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Introduction
Cacao (Theobroma cacao L.) production assumed a commercial dimension in the early 19th century in Ghana (Peprah, 2019), and since then, together with Ivory Coast, they have been at the forefront of world production (Coulibaly, 2019). In 2018, world production was 5.25 million tons, where Ivory Coast was the largest producer with an estimated 1.96 million tons (37 %), followed by Ghana (947,632 t) and Cameroon (307,867 t).
In Colombia, for the same year, 145,471 ha with cacao trees were reported, with a dry bean production of 52,743 t (FAO, 2020). In the last three decades, a decrease in yield has been observed, going from 0.46 t ha-1 in 1990 to 0.36 t ha-1 in 2018 (FAO, 2020). There is a variety of agronomic factors that influence yield; the basic lesson learned is that the desired effect of efforts to expand the area will not be very noticeable if productive capacity is not addressed simultaneously (Abbot et al., 2017). Ramírez et al. (2009) indicated that among the main reasons for cacao to reduce its productivity is the advanced age of the plantations (> 20 years), the age at which the cacao tree decreases its production. The lack of proper crop management, especially the lack of pruning, both in cacao trees and shade trees, makes their management and harvest difficult, and increases the incidence of pests and diseases; this, in turn, increases production costs and reduces crop profitability.
In Colombia, most of the cocoa farms (94%) are managed by small producers, where the extensions of land dedicated to cacao cultivation are less than 5 ha (equivalent to 60 % of the area dedicated to cacao cultivation), together with peasant economy production systems of and in some cases, subsistence (Castellanos et al., 2007).
Likewise, more than 60 % of the cacao trees are plantations older than 30 years that are characterized by being unproductive, established from hybrid genetic materials obtained by crosses between Trinitarian and Amazonian clones, and in good proportion, offspring of hybrids. Only a low percentage is established with genetic materials from universal clones; thus, 32 % of the cocoa-producing areas are planted with common and universal materials (clones), and 58 % with hybrids (MADR, 2005).
According to Ramírez et al. (2009), a drastic intervention is required to recover the productive capacity and profitability of a cacao plantation. For this, two intervention strategies are proposed: renovation and rehabilitation. Renovation consists of the gradual or rapid replacement of the existing genetic material, generally hybrids, by cacao clones with higher productive potential and better quality. On the other hand, Wood and Lass (2001) defined rehabilitation as the restoration of yields to their maximum level in a cacao plantation.
Wood and Lass (2001) consider that the mere fact of implementing good management in unproductive cocoa farms to recover crop yield is a form of rehabilitation. Among the cultural methods that can be considered as rehabilitation strategies, the adjustment of shade, application of fertilizers, weed control, sanitary management, improvement of drainage and management of the tree architecture through pruning stand out (Petithuguenin, 1995).
In Colombia, according to Ministerio de Agricultura y Desarrollo Rural (MADR-CNC, 2008) in its ten-year cacao plan 2012-2021, it was expected to have 130,000 modernized ha and a production of 156,000 t by year 2020. This approach, proposed from the institutional point of view, recognizes the cocoa-derived market potential, and in general, the production chain, as well as the production of derivatives (Cely, 2017). This reveals the need to reactivate the productive system based on rehabilitation strategies that will allow to reactivate and promote productivity. Accordingly, the aim of this study was to evaluate renovation/rehabilitation strategies as an alternative to increasing the yields of unproductive cacao plantations in the Colombian dry Caribbean.
