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Article

Assessment of Biostimulant Derived from Moringa Leaf Extract on Growth, Physiology, Yield, and Quality of Green Chili Pepper

by
Nita Yuniati
1,*,
Kusumiyati Kusumiyati
1,*,
Syariful Mubarok
1 and
Bambang Nurhadi
2
1
Faculty of Agriculture, Padjadjaran University, Jalan Raya Bandung-Sumedang Kilometer 21 Jatinangor, Sumedang 45363, Indonesia
2
Faculty of Agro-Industrial Technology, Padjadjaran University, Jalan Raya Bandung-Sumedang Kilometer 21 Jatinangor, Sumedang 45363, Indonesia
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(9), 7113; https://doi.org/10.3390/su15097113
Submission received: 4 March 2023 / Revised: 19 April 2023 / Accepted: 23 April 2023 / Published: 24 April 2023
(This article belongs to the Section Sustainable Agriculture)
Browse Figure
Review Reports Versions Notes

Abstract

:
With the rapid growth in global population and standards of living, improving food production and quality are the greatest challenges in agriculture. The application of biostimulant derived from moringa leaf extract (MLE) has attracted a great deal of interest to support these efforts in a sustainable approach. A field study was conducted using a randomized complete block design with four replications. The effect of individual and combined application of MLE through seed priming (seed soaking) and foliar spray at different rates (1:30, 1:20, and 1:10, v/v) on growth, physiological, yield, and quality traits of green chili pepper were investigated, which was the aim of this study. In general, the responses generated by the combined MLE methods were more pronounced compared to their single applications. Among all treatments, MLE priming plus foliar spray at 1:30 was effective in improving most traits observed, including chlorophyll fluorescence (6.49%), stomatal conductance (57.19%), plant height (30.57%), leaf number (88.89%), leaf area index (116.67%), fruit weight per plant (46.27%), average fruit weight (39.62%), length (9.89%), diameter (29.65%), firmness (27.77%), and vitamin C content (29.07%) of fruit. Therefore, it is regarded as an appropriate treatment to maximize the potential use of MLE in green chili.

1. Introduction

The demand for foods with good nutritional and health values continues to escalate in response to the rapid growth in global population and standards of living [1,2]. Synthetic agrochemicals are widely applied to meet these needs, but excessive use of such chemicals can cause environmental pollution, food security issues, and yield reduction [3]. Efforts should be geared toward adopting more sustainable practices. Sustainable agriculture has several benefits on agricultural production; in addition to reducing the dependence on chemical inputs, it also preserves the environment and natural resources and provides healthy food for present and future generations [4,5].
In recent years, biostimulants have attained much attention from plant scientists as a technological innovation for improving yield and quality of valuable commodities in a sustainable approach, such as pepper [6], potato [7], radish [8], and tomato [9]. Yakhin et al. [10] described a biostimulant as a product formulated from biological origin that has complex constituents, including plant protective compounds, plant nutrients, and plant regulators. These substances affect various physiological processes in plants that stimulate plant growth and development [11].
Moringa oleifera leaf extract (MLE) is one of the most promising biostimulants and has been used by farmers as a viable complement and/or substitute for synthetic fertilizers [3]. Moringa belongs to the family Moringaceae and is a fast-growing crop in tropical and subtropical regions [12]. MLE is characterized by a high content of vitamin A, vitamin C, Ca, K, Mg, P, cytokinin, gibberellin, auxin, flavonoids, proteins, sugars, and more [11,13,14]. Being a good source of antioxidant compounds, MLE is very effective in minimizing the adverse impact of climatic variability on plants [15]. Additionally, it is cheap, safe, easy to prepare, and environmentally friendly. Many investigators have proved the stimulatory effect of MLE on germination, photosynthesis processes, growth, yield, and quality of several vegetable crops [3,9,16].
Chili pepper (Capsicum annuum L.) is one of the most cultivated vegetable crops in the world [17]. In 2021, green chili and pepper production worldwide totaled about 36.2 million tons [18]. The fruit is marketed directly to consumers and/or processed into frozen or canned products [19]. Green chili is a popular commodity because of its pungent flavor and high content of nutrients. It possesses mineral nutrients, flavonoids, proteins, vitamin A, vitamin C, vitamin E, folic acid, volatile oil, and capsaicin, which is responsible for the pungency of the fruit [20].
Plant response to MLE depends on the method and concentration used [21]. MLE can be directly applied through foliar spray or seed priming, but foliar spray is the prevalent method. Based on our previous study on chili pepper [22], MLE priming, in which the seeds were soaked in MLE solution at a concentration of 1:20, showed better results in germination and seedling growth. An improvement in chlorophyll content, plant height, and yield of maize was also observed after priming with this extract [23]. It has been well documented that foliar spray of MLE enhances chlorophyll fluorescence, number of leaves, yield, vitamin C, and total soluble solids [24,25,26]. In another study, MLE performed better as a foliar spray than as a seed primer in terms of the growth and yield of wheat [27]. The same trend was reported in radish considering quality attributes due to biostimulant application [28]. Interestingly, the growth and yield of maize [29] and wheat [30] were more intensified by the combined treatment of seed priming and foliar spray with MLE compared to those of single applications.
So far, no study has assessed the potential use of MLE for seed priming, foliar application, and their combined use in green chili. In this regard, it is also necessary to determine the proper concentration for foliar treatment, which is the most frequent method used. An important question is whether these application methods of MLE can increase yield and quality of green chili. Therefore, the goal of this study was to investigate the effect of individual and combined application of MLE through seed priming and foliar spray at different rates on growth, physiological, yield, and quality traits of green chili pepper. We hypothesized that the combined methods of MLE can better increase plant yield and quality through the improvement in physiological- and growth-related parameters.

