Introduction

Cacao (Theobroma cacao L.) is a dicotyledonous plant in the Malvaceae family, native to the Amazon rainforest and dispersed throughout the humid tropical forests of South and Central America1,2. Cacao is cultivated in many countries and is of significant economic and social importance worldwide. However, as the productivity of current cacao plantations stagnates or declines and global demand for cacao products increases, there is growing pressure to clear tropical primary forests to make way for new cacao plantations3,4. Until recently, the price of cocoa fluctuated around $2,500 per metric ton. In recent months, the expectation of a sharp drop in global cocoa production has driven the price to an all-time high of over $12,000 per metric ton in April 2024. To address these issues, increasing cacao productivity is essential.

The production of chocolate, one of the main cacao products, will mobilize about US$133 billion in 2024, and this market is expected to grow annually by 4.7%5. In addition, cacao is crucial for the cosmetics industry and other food industries4,6. World cacao production is projected at 4,598,000 tons, while grinding is expected to reach 5,072,000 tons7. Brazil is the seventh-largest producer of cacao globally. In the 2022 crop season, Brazil harvested approximately 290,000 tons of cacao beans on nearly 600,000 hectares of cultivated area. Cacao is mainly grown in five Brazilian states: Pará, Bahia, Espírito Santo, Rondônia, and Amazonas. Pará (50.3%) and Bahia (43.4%) are the main cacao producers. Espírito Santo contributes with 4% to the Brazilian production, about 12,000 tons of beans8. Cacao is the second most cultivated fruit tree in the state, and the city of Linhares is the largest state producer9.

Cacao is traditionally grown under natural shade in the understory of tropical forests4,10,11,12. Some advantages of this production system include less modification of the natural environment, higher humidity, lower light incidence, more moderate temperatures, and less environmental variations11,13, which helps maintain greater stomatal openness and, when light is not limiting, higher photosynthetic rates13. Another important benefit of cacao agroforestry is climate change mitigation, as it stores 2.5 times more carbon than cacao monoculture12. However, high humidity in shaded environments such as the cacao agroforestry system favors the proliferation of pathogens14. The fungus Moniliophthora perniciosa stands out, causing witches’ broom, the main disease of the crop, responsible for significant economic and social impacts in the cacao-growing regions of the states of Bahia and Espírito Santo15,16.

In addition to the high incidence/severity of witches’ broom in shaded cacao agroforestry, which in many cases makes the system infeasible, there is also the complex shade effect. Although cacao is a typical shade-tolerant species17, low light intensity in cacao agroforestry reduces its yield1 up to 25%12. For many years, general practice was to grow cacao under shade of other trees, but there has been a trend towards reducing shade on cacao farms as higher light levels have been associated with increased yields18. However, yields have also been reported to decline faster in these conditions19, particularly where no fertilizer is used18. Canopy cover up to 30–40% has been shown to increase bean yields in Ghana compared to cacao grown in full sun20, but increasing shade above this level can limit yields21,22. In turn, in Cameroon, increasing canopy cover up to 47% enhanced yield, but greater than 60% cover caused yield limitations23. It is important to keep in mind that the combination of high temperature and water deficit causes a reduction in photosynthesis, growth and water use efficiency in cultivated cocoa trees24. There is therefore increasing interest in growing this species in full sun25,26,27, and some studies have shown that yield responds positively to increases in light28,29, particularly where fertigation is used29.

In Brazil, cacao grown under full sun yields more than 3,500 kg/ha/year29, up to eight times more than under shade, making this system very appealing. Ten Hoopen et al.30 advocate the cultivation of cacao and coffee in agroforestry systems to reconcile food production in climate change scenarios. However, the traditional cacao-based agroforestry system in Brazil8and Côte d’Ivoire31 has an average annual yield of 430 kg/ha and 207.7 kg/ha, respectively, much lower than in full sun crop. Thus, full sun cacao farming and cacao-based agroforestry system are not mutually exclusive. Indeed, they can coexist; where technological and financial conditions exist, full sun cacao farming should be implemented.

