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Open Access Peer-reviewed

Adaptation of Latex Harvesting Technologies to the Three Metabolic Activity Classes of Rubber Clones According to Socio-economic Conditions in Côte d'Ivoire

Diarrassouba Moussa , Tuo Seydou, Camara Brahima, Obouayeba Samuel
American Journal of Food and Nutrition. 2022, 10(1), 1-15. DOI: 10.12691/ajfn-10-1-1
Received October 27, 2021; Revised November 28, 2021; Accepted December 07, 2021

Abstract

Two concerns of rubber farmers are the development of latex harvesting technologies to improve the production potential of the trees and the availability and cost of labour for tapping. To achieve this, some rubber farmers opt for over-harvesting the trees. This way of doing things disturbs the physiological balance of the rubber trees, which leads to the increase of tapping Panel dryness (TPD) and rather to the fall of the production. To solve this problem, the present study proposes to define one or more latex harvesting technologies by metabolic class allowing the improvement of plantation yield and the increase of the economic life of the trees. To achieve this, the clones IRCA 111, IRCA 130 and PB 260 from the active metabolic class, GT 1, RRIC 100 and BPM 24 from the moderate metabolic class; PB 217 and PR 107 from the slow metabolic class were used as plant material. Results showed that clones in the slow metabolism class were less susceptible to TPD and performed better in intense latex harvest than those in the active and moderate metabolism classes. Regardless of metabolic class, the reduction in tapping frequency had no negative effect on the vegetative state of the trees. Instead, the reduction in tapping frequency was compensated by a large number of annual stimulations, which resulted in high dry rubber production. Analysis of dry rubber production, rubber tree radial growth and TPD rate indicates that the metabolically active class clones performed better with the S/2 d3 6d/7 ET2 latex harvesting technologies. 5% Pa1(1) 4/y; S/2 d4 6d/7 ET2.5% Pa1(1) 4/y; S/2 d5 6d/7 ET2.5% Pa1(1) 8/y and S/2 d6 6d/7 ET2.5% Pa1(1) 10/y. Those of the moderate metabolism class are with the motifs S/2 d3 6d/7 ET2.5% Pa1(1) 6/y; S/2 d4 6d/7 ET2.5% Pa1(1) 6/y and S/2 d5 6d/7 ET2.5% Pa1(1) 10/y. For the slow metabolism class clones, the following latex harvesting technologies were recommended: S/2 d3 6d/7 ET2.5% Pa1(1) 8/y; S/2 d4 6d/7 ET2.5% Pa1(1) 12/y and S/2 d6 6d/7 ET2.5% Pa1(1) 18/y.

1. Introduction

There are three metabolic classes of Hevea brasiliensis clones. They include the classes of fast or active metabolizing clones, intermediate or moderate metabolizing clones and slow or low metabolizing clones. Clones in the active metabolism class have high latex production in the absence of hormonal stimulation. Latex flow is very easy in these clones. This class is the most sensitive to tapping panel dryness (TPD) 1, 2, 3. Clones in the moderate metabolic class have an easy flow of latex. In this class, we find clones giving an average production in the absence of any stimulation. Strong stimulation is detrimental to the survival of this class of rubber trees. The response to hormonal stimulation of rubber production is weak. And finally, clones in the slow-metabolizing class have low production in the absence of hormonal stimulation. This class is characterized by clones with difficult latex flow and low rubber production. Despite the high level of hormonal stimulation, these clones remain, however, not very susceptible to the TPD syndrome 1. Genetic improvement work in the 1970s, 1980s and 1990s led to the creation of new elite clones capable of producing 2,000 to 3,000 kg.ha-1.yr-1 of dry rubber 4, 5. Several studies have been carried out in the field of Hevea brasiliensis latex harvesting technologies to enhance the agronomic performance of these elite clones 6, 7, 8, 9, 10, 11, 12, 13 and to provide a solution to these problems that continue to generate much interest in rubber cultivation 14, 15, 16, 17, 18, 19. To this end, the constant search for profitability in Hevea brasiliensis has led to the development of latex harvesting systems that take advantage of the virtues of stimulant products in improving rubber production. The general objective of the present study is therefore to maximize rubber production through the choice of latex harvesting technologies adapted to the three clone classes of metabolic activity in the rubber growing areas of Côte d'Ivoire.

2. Material and Methods

2.1. Plant Material

The plant material consisted of eight Hevea brasiliensis clones, distributed in the three classes of metabolic activities. These are the clones IRCA 111, IRCA 130, PB 217, PB 260, GT 1, RRIC 100, BPM 24 and PR 107 (Table 1).