2. Materials and Methods

2.1. Experimental Site

A field trial was conducted from August to November 2022 at the Faculty of Agriculture, Universitas Padjadjaran, Indonesia (6°55′10” S 107°46′20” E). The characteristics of experimental soil were 35% sand, 28% silt, 37% clay, 0.10% total nitrogen, 9.46 ppm available phosphorus, 147.40 mg 100 g−1 potassium, and pH 6. According to Table 1, the monthly average air temperature and relative humidity (RH) in the experimental area are suitable for growing chili plants. The temperature was relatively stable (22.00–22.74 °C) with RH of 86.67–91.07%.

2.2. Experimental Design

The experiment was carried out according to a randomized complete block design with four replicates. It was comprised of eight treatments, viz. (1) control, (2) seed priming with MLE, (3) foliar spray with MLE 1:30, (4) foliar spray with MLE 1:20, (5) foliar spray with MLE 1:10, (6) seed priming with MLE + foliar spray with MLE 1:30, (7) seed priming with MLE + foliar spray with MLE 1:20, and (8) seed priming with MLE + foliar spray with MLE 1:10. The control treatment was represented by priming and foliar spraying with distilled water.

2.3. MLE Preparation

Water solvent was used for the extraction of moringa leaves, since it is cheap, environmentally friendly, and readily available. It was prepared following the method of El Sheikha et al. [31]. Briefly, 30 g of fresh moringa leaves were mixed with 300 mL of distilled water using a household blender for 15 min and filtered through Whatman No.1 filter paper. The mixture was then centrifuged for 15 min at 8000 rpm. Afterward, the supernatant was collected and diluted with distilled water at ratios of 1:30, 1:20, and 1:10. The chemical compositions of aqueous MLE used in this study have been reported previously [22], and consisted of a considerable amount of gibberellin (GA3), cytokinin, P, K, Ca, phenolics, flavonoids, and vitamin C.

2.4. Experimental Procedures

Chili pepper seeds of the variety ‘Tanjung-2’ were used in this study. This variety is adaptive to all altitude levels and slightly tolerant to anthracnose [32]. Its plant height is about 55 cm.
The seed surface was sterilized for 30 s using 1% sodium hypochlorite, rinsed with distilled water, and air-dried under the shade. The method and concentration used for MLE priming were selected according to our recent study [22]. In this respect, the seeds were soaked in MLE solution at a concentration of 1:20 for 24 h and re-dried to their initial weight at room temperature. At the same time, the seeds used for control and individual foliar MLE treatments were soaked in distilled water. The seeds were sown in trays filled with a mixture of rice husk charcoal and compost (1:1).
Twenty-seven-day old pepper seedlings were transplanted into a double-row bed, covered by plastic mulch. Each plot consisted of six plant samples and thus, a total of twenty-four plants per treatment was set up, with 50 cm spacing between plants. Referring to soil properties and plant needs, chicken manure (20 tons ha−1) and NPK 16:16:16 (800 kg ha−1) were supplemented to the experimental soil during the preparation of the bed. Two commercial protective products, viz. Antracol® (Propineb) and Pegasus® (Diafenthiuron), were applied to protect plants against fungal infection and insects, respectively.
Plants were foliar sprayed with three dilutions of MLE (1:30, 1:20, and 1:10), starting 14 days after transplanting (DAT) and repeated five times at fortnightly intervals. The spraying volume was 160 L ha−1 (5 mL per plant) for the first spray, 320 L ha−1 (10 mL per plant) for the second spray, 480 L ha−1 (15 mL per plant) for the third spray, and lastly, 640 L ha−1 (20 mL per plant) for the fourth and fifth sprays. All sprays were done using a hand sprayer in the early morning. The fruits from all plants were then hand-harvested at the horticultural green mature stage (45 d after anthesis).