Plant survival is known to be directly related to the regulation of the photosynthetic process, which is directly influenced by available light32. Thus, understanding the effects of light intensity on the photosynthetic process and the responses of plants to variations in environmental conditions can ensure their proper development and survival33. Responses to increased light intensity can occur either at the leaf level, involving acclimatization of the photosynthetic machinery, or at the whole plant level, resulting in changes in growth patterns and allocation of photoassimilates34. Cacao exposed to higher light intensities is expected to increase its CO2fixation rates, resulting in positive changes in its yield components35. Radiation stress is expected to affect cacao genotypes differently. Suárez et al.36, evaluating three levels of radiation on water status and gas exchange in five cocoa clones, reported that some clones acclimatized to full sun conditions. This finding may be due to the greater efficiency of carbon use, with maximization of photosynthetic rates combined with greater efficiency of energy dissipation mechanisms.

Leaf traits are crucial for understanding plant growth and acclimation mechanisms. They are strong indicators of plant performance, both in full sun and in the forest understory. High growth in full sun is favored by cheap, short-lived, and physiologically active leaves37. Traits like leaf size, shape, thickness, and chemical composition reflect a plant’s adaptation to its environment and its resource-use strategies38. Plants can adjust their leaf traits in response to environmental changes through acclimation. For instance, a high specific leaf area indicates a thin, large leaf, which maximizes sunlight interception for photosynthesis, especially in resource-rich environments. A high leaf mass per area suggests a thicker, denser leaf, often associated with resource-conservative strategies like water and nutrient conservation. Stomatal density and conductance influence water loss through transpiration; low stomatal density and conductance help plants conserve water in arid environments. Some leaf shapes, like those with deeply lobed margins, can increase heat dissipation. Chemical compounds produced by plants can deter herbivores and pathogens.

Additionally, understanding the characteristics of the fruits and seeds of clones in this new cultivation system is essential for genetic breeding. The composition of production factors may be related to the distribution of photoassimilates or to the final product quality, such as seed weight and seed weight per fruit39. For the success and consolidation of this new cropping system, it is crucial to understand the behavior of the clones in order to manage them properly. Therefore, we hypothesized that physiological components might respond differently in cacao clones grown in the full sun system, which could translate into higher yields. To test this hypothesis, we analyzed physiological and agronomic traits in cacao clones commercially grown in full sun and fertigated.

Materials and methods

Clones, trial, and growing conditions

The trial was conducted at Fazenda Três Lagoas (lat 19° 17’ 28.3” S, long 40° 10’ 13.3” W, 75 m alt asl), located in Linhares, state of Espírito Santo, Brazil. Fluvic Cambisol is the predominant soil type in the region40. Based on historical climate data for Linhares (collected between 1985 and 2022), the city has a humid tropical climate (Köppen classification Aw; Alvares et al.41), characterized by dry winters and rainy summers. The average annual temperature is 24.5 °C, with a maximum of 29.5 °C and a minimum of 20.5 °C. The average annual rainfall is 1,400 mm. The rainiest and driest months are November (162 mm) and June (27 mm), respectively. The average number of rainy days per year is 158, with November (22 days) and June (6 days) being the most and least rainy months. The annual average of sunshine hours is 2,600, with December (290 h) and June (130 h) having the highest and lowest sunshine hours.

We monitored the climate using data on rainfall, radiation, and temperature collected from a meteorological station (E 5.000/IRRIPLUS model) near the trial site. During the trial period, the average annual temperature ranged from 21.51 °C (July) to 29.60 °C (September) (Fig. 1). Regarding rainfall (Fig. 1), the highest rainfall occurred in spring (37%) and summer (31%), while the lowest was in autumn (23%) and winter (9%), resulting in a wetter main cropping season and a drier intercropping season. Data on solar radiation in Linhares for 2018 showed that June had the lowest radiation (15.57 MJ/m²/day), while January and February had the highest solar index (ranging from 22.32 to 22.42 MJ/m²/day, respectively) (Fig. 1).