  • Table 1. Physiological and agronomic characteristics of Hevea brasiliensis clones IRCA 111, IRCA 130, PB 260, GT 1, RRIC 100, BPM 24, PB 217 and PR 107 distributed in the three metabolic classes (active, moderate and slow)

2.2. Methods
2.2.1. Study Site

The study site is the experimental station of Gô (Ex HEVEGO) in the southwest of Côte d'Ivoire (Figure 1). This part of the country is covered by dense humid forest. The soils are ferrallitic and highly desaturated, characterized by an abundance of exchangeable bases with the appearance of laterite armour in places at a depth of 1 m. In this region, the soils are also of a sandy-clay nature. They are derived from schists and contain gravelly horizons 20, 21, 22, 23. The climate of the area is humid with four (4) seasons, two (2) dry and two (2) rainy. The average annual rainfall is between 1800 and 2000 mm with average annual temperatures ranging between 28.5 and 29°C 24. The insolation is estimated at 1500 hours 23.


2.2.2. Preliminary Work

The homogeneity of the plant material was previously checked before the beginning of the trials. The selected trees must be as homogeneous as possible in terms of absence of diseases. The selection is essentially based on the measurement of the circumference of the trees at 1 m from the ground when the trial is set up. This measurement is made at 1.70 m from the ground during the experiment.


2.2.3. Experimental Design

The design used in all our experiments is a Fisher block design with 6 treatments and 4 replications with 100 trees per plot. Each trial covers an average area of 4.7 ha.


2.2.4. Tappings

The type of tapping adopted in the experiment was downward half-spiral bleeding for all six treatments. Regardless of the clone and its metabolic class, five tapping frequencies were used (d2, d3, d4, d5 and d6). The hormonal stimulation regime for production was defined according to the metabolic class of the clones. The notations used are the international notations of latex harvesting technologies 25, 26. The tapping frequencies practiced (Table 2) were every second day or three weekly bleeds, (S/2 d2); every 3 days or two weekly bleeds (S/2 d3); every 4 days or three fortnightly bleeds (S/2 d4); every 5 days (S/2 d5) or 6 bleeds in 5 weeks and every 6 days or one weekly bleed (S/2 d6). Bleeding was conducted 6 out of 7 working days (6d/7), with Sunday being a tapping rest day. The latex harvesting treatments or technologies applied were defined in Table 2.


2.2.5. Measured Parameters
2.2.5.1. Measurement of Dry Rubber Production

During the experimental period from the opening or tapping to 9 years of latex harvest, the production was recorded by treatment, by clone, and by metabolic class. This activity consisted of collecting the rubber production contained in the cups and weighing it (fresh weight: Pf). It is done every 4 weeks. A sample of each treatment was then creped (creped weight: CW) and oven dried at 80°C for 24 hours and reweighed (dry weight: DW). The crimping consisted in crushing the coagulum between two metallic rollers rotating in opposite directions. The flattened coagulum is much easier to dry. This process allows to eliminate a large part of the water contained in the coagulum. Dry rubber production was expressed in kilograms per hectare per year (kg.ha-1.yr-1), grams per tree per year (g.t-1.yr-1) and grams per tree per tapping (g.t-1.t-1). The production in kg.ha-1.yr-1 expresses the annual production of dry rubber per hectare of rubber trees. Since for each hectare the number of trees was not the same, the production in g.t-1.yr-1 remedies the influence of the area on the production.


2.2.5.2. Vegetative Growth

Trees were selected on the basis of trunk circumference measured at a height of 1 m before tapping. During tapping, circumferences were measured at 1.70 m from the ground. All measurements were made with a tape measure. Each year at the end of each physiological cycle, i.e. before the start of defoliation (which corresponds to the months of January and February), the trunk circumference of each selected tree was measured again at a height of 1.70 m from the ground. This made it possible to determine the circumferences of the trees still tappable at the end of the trial.


2.2.5.3. Evaluation of the Tapping Panel Dryness (TPD) Rate

The TPD rate is assessed visually. From one year to the next, broken, uprooted or dry-notched trees were removed from the base file.


2.2.6. Statistical Analysis

XLSTAT-Pro 6.1.9 software was used for the analyses of variance of the data on dry rubber production, TPD rate and tree circumferences. The Newman-Keuls test at the 5% threshold was used to distinguish between the different groups.

3. Results

3.1. Impact of Different Latex Harvesting Technologies on Dry Rubber Production, Radial Vegetative Growth and Tapping Panel Dryness Rate of Rapid Metabolizing Hevea brasiliensis Clones IRCA 111, IRCA 130 and PB 260
3.1.1. Rubber Production

Table 3 shows the average annual dry rubber production expressed as g.t-1.t-1, g.t-1.yr-1 and kg.ha-1.yr-1 under different treatments of all three clones (IRCA 111, IRCA 130 and PB 260).


3.1.1.1. Dry Rubber Production in g.t-1.t-1

At the same level of stimulation 4/y and 8/y, productions increased from 53 to 69 g.t-1.t-1 and from 68 to 79 g.t-1.t-1, respectively, with the reduction of the tapping frequency. Treatments d4-4/y (treatment 3) and d4-8/y (treatment 4) of trees that were tapped at the same frequency, had productions of 69 and 68 g.t-1.t-1respectively. Rubber production was inversely proportional to tapping frequency (Table 3).