2.5. Measurement of Growth, Physiological, and Yield Traits

Seven weeks after transplanting or after three foliar applications of MLE, plant height, number of leaves, and leaf area index (LAI) were evaluated. LAI was achieved using the gravimetric method [33]. A SPAD-502 chlorophyll meter (Konica Minolta, Inc., Tokyo, Japan) was used to calculate chlorophyll content index. Stomatal conductance and chlorophyll fluorescence were determined using an SC-1 leaf porometer (Decagon Devices, Inc., Pullman, WA, USA) and a Handy PEA fluorometer (Hansatech Instruments, Kings Lynn, UK), respectively. These physiological parameters were measured on fully developed leaves near the shoot apex. In terms of yield-contributing traits, the harvested fruits were counted and weighted to obtain the number of fruits, fruit weight per plant, and average fruit weight.

2.6. Determination of Fruit Physical Quality

Fruit length and diameter were measured for a sample of forty-eight fruits per treatment using a Vernier caliper. To assess color and firmness, sixteen fruits (15–17 g each) from eight different plants per treatment were picked. Three measurements were made on each fruit, and the results were averaged. A portable spectrophotometer (CM-600d, Konica Minolta Co., Ltd., Osaka, Japan) was used to analyze the color attributes (L*, a*, b*) of the fruit peel surface. L* refers to lightness, ranging from black (0) to white (100). The a* values represent green (−) to red (+), while the b* values indicate blue (−) to yellow (+). On the other hand, fruit firmness was determined following the procedure described by Wang et al. [34] with some modifications. It was acquired through a TA.XT Plus Texture Analyzer (Stable Micro. Systems Ltd., Godalming, UK) with a 2 mm cylindrical probe and a speed of 2 mm s−1.

2.7. Determination of Fruit Chemical Quality

A total of six green chili fruits (15–17 g each) per experimental plot were collected for chemical analysis. Total soluble solids (TSS) of fruit were determined using a digital refractometer (Atago Co., Tokyo, Japan) and expressed as °Brix.
Vitamin C content was estimated by the method of Chebrolu et al. [35] with some modifications. About 2.5 g of fresh sample and 2.5 mL of trichloroacetic acid (TCA) at 3 g 100 mL−1 were vortexed and centrifuged for 15 min at 4000 rpm. The supernatant was filtered through 0.45 μm syringe filter and injected into a high-performance liquid chromatograph (HPLC) (LC-20AT, Shimadzu Co., Kyoto, Japan) with a 20 µL injection volume. A reverse-phase HPLC assay was done using a non-polar C18 column (150 mm × 4.6 mm; 5 µm) with isocratic mode at a flow rate of 1 mL min−1. The ammonium dihydrogen phosphate assay was performed as a polar mobile phase. Elution was carried out for 30 min followed by ultraviolet (UV) detection at 254 nm.
Capsaicin and dihydrocapsaicin were evaluated according to the method of Thapa et al. [36] with slight modifications. Approximately 0.5 g of dried sample was added to 10 mL of methanol and incubated in a water bath (B-100, Buchi, Flawil, Switzerland) at 50 °C for 4 h. The mixture was centrifuged for 15 min at 4000 rpm and passed through a 0.45 μm syringe filter. A high-performance liquid chromatography-ultraviolet (LC-20AT, Shimadzu Co., Kyoto, Japan) was set up for the separation and quantification. For this purpose, a C18 column (150 mm × 4.6 mm; 5 μm) was used, and the mobile phase comprised 0.1% of phosphoric acid and acetonitrile at a ratio of 60:40 (v/v). The temperature of the column was adjusted at 30 °C with a flow rate of 1 mL min−1.
The Scoville heat unit (SHU) represents the degree of pungency and was determined based on the concentration (ppm) of capsaicin and dihydrocapsaicin, using the following equation [37]:
SHU = (capsaicin × 16.1) + (dihydrocapsaicin × 16.1)
There are five levels of pungency referring to SHU values: 0–700 (non-pungent), 700–3000 (mildly pungent), 3000–25,000 (moderately pungent), 25,000–75,000 (highly pungent), and >80,000 (very highly pungent) [37].