Fig. 1
figure 1

Data of mean temperature (A), rainfall (B) and solar radiation (C), regarding year 2018 in the municipality of Linhares, Espírito Santo, Brazil.

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We conducted our trial between February 2018 and February 2019, covering both the off-season (May to June) and the main harvest season (October to January) of cacao cultivation at Fazenda Três Lagoas. We studied six cacao clones (PS 1319, CCN 10, CCN 51, PH 16, SJ 02, and CP 49; see Table 1) that had been planted on the farm eight years prior. These clones were spaced 3.5 m x 2.5 m, fertigated by drip irrigation, and grown in a full sun cropping system. Since the crop was already established in the area, the implementation of a classic conventional design was not possible. Instead, we randomly assigned 14-plant plots to each of the six clones.

Table 1 Agronomic characterization of the six cacao clones from two sources, which were grown in full sun.
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Leaf gas exchanges (A, g s, E,  Ci, Vpd L, A/E, and F v/F mratio)

We simultaneously measured leaf gas exchange parameters using a portable open-flow gas exchange system (LI-6400XT; Li-Cor Inc., Lincoln, NE) equipped with an integrated fluorescence chamber head (LI-6400-40; Li-Cor Inc.). The following parameters were measured on the third fully expanded leaf from the apex of the orthotropic stem: The CO2 assimilation photosynthesis (A, µmoL/m2/s), stomatal conductance (gs, moL/m2/s), transpiration (E, mmoL/m2/s), internal CO2 concentration (Ci, µmoL/moL) in the leaf mesophyll, leaf-to-air water vapor pressure deficit (VpdL, kPa), and water use efficiency (A/E, [(µmoL/m2/s)/(mmoL H2O m2/s)]). We sampled one leaf per plant from six randomly selected plants (n = 6) within each 14-plant plot, between 9:00 and 11:00 AM (solar time). For each leaf, we measured A under saturating photon flux density (PPFD) of 1,000 µmoL/m/s, with the leaf chamber set at a CO₂ concentration of 400 µmoL/moL, temperatures of 25 ± 1 °C (intercrop season) and 28 ± 1 °C (main crop season), and vapor pressure deficit maintained at approximately 1.0 kPa.

We calculated maximum quantum efficiency (Fv/Fm = [(Fm – F0)/Fm)]) on leaves that were previously dark-adapted for 60 min. Leaf tissues were illuminated with weak, modulated measuring beams (0.03 µmoL photons/m²/s) to obtain initial fluorescence (F0). Saturating white light pulses of 8,000 µmoL photons/m²/s were applied for 0.8 s to ensure maximum fluorescence emissions (Fm)42. We conducted off-season evaluations on July 26, 2018, and main crop season evaluations on November 26, 2018.

Chloroplastidic pigment content (Chl T, Chl a/b and Chl T/Car)

Chlorophyll content was determined using the method proposed by Lichtenthaler43. For each clone, we sampled one leaf of every seven plants randomly selected (n= 7), within the 14-plant plot. These leaves were quickly frozen in liquid nitrogen and stored at −80°C. In the lab, we extracted chlorophyll from 2 g of fresh leaf tissue by macerating the leaves in a mortar with 7 mL of 80% acetone and a bit of sand in a dark chamber. The resulting extract was filtered, stored in volumetric flasks wrapped in aluminum foil to protect it from light, and then diluted to 25 mL with 80% acetone. Absorbance of the extract was measured at 470, 646.8, and 663.2 nm using a Genesys spectrophotometer (model 10 S UV-Vis). Chlorophyll content, expressed in mg/L, was calculated using the formula proposed by Lichtenthaler43.

$$\:Chlorophyll\:a\:\left(Chl\:a\right)=12.25*{A}_{663.2}-2.79*{A}_{646.8}$$
$$\:Chlorophyll\:b\:\left(Chl\:b\right)=21.5*{A}_{646.8}-5.1*{A}_{663.2}$$
$$\:Chlorophyll\:a+b\:\left(Chl\:T\right)=7.15*{A}_{663.2}-18.71*{A}_{646.8}$$