Materials and methods
Study site
This study was carried out in the Colombian dry Caribbean region in two locations: in the district of El Palmar, municipality of Valledupar, department of Cesar, located at the coordinates 10º 28ꞌ 43.5" N and 73º 25ꞌ 9.6" W, at an altitude of 500 masl, and in the municipality of Zona Bananera, department of Magdalena, at the Research Center C. I. Caribia of Corporación Colombiana de Investigación Agropecuaria (Agrosavia), located at the coordinates 10° 45ꞌ 50.6" N and 74° 08ꞌ 48.8" W, at 20 masl. Both plantations had low yields (< 400 kg ha-1) and a high incidence of pests and diseases (> 70 %). The climatic conditions of the studied locations in the first quarter of the year depend on a dry period in both locations, with low rainfall and where evapotranspiration (ET) exceeds precipitation (P). This is why an irrigation system is required in these periods to guarantee water and nutrients for plants (Palmar, P = 152.5 mm, ET = 351.53 mm; Caribia, P = 150.20 mm, ET = 351.53 mm). From April to November, rainfall increases, significantly exceeding ET (Palmar, P = 1783.20 mm, ET = 956.90 mm; Caribia, P = 1882.18 mm, ET = 947.31 mm). In addition, temperatures follow a linear trend pattern, where abrupt changes between temperatures are not reflected during all months of the year (average temperature, Palmar = 26.45 °C; Caribia = 27.15 °C).
Farm diagnosis
After the selection of plots, a tree-by-tree diagnosis was made to assess the phytosanitary status and define the type of intervention to be used according to the case. Two strategies were implemented. 1) renovation strategy: in this case two treatments evaluated were E1: lateral graft in adult tree implemented in older trees (> 20 years), unproductive (< 400 g dry cocoa/tree/year) and with deterioration in their productive branches; however, their trunk should have good phytosanitary conditions and a diameter of less than 15 cm. E2: grafting in basal sucker implemented in unproductive trees, with a high incidence of pests and diseases in the trunk. These trees were pruned at ground level, after which the cut area was healed and covered with organic fertilizer to stimulate the emission of new suckers from the ground base; finally, the best developed one was selected and based on this one, a new crown was grafted with an approach graft. In both strategies (E1 and E2), the practice of grafting allowed to renew the unproductive genetic material with new materials. For this purpose, the same cacao genetic materials were evaluated in E1 and E2: clones CCN51, EE8 and TSH565 in Zona Bananera, and clones CCN51, EET8 and FLE2 in Valledupar.
The second strategy implemented was the cacao trees rehabilitation. E3: structural rehabilitation by strong pruning; this practice consisted of cutting branches, leaving between two and three main branches on each tree, and reducing the height of the trees by up to 3 m; moreover, diseased branches and suckers were removed; and E4: control treatment, this treatment consisted in selecting trees that remained under the traditional management of the producer, to which no intervention was made in terms of canopy pruning. In Zona Bananera the clone CCN51 was used for the rehabilitation strategy, and in Valledupar, a creole hybrid material from seed (IMC67) was used. In all the treatments a plant density of 1,111 trees ha-1 was adjusted, with a distance of 3 × 3 m between cacao trees.
Experimental design
Two independent experiments were established under a completely randomized design with three replications and an experimental unit composed of five trees was used. The firs experiment consisted of evaluating the renovation strategy, with two treatments (E1: lateral graft in adult tree, and E2: grafting in basal sucker). The second experiment aimed to evaluate the rehabilitation strategy (E3: structural rehabilitation, and E4: control, without rehabilitation).
Evaluated traits
The variables evaluated were pod weight, number of grains per pod, fresh and dry cocoa beans, two yield components - pod index (PI) and grain index (GI), and cocoa dry bean yield (kg per tree). Grain and pod index are the most important variables for commercialization and determine the performance of a cocoa phenotype (Jiménez et al., 2018; Vera et al., 2014), these two yield components were determined as follows: PI as the average number of pods needed to obtain 1 kg of dry bean cocoa, and the GI as the average weight of grain in g, taken from a sample of 100 dry cocoa beans.
Additionally, in the renovation experiment, the growth of the cocoa pod was characterized for each of the clones evaluated from measurements of the length and width of the pod, in the localities of Zona Bananera and Valledupar.