2.8. Statistical Analysis

Data were analyzed for significance with analysis of variance (ANOVA) using SPSS v21 software (SPSS Inc., Chicago, IL, USA). Mean values of treatments were evaluated with Duncan’s multiple range test (DMRT), and results were considered significant at p < 0.05.

3. Results

The physiological data in Table 2 revealed that there were significant differences due to MLE application. Seeds primed with MLE provided the highest chlorophyll content index when combined with foliar treatment at 1:20 (94.50). Meanwhile, the lowest value was recorded in the control group (70.55), which was statistically at par with MLE priming and foliar treatments alone. Furthermore, all MLE applications outperformed the control in chlorophyll fluorescence (Fv/Fm) at about 5.19 to 6.49%, except for MLE priming. Compared to the control, MLE priming plus foliar treatment at 1:30 significantly increased stomatal conductance (210.13 mmol m−2 s−1), and this increment was similar to the combined treatment using foliar MLE 1:10 (196.98 mmol m−2 s−1).
The treatments significantly changed plant growth-related parameters, except for fruit set (Table 3). Plant height showed a notable increase by up to 30.61% in response to MLE priming, foliar spray of MLE 1:10, and all of the combination treatments. The shortest plants were measured in the control group (49.73 cm) and were statistically the same as foliar MLE 1:30 (59.83 cm) and 1:20 (57.05 cm) treatments. Moreover, all MLE treatments dramatically enhanced the number of leaves by up to 88.89%. The results also showed that MLE priming plus foliar treatment at 1:10 produced the maximum leaf area index (1.33) in comparison to the control. However, this increase was similar to MLE priming (1.20) and in combination with foliar treatment at 1:30 (1.04).
As shown in Figure 1a, the number of fruits per plant was not significantly affected by MLE application. On the other hand, the treatments contributed to a significant increase in fruit weight per plant (Figure 1b). MLE priming combined with foliar treatment at 1:30 produced 46.27% higher fruit weight per plant (642.88 g) than the control (439.50 g). In comparison to the control, an improvement in average individual fruit weight was also detected by this treatment (22.06 g) and was statistically at par with MLE priming combined with foliar application at 1:20 (19.71 g) (Figure 1c). Both treatments were increased by about 39.62% and 24.75%, respectively, compared to the control.
Fruit length and diameter of green chili varied among the treatments (Table 4). In this regard, MLE priming plus foliar spray at 1:20 exhibited the maximum fruit length (13.78 cm) compared to the control (12.33 cm), but it was statistically equivalent to foliar MLE 1:30 alone (13.68) and the combined treatments using foliar MLE 1:30 and 1:10 (13.55 and 13.51 cm, respectively). In addition, MLE priming combined with foliar treatment at 1:30 yielded fruit with the highest diameter (2.23 cm) compared to the control (1.72 cm). However, the difference was similar to other combination treatments.
The color characteristics of fruit peel are summarized in Table 4. A significant effect was only evident in fruit lightness (L*). Foliar spray of MLE 1:20 exhibited brighter fruit (37.54) than the control (35.71) and the combination treatments. According to a* and b* values, all fruits showed a green coloration and greater yellow contribution. Moreover, data on fruit firmness indicated that seed priming and/or foliar spray with MLE significantly affected this parameter (Table 4). Compared to the control (4.43 N), foliar spray of MLE 1:10 and the combination of MLE priming plus foliar treatment at 1:30 and 1:20 successfully enhanced the firmness of green chili fruit (5.59, 5.66, and 5.89 N, respectively).
According to Table 5, no treatment increased the total soluble solids (TSS) of green chili fruit. Conversely, the vitamin C content in fruit reacted differently to MLE application (Table 5). Both single and combined applications of MLE through seed priming and foliar spray significantly enhanced vitamin C content. Foliar spray of MLE 1:20 gave greater values of this parameter by about 50.00% compared to the control but did not differ from foliar MLE 1:10 (44.77%), MLE priming (30.23%), and MLE priming plus foliar treatment at 1:30 (29.07%).
There were no significant variations in the pungency traits of green chili fruit due to MLE addition (Table 5). More specifically, the treatments had a similar effect on capsaicin, dihydrocapsaicin, and Scoville heat units (SHU). The values of SHU showed that all fruits were classified as moderately pungent.