We measured total carotenoid content using the same extract prepared for chlorophyll analysis. We measured absorbance at 470 nm and calculated the concentration in mg/L using a formula proposed by Lichtenthaler43. We calculated Chl a/b and Chl T/Car ratios based on the chlorophyll and carotenoid concentrations.

$$\:Total\:carotenoids\:\left(Car\right)=\frac{(\text{1,000}*{A}_{470}-1.82*Chl\:a-95.02*Chl\:b)}{198}\:\:$$

Specific leaf area (SLA) and Stomatal density (SD)

For each clone, we collected eight leaves from eight randomly selected plants (n = 8), within 14-plant plot. We measured leaf area (LA) using a LI-COR 3100 C LA meter with a high-resolution laser scanner. After drying the leaves at 65 °C for 72 h, and weighing them, we calculated specific leaf area (SLA) as the ratio of leaf area (LA, cm²) to dry mass (DM, g).

$$\:SLA=\frac{LA}{{DM}_{leaves}}$$

For each clone, we collected eight healthy, lesion-free leaves from eight randomly selected plants (n = 8), within 14-plant plot. We prepared these leaves by applying colorless enamel to the abaxial surface, allowing it to dry, and then transferring the leaf epidermis to a glass slide using adhesive tape. We visualized stomata under a 40x objective lens and counted them manually. Stomatal density (SD) was calculated using the following formula:

$$\:SD=\frac{Nr.\:stomata}{0.27292\:{mm}^{2}}$$

Yield and its components

We analyzed fruits and seeds between March 2018 and March 2019. For each clone, we sampled eight ripe and healthy fruits from eight randomly selected plants (n = 8) within 14-plant plot. We measured the following traits: fruit weight (FW), fruit length (FL), fruit diameter (FD), fresh shell weight (FSW), wet seed weight (WSW), number of seeds per fruit (NSF), and individual dry bean weight (IDBW). After collecting the fruits, we identified and packaged them for shipment to the laboratory. We weighed the fruits and seeds on a precision scale and measured their length and diameter with a digital caliper. We also counted the seeds and weighed the fresh fruit shells and seeds. After weighing, we dried the shells and seeds in an oven at 60 °C until they reached a constant weight to determine their dry matter mass. We evaluated bean yield throughout the main and intercropping seasons (February 2018 to February 2019). For each clone, we harvested, counted, and weighed all healthy fruits produced in the 14-plant plot. We then extrapolated the yield per plot to a hectare.

Statistical analyses

We first checked the trial data for normal distribution (Shapiro-Wilk test) and homogeneity of variance. Then, we analyzed the data using a nested classification scheme44,45, accounting for the varying number of replicates (six for photosynthetic parameters, seven for chloroplastidic pigments, eight for SLA, SD, fruits and seeds, and fourteen for bean yield). We performed one-way analysis of variance (ANOVA) for fruit and seed data, SLA, SD, and bean yield data. For leaf gas exchange and chloroplastidic pigment content data, we performed two-way ANOVA (clones and seasons). We compared the means of the clones using the Scott-Knott test (p< 0.05). We measured the association between variables using Pearson’s correlation coefficient. We used Rbio software46 for data analysis.

Ethical statement

The plant species (Theobroma cacao L.) used is a cultivated plant, and the clones evaluated are cultivated at Fazenda Três Lagoas, located in the municipality of Linhares, in the state of Espírito Santo, Brazil. We thank Vanderlei Ceolin, owner of the Três Lagoas farm, who gave us permission to carry out field research with the cultivated cacao clones. We confirm that we comply with all necessary standards for this type of research.

