhu et al. 2020). Under stress conditions, Si‐NPs prevent the upsurge in the Na⁺/K⁺ ratio and lead to augmented water absorption and stomatal conductance, therefore increasing photosynthetic activities and plant growth (Liang et al. 2024).

We observed strong correlations between various growth traits and physiological and biochemical markers, confirming the interconnected nature of plant responses to drought stress and MeJA and Si‐NP application. Furthermore, PCA results confirmed outcomes of Tukey's HSD test and highlighted the different effects of MeJA and Si‐NP concentrations on cluster bean growth and drought tolerance.

These findings demonstrate that edible cluster bean may be a valuable horticulture crop resistant to changing climatic conditions, particularly in arid or semiarid areas. As water shortages threaten conventional vegetable agriculture, production of drought‐resistant crops developing yields and maintaining nutritional integrity may prove increasingly vital to sustainable agriculture and food security worldwide (Batayneh et al. 2022). Although drought significantly reduced PY and quality, the combined treatment effectively alleviated these adverse effects by improving vegetative growth, PY, crude protein, fiber, mineral composition (P, K, and Ca), and pod DM. These improvements are particularly valuable for commercial vegetable cluster bean, where market acceptance depends not only on yield but also on pod nutritional quality and fresh‐market value. The results suggest that integrating Si NPs and MeJA into deficit‐irrigation management could enhance water‐use efficiency while maintaining economically acceptable yields in water‐limited environments. This approach may contribute to more resilient vegetable production systems in low and semiarid regions, where increasing water scarcity threatens horticultural productivity. Furthermore, preserving the nutritional quality of edible pods under drought conditions enhances the potential role of vegetable cluster bean in improving food security and diversifying climate‐resilient vegetable cropping systems. The use of Si NPs in combination with MeJA therefore offers growers a practical management option to reduce drought‐related production losses while maintaining crop quality for fresh‐market consumption. Cumulatively, 100‐ppm Si‐NP + 40‐μmol L⁻¹ MeJA was determined to be the most effective treatment on edible cluster bean production when applying different combinations of these treatments.

Despite the promising results, several limitations should be considered when interpreting these findings. First, the study was conducted during a single growing season under controlled experimental conditions; therefore, multilocation and multiyear field trials are required to validate the consistency and economic feasibility of the proposed treatment under diverse environmental conditions. Second, only two Si NP concentrations (50 and 100 ppm) and one MeJA concentration (40 μmol L⁻¹) were evaluated. Further research should optimize application rates, timing, and frequency, and investigate whether higher or intermediate MeJA concentrations could further enhance drought tolerance.

Additionally, although the physiological responses suggest that Si NPs and MeJA interact through hormonal and stress‐signaling pathways, the molecular mechanisms underlying their synergistic effects remain unclear. Future studies integrating transcriptomic, metabolomic, and hormone profiling analyses are needed to elucidate the interactions among Si NPs, jasmonate signaling, ABA regulation, and other drought‐responsive pathways. Although several growth, biochemical, nutritional, and mineral traits were evaluated, important physiological parameters including chlorophyll fluorescence, photosynthetic rate, relative water content, antioxidant enzyme activity, and osmolyte accumulation were not measured. Therefore, the proposed physiological mechanisms should be regarded as indirect interpretations based on previous studies rather than direct experimental evidence.

5. Conclusion

The combined use of Si NPs and MeJA represents an effective means to enhance growth, pod productivity, and nutritional quality in the vegetable cluster bean ( Cyamopsis tetragonoloba L.) under drought deficits. Unlike most previous studies that investigated cluster bean seed yield for industrial gum production, the present study has focused on immature edible pods as an important vegetable product and the impact of insufficient water on the nutritional quality of those immature pods. Drought stress significantly reduced all growth and yield among plants and edible pods (including crude protein content, fiber content, and mineral composition), suggesting that vegetable cluster bean is particularly susceptible to quality loss due to water‐deficit irrigation. The combination of Si NPs with MeJA treatment significantly ameliorated the negative consequences of low and moderate drought stress on the growth and yield of vegetable cluster bean. The results obtained from this research indicate a combination effect of Si NPs and MeJA on both productivity and nutritional quality of vegetable cluster bean harvested under conditions of limited water. Specifically, the combination of 100‐ppm Si NPs along with 40‐μmol L⁻¹ MeJA produced the greatest PYs and most desirable nutritional quality parameters compared to the control. Therefore, we recommend this combination for cluster bean cultivation under moderate drought conditions after economic feasibility and field‐scale validation studies. Overall, the findings of this study present the potential for vegetable cluster bean as an important source of plant protein for use in human consumption. Future studies should validate these findings under multilocation and multiseason field conditions to confirm the stability of the observed responses. Additional research is also needed to investigate the physiological and molecular mechanisms underlying the combined effects of Si‐NPs and MeJA, evaluate their economic feasibility for commercial vegetable cluster bean production, and assess the long‐term environmental safety of repeated NP application before recommending large‐scale adoption.

Author Contributions

Heidar Meftahizade performed the experiment, contributed to data collection, and wrote the final manuscript. Ali Sabah Alhasan analyzed the data, and both wrote the primary manuscript. Both authors read and approved the final version of the manuscript. The authors conducted the experiments in collaboration and wrote the manuscript.

Funding

The authors have nothing to report.

Ethics Statement

The authors have nothing to report.

Consent

The authors declare their consent to the publication of this article.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

All data generated during this study are included in this article.