4. Discussion

In the present study, the integrated application of MLE through seed priming and foliar spray at 1:20 exhibited the highest chlorophyll content index (94.50). Our findings were consistent with Bakhtavar et al. [29], who reported that the maximum chlorophyll content of early-sown maize was obtained from MLE priming combined with foliar treatment. MLE stimulates earlier formation of cytokinin, thus avoiding premature leaf senescence and resulting in higher photosynthetic pigment contents [38]. Cytokinin present in MLE induces the activation of isopentenyl transferase (IPT), a critical enzyme involved during cytokinin biosynthesis, and leads to improved chlorophyll concentration [39]. This increase might also be due to the fact that MLE is a good source of Fe and Mg, the key elements for chlorophyll biosynthesis, which play a role in the conversion of proporphyrine to chlorophyllide [25].
The greatest chlorophyll fluorescence (Fv/Fm) was reached by all foliar MLE treatments and their combination with seed-priming treatments (0.81–0.82). Similar results were found in safflower [40], squash [11], and radish baby leaves [3]. Fv/Fm reflects the maximum photosynthetic efficiency of optical system II and is commonly used as an indicator of photosynthetic performance [41]. MLE induces more leaf photosynthetic pigment synthesis as a result of its high content of phytohormone and mineral nutrients, which leads to improved chlorophyll fluorescence and photosynthesis [11]. Lower values of Fv/Fm denote the downregulation of photosynthesis and closure of photosystem II reaction centers related to stress [42]. Accordingly, the results of our experiment suggest that MLE application did not damage the efficiency of the photosynthetic apparatus of chili plant.
From the findings of this study, MLE priming combined with foliar treatment at 1:30 and 1:10 established a remarkable increase by up to 57.19% in stomatal conductance. Under well-watered growth conditions, greater stomatal conductance, which regulates gas-exchange processes, can allow plants to improve their CO2 uptake and consequently increase photosynthesis [43]. Usage of foliar MLE at 1:30 produced a higher stomatal conductance of wheat, but its combination with seed priming in rhizobacteria showed maximum improvement [44]. The positive results were also noticed in rice seedlings after priming with MLE [45]. Potassium found in MLE is an essential element for stomatal adjustments by maintaining turgor pressure [46].
MLE priming, foliar spray of MLE 1:10, and the combined treatments resulted in taller plants (by up to 60.31%) compared to the control. An increment in plant height as a result of MLE priming was recently reported in wheat [27]. Latif and Mohamed [38] observed a positive impact of foliar MLE application in common beans regarding this trait. It is evident that GA metabolism and signaling are two essential factors in controlling stem elongation, and this hormone is found in moringa leaves [14].
The enhancement in the number of leaves (up to 88.89%) was attained in all MLE treatments in the present investigation. Matthew [47] detected more leaves in pepper plants after foliar spraying with MLE. Similar results were recorded when MLE was used as a seed-priming agent in bitter kola [48]. Additionally, seed priming plus foliar spray with MLE in sorghum produced the maximum number of leaves as a result of faster emergence and better seedling establishment [49]. A higher number of photosynthetically active leaves was observed in MLE treatments, indicating that this extract positively maintained chlorophyll and delayed senescence [30]. Furthermore, cytokinin present in MLE stimulated cell division and leaf bud initiation, which eventually improved leaf number and leaf area [50].
Seed priming followed by foliar spraying with MLE 1:10 showed the maximum values in leaf area index (1.33) compared to the control, although statistically at par with priming alone (1.20) and combined with foliar treatment at 1:30 (1.04). Similarly, MLE application through seed priming together with foliar treatment resulted in earlier germination and better vigor, which then affected plant growth in a positive way, as reflected by higher leaf area and photosynthetic rate [29]. Ahmad et al. [49] reported a significant improvement in leaf area from MLE priming plus foliar treatment. They stated that the increase was closely correlated with the cumulative effect of phytohormones, nutrients, and secondary metabolites found in this extract, i.e., zeatin (a type of cytokinin), potassium, calcium, phenolics, and ascorbic acid. After spraying, these substances may easily translocate from stomata to active parts, such as meristematic cells [11].
Plant responses to seed priming and/or foliar spray with MLE were not significantly different in terms of fruit set. These results are in a line with a previous report by Francis and Stark Jr [51] that biostimulant addition showed no effect on flowering and fruit set of tomato. The fruit set was associated with fruit number, such that with a higher fruit set, more fruit will be produced [26]. This is confirmed in our study. MLE application did not alter the number of green chili fruits, which might be attributed to the insignificant results in fruit set. Furthermore, fruit number of okra harvested 6 weeks after planting was not notably affected by MLE treatment [52]. In tomato, foliar spray of MLE at 1:10 also failed to improve this parameter [21].