Results

Leaf gas exchanges (A, gs, E, Ci, F v/F m ratio, Vpd L, and A/E)

The A and gs values were higher for clones CCN 51, PH 16, PS 1319, and SJ 02, distinguishing these clones from CCN 10 and CP 49. However, no significant difference was observed for A between the two evaluation seasons (Table 2). The A and gs values showed a significant positive correlation between them (r = 0.94), as well as between A and E (r = 0.89) (Table 3). However, a significant statistical difference was observed between the two seasons for gs, and the values of the main cropping season were higher than those of the intercropping season (Table 2). Regarding E and Ci, no significant differences were observed among the clones, but there was a difference for the season of evaluation. E and Ci values of the main cropping season (2.64 moL/m2/s and 293.06 µmoL/moL) were 87.2% and 19.9% higher than those of the intercropping season, respectively (Table 2). There was a significant positive correlation between gs and E (r = 0.95) and a significant negative correlation between gs and VpdL (r=−0.81) (Table 3).

Table 2 Means of net photosynthetic rate (A; µmoL CO2/m2/s), stomatal conductance to water vapor (gs; mmoL/m2/s), transpiration rate (E; mmoL H2O/m2/s), internal CO2 concentration (ci; µmoL/moL) in the leaf mesophyll, potential quantum yield of photosystem II (Fv/Fm), leaf-to-air water vapor pressure deficit (VpdL; kPa), and efficiency of water use (A/E; [µmoL CO2/(mmoL H2O)]) in ripe leaves of six cacao clones grown under full sun.
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Table 3 Correlation coefficients (r, above) and p-values (bellow) between net photosynthetic rate (A), stomatal conductance to water vapor (gs), internal CO2 concentration (Ci) in the leaf mesophyll, transpiratory rate (E), efficiency of water use (A/E), leaf-to-air water vapor pressure deficit (VpdL), potential quantum yield of photosystem II (Fv/Fm), contents of total chlorophyll content (chl T), chlorophyll a/b (Chl a/b) ratio, chlorophyll total/carotenoids (ChlT/Car) ratio, specific leaf area (SLA; cm2/leaf dry mass), and stomatal density (SD; stomata/mm2) in ripe leaves of six cacao clones grown under full sun.
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The values of the Fv/Fm ratio did not differ significantly among the clones and seasons studied. The low variation of the values (0.78–0.79) allowed us to conclude that there was no photoinhibition in both seasons. With respect to VpdL, significant differences were observed among the clones, with CCN 10 and CP 49 having higher values than the others. Regarding the A/E ratio, there was no significant difference among the clones, but the value of the intercropping season was 80.4% higher than that of the main cropping season (Table 2). The A/E and SD values were significantly correlated (r = 0.82) (Table 3).

Chloroplastidic pigment content (Chl T, Chl a/b and Chl T/Car)

The concentrations of chloroplastidic pigments (Table 4) varied significantly between seasons for Chl T and Chl a/b, with higher values in the intercropping season. However, Chl T concentrations did not differ significantly among clones (p > 0.05) and ranged from 0.93 to 1.47 mg/g. For the Chl a/b ratio, only clone PH 16 differed from the others. Similarly, the Chl T/Car ratio also varied significantly among clones, with PH 16 showing a lower value (4.03 mg/g) compared to the others. The Chl a/b and Chl T/Car ratio were significantly correlated (r = 0.84) (Table 3).

Table 4 Means of total chlorophyll content (chl T), chlorophyll a/b (Chl a/b) ratio, and chlorophyll total/carotenoids (Chl T/Car) ratio expressed in fresh biomass (mg/g), in ripe leaves, of six cacao clones grown under full sun.
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Specific Leaf Area (SLA) and Stomatal Density (SD)

Regarding specific leaf area (SLA), significant differences were observed among clones. The Scott-Knott test grouped the clones into three categories: High SLA: CCN 51 (189.03 cm²/g), Medium SLA: SJ 02, CCN 10, and PS 1319 (156.24, 155.86, and 152.60 cm²/g, respectively), Low SLA: CP 49 and PH 16 (134.68 and 124.87 cm²/g, respectively) (Fig. 2). Stomatal density (SD) values ranged from 700 to 913 mm². SJ 02 had the highest SD, followed by CCN 51. Clones PS 1319, PH 16, CP 49, and CCN 10 had lower SD values, differing from the others (Fig. 2).