Statistical analysis
The data from the morpho-agronomic characterization were analyzed using the SAS statistical program version Enterprise Guide 5.1 (SAS Institute, 2007). A descriptive analysis (mean, standard deviation, standard error, coefficient of variation, and minimum and maximum values) was performed to establish the variability of the quantitative characteristics at the treatment level; an analysis of variance and Tukey mean multiple comparison test (P ≤ 0.05) were used to carry out the multiple mean comparisons for variables pod weight, number of grains per pod, grain weight in slime and dry, pod index, grain index and grain yield.
Results and discussion
Renovation strategy
After three years of implementing the renovation strategies (lateral grafting and grafting on a basal sucker) at the locations of Zona Bananera and Valledupar, there were significant differences between treatments for production of dry cocoa, being higher in trees intervened with lateral graft, with productions of 0.81 kg/tree (second year) and 0.72 kg/tree (third year) in the C.I. Caribia; and 0.24 kg/tree (second year) and 0.50 kg/tree (third year) in Valledupar (Table 1). In contrast, the trees intervened through the practice of basal sucker grafting only produced dry cocoa bean in the third year after implanting the grafting on the trees, which indicates a late response with an effect on the dry cocoa yield.
Table 1 Production of dry bean (kg/tree) of cocoa trees intervened with different renovation practices in Zona Bananera (C. I. Caribia) and Valledupar (El Palmar district), Colombia.
| Treatment | Year 1 (kg/tree) | Year 2 (kg/tree) | Year 3 (kg/tree) | |||
| Caribia | Palmar | Caribia | Palmar | Caribia | Palmar | |
| Lateral graft | 0.0 | 0.0 | 0.81 b | 0.24 b | 0.72 b | 0.50 c |
| Basal sucker graft | 0.0 | 0.0 | 0.0 a | 0.0 | 0.06 c | 0.03 d |
Lower case letters in the same column indicate a non-significant statistical difference (Tukey, P ≤ 0.05).
The lateral graft treatment had a positive effect on earliness, compared to the basal sucker graft, regardless of not exceeding the yield of the control treatment. It is expected that from the third year, production will increase due to the fact that the plants recover the photosynthetically active leaf surface, which allows increasing the capture of light energy, and improving its photosynthetic activity, to distribute assimilates to the organs such as flowers and fruits. Monteith (1972) mentioned that the estimation of the productivity of a crop is based on the fraction of radiation absorbed by the photosynthetically active elements of plants and its efficiency to convert it into biomass.
Regarding the treatment of graft in a basal sucker, after three years of its implementation, the established crowns have not started the production cycle, which represents a slow development compared to the lateral graft that showed higher production, being consistent with what López (2019) described. By the third year of the intervention in both locations, when comparing the productivity (kg of dry cocoa/tree/year) between the different materials, significant differences were found, being the productivity of clone CCN51 higher compared to that of clones TSH565 and EET8 in the locality of Zona Bananera, and clones TSH565 and FLE2 in Valledupar (Table 2).
Table 2 Production of dry cocoa (kg/tree) in cacao trees intervened with different practices such as lateral grafting and grafting on the basal sucker in Zona Bananera (C. I. Caribia) and Valledupar (El Palmar district) in Colombia during year 3.
| Treatment | Basal sucker | Lateral graft |
| Caribia | ||
| CCN51 | 0.0 | 1.21 c |
| TSH565 | 0.0 | 0.64 b |
| EET8 | 0.0 | 0.17 a |
| El Palmar | ||
| CCN51 | 0.0 | 0.90 b |
| TSH565 | 0.0 | 0.42 a |
| FLE2 | 0.0 | 0.64 a |
Lower case letters in the same column within each location indicate a non-significant statistical difference (Tukey, P ≤ 0.05).