In the current study, MLE priming incorporated with foliar treatment at 1:30 remarkably enhanced fruit weight per plant by about 46.27%. Similarly, the combined MLE application in wheat recorded the highest yield [30]. Priming accelerated seed emergence and increased uniform seedlings, which contributed to better plant vigor and yield potential [53]. Spraying leaves with MLE resulted in greater fruit weight per tomato plant [9] and higher pod weight of snap beans [54] compared to untreated plants. This can be related to the fact that MLE contains appreciable amounts of phytohormones (auxin and zeatin) and minerals (K, Ca, Fe, and Zn), which have a beneficial influence during fruit growth and development stages [26].
The highest average fruit weight was observed following the combined application of MLE through seed priming plus foliar spray at 1:30 and 1:20 (22.06 and 19.71 g, respectively). It is possible that biostimulants can display stronger effects when applied with more than one method [55]. In tomato, MLE improved nutrient uptake and subsequently, resulted in heavier fruit [56]. Moreover, cytokinin and K have important roles in this regard. Cytokinin enables better sink capacity of a plant, as a result of extended green leaf area, while K increases the translocation of photoassimilates towards developing fruit [15,57].
Compared to the control, the combination of MLE priming plus foliar treatment was effective to improve fruit length and diameter of green chili by up to 11.76 and 29.65%, respectively. The present findings agree with Bakhsh et al. [58], who found considerable enhancement in fruit diameter of peach following foliar MLE application. The same results were recorded in sweet pepper [16] and artichoke heads [59]. In addition, maize seeds primed in MLE produced greater cob length and diameter [60]. A potential reason for this may be the presence of K, Zn, and zeatin in MLE, in which K helps the accumulation of sugar/starch of fruit and increases the relationship between source–sink, Zn acts as a tryptophan precursor in IAA (indole acetic acid) synthesis, and zeatin is involved in cell expansion and photoassimilate translocation to fruit [26].
Results on color attributes of fruit peels showed that plants treated with foliar MLE at 1:20 had higher L* values (37.54) compared to the control. Thanaa et al. [61] and Mahmoud et al. [62] found similar results when using pre-harvest MLE treatment on L* in plum fruit. Meanwhile, our study revealed that a* and b* values were negatively influenced by the treatments. These findings are in agreement with those obtained by Godlewska et al. [63] that the application of plant extracts did not change celeriac color in general, including a* as well as b*.
The shelf life and market values of fruit can be assessed by the firmness parameter [61]. The results of our experiment showed a higher fruit firmness following foliar spray of MLE at 1:10 and the combined treatments using foliar MLE 1:30 and 1:20, which enhanced firmness by up to 32.96% compared to the control. Ali et al. [64] validated the foliar MLE effect that subsequently improved berry firmness. The increase also was noted in plum fruit because of the high Ca content of this biostimulant [61]. Ca is involved in the formation of the cell wall, playing a binding role in complex polysaccharides and proteins, which leads to enhanced fruit firmness [57].
In addition, our study indicated that MLE application did not have any significant effect on total soluble solids (TSS). Similarly, spraying leaves with MLE at 2.5% had no effect on TSS of grape berry [64]. According to Nasir et al. [65], TSS is correlated with fruit size, such that smaller fruit size results in greater TSS and vice versa. Thus, they concluded that since MLE treatment successfully enhanced fruit size, TSS did not improve in fruit.
Supplementing chili pepper with individual application of MLE through seed priming, foliar spray at 1:20, 1:10, and the combined treatment using foliar MLE 1:30 exhibited the highest vitamin C content in fruit, which increased by up to 50.00% over the control. Likewise, the greatest vitamin C in citrus was achieved by foliar MLE treatment before flowering as well as at the fruit set stage [65]. Other studies proved that foliar MLE markedly enhanced this compound in grape berry [66], broccoli [67], and lettuce [68]. This may be explained by the fact that MLE is a plentiful source of protein and vitamin C, thereby facilitating better ascorbic acid formation in fruit [57].
Capsaicin and dihydrocapsaicin constitute up to 90% of the pungency in pepper, and their content in green fruit was relatively lower than in red fruit [69,70]. In the present experiment, the use of MLE through seed priming and/or foliar spray did not change capsaicin, dihydrocapsaicin, and Scoville heat units (SHU) of green chili fruit. The number of reports considering the effects of MLE on the above parameters is scarce. A previous study demonstrated the effectiveness of biostimulants derived from honey bees and silymarin in chili pepper and revealed that both biostimulants negatively affected capsaicin content under non-stress growth conditions [71]. The capsaicin content in chili can differ depending on the temperature and light intensity during cultivation, as well as the age of the fruit [72].