Fig. 2
figure 2

(A) Specific leaf area (SLA - cm2/leaf dry mass) and (B) stomatal density (SD – stomata/mm2) from the Scott-Knott test in leaves of cacao clones grown in full sun, in the municipality of Linhares, northern Espírito Santo State, Brazil.

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Yield and its components

Our analysis of fruit and seed traits revealed significant differences among clones for fruit length (FL), fruit diameter (FD), fresh shell weight (FSW), wet seed weight (WSW), number of seeds per fruit (NSF), and individual dry bean weight (IDBW) (Table 5). Clones CP 49, CCN 51, and CCN 10 produced the longest fruits. Clones CCN 10, CCN 51, PS 1319, and PH 16 had the highest wet seed weight (WSW). When considering the number of seeds per fruit (NSF), CCN 10 differed from the other clones, producing fewer seeds (30). However, this same clone had the highest individual dry bean weight (IDBW) at 2.31 g. We found significant correlations between FW and FL (r = 0.84), NSF and NFP (r = 0.86), NSF and YIELD (r = 0.88), and NFP and YIELD (r = 0.85) (Table 6).

Table 5 Summary of the ANOVA and means of fruits and seeds of six cacao clones grown under full sun regarding fruit weight (FW), fruit length (FL), fruit diameter (FD), fresh shell weight (FSW), wet seed weight (WSW), number of seeds per fruit (NSF), and individual dry bean weight (IDBW).
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Table 6 Correlation coefficients (above) and p-values (bellow) between fruit weight (FW), fruit length (FL), fruit diameter (FD), fresh shell weight (FSW), wet seed weight (WSW), number of seeds per fruit (NSF), individual dry bean weight (IDBW), number of fruits per plant (NFP), and dry bean yield (YIELD) of six cacao clones grown under full sun.
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Regarding dry bean yield, CCN 51 was the most productive clone, yielding 2,890 kg/ha (Table 7). This high yield was likely due to the high number of fruits per plant, as NFP and YIELD are strongly correlated (r = 0.85, Table 6). PH 16 and PS 1319 also showed high productivity, exceeding 2,000 kg/ha. CP 49, SJ 02, and CCN 10 had lower yields, although still considered satisfactory for the growing conditions. Interestingly, when examining the associations between dry bean yield and gas exchange parameters, chlorophyll content, and leaf structure, the only significant correlation (−0.89) was with leaf-to-air water vapor pressure deficit (VpdL) (Table 3).

Table 7 Means of number of fruits per plant (NFP) and dry bean yield (YIELD) of six cacao clones grown under full sun.
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Discussion

The photosynthetic capacity of cacao varies between 2 and 8 µmoL/m²/s, which is considered low47,48. The A values presented in this study were similar to those reported by Araújo et al.49for monocrops in full sun, or higher than those found in the literature50,51,52. This may be attributed to the fact that plants developed in environments with higher sunlight availability have a photosynthetic machinery capable of dealing with high irradiance values, thus presenting higher A values, high stomatal conductance (gs), and an increase in photoprotective capacity34,53. Although cacao is a crop tolerant to shade conditions, some clones (e.g., CCN 51) have higher CO₂ assimilation rates when grown in full sun compared to shade cultivation in agroforestry systems, as reported by Suárez Salazar et al.54.

Besides the acclimatization to the sunlight intensity, another relevant factor for the high values of A of some clones can be justified by the architecture of the plant crown observed in the trial. Although all of them are in similar field conditions (cultivation in full sun, spacing and management), clones PS 1319 and PH 16 presented a more open and less dense crown (Fig. 3). Therefore, this larger aperture could have allowed for better light interception across the canopy, with consequent gains in the efficiency of CO₂ assimilation at the whole plant level. In addition, achieving high levels of Adepends on the availability and performance of water and nutrients in the soil as well as sunlight intensity55,56,57. Thus, this relationship between A and the aforementioned factors was confirmed in the present study, as the culture was fertigated and exposed to full sun. Furthermore, irrigated cacao (without water stress) tends to present increasing values of carbon assimilation with the increase of solar radiation58, which also indicates the contribution of irrigation to these high values obtained. The water use efficiency (A/E) values suggest an efficient plant control to avoid excessive water loss in conditions of higher radiation33, especially during the intercropping season, which is drier compared to the main crop season.

