Shade as an Agro-Technique to Improve Gas Exchange, Productivity, Bioactive Potential, and Antioxidant Activity of Fruits of Hylocereus costaricensis

Abstract

Hylocereus species are promising for enhancing fruit productivity in arid regions, but high solar radiation often leads to yield loss. This study aimed to evaluate the short-term impact of different shading levels on the physiological performance, productivity, and post-harvest quality of Hylocereus costaricensis under semi-arid conditions. Plants were grown in the field under two shade levels, i.e., 35 and 50% and their performances were compared to plants under control, i.e., 0% of shade or full sunlight. The nighttime CO₂ assimilation and productivity increased significantly by 310.5 and 114.6% and 34.3 and 50.14% for plants under 35 and 50% of shade, respectively, compared to the control. A Principal Component Analysis (PCA) revealed that shade enhanced skin betalain (BETS) and phenolic content (PETP), whereas non-shaded plants expressed traits more closely associated with plant and fruit photoprotective pigment synthesis, i.e., total carotenoids and yellow flavonoids, respectively, along with total sugar accumulation, underscoring the significant impact of shading on both metabolic activity and overall agronomic outcomes. Shading within the 35% to 50% range is effective to cope with high solar radiation by improving photosynthetic capacity, productivity, and post-harvest quality, especially regarding the accumulation of pigments such as betalains, indicating that shade as an agro-technique is a valuable approach for the cultivation of Hylocereus species in dryland regions.

1. Introduction

The agronomic interest in Hylocereus, known as pitaya or dragon fruit, has soared over recent decades [1]. These species have increased popularity due to their very attractive-looking fruits and their keen effects on human health, which are attributed to their high levels of vitamins, minerals, and bioactive content and antioxidant activity [2,3,4,5]. Hylocereus sp. fruits are valued not only for productivity but also for their rich profile of bioactive compounds, including betalains (betacyanins and betaxanthins), phenolic acids, flavonoids, carotenoids, and significant total antioxidant activity via FRAP, measures the antioxidant potential of a sample based on its ability to reduce ferric (Fe³⁺) to ferrous (Fe²⁺) ions and DPPH assays [6,7,8,9,10]. Metabolic profiling has revealed substantial quantities of soluble sugars—primarily glucose and fructose—and organic acids in pulp and peel, which correlate positively with pigment accumulation, especially betalains [6,7,8,9,10].

Hylocereus species are native to the shaded and warm-humid areas of the Americas [11]. These species have made a valuable contribution as exotic fruit crops wherever water is scarce due to their Crassulacean acid metabolism (CAM), a photosynthetic adaptation which allows them to withstand severe dry conditions due to the nighttime CO₂ assimilation (the stomata open during the night when the air temperature is lower and relative humidity is higher) [12]. The demand for pitaya fresh fruit has increased throughout the years, and its high profitability has encouraged more farmers worldwide to venture into this crop [1]. Orchards in dryland areas are challenged by high temperatures and solar radiation, which trigger several stress factors, resulting in damage to Hylocereus plants, such as sunburn and impairment in CO₂ assimilation and maximum quantum efficiency of photosystem II (Fv/Fm) [13]. These stresses can potentially affect both fruit yield and quality [14]. This requires a series of adaptations beyond a higher total chlorophyll content, including: smaller chloroplasts; a higher thylakoid/stroma volume ratio; and additionally, a higher chlorophyll a/b ratio and a more extensive electron transport chain [15].

The influence of different light conditions results in adjustments associated with the levels of photosynthetic pigments. In the photosynthetic process, light is first absorbed by active photosynthetic pigments found in chloroplasts—chlorophylls and carotenoids. These pigments absorb light, facilitating the transfer of light energy that triggers CO₂ fixation and carbohydrate production [16]. Chlorophyll a is present in all organisms that perform oxygenic photosynthesis; chlorophyll b is synthesized through the oxidation of the methyl group in chlorophyll a into an aldehyde group and, together with carotenoids and phycobilins, constitutes the so-called accessory pigments. Carotenoids, tetraterpenoid chemical substances, may assist in the absorption and transfer of radiant energy, as well as in protecting chlorophyll from photo-oxidation when the light intensity exceeds the plant’s threshold [17].