5. Conclusions

This study was performed to investigate the effect of individual and combined application of MLE through seed priming and foliar spray at different rates on growth, physiological, yield, and quality traits of green chili pepper. Seed priming and/or foliar spray with MLE had a significant influence on all parameters, except for the number of fruits per plant, fruit color (a* and b*), total soluble solids, capsaicin, dihydrocapsaicin, and Scoville heat units. On an overall basis, the combined MLE treatments had more stimulatory effects compared to their single application. In particular, the integrated application of MLE priming and foliar spray at 1:30 was effective in increasing most traits explored, including chlorophyll fluorescence (6.49%), stomatal conductance (57.19%), plant height (30.57%), number of leaves (88.89%), leaf area index (116.67%), fruit weight per plant (46.27%), average fruit weight (39.62%), fruit length (9.89%), diameter (29.65%), firmness (27.77%), and vitamin C content (29.07%). Hence, this method is regarded as the best treatment. As a continuation of this study, it will be useful to evaluate plant response to MLE at the biochemical and molecular levels for more comprehensive results.

Author Contributions

Conceptualization, N.Y. and K.K.; methodology, N.Y. and S.M.; software, N.Y.; validation, B.N.; formal analysis, N.Y. and K.K.; investigation, N.Y. and B.N.; resources, N.Y.; data curation, S.M.; writing—original draft preparation, N.Y.; writing—review and editing, N.Y., K.K., S.M. and B.N.; visualization, N.Y.; supervision, K.K., S.M. and B.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Indonesia’s Ministry of Education, Culture, Research and Technology, grant number 094/E5/PG.02.00.PT/2022. The APC was funded by Padjadjaran University.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to thank our laboratory and field staff for their help during the experiment.

Conflicts of Interest

The authors declare no conflict of interest.