Fig. 3
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Experimental field at Três Lagoas farm, located in Linhares, northern Espírito Santo State, Brazil. (A) Area planted with clone PS 1319 and (B) area planted with clone PH 16.

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When stomatal conductance (gs) was correlated with photosynthesis (A), both showed the same trend, indicating the importance of diffusive limitation in the photosynthetic control of cacao59. However, gs did not correlate significantly with stomatal density (SD) (r = 0.58), suggesting that higher gs values were not due to a greater number of stomata. According to Faralli et al.60, higher stomatal density is often associated with smaller stomata, which respond more rapidly to environmental changes. Therefore, higher gs likely resulted from greater stomatal opening, probably due to favorable environmental conditions for gas exchange.

The Fv/Fmratio is a well-established measure of plant photosynthetic performance61. Changes in Fv/Fmcan indicate disturbances in the plant’s photosynthetic apparatus caused by biotic and abiotic stresses62,63,64. In both harvest seasons, the Fv/Fmratio values indicated the absence of photoinhibitory signals and damage to photosystem II, according to Maxwell and Johnson42. Fv/Fmratio values averaging between 0.65 and 0.77 have been reported in full sun cacao plantations65,66. However, our results differed from those found by Araújo et al.49, where cacao genotypes grown in pots in a full sun nursery showed a reduction in the Fv/Fmratio (ranging from 0.59 to 0.70), which indicates photoinhibitory damage caused by excess light. It is well known that studies conducted in the field differ from those conducted in greenhouses, nurseries, and laboratories, mainly due to the higher evaporative demand and greater climatic variation in the field. Studies whose scale is the whole plant represent a better level to integrate environmental conditions and physiological responses42,67,68,69. Thus, comparing this study with the study of Araújo et al.49, we speculate that plants grown in the field may have a greater capacity for energy dissipation than those grown in pots, mainly because of the higher prevalence of drainage and vegetative growth, for example.

Cacao has significant genetic variability1. Variation in leaf characteristics, including specific leaf area, stomatal density and E rate, has been documented in other studies65,70. The total concentration of photosynthetic pigments and their proportions, both among themselves and in relation to chlorophylls a (Chl a) and b (Chl b), change depending on the available light intensity62,71. Consequently, leaves grown under high light conditions tend to have a higher proportion of Chl a compared to Chl b, resulting in a higher Chl a/b ratio for sun-exposed leaves compared to shaded leaves62,72. The Chl a/b ratio values from this study are consistent with those reported by Lennon et al.62, Suárez Salazar et al.54, and Araújo et al.49.

In high-light environments, plants often exhibit a reduced Chl T/Car ratio33,54,62, suggesting a higher relative amount of carotenoids to chlorophyll in full sunlight. This was observed in clone PH 16, which had the lowest ratio, indicating the protective role of carotenoids in protecting the photosynthetic apparatus against photooxidative damage to chlorophyll molecules. However, cacao has additional photoprotective mechanisms. This is evident because the Chl T/Car ratio remained unchanged in the other clones, which also showed no signs of photoinhibition.

Cacao exhibits considerable genetic variability in various traits, particularly in the size, shape, and color of its fruits and seeds1. The biometric data of the fruits and seeds of the clones studied further underscore this variability, even under full sun cultivation conditions. This variability is mainly because of natural crossing and hybridization processes39,73. Overall, the fruit weight of the clones ranged from 627 to 701 g. In a study by Alexandre et al.74 on cacao cultivation intercropped with rubber plants in the coastal region of São Mateus (Espírito Santo state), significant differences in average fruit weight were observed among clones CCN 10, CCN 51, PS 1319, and PH 16, with clone CCN 51 recording the highest weight at 820 g. In addition, Alexandre et al.74 also reported larger fruit diameter (FD) and length (FL) values compared to those observed in the present study.