A suitable strategy for counteracting the extreme solar radiation in dragon fruit arises from the use of shading cloths, which reduce the solar radiation by attenuating the maximum daytime air and soil temperatures [14,18]. However, the effectiveness of this agro-technique depends on the degree of shade, genotype, and growing conditions [19,20].

The use of shade to reduce plant damage from excessive radiation in Hylocereus has been addressed, but mostly concerning plant morphology and physiology [18,21]. In previous work, our research group evaluated shading (0, 35, 50, 65, and 80% of shade) as a strategy for coping with high solar radiation in the red pitaya (Hylocereus costaricensis). Through a long-term field experiment under the semi-arid conditions of Brazil, we found that shade significantly improved plant growth and physiological performance of red pitaya. Specifically, shaded plants improved Fv/Fm and total chlorophyll content, with no signs of photoinhibition or sunburn vs. plants under full sunlight. Despite these promising results, substantial knowledge gaps remain, particularly on the ecophysiological responses, productivity, and fruit post-harvest attributes, especially on the bioactive potential and antioxidant activity of Hylocereus fresh fruits, under shade conditions compared to cultivation under high solar radiation [14].

While shading has been proposed as a beneficial strategy for cultivating Hylocereus species, most studies—including our previous work [14,18,22]—have focused on long-term physiological and agronomic outcomes. However, a detailed understanding of how short-term shading influences plant physiology, productivity, and post-harvest fruit quality, particularly during the first harvest, remains limited. This study addresses that gap by examining the short-term effects of shading on Hylocereus costaricensis (H. costaricensis) under semi-arid conditions, with a focus on commercially relevant traits such as fruit bioactive compounds and antioxidant activity.

The early production stage is of practical significance to growers, as first-year fruits—despite typically being smaller and less developed than those from later seasons—are still marketed to help start recovering initial production costs. While previous research has noted improvements in fruit size and pulp quality over time, there is limited information on how early shading interventions may influence key attributes, especially bioactive compound content and antioxidant activity of fruits during the first harvest. Therefore, the aim of this study was to evaluate the impact of different shading levels (35%, 50%, and full sunlight) on the gas exchange, productivity and post-harvest quality of H. costaricensis in semi-arid Brazilian conditions, with a focus on improving photosynthetic performance, productivity, bioactive potential and antioxidant activity of fruits, while mitigating stem sunburn and enhancing overall plant performance under high solar radiation. We hypothesized that the short-term cultivation of H. costaricensis under different shading levels improves physiology, productivity, and post-harvest quality of fresh fruits, as well as prevents stem sunburn.

2. Materials and Methods

2.1. Plant Material and Growing Conditions

The study was conducted at the Center of Agricultural Sciences of the Federal University of Ceará, Horticulture Sector of the Plant Science Department (3°43′02″ S and 38°32′35″ W) in Fortaleza, Ceará State, Brazil. The local climate is an Aw type, which stands for tropical rainy according to Köppen’s classification [23].

Red pitaya [H. costaricensis (F.A.C. Weber) Britton & Rose; clone number 99005] plants [14] were acquired from the Brazilian Pitaya nursery, Tomé-Açu, Pará, Brazil. The plants were initially grown at 25/20 °C day/night at air temperature in a greenhouse for over ten months. Vegetative propagation was carried out by taking 30 cm of mature stems from donor plants, which were previously left to heal for 30 days, and were then placed in 2-L pots filled with soil, clay and organic material (1:1:1). Plants were grown under greenhouse conditions with a light intensity of 550 μmol photons m⁻² s⁻¹ for 150 days, maintained at full soil field capacity (previously verified for water stress avoidance) of 250 mL pot⁻¹ day⁻¹. After rooting, the plants were transferred to the open-field conditions in Red-Yellow Argisol [14], spaced 3 m between rows and 1 m within rows.