3.1.1.2. Dry Rubber Production in g.t-1.yr-1

The production of treatment 1 (5505 g.t-1.yr-1) was higher than all other treatments. The patterns tapped in d3-4/y (treatment 2), d4-4/y (treatment 3) and d4-8/y (treatment 4), which generated 5323 g.t-1.yr-1; 5230 g.t-1.yr-1; and 5173 g.t-1.yr-1, respectively, had identical productions (Table 3). The lowest dry rubber production (4546 g.t-1.yr-1) was observed with the pattern tapped at d6-10/y (treatment 6). For the same level of stimulation 8/y, reducing the tapping intensity from d4 (treatment 4) to d5 (treatment 5) resulted in a decrease in production from 5173 to 4945 g.t-1.yr-1.


3.1.1.3. Dry Rubber Production in kg.ha-1.yr-1

The yields in kg.ha-1.yr-1of trees tapped in d2-nil stimulation (2398 kg.ha-1.yr-1) and d3-4/y (2356 kg.ha-1.yr-1) were identical. These values were higher than those of rubber trees tapped into d4-4/y (2277 kg.ha-1.yr-1), d4-8/y (2268 kg.ha-1.yr-1), d5-8/y (2187 kg.ha-1.yr-1) and d6-10/y (2001 kg.ha-1.yr-1). The lowest yield was obtained with the treatment having the lowest tapping frequency (d6-10/y), i.e. 2001 kg.ha-1.yr-1. At the same tapping intensity (d4), increasing the number of annual stimulations from 4/y (2277 kg.ha-1.yr-1) to 8/y (2268 kg.ha-1.yr-1) had no effect on the yield of the rubber trees. These yields were equivalent. At the same 4/y or 8/y stimulation regime, yields decreased from 2356 kg.ha-1.yr-1 (treatment 2) to 2277 kg.ha-1.yr-1 (treatment 3) and from 2268 kg.ha-1.yr-1 (treatment 4) to 2187 kg.ha-1.yr-1 (treatment 5) respectively. This decrease was recorded with the reduction of the tapping frequency (Table 3).

  • Table 3. Average annual dry rubber production of all IRCA 111, IRCA 130, PB 260 clones of the metabolically active class, expressed in g.t-1.t-1 ; g.t-1.yr-1 and in kg.ha-1.yr-1 as a function of treatments in the southwest of Côte d'Ivoire after nine years of experimentation

3.2. Average Radial Vegetative Trunk Growth of the Three Clones IRCA 111, IRCA 130 and PB 260

Figure 2 shows the effect of the six patterns on radial vegetative tree growth across the three Hevea brasiliensis clones IRCA 111, IRCA 130 and PB 260. The circumferences of trees in treatment 1 were the largest (75.7 cm). They were identical to those of rubber trees in patterns 2 (73.1 cm); 3 (73.2 cm) and 6 (73.3 cm). All treatments whose trees were stimulated, namely latex harvesting technologies 2; 3; 4; 5 and 6, had circumferences of the same order of magnitude. At the same level of stimulation 4/y or 8/y, the circumferences of the rubber trees were identical. In fact, under the 4/y stimulation regime, the circumferences of the trees were equal to 73.1 and 73.2 cm, respectively for treatments 2 and 3. At the 8/y stimulation level, trees in treatments 4 and 5 had identical circumferences of 72.2 cm and 72.6 cm respectively. At the same tapping frequency d4 of patterns 3 (73.2 cm) and 4 (72.2 cm), circumferences were equivalent.

  • Figure 2. Average trunk circumferences of all trees according to treatments for the IRCA 111, IRCA 130 and PB 260 clones after nine years of experimentation in southwestern Côte d'Ivoire (Trait: treatment; Treatment 1: S/2 d2 nil stimulation; Treatment 2: S/2 d3 6d/7 ET2.5 % Pa1(1) 4/y; Treatment 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 4/y; Treatment 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Treatment 3: S/2 d5 6d/7 SD2.5 % Pa1(1) 8/y; Treatment3 : S/2 d6 6d/7 SD2.5 % Pa1(1) 10/y; a, b: results with the same letter are not significantly different (Scheffe test at 5%))
3.3. Average Tapping Panel Dryness (TPD) Rate for All Clones

Figure 3 shows the percentage of TPD rate generated by each treatment applied to trees of all Hevea brasiliensis clones IRCA 111, IRCA 130 and PB 260 in southwestern Côte d'Ivoire. In general, treatments 1 (d2-nil stimulation) and 4 (d4-8/y) produced the highest rates of TPD, which were 9.3% and 8.7%, respectively, while pattern 3 (d4-4/y) gave the lowest rate (4.3%). For trees tapped at the same frequency such as those in treatments 3 (d4-4/y) and 4 (d4-8/y), the rate of TPD was greater with treatment 4 (8.7%) than with pattern 3 (4.3%). However, when trees were stimulated at the same level (treatment 2: d3-4/y and 3: d4-4/y), the TPD rate was higher in the rubber trees tapped at the highest frequency (treatment 2: d3-4/y) with a value of 6.8% than in those in pattern 3, which had a rate of 4.3%. When trees were stimulated at the same level (4/y or 8/y), the TPD rate decreased with the reduction in tapping frequency.