Plants that produce larger fruits tend to have fewer fruits overall. This can be attributed to reduced competition among reproductive sinks, leading to greater allocation of photoassimilates to individual fruit growth75. However, under the highly specialized management conditions of our study, the primary limiting factor for clone productivity was the number of reproductive sinks, with no significant effect of leaf-level source capacity. The reduced number of fruits per plant (NFP) was the main contributor to the lower yields observed in clones CCN 10 and CP 49. In particular, the superior individual dry bean weight (IDBW) of CCN 10 enabled it to achieve yields comparable to SJ 02, despite having fewer NFP and NSF.

Seeds, which have significant commercial value, must meet quality standards set by the industry. For cacao producers, this trait is equally important, as larger seed size reduces harvesting labor and minimizes breakage76. Thus, dry bean weight per fruit is recognized as a key yield component77. The use of clones with increased bean weight is essential to meet the requirements of the chocolate industry. Economically, it is advantageous to produce larger beans with a high bean to shell mass ratio. Commercially, dry seeds should ideally average 1.07 g or more78; this benchmark guides research centers in clone selection. Notably, all clones evaluated in this study exceeded the minimum desirable dry bean weight, ranging from 1.11 g (CP 49) to 2.31 g (CCN 10). As stressed by Campuzano79, the number of seeds in cacao fruits shows considerable variability, influenced by both genetic factors and environmental conditions. As a result, fruits of the same genotype can exhibit considerable variation in seed number. This variability may explain the differences observed both in our study and in previous research, where identical clones showed different biometric characteristics.

According to Zuidema et al.28, low annual radiation and dry periods account for 70% of the variation in cocoa bean yield. Interestingly, the last limiting condition did not occur in the present fertigated full sun crop, which partly explains the high yields recorded above 2,000 kg/ha (clones PH 16 and PS 1319) or 2,900 kg/ha (clone CCN 51). Santos and Sodré29 documented that CCN 51 exceeded 2,500 kg/ha in the southern region of Ecuador under irrigated conditions. Similarly, Puentes-Páramo et al.80 reported a dry bean yield of 2,020 kg/ha/year for this clone when evaluated under different NPK fertilization rates and a plant density of 952 plants per hectare. Alexandre et al.74further corroborated these findings, noting that clone CCN 51 outperformed PS 1319 in bean yield. Pereira and Valle81showed that, besides its impressive productivity, CCN 51 is a prominent clone that combines disease tolerance, adaptability to different edaphoclimatic conditions, high yields82, and tolerance to water stress83. Furthermore, its yield shows an incremental improvement under fertigation conditions.

Finally, it is necessary to emphasize the significant inverse correlation (−0.89) found between dry bean yield (YIELD) and leaf-to-air water vapor pressure deficit (VpdL). VpdL is a key environmental factor that influences cacao dry bean yield, representing the difference between the water vapor pressure in the leaf and the surrounding air. As VpdL increases, the rate of water loss from the leaf through transpiration also increases84. This can lead to a decrease in photosynthesis and plant growth, ultimately affecting cacao dry bean yield. In our study, the clones that exceeded 2,000 kg/ha of dry bean yield, in this case PH 16, PS 1319, and CCN 51, were those that presented the lowest VpdL values. This result suggests that VpdL can be a parameter to be used in the selection of high-performance clones for fertigated full sun crop.

Final consideration

We present a comprehensive analysis of cacao grown in full sun with fertigation, evaluating leaf physiological traits, leaf structure, and yield components of six cacao clones (PS 1319, CCN 51, CCN 10, SJ 02, CP 49, and PH 16). Our findings demonstrate a positive response from cacao to light exposure, with favorable physiological adaptations for full sun cultivation. Importantly, yields ranged from 1,220 kg/ha (CCN 10) to a remarkable 2,900 kg/ha (CCN 51), representing up to a sevenfold increase compared to traditional agroforestry systems. These results suggest that full sun cultivation, combined with clonal selection, optimized management practices, and readily available water and nutrients, offers significant potential for high-yield cocoa production. To the best of our knowledge, this is the first comprehensive description of this novel cropping system.