Monthly climatic records were obtained from the Meteorological Station at the Federal University of Ceará in Fortaleza, Ceará State, Brazil. Photosynthetically active radiation (PAR, μmol m⁻² s⁻¹) was obtained using a quantum sensor (model LI-190SA, LI-COR Inc., Lincoln, NE, USA) connected to a data logger (model CR10X, Campbell Scientific, Logan, UT, USA). During the experiment, readings were taken from 6 a.m. to 6 p.m. in full sunlight. Climatic conditions during the trial were as follows: 26 °C monthly average temperature; 74% monthly average relative humidity (RH); 1200–1400 mm annual average rainfall (with over 80% during February to May), and 1377 μmol m⁻² s⁻¹ monthly average PAR (20% of PAR from February to May).

Mineral fertilization was carried out monthly according to Almeida et al. [24] and Corrêa et al. [25]. In the field, 13 L plant⁻¹ week⁻¹ were applied by drip irrigation [20,26,27]. During the rainy season (December to May), plants were irrigated every two to three days.

2.2. Experimental Design and Shade Conditions

The experiment was designed in a completely randomized block design (RCBD), with four replicates, each consisting of two plants per plot. To minimize edge effects, two border plots (two plants per plot) were positioned both within the rows between shading nets and along the edges of the experimental rows, ensuring that the plants used for measurements were surrounded by neighboring plants and thus experienced uniform light and microclimatic conditions.

Plants were grown for 18 months at two shade levels, i.e., 35 and 50% and their performances were compared to plants under control, i.e., full sunlight.

Light interception was established according to the black shade net manufacturer (AMC agricultural and decorative screens S.A., Athens, Greece), an effective light scattering net. Based on the PAR at full sunlight (1377 μmol m⁻² s⁻¹), the PAR rates for 35 and 50% shading were 895 and 689 μmol m⁻² s⁻¹, respectively. The shade cloths were installed in a trellis-based production system (arbor-type) according to Oliveira et al. (2021) [14].

2.3. Physiological Performance

2.3.1. Nighttime CO₂ Assimilation

Nighttime CO₂ assimilation (A; μmol CO₂ m⁻² s⁻¹) was assessed with an infrared portable gas analyzer—IRGA (ADC, Bioscientific Ltd., Hoddesdon, UK). The analysis was performed on healthy and vigorous stems of thirteen-month-old plants. Readings were obtained from 02:00 a.m. to 04:00 a.m., due to Hylocereus’ CAM metabolism. This time was defined as the maximum period of CO₂ fixation in the plant in previous monitoring tests performed by our research group [18].

2.3.2. Total Carotenoids

To determine total carotenoids, 100 mg of fresh stem tissues (removed from the middle section of mature stems) were used. Samples were stored in 1 mL of 99% ethanol in a dark room for 48 h at 4 °C, then centrifuged at 14,000× g for 15 min. Total carotenoid content was determined spectrophotometrically at A₄₇₀ in 200-μL samples of supernatant. The absorbance values were used to calculate total carotenoid content as described by Wintermans and De Mots [28], and total carotenoids were determined in percentage based on the content of total photosynthesizing pigments.

2.4. Productivity Estimation

The fruits were monitored and harvested when fully ripe (red skin color), approximately 25 days after anthesis. The productivity was determined by the arithmetic mean of the mass of fruits obtained in each plot, expressed in grams (g), measured with a semi-analytical scale.

2.5. Post-Harvest Evaluation

Fruits with total mass from 150 to 400 g, based on the classification of local farmers (described in detail by Oliveira et al. [14]), were used for the post-harvest evaluation.

Fruits were harvested in the early morning and sent to the Brazilian Agricultural Research Corporation, Tropical Agroindustry (EMBRAPA/CNPAT), Fortaleza, Brazil, where they were sanitized with neutral detergent and water and dried with a paper towel for further post-harvest evaluation.