  • Figure 3. Average tapping panel dryness (TPD) rates of trees of the Hevea brasiliensis clones IRCA 111, IRCA 130 and PB 260, of the metabolically active class, in the southwestern region of Côte d'Ivoire after nine years of latex harvesting in downward bleeding on virgin bark of the low panel (Trait treatment, Trait 1: S/2 d2 nil stimulation; Trait 2: S/2 d3 6d/7 ET2.5 % Pa1(1) 4/y; Trait 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 4/y; Process 4: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Process 5: S/2 d5 6d/7 SD2.5 % Pa1(1) 8/y; Process 6: S/2 d6 6d/7 SD2.5 % Pa1(1) 10/y)
3.4. Impact of Different Latex Harvesting Technologies on Dry Rubber Production, Radial Vegetative Growth and Tapping Panel Dryness Rate of Three Moderate Metabolism Hevea brasiliensis Clones: GT 1, RRIC 100 and BPM 24
3.4.1. Average Annual Dry Rubber Production Of Clones

Table 4 shows the average annual dry rubber production of the clones GT 1, RRIC 100 and BPM 24 under different treatments in southwestern Côte d'Ivoire during nine years of experimentation.


3.4.1.1. Dry Rubber Production in g.t-1.t-1

Trees in treatment 6 (d6-10/y) produced 77 g.t-1.t-1 which was higher than those in treatments 1 (29 g.t-1.t-1); 2 (47 29 g.t-1.t-1); (59 29 g.t-1.t-1), 4 (59 29 g.t-1.t-1) and 5 (67 29 g.t-1.t-1). The productions of rubber trees tapped at the same frequency d4, treatments 3 (d4-6/y) and 4 (d4-10/y) were identical (59 g.t-1.t-1). For trees stimulated at the same level, 6/y, productions were higher with treatment 3 (59 29 g.t-1.t-1 than with treatment 2 (47 29 g.t-1.t-1). For the 10/y stimulation regime, productions were higher (Table 4) with rubber trees in treatment 5 (67 29 g.t-1.t-1) than with those in pattern 4 (59 29 g.t-1.t-1).

  • Table 4. Average annual dry rubber production of all GT 1, RRIC 100 and BPM 24 clones of the moderate metabolism class, expressed in g.t-1.t-1; g.t-1.yr-1 and in kg.ha-1.yr-1 as a function of treatments in southwestern Côte d'Ivoire after nine years of experimentation


3.4.1.2. Dry Rubber Production in g.t-1.yr-1

The results showed that the production of treatment 2 (4677 g.t-1.yr-1) was higher than those of patterns 1 (4439 g.t-1.yr-1), 3 (4472 g.t-1.yr-1), 4 (4481 g.t-1.yr-1), 5 (4278 g.t-1.yr-1) and 6 (3849 g.t-1.yr-1). The production of d2-bleached and unstimulated trees in treatment 1 (467 g.t-1.yr-1) was equal to that of treatments 3 (d4-6/y) (4472 g.t-1.yr-1), 4 (d4-10/y) (4481 g.t-1.yr-1) and 5 (d5-10/y) (4278 g.t-1.yr-1). For trees tapped at the same frequency d4, the productions of trees in treatments 3 (4472 g g.t-1.yr-1 and 4 (4481 g.t-1.yr-1) were identical (Table 4).


3.4.1.3. Dry Rubber Production in kg.ha-1.yr-1

The yields of the d2 tapped and unstimulated trees of treatment 1 (2057 kg.ha-1.yr-1) and of the d4 tapped and 10 times stimulated trees of treatment 4 (2066 kg.ha-1.yr-1), were identical to those of the d3 iapped and 6 times stimulated trees of treatment 2 (2145 kg.ha-1.yr-1) Treatments 3 (2038 kg.ha-1.yr-1) and 5 (1980 kg.ha-1.yr-1), whose trees were stimulated 6 and 10 times per year respectively and tapped at frequencies d4 and d5, had identical productions. For rubber trees tapped at the same frequency d4, the yields of latex harvesting technologies 3 (2038 kg.ha-1.yr-1) and 4 (2066 kg.ha-1.yr-1) were equivalent (Table 4).


3.4.2. Radial Vegetative Trunk Growth of Clones

Figure 4 shows the effect of the six treatments on the average vegetative growth of trees of Hevea brasiliensis clones GT 1, RRIC 100 and BPM 24. In general, treatments 1 (69.4 cm), 3 (67.5 cm) and 6 (68.5 cm) produced radial vegetative growth of the same magnitude. The circumferences of latex harvesting technologies 2 (66.2 cm), 4 (66.5 cm) and 5 (66.7 cm) were similar. At equal tapping frequency (d4), trees in patterns 3 and 4 had circumferences of 67.5 cm and 66.5 cm, respectively, which were identical. Similarly, for rubber trees stimulated with the same regime (6/y for treatments 2 and 3 and then 10/y for patterns 4 and 5), the circumferences were identical. The circumference value of trees in treatment 3 (67.5 cm), was identical to those in treatments 2 (66.2 cm), 4 (66.5 cm) and 5 (66.7 cm).