Regarding the yield components in Zona Bananera, significant differences were found in pod length, with the largest pod size found in clones TSH565, and the lowest GI in clone TSH565 (Table 3). According to Fedecacao (2015), a number of grains per pod greater than 46 is considered superior, from 36 to 45 intermediate, and less than 35 is inferior; therefore, clones CCN51 and TSH565 were classified as intermediate, while clone EET8 is classified as an inferior material. Likewise, a pod index (PI) less than or equal to 17 is considered very good, 18 to 20 is good and greater than 21 is not adequate. In this sense, clone CCN51 outperform clones TSH65 and EET8, being considered very good; meanwhile, the ETT8 clone is classified as good, and TSH565 is adequate.
Table 3 Morphological characteristics and yield components of the cacao clones evaluated in Zona Bananera (C. I. Caribia) and Valledupar (El Palmar district), Colombia.
| Clone | Fruit weight (g) | Fruit length (cm) | Fruit diameter (cm) | Grains per pod | Slime weight per pod (g) | GI (g) | PI |
| Caribia | |||||||
| TSH565 | 881.9 a | 23.60 a | 9.44 a | 39.60 a | 171.68 a | 1.22 b | 21.23 a |
| CCN51 | 621.6 a | 19.82 b | 9.16 a | 39.00 a | 178.56 a | 1.53 a | 17.95 a |
| EET8 | 604.0 a | 20.90 ab | 9.26 a | 32.20 a | 139.06 a | 1.56 a | 20.34 a |
| El Palmar | |||||||
| FLE2 | 1.188.6 a | 27.30 a | 9.90 a | 45 a | 240.0 a | 1.50 a | 14.78 a |
| CCN51 | 874.0 ab | 23.40 b | 9.72 ab | 42 a | 214.1 ab | 1.58 a | 16.38 a |
| EET8 | 616.8 b | 19.32 c | 8.36 b | 36 a | 169.0 b | 1.45 a | 19.41 a |
Lower case letters in the same column within each location indicate a non-significant statistical difference (Tukey, P ≤ 0.05). GI: average cocoa bean weight in a sample of 100 g, PI: number of pods necessary to obtain 1 kg of dry cocoa grains.
In Valledupar (El Palmar district), significant differences were found in the variables weight, length and diameter of the fruit, the pod size of clone FLE2 being larger than that of the EET8 and CCN51 clones and the hybrid. Additionally, there was a difference in the weight in slime per pod (Table 3). The three clones showed a number of pod grains from 36 to 45, being classified in the intermediate class, according to Fedecacao (2015). The FLE2 and CCN51 clones presented pod indexes equal to or less than 17, i.e., considered to be very good, while the EET8 clone was in the range of 18 to 20, i.e., in a good range. The material of the producer was classified in the unsuitable range for having a PI higher than 21 (Table 3); however, the productivity showed in the structural pruning treatment was high (3.34 kg dry cocoa/tree/year) because the number of pods harvested per tree was high (> 50 pods/tree/year).
Regarding the yield components of clones CCN51 and EET8, Perea et al. (2013) reported MI values of 15 and 13, and IG of 1.6 and 1.58 respectively, values that show a better response than those found in the Zona Bananera and Valledupar for CCN51, with MI of 17.95 and 16.38, and GI of 1.53 and 1.58 respectively; and for EET8 in the same locations with MI of 20.34 and 19.41, and IG of 1.56 and 1.45 respectively (Tables 3 and 4). For the specific case of clone TSH565, the mentioned authors also found a better response for these indicators, with MI of 19 and GI of 1.2, while in Zona Bananera MI value of 21.23 and a GI of 1 were reported (Table 3).
Table 4 Production of dry cocoa of cocoa trees intervened with different rehabilitation practices in Zona Bananera (C.I. Caribia) and Valledupar (El Palmar district), Colombia.
| Treatment | Year 1 (kg/tree) | Year 2 (kg/tree) | Year 3 (kg/tree) | |||
| Caribia | Palmar | Caribia | Palmar | Caribia | Palmar | |
| Structural pruning | 1.78 a | 1.49 a | 1.86 a | 1.63 a | 1.86 a | 3.34 a |
| Control without pruning | 0.52 b | 0.0 b | 0.82 b | 0.76 b | 0.75 b | 1.44 b |
Lower case letters in the same column indicate a non-significant statistical difference (Tukey, P ≤ 0.05).