Bioactive potential and antioxidant activity were assessed. For that, a total of 12 fresh fruits were considered per treatment (n = 4 biological replicates; three fruits were harvested from each repetition or biological sample, i.e., the minimum number of fruits that could be harvested homogeneously, in all treatments). This approach was applied consistently across all traits. The fruits were cut lengthwise, and the pulp (endocarp) was separated from the skin (exocarp + mesocarp) and the seeds. For the physico-chemical analysis, the fruits used for the physical evaluations were processed, using the endocarp without seeds from each fruit (n = 4 biological replicates; the three fruits were pooled thoroughly and considered to be one independent biological repetition) [14].

2.5.1. Total Soluble Sugars

Total soluble sugars (%) were determined by the Antrona method, according to Yem and Willis [29].

2.5.2. Bioactive Potential and Antioxidant Activity

Total anthocyanins and yellow flavonoids of the pulp (mg 100 g⁻¹ fw) according to Francis [30], with modifications. Betalain (betacyanin) content of the skin and pulp (mg 100 g⁻¹ of fw) according to Lim et al. [31], with modifications. Total extractable polyphenols (mg 100 g⁻¹ of fresh weight, fw), according to Larrauri et al. [32] with modifications. The ferric reducing antioxidant power (FRAP) method was carried out as described by Benzie and Strain [33] with modifications. The results were expressed as μmol Fe₂SO₄ g⁻¹ fw.

2.6. Statistical Analysis

Statistical analyses were performed in R (version 4.5.0) [34] and the libraries ggplot2 [35], multcompView [36] and dplyr [37] [MO4.1] were used. The effects of shade treatments on the response variables, nighttime CO₂ assimilation (A), total carotenoids (TC), productivity, total soluble sugars (TSS), bioactive potential, i.e., pulp anthocyanins (ANT); pulp yellow flavonoids (YF); pulp betalains (betacyanin) (BETP); skin betalains (BETS); pulp total phenolics (PETP); skin total phenolics (PETS) and total antioxidant activity by the FRAP method of the pulp (FRAPP) and skin (FRAPS) were examined using a one-way ANOVA. Post hoc Tukey-HSD test was used to perform comparisons between treatments and significant differences (p < 0.05) are displayed with different letters in the figures. The integration of gas exchange, productivity and post-harvest quality responses was explored with Principal Component Analysis (PCA) using the packages FactoMineR [38] and factoextra [39].

3. Results

A significant effect of shading treatments was observed on CO₂ assimilation, total carotenoids, productivity, total soluble sugars, pulp yellow flavonoids, skin betalains (betacyanin), and total phenolics. The antioxidant activity (FRAPP and FRAPS) was not influenced by the shade (

Table 1. ANOVA results for nighttime CO₂ assimilation (A), total carotenoids (TC), productivity, total soluble sugars (TSS), bioactive potential and antioxidant activity of fruits, i.e., pulp anthocyanins (ANT); pulp yellow flavonoids (YF); pulp betalains (betacyanin) (BETP); skin betalains (BETS); pulp total phenolics (PETP); skin total phenolics (PETS) and total antioxidant activity by the FRAP method of the pulp (FRAPP), and skin (FRAPS).

Traits	DF	F	p-Value
Physiological performance
A (µmol m−2 s−1)	2	5.517	0.0437 *
TC (%)	2	7.046	0.0266 *
Productivity
PROD (g)	2	5.859	0.0388 *
Physico-chemical evaluation
TSS (%)	2	24.26	0.0013 **
Bioactive compounds
ANT (mg 100 g−1 fw)	2	1.586	0.2800 ns
YF (mg 100 g−1 fw)	2	10.55	0.0109 *
BETP (mg 100 g−1 fw)	2	0.705	0.5310 ns
BETS (mg 100 g−1 fw)	2	91.25	0.0001 ***
PETP (mg 100 g−1 fw)	2	2.861	0.1340 ns
PETS (mg 100 g−1 fw)	2	5.196	0.049 *
Antioxidant activity
FRAPP (μmol of Fe2SO4 g−1 fw)	2	0.556	0.6000 ns
FRAPS (μmol of Fe2SO4 g−1 fw)	2	0.302	0.7500 ns

Statistically significant effects are in bold. DF, degrees of freedom. *, significant at 0.05 level; **, significant at 0.01 level; ***, significant at 0.001 level; ns, no significant difference.