  • Figure 4. Average tree trunk circumferences as a function of treatments for the GT 1, RRIC 100 and BPM 24 clones after nine years of experimentation in southwestern Côte d'Ivoire (Trait: treatment; Treatment 1: S/2 d2 nil stimulation; Treatment 2: S/2 d3 6d/7 ET2.5 % Pa1(1) 6/y; Treatment 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 6/y; Process 4: S/2 d4 6d/7 SD2.5 % Pa1(1) 10/y; Process 5: S/2 d5 6d/7 SD2.5 % Pa1(1) 10/y; Process 6: S/2 d6 6d/7 SD2.5 % Pa1(1) 12/y; a, b: mean circumferences assigned the same letter are not significantly different (Scheffe's test at 5%))

3.4.3. Average Tapping Panel Dryness Rate for the Three Clones

Figure 5 shows the percentage TPD rate generated by each treatment applied to trees of the Hevea brasiliensis clones GT 1, RRIC 100 and BPM 24 in southwestern Côte d'Ivoire. In general, TPD rates were moderate to moderate regardless of treatment. These rates ranged from 2% to 6%. Treatment 4 (d4-10/y) produced the highest TPD rate at 5.8%, while the lowest rate was obtained with trees in patterns 5 (2.5%) and 6 (2.9%). For trees tapped at the same d4 frequency, such as those in treatments 3 (3.6%) and 4 (5.8%), the TPD rate was higher with treatment 4. For the same 10/y stimulation level, latex harvesting technologies 4 (5.8%) and 5 (2.6%), TPD rates were higher with treatment 4.

  • Figure 5. tapping panel dryness rate of trees in the GT 1, RRIC 100 and BPM 24 clone set of Hevea brasiliensis, from the moderate metabolic class of clones, in the southwestern region of Côte d'Ivoire after nine years of latex harvesting in downward tapping on virgin bark of the lower panel (trait treatment; Trait1: S/2 d2 nil stimulation; Treatment2 : S/2 d3 6d/7 ET2.5 % Pa1(1) 6/y; Trait3: S/2 d4 6d/7 SD2.5 % Pa1(1) 6/y; Process4: S/2 d4 6d/7 SD2.5 % Pa1(1) 10/y; Process5: S/2 d5 6d/7 SD2.5 % Pa1(1) 10/y; Process6: S/2 d6 6d/7 SD2.5 % Pa1(1) 12/y)
3.5. Impacts of Different Latex Harvesting Technologies on Dry Rubber Production, Radial Vegetative Growth and Tapping Panel Dryness Rate of Slow Metabolizing Hevea brasiliensis Clones: PB 217 and PR 107
3.5.1. Average Annual Dry Rubber Production of Clones

Table 5 presents the average annual dry rubber production expressed in g.t-1.t-1; g.t-1.yr-1 and kg.ha-1.yr-1 of the clones PB 217 and PR 107 under different treatments in southwestern Côte d'Ivoire.


3.5.1.1. Dry Rubber Production in g.t-1.t-1

Production increased with the reduction in latex harvesting intensity. In fact, the lower the tapping frequency, the higher the production (Table 5). The production (73 g.t-1.t-1) of pattern 6 (d6-18/y) was higher than that of the other treatments. For the same tapping frequency d4, production was higher with pattern 4 (58 g.t-1.t-1) than with treatment 3 (53 g.t-1.t-1). At the same stimulation rate of 8/y, the rubber trees in treatment 3 produced 53 g.t-1.t-1 more than those in treatment 2, which produced 46 g.t-1.t-1.


3.5.1.2. Dry Rubber Production in g.t-1.yr-1

Plants tapped in d4 and stimulated 12 times per year (treatment 4) gave a production of 4473 g.t-1.yr-1 identical to that of pattern 2 (4645 g.t-1.yr-1). This production was higher than that of the other treatments (Table 5). Treatment 5 (4146 g.t-1. yr-1) had the same production as treatment 3 (3968 g.t-1.yr-1). This value was higher than those of treatments 1 (3617 g.t-1.yr-1) and 6 (3777 g.t-1.yr-1). Latex harvesting technology 3 (3968 g.t-1.yr-1) had the same production as motif 6 (3777 g.t-1.yr-1). The most frequently tapped rubber trees (treatment 1) had productions of 3617 g.t-1.yr-1, which were identical to the most, stimulated trees (treatment 6) which were 3777 g.t-1.yr-1.