As mentioned, when finding that the results of the present investigation are less inferior to that documented by Perea et al. (2013), it can be deduced that the yield responses could be related to the wide climatic differences of the study areas; for example, in the Colombian Caribbean (Zona Bananera and Valledupar) the conditions are not favorable for cultivation, mainly due to prolonged dry seasons (first months of the year), since according to Zuidema et al. (2005), cocoa yields depend to a great extent on the water inputs during the two driest months of the year. Another relevant aspect is the genotype × environment interaction, highlighting the importance of optimizing the use of genetic resources and proposing basic collections for the design of improvement programs (Osorio-Guarín et al., 2017).
Within the cocoa market, in addition to bulk cocoa, a new category known as specialty cocoa has been established, which has experienced the highest percentage of growth compared to other cocoa segments (Santander et al., 2019). This category includes fine or flavored cocoas and those that are characterized by differentiating factors such as origin, certifications and uniqueness (Ríos et al., 2017). Given the above, it is important to carry out the renovations of the old plantations of the country with outstanding genetic materials that allow to generate a fine cocoa line differentiated by its quality.
Figure 1 shows the growth of cocoa pods from clones in renovation in Zona Bananera (clones CCN51, EET8 and TSH565). Clone CCN51 is the one that requires the longest time to complete its maturation cycle and to reach an optimal stage for harvest (162 days), while clones EET8 and TSH565 required an average of 138 and 141 days, respectively.
Figure 1 Fruit growth from the cucumber-shaped stage (< 10 cm) until harvest under the edaphoclimatic conditions of Zona Bananera (C. I. Caribia), Magdalena department, Colombia.
On the other hand, according to information from Valledupar, clone CCN51 was also the one that needed the longest time to reach an optimal harvest stage (140 days); however, the time was less than 22 days compared to the time recorded in Zona Bananera. Conversely, the FLE2 and ETT8 clones needed an average of 127 days to reach an optimal stage for harvest (Figure 2).
Figure 2 Fruit growth from the cucumber-shaped stage (< 10 cm) to harvest under edaphoclimatic conditions of Valledupar, El Palmar district, Cesar department, Colombia.
Pinzón et al. (2014) mentioned that productive behavior is highly related to agroclimatic conditions, cultural practices implemented in cultivation, and sexual compatibility between clones. Cacao trees grow best in tropical areas, being cultivated from the sea level to more than 2,000 meters above sea level; however, according to García et al. (2009; Com. Pers.)1, the optimal altitude range for cacao cultivation is between 400 and 1200 meters of altitude. For this reason, climatic factors influence the production of a plantation.
According to Paredes (2003), the optimal rainfall for cacao is between 1600 and 2500 mm distributed throughout the year, and temperature should be between the following values: minimum 23 °C, maximum 32 °C, and optimal 25 °C. Comparing with the climatic conditions of Zona Bananera, a contrast is observed, in which the altitude is significantly lower (30 masl), the maximum temperature in some months can reach 38 °C, and the minimum temperature is 19 °C; however, under these conditions, cacao trees have shown good yields and behavior, which potentiates and widens the adaptation range.
Rehabilitation strategy
For the implementation of the rehabilitation strategies (structural pruning) in the locations of Zona Bananera and Valledupar, there were significant differences in the production of dry cocoa between treatments, being higher in trees intervened with structural pruning, with productions of 1.78 kg/tree (first year), 1.86 kg/tree (second year) and 1.86 kg/tree (third year) in the C. I. Caribia; and 1.49 kg/tree (first year), 1.63 kg/tree (second year) and 3.34 kg/tree (third year) in Valledupar (Table 4).
Results in both localities show a positive effect in the short term when performing structural pruning. Trees subjected to this practice showed higher production compared to trees of the control treatment without any intervention.