).

Nighttime CO₂ assimilation and productivity revealed significant increases of 310.5 and 114.6% and 34.3 and 50.14% for plants under 35 and 50% of shade, respectively, compared to plants exposed to full sunlight (Figure 1A,B).

The average yellow flavonoids showed a large significant increase (74.8%) under sun exposure (9.88 mg 100 g⁻¹) vs. 50% shade (5.65 mg 100 g⁻¹), as well as an increase of 43.3% under 35% of shade (8.10 mg 100 g⁻¹) vs. 50% shade (Figure 1C).

The average betalain (betacyanin) content of the skin showed increases of 87.6 and 101.7% under 35 and 50% shade compared to fruits exposure to the sunlight (123.43 and 132.70 mg 100 g⁻¹ vs. 65.81 mg 100 g⁻¹, respectively) (Figure 1D).

The average total polyphenols in the skin increased by 21.4% under full sunlight (50.02 mg 100 g⁻¹) vs. average across both shade conditions (41.19 mg 100 g⁻¹ fw) (Figure 2). TSS was significantly affected by shade by showing an average increase of 32.6% compared to the average across both shade conditions. The average total carotenoids increased by 1 and 2.4% under full sunlight vs. 35 and 50% shade (Figure 2).

The PCA conducted on the CO₂ assimilation, production, and post-harvest traits explained 63.4% of the total variation across the first two axes (Figure 3). PC1 (42.2%) primarily separated plants under full sunlight (0% shade) from those under 35% and 50% shade. Traits such as BETS, A, PROD, and PETP loaded positively on PC1 and were strongly associated with shaded plants, while YF, TSS, and TC loaded negatively and were linked to plants grown under full sunlight. This indicates that shading enhanced nighttime CO₂ assimilation (A), productivity (PROD), betalain (BETS), and phenolic content (PETP), whereas non-shaded plants expressed traits more closely associated with plant and fruit photoprotective pigment synthesis, i.e., TC and YF, respectively, as well as sugar accumulation (TSS).

PC2 (22.1%) further differentiated the shaded treatments, with PETP, YF, and PROD contributing positively, while BETP, ANT, and PETS contributed negatively. The biplots exhibited a clear separation of shade levels in three categories corresponding to shade levels (0%, 35%, 50%), showing positive contributions of all global traits in explaining the variability when exposed to the treatments.

4. Discussion

The findings of this investigation show that the use of shade improved the overall photosynthetic performance, productivity, and bioactive potential in H. costaricensis. Our strategy to cope with high solar radiation using shading cloths is indeed valuable for dryland regions such as the Northeast semi-arid of Brazil.

This study focused on the short-term impact (first harvest) of shading on H. costaricensis grown under a semi-arid environment. One of the main reasons for investigating the short-term effect of shading on dragon fruit is its practical relevance to farmers: although these early fruits are often smaller and lighter, with size and pulp characteristics improving in subsequent seasons [40], first-harvest fruits are still sold commercially to help offset growers’ first-year investments. We aimed to examine whether a brief shading treatment could alter key traits, particularly the bioactive compounds and antioxidant activity, in those initial fruits.