3.5.1.3. Dry Rubber Production in kg.ha-1.yr-1

The dry rubber production in kg.ha-1.yr-1 of treatment 2 (2107 kg.ha-1.yr-1) was higher than that of the other treatments. On the other hand, the dry rubber yields of the most frequently tapped (d2) and unstimulated trees in treatment 1 (1561 kg.ha-1.yr-1), as well as that of the lowest frequency tapped(d6) rubber trees in pattern 6 (1605 kg.ha-1.yr-1) and stimulated at the highest intensity (18/y), were identical. The yields of treatments 3 (d4-8/y) and 5 (d5-15/y) with values of 1771 and 1779 kg.ha-1.yr-1 respectively were equivalent (Table 5). At equal stimulation regimes (8/y), rubber production was higher with treatment 2 (2107 kg.ha-1.yr-1) than with pattern 3 (1771 kg.ha-1.yr-1). For the same tapping frequency d4, the yield of treatment 4 (1923 kg.ha-1.yr-1) was higher than that of treatment 3 (1771 kg.ha-1.yr-1).

  • Table 5. Average annual dry rubber production of the PR 107 and PB 217 slow-metabolizing clones expressed in g.t-1.t-1; g.t-1.yr-1 and kg.ha-1.yr-1 as a function of treatments in the southwest region of Côte d'Ivoire after nine years of experimentation


3.5.2. Average Radial Vegetative Trunk Growth of All Clones

Figure 6 shows the impact of the six latex harvesting technologies on the mean radial vegetative growth of trees of Hevea brasiliensis clones PB 217 and PR 107. In general, the girth, 77.9 cm, of unstimulated trees (treatment 1) was higher than that of trees in patterns 2 (d3-8/y), 4 (d4-12/y) and 5 (d5-15/y), whose values were 73.3, 73.9 and 73.5 cm, respectively. These were identical. Trees in treatments 1 (77.9 cm); 3 (75 cm) and 6 (74.7 cm) had identical circumferences. These values were equivalent to those of trees in treatments 2, 4 and 5. For the same tappings frequency d4, treatments 3 (75 cm) and 4 (73.9 cm) had circumferences of the same order of magnitude. Similarly, when the rubber trees were stimulated at the same level, 8/y (treatments 2 and 3), the tree circumferences were identical.

  • Figure 6. Average tree trunk circumferences as a function of treatments for the PB 217 and PR 107 clones after nine years of experimentation in southwestern Côte d'Ivoire (Trait: treatment; Treatment1 : S/2 d2 nil stimulation; Treatment2 : S/2 d3 6d/7 ET2.5 % Pa1(1) 8/y; Treatment3: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Process4: S/2 d4 6d/7 SD2.5 % Pa1(1) 12/y; Process5: S/2 d5 6d/7 SD2.5 % Pa1(1) 15/y; Process6: S/2 d6 6d/7 SD2.5 % Pa1(1) 18/y; Process6: S/2 d6 6d/7 AND 2.5 % Pa 1(1) 18/y; a,b, : mean circumferences assigned the same letter are not significantly different (Scheffe's test at 5%))

3.5.3. Average Tapping Panel Dryness Rates for All Clones

The dry tapping panel dryness (TPD) rates generated by each treatment applied to trees of Hevea brasiliensis clones PB 217 and PR 107 in southwestern Côte d'Ivoire were presented in Figure 7. The results show that the TPD rate is low (less than 3.5%) regardless of treatment. Trees harvested under pattern 1 (d2-nil stimulation) showed the highest TPD rate (3.25%), while those under treatment 3 (d4-8/y) gave the lowest rate (1.3%). When trees were tapped at the same frequency d4 (treatments 3 and 4), the TPD rate of treatment 4 (2.2%) was higher than that of pattern 3 (1.3%). In contrast, when the rubber trees were stimulated at the same rate (8/y), (treatments 2 and 3), the TPD rates of treatment 2 (1.6%) were of the same order of magnitude as those of treatment 3 (1.3%).

  • Figure 7. Tapping panel dryness rate of trees in the PB 217 and PR 107 clones of Hevea brasiliensis, from the slow-metabolizing clone class, in the southwestern region of Côte d'Ivoire after nine years of downward bleeding latex harvesting on virgin bark of the lower panel (trait: treatment; Trait1: S/2 d2 nil stimulation; Treatment2 : S/2 d3 6d/7 ET2.5 % Pa1(1) 8/y; Trait3: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Process4: S/2 d4 6d/7 SD2.5 % Pa1(1) 12/y; Process5: S/2 d5 6d/7 SD2.5 % Pa1(1) 15/y; Process6: S/2 d6 6d/7 SD2.5 % Pa1(1) 18/y)
3.6. Relationships between Metabolic Classes in Relation to Dry Rubber Production

Regardless of dry rubber production (expressed in kg.ha-1.yr-1 or in g.t-1.t-1) and tapping frequency, the group or class of clones with active metabolism gave the highest production, followed by the group of clones with moderate metabolism and finally the group with slow metabolism (Table 6). The differences in productivity between the clones of the active metabolism class and those of the moderate and slow metabolism classes were greater under unstimulated conditions (24 and 50%) than under stimulated conditions (16.4 and 19.6%). However, in the stimulated regime, this difference in productivity increased with the reduction in tapping frequency (Table 7). The average annual increase in rubber trunk circumferences was lower in the moderate metabolic class clones than in the active and slow metabolic classes (Table 8). In Table 8, TPD rates were lower for the slow metabolic clones (1.3 to 3.3%) than for the moderate (2.5 to 6.7%) and active (4 to 9.5%) metabolic classes.