Trees of the control treatment were managed agronomically according to the criteria of producers, and their production in year three after the implementation of the treatments was 0.75 kg of dry cocoa/tree/year for the C. I. Caribia and 1.44 kg of dry cocoa/tree/year for the El Palmar district, contrary to what happened in trees intervened with structural pruning in the two localities, where productions in the third year increased compared to the control by 131 % (3.34 kg of dry cocoa/tree/year) in Valledupar, and 148 % (1.86 kg of dry cocoa/tree/year) in Zona Bananera. These data show the benefits of rehabilitation strategies, which allow the producer to recover an unproductive plantation and increase production compared to the cultivation without intervening.
Leiva-Rojas et al. (2019) mentioned that intensifying pruning decreases the capacity of trees to maintain fruits due to the alteration in the physiological balance, mainly in the source/sink relationship. Villacis et al. (2019) stated that unpruned cacao trees that reach a height greater than 10 m must be pruned after harvest to control diseases, improve grain quality and increase yields. The foregoing favored the structural rehabilitation treatment of the present investigation, since the physiological conditions of the canopy were improved.
Pruning regulates the vegetative capacity to generate terminal buds and increase flowering and fruit production (Bedker et al., 2004). It is important to carry out pruning taking into account the weather forecasts, in order to reduce risks due to droughts and heat waves, as occurs in the study area, where rainfall is reduced in the months of January and February, which is unfavorable for cacao.
According to Quiroz and Amores (2010), within the renovation strategies, strong prunings to the cacao treetops should be carried out eliminating 70 % of the volume to obtain a low height renewed crown (5-8 m) and stem cuts at different heights, including a) 0.3 m for trees older than 40 years, b) 1.0 m for trees between 25 and 35 years old, and c) 2.0 m in trees younger than 25 years. Assiri et al. (2012) demonstrated that the rehabilitation of cacao tree plantations between 20 to 30 years old increases production from 20 to 221 %, with an average rate of return that reaches 377 % compared to the control treatment; moreover, mineral fertilization contributes to an additional production percentage from 35 to 65 % from the second year in rehabilitated cacao plantations. This is in agreement with the results of Wessel and Quist-Wessel (2015), who demonstrated that rehabilitation of cacao plantations is feasible and profitable with good maintenance and integrated control of pests and diseases, increasing yield up to 40 %, from around 500 to 700 kg ha-1 in four years of study on cacao trees of 25-30 years; additionally, the use of fertilizers increased yield to 1000 kg ha-1 from the third year of application onwards.
In studies conducted in West and Central Africa, Asare et al. (2018) found that rehabilitated cacao trees older than 15 years had a survival rate of 79 %. It is important to mention that the government of Ghana grants financial benefits to farms that decide to rehabilitate their cocoa plantations through the following criteria: the cacao plantation cannot be in a site with a slope greater than 3 %, it must not be in flooded land, near a forest or a natural reserve, the cacao plantation must be more than 25 years old and have productions of less than 200 kg ha-1 (O'Sullivan et al., 2018).
Riedel et al. (2019) found that the unproductive period of cacao trees is reduced to 2 years when performing a renovation pruning, compared to the method of replanting trees that extends the unproductiveness period from 3 to 5 years, suggesting that the yields of the pruned systems allow small farmers to wait for a short unproductive phase moving from monoculture to a sustainable cocoa production system.
Conclusions
The structural pruning increased the cocoa bean yield productions in Valledupar and Zona Bananera, Colombia compared to the control treatment. The lateral graft treatment showed a positive effect on earliness, compared to the basal sucker graft. CCN51 clone showed higher yields compared to the TSH565 and EET8 clones in the locality of Zona Bananera and TSH565 and FLE2 clones in Valledupar. In materials with unsatisfactory behavior it is suggested to implement crown renovations through lateral grafting and renewing the crown with more productive and better-behaving materials.