The use of shade in pitaya cultivation has been investigated in both short and long-term studies. However, to date, the majority of these experiments have been conducted under controlled environments, such as in nethouses [21] or using potted plants in the field [18]. Building upon this foundation, our investigation was carried out under open-field conditions. The specific shade treatments of 35% and 50% were selected based on a prior long-term study by our research group, which demonstrated this range to be optimal for red pitaya in the semi-arid region of Brazil [14]. A critical unanswered question was whether the short-term cultivation of H. costaricensis under these shading levels in an open-field system would improve physiological performance, productivity, and post-harvest quality.

In our study, the recorded PAR under full sunlight (≈1377 μmol m⁻² s⁻¹) far exceeds the natural conditions for Hylocereus spp., which thrives in the understory of tropical forests with an irradiance around 500 μmol m⁻² s⁻¹, making protection from direct solar radiation necessary for cultivation [27,41]. Our data confirm that this high radiation exceeds the species’ tolerance, as demonstrated by the photoinhibition and sunburn in control plants. In contrast, the PAR levels under 35% and 50% shading (895 and 689 μmol m⁻² s⁻¹, respectively) successfully mitigated this stress. The resulting environment, particularly under 50% shade (≈689 μmol m⁻² s⁻¹), which is closer to the species’ natural optimum, proved to be highly effective, yielding the highest productivity and improved fruit quality.

Taking into consideration their natural shaded environment, the optimal photosynthetic photon flux (PPF) for maximum total daily net CO₂ uptake in H. undatus is only 23 µmol m⁻² s⁻¹, while above 231 mol m⁻² s⁻¹, photoinhibition may reduce net CO₂ and yield [14,18,42]. In Yucatán, Mexico, the ideal microenvironment for H. undatus consists of a reduction of between 48 and 36% in the PPF, resulting in increases in both growth (66%) and photosynthetic rate (36%) when compared to plants grown without the use of a radiation protection system [43]. In Israel, pitayas perform better under shade (20% to 60% shade [21]), as high solar radiation of about 2200 µmol m⁻² s⁻¹ in the summer, along with air temperatures above 40 °C, leads plants to collapse and die [20].

This study revealed that the use of moderate shading (35% and 50% shade) in the Northeast semi-arid of Brazil enhanced the short-term nighttime CO₂ assimilation and fruit production, likely because reduced solar radiation and heat stress mitigated the constraints on photosynthesis that typically would impair productivity under high solar radiation [44]. Our results align with findings from Almeida et al. (2018) [18], who demonstrated that red pitaya grown for 180 days under similar experimental conditions (except for pot cultivation) experienced compromised gas exchange and reduced growth in full sunlight, whereas plants under 35% shade exhibited improved photosynthetic rates, water-use efficiency, carboxylation efficiency, and vegetative growth.

Although moderate shading can be beneficial, heavier shade (60–80%) is known to induce flowering and fruit abortion in pitaya and even inhibit net CO₂ assimilation in Opuntia ficus-indica after just 15 days of shading [45,46]. Excessive shading (80%) can increase the thickness of the epidermis-hypodermis to capture scarce light, which reduces overall light capture and potentially plant growth pitaya [14,18]. It is important to note that our study assessed the effect of continuous shading from planting to first harvest but did not focus on the impact of shade on crop phenology. Future research should investigate how shading applied selectively during different phenological stages (e.g., flowering vs. fruit development) affects productivity and fruit quality, as this could lead to more efficient and cost-effective shade management strategies for growers.

In this study, fruits under full sunlight showed high yellow flavonoid content in the pulp, which might be associated with a strategy to avoid photooxidative stress [17]. Some stems of the plants under full sunlight showed a yellowish color; however, the fruits did not show visual differences. Our findings are in agreement with Cohen and Kennedy [47], who report a positive correlation between the increase in solar radiation and the production of flavonoids, which in turn are accumulated and used as UV filters to protect against plant photodamage. It has been reported that H. costaricensis contained the highest levels of yellow flavonoids, averaging 6.03 mg 100 g⁻¹; in contrast, our study revealed concentrations nearly 10 times greater than those observed in S. megalanthus (1.89 mg 100 g⁻¹), suggesting a stronger photoprotective response from the non-shaded plants, likely enabling more effective mitigation of excess light intensity and oxidative stress [48].