  • Table 7. Difference in productivity (%) between the group of clones of the active metabolism class and the groups of clones with moderate and slow metabolism under stimulated and unstimulated regimes according to the tappings frequencies

3.7. Relationships between Metabolic Classes in Relation to Tree Circumference, Tapping Panel Dryness Rate and Tapping Intensity of Clones

For clones with active metabolism (Figure 8): dry rubber production was very strongly related, by a polynomial relationship, to tree circumference (R² = 0.9237 (Figure 8A)), to TPD rate (R² = 0.9285 (Figure 8B)) and to tapping intensity (R² = 0.9977 (Figure 8C)) For the moderate metabolism clones (Figure 9): dry rubber production was related by a very strong polynomial relationship to rubber circumference (R² = 0.9833 (Figure 9A)), by an exponential relationship to TPD rate (R² = 0.4265 (Figure 9B)) and by a very strong polynomial relationship to tapping intensity (R² = 0.9996 (Figure 9C)). As for the slow metabolism clones (Figure 10): dry rubber production was very strongly related by a polynomial relationship to tree circumference (R² = 0.9646 (Figure 10A)), as well as to TPD rate by the same type of relationship (R² = 0.7348 (Figure 10B)). On the other hand, production was linked by a very strong linear relationship (r² = 0.9980) to tapping intensity (R² = 0.9962 (Figure 10C)).

  • Figure 10. Relationship between production g.t-1.t-1and rubber tree circumference, tapping panel dryness rate and tapping intensity of slow metabolism clones (A: Polynomial regression between tree circumferences and production g.t-1.t-1; B: Polynomial regression between dry notch rates (%) and production g.t-1.t-1; C: Linear regression between bleeding intensity and production g.t-1.t-1)