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Sustainability 15 07113 g001 550
Figure 1. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on the number of fruits per plant (a), fruit weight per plant (b), and average fruit weight (c). Values followed by different letters indicate statistical differences at p < 0.05 according to DMRT. C—control; SP—seed priming with MLE; FS—foliar spray with MLE.
Figure 1. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on the number of fruits per plant (a), fruit weight per plant (b), and average fruit weight (c). Values followed by different letters indicate statistical differences at p < 0.05 according to DMRT. C—control; SP—seed priming with MLE; FS—foliar spray with MLE.
Sustainability 15 07113 g001
Table
Table 1. Monthly average air temperature and relative humidity during the growing season of chili crop.
Table 1. Monthly average air temperature and relative humidity during the growing season of chili crop.
MonthAir Temperature (°C)Relative Humidity (%)
August22.0086.67
September22.3687.07
October22.6790.71
November22.7491.07
Mean22.4488.88
Table
Table 2. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on chlorophyll content index, chlorophyll fluorescence (Fv/Fm), and stomatal conductance of chili pepper plants.
Table 2. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on chlorophyll content index, chlorophyll fluorescence (Fv/Fm), and stomatal conductance of chili pepper plants.
TreatmentsChlorophyll
Content Index		Fv/FmStomatal
Conductance
(mmol m−2 s−1)
Control70.55 d0.77 b133.68 c
MLE priming75.75 cd0.80 ab184.43 abc
Foliar MLE 1:3077.15 cd0.81 a137.55 c
Foliar MLE 1:2076.93 cd0.82 a150.03 bc
Foliar MLE 1:1076.55 cd0.82 a192.63 abc
MLE priming + foliar MLE 1:3085.15 b0.82 a210.13 a
MLE priming + foliar MLE 1:2094.50 a0.82 a188.48 abc
MLE priming + foliar MLE 1:1080.05 bc0.82 a196.98 ab
Values followed by different letters within a column indicate statistical differences at p < 0.05 according to DMRT.
Table
Table 3. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on plant height, number of leaves, leaf area index (LAI), and fruit set of chili pepper plants.
Table 3. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on plant height, number of leaves, leaf area index (LAI), and fruit set of chili pepper plants.
TreatmentsPlant Height
(cm)		Number of LeavesLAIFruit Set
(%)
Control49.73 b38.25 b0.48 d85.03 a
MLE priming63.80 a64.75 a1.20 abc85.44 a
Foliar MLE 1:3059.83 ab67.75 a0.86 abcd84.53 a
Foliar MLE 1:2057.05 ab61.00 a0.81 bcd84.49 a
Foliar MLE 1:1060.90 a63.00 a0.54 cd85.58 a
MLE priming + foliar MLE 1:3064.93 a72.25 a1.04 abc82.50 a
MLE priming + foliar MLE 1:2064.13 a65.75 a0.98 abcd80.21 a
MLE priming + foliar MLE 1:1064.95 a66.25 a1.33 a80.66 a
Values followed by different letters within a column indicate statistical differences at p < 0.05 according to DMRT.
Table
Table 4. Effect of MLE used as seed priming agent and/or foliar application at different rates on the length, diameter, peel color (L*, a*, b*), and firmness of green chili pepper fruit.
Table 4. Effect of MLE used as seed priming agent and/or foliar application at different rates on the length, diameter, peel color (L*, a*, b*), and firmness of green chili pepper fruit.
TreatmentsFruit Length
(cm)		Fruit Diameter (cm)L*a*b*Firmness
(N)
Control12.33 c1.72 d35.71 bc−9.64 a19.78 a4.43 b
MLE priming12.85 abc1.79 cd36.45 ab−9.95 a20.04 a5.24 ab
Foliar MLE 1:3013.68 a1.94 cd36.18 abc−9.90 a19.80 a5.24 ab
Foliar MLE 1:2012.62 bc1.82 cd37.54 a−10.05 a20.95 a5.16 ab
Foliar MLE 1:1013.15 abc1.99 bc36.49 ab−9.85 a20.04 a5.59 a
MLE priming + foliar MLE 1:3013.55 ab2.23 a34.58 c−9.11 a17.39 a5.66 a
MLE priming + foliar MLE 1:2013.78 a2.05 ab35.77 bc−9.81 a19.36 a5.89 a
MLE priming + foliar MLE 1:1013.51 ab2.00 ab35.01 bc−9.55 a18.00 a5.13 ab
Values followed by different letters within a column indicate statistical differences at p < 0.05 according to DMRT.
Table
Table 5. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on total soluble solids (TSS), vitamin C, capsaicin, dihydrocapsaicin, and Scoville heat units (SHU) of green chili pepper fruit.
Table 5. Effect of MLE used as a seed-priming agent and/or for foliar application at different rates on total soluble solids (TSS), vitamin C, capsaicin, dihydrocapsaicin, and Scoville heat units (SHU) of green chili pepper fruit.
TreatmentsTSS
(°Brix)		Vitamin C
(mg 100 g−1 FW)		Capsaicin
(mg 100 g−1 DW)		Dihydrocapsaicin
(mg 100 g−1 DW)		SHU
Control4.43 a1.72 c23.74 a6.97 a4945.39 a
MLE priming4.63 a2.24 ab28.92 a9.80 a6233.12 a
Foliar MLE 1:304.62 a2.18 b26.27 a9.21 a5711.44 a
Foliar MLE 1:204.32 a2.58 a24.30 a7.28 a5084.88 a
Foliar MLE 1:104.21 a2.49 ab30.27 a9.62 a6423.18 a
MLE priming + foliar MLE 1:304.60 a2.22 ab30.25 a10.00 a6479.43 a
MLE priming + foliar MLE 1:204.78 a2.11 b26.87 a8.15 a5636.89 a
MLE priming + foliar MLE 1:104.75 a2.13 b22.47 a7.04 a4751.37 a
Values followed by different letters within a column indicate statistical differences at p < 0.05 according to DMRT. FW—fresh weight; DW—dry weight.
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Yuniati, N.; Kusumiyati, K.; Mubarok, S.; Nurhadi, B. Assessment of Biostimulant Derived from Moringa Leaf Extract on Growth, Physiology, Yield, and Quality of Green Chili Pepper. Sustainability 2023, 15, 7113. https://doi.org/10.3390/su15097113

AMA Style

Yuniati N, Kusumiyati K, Mubarok S, Nurhadi B. Assessment of Biostimulant Derived from Moringa Leaf Extract on Growth, Physiology, Yield, and Quality of Green Chili Pepper. Sustainability. 2023; 15(9):7113. https://doi.org/10.3390/su15097113

Chicago/Turabian Style

Yuniati, Nita, Kusumiyati Kusumiyati, Syariful Mubarok, and Bambang Nurhadi. 2023. "Assessment of Biostimulant Derived from Moringa Leaf Extract on Growth, Physiology, Yield, and Quality of Green Chili Pepper" Sustainability 15, no. 9: 7113. https://doi.org/10.3390/su15097113

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