Our investigation showed that 50% shade led to marked accumulation of betalain (betacyanin) in the skin is in line with Chang et al. [49] who reported to 50% shade a significant increase of the total accumulation of betacyanin in the pulp of the fruits. These studies highlight that shading may be associated with fruit maturation, and thus hastens the formation of betacyanin in the pulp, whereas our investigation found it also in the skin.

UV-B radiation is linked to CO₂ assimilation by the rate at which the carbon skeleton is diverted from the primary metabolism to the secondary one [48,50]. The accumulation of polyphenols leads to the protection against solar radiation, being used as UV filters, similar to yellow flavonoids, since it includes a class of polyphenols of plant origin [51]. This group of substances is mostly concentrated in fruit skin and seed [52]. Natural polyphenols are highly effective in mitigating oxidative stress [48,53], particularly under conditions of intense solar radiation, by dissipating excess UV energy and neutralizing free radicals generated by light stress. Therefore, the observed increase in total polyphenols in the skin of red pitaya fruits is likely an adaptive photoprotective response to high solar radiation. Rather than considering polyphenols in isolation, they can be viewed as part of the plant’s coordinated response to light stress, a pattern that is reflected in the grouping of traits revealed by the PCA analysis.

PCA conducted on the gas exchange, production, and post-harvest traits revealed that varying shade levels led to noticeable and consistent changes in both plant physiology and post-harvest traits. All measured characteristics played a positive role in accounting for the observed variation, underscoring the significant impact of shading on both metabolic activity and overall agronomic outcomes. PCA outlined two distinct metabolic strategies: under shading, resources were allocated towards skin betalain and phenolic content, whereas full sunlight induced a shift towards photoprotective compounds, namely total carotenoids and yellow flavonoids, and elevated sugar levels. This clear separation underscores the significant impact of light regime on defining fruit metabolic activity and resultant agronomic quality. The elevated sugar concentration in smaller, sun-exposed fruits can be interpreted as a biomarker of physiological stress, not a direct quality enhancement, per se. This aligns with a common plant defense mechanism, where plants under stress trigger the accumulation of compatible solutes such as sugars and protective secondary metabolites such as carotenoids and flavonoids [54]. The increase in pigments and reduction in fruit size under full sun further support this stress-induced resource reallocation. While the intricate relationship between light stress and metabolite partitioning warrants deeper investigation, it lies beyond the scope of this study.

Our strategy to cope with high solar radiation by shading to improve photosynthetic capacity, productivity, and post-harvest quality was highly effective. The results demonstrate that for the short-term cultivation of H. costaricensis under semi-arid conditions, an optimal shading range of 35% to 50% significantly improved photosynthetic performance, yield, and key fruit quality attributes—most notably the accumulation of betalains—compared to full sunlight.

The current investigation sheds light on scientific gaps regarding the responses of Hylocereus species to high solar radiation in open-field conditions, showing that shading strategy can indeed be used to enhance photosynthetic capacity, productivity, and post-harvest aspects in dryland regions.

5. Conclusions

The present study reports the efficacy of the shading technique for field cultivation of H. costaricensis under dryland agriculture. Overall, the use of shading within the 35% to 50% range in red pitaya effectively mitigated harsh solar radiation in field conditions, leading to substantial increases in nighttime CO₂ assimilation (up to 310.5% under 35% shade), higher fruit productivity (up to 50.1% under 50% shade), and enhanced post-harvest quality through greater skin betalain and phenolic accumulation, while unshaded plants prioritized carotenoid and yellow flavonoid synthesis for photoprotection. Therefore, further investigations of the shade responses of red pitaya, as well as some other Hylocereus species, based on morpho-physiological, biochemical, and molecular approaches, are needed to better understand their adaptive mechanisms, optimize cultivation practices, and enhance their resilience to environmental stresses.