4. Discussion

Our rubber production results for the three metabolic classes and four tapping frequencies are presented as follows: for active metabolism d3 (53 g.t-1.t-1), d4 (68 g.t-1.t-1), d5 (79 g.t-1.t-1), d6 (91 g.t-1.t-1) for moderate metabolism d3 (47 g.t-1.t-1), d4 (59 g.t-1.t-1), d5 (67 g.t-1.t-1), d6 (77 g.t-1.t-1) and finally for slow metabolism d3 (46 g.t-1.t-1), d4 (58 g.t-1.t-1), d5 (66 g.t-1.t-1), d6 (73 g.t-1.t-1). These values showed that regardless of clone and metabolic activity class, rubber production per tree and per tapping expressed in grams (g.t-1.t-1) increased with the reduction of tapping frequency. Low tapping frequency is positively correlated with high rubber production. However, the time (in days) between two consecutive tappings is important for rubber production. For example, there are 3, 4, 5 and 6 days between one tapping and the next for tapping frequencies d3, d4, d5 and d6 respectively. Consequently, the longer the time between two consecutive tappings, the greater the quantity of rubber harvested, which reflects a better in situ regeneration of latex and therefore of rubber 1, 2, 27, 28, 29. This production, which expresses the productivity of a tree when tapped, appears to depend on two important factors: the latex regeneration capacity, ensured by the laticifere cell, a real rubber factory as already shown by some authors 30, and the flow time, which is linked to the intrinsic value of the clone, but also in part to the tapping frequency. The first factor, regeneration, is very strongly influenced by the frequency of tapping, and thus by the time in days between two consecutive tappings. In this respect, our results, in agreement with those of several authors 9, 10, 28, 31, 32, are explained by the fact that the practice of tappings leads the tree to reconstitute the harvested latex. The greater the volume of latex to be produced, the greater the energy required to reconstitute it, and vice versa. For the second factor, the time of flow is strongly dependent on the clone and the activity class of its latex (rubber) producing metabolism. The importance of the resulting rubber production is variable among the clone groups in our study. Indeed, without stimulation, the rubber productivity of the clones with active metabolism (36 g t-1t-1) is 24 and 50% higher than that of the clones with moderate (29 g t-1t-1) and slow (24 g t-1t-1) metabolism respectively. However, this result shows, in relation to the first factor, that the greater the amount of energy expended to reconstitute this latex, the less activated the intrinsic metabolism of the clone concerned is. This corroborates the work of 2, 3, 9, 10, 28, 32. We deduce that the energy, ensuring the reconstitution of rubber production between two consecutive tappings, being proportional to the initial (intrinsic) activation, probably allowed this author 33, 34 to define the very important notion of clonal typology of metabolic functioning. The clones with an active or fast metabolism are therefore a reference since their metabolism has enough energy, without stimulation, to activate the production of rubber, in order to reach a good level of production. The other groups or classes of clones with moderate or medium or intermediate and slow or not very active metabolisms need additional energy for the activation of their metabolism in order to reach, approach, or even exceed the rubber production of the group of clones with active metabolism. This additional energy is exogenous 9, 10, 29, 35 and is provided by stimulation, usually hormonal, almost exclusively from Etherephon (2-Chloroethyl Phosphonic Acid or CEPA) 36, 37, 38. Etephon applied to the tree generates ethylene, a plant hormone that activates the regeneration metabolism in situ 9, 10, 39, 40. In the case of rubber production per hectare, (ha) per year, regardless of the clone and the metabolic activity class, rubber production is more important when the tapping frequency is high. Indeed, the production for the three metabolisms and the four tapping frequencies are as follows: for the active metabolism d2 (2398 kg.ha-1.yr-1); d3 (2356 kg.ha-1.yr-1); d4 (2277 kg.ha-1.yr-1); d5 (2187 kg.ha-1.yr-1); d6 (2001 kg.ha-1.yr-1), for the moderate metabolism d2 (2057 kg.ha-1.yr-1); d3 (2145 kg.ha-1.yr-1); d4 (2066 kg.ha-1.yr-1); d5 (1980 kg.ha-1.yr-1); d6 (1763 kg.ha-1.yr-1), and finally for slow metabolism d2 (1561 kg.ha-1.yr-1); d3 (2107 kg.ha-1.yr-1); d4 (1923 kg.ha-1.yr-1); d5 (1779 kg.ha-1.yr-1); d6 (1605 kg.ha-1.yr-1). In contrast to the production per tapping and per tree, the higher the tapping frequency, the higher the production. Tappings frequencies, independently of the clone and its metabolism, are also characterized by the number of annual tappings. Thus, we note 156, 104, 78, 62 and 52 annual tappings for bleeding frequencies d2, d3, d4, d5 and d6 respectively. Our yield results (kg.ha-1.yr-1) show that the quantity of rubber harvested increases with the number of annual tapping operations. This observation is contrary to the results obtained on the production per tree per tapping. However, this type of production (kg.ha-1.yr-1) is the one that interests all the growers who expect more rubber production per unit area, especially per hectare. This parameter is therefore the most important in the rubber industry. Our results have the advantage of showing the impact of hormonal stimulation of rubber production on the productivity of plantations, depending on the metabolic class of the clone. Indeed, we have already shown that in the absence of hormonal stimulation of rubber production, the difference in productivity between clones with active metabolism and those with moderate and slow metabolism is respectively 24 and 50%. Under stimulation, this difference in productivity, all tapping frequencies combined, is reduced to 16.4 and 19.6% respectively. This means that the effect of stimulation is equivalent to 7.6 and 30.4% between the metabolically active clones and those with moderate and slow metabolisms respectively. These results highlight the involvement of clone metabolism, and therefore the intrinsic metabolic energy of the clone, in the expression of the response to hormonal stimulation. Indeed, compared to our initial metabolic energy reference, the effort or exogenous energy input 9, 10, 40 to achieve a good production, is all the greater as the clone metabolism, in the absence of stimulation, is little or not active. The amount of exogenous energy provided by the stimulation coupled with the level of rubber production, determines in the same way, the response to hormonal stimulation of the clone's rubber production.

5. Conclusion and Recommendation

At the end of the present work, our general hypothesis that rubber production can be improved while maintaining a good physiological condition of rubber trees by choosing latex harvesting technologies according to metabolic class was verified. Indeed, by choosing latex harvesting technology according to metabolic class, rubber production as well as radial vegetative growth were significantly improved. The sensitivity to dry rot was reduced. Our results showed that, regardless of clone and metabolic class, the hormonally unstimulated rubber trees bled at the d2 frequency showed the largest girths. This is a physiological advantage. Therefore, it would be important to verify the influence of the absence of hormonal stimulation on radial vegetative growth, rubber production and susceptibility to dry notching with bleeding frequencies d3, d4, d5 and d6. The expected results will allow producers to make considerable gains, since the investment in the purchase of stimulants and in labor will be reduced. Our results provide effective solutions to both concerns of rubber farmers, namely the development of latex harvesting technologies to improve the production potential of trees and the availability and cost of labour for tapping.

The work we have developed related to Hevea brasiliensis latex harvesting technologies, and aiming to produce more than 1700 kg.ha-1.yr-1 of dry rubber with high vegetative growth (average annual increment ≤ 2 cm/yr), moderate bark consumption (15 < Bark Consumed < 18cm), low dry notch rate (< 5%), are strongly in favor of abandoning latex harvesting technologies based on the d2 tapping frequency.

We therefore recommend the following latex harvesting technologies:

Clones of the metabolically active class:

v S/2 d3 6d/7 ET2.5% Pa1(1) 4/y

v S/2 d4 6d/7 ET2.5% Pa1(1) 4/y

v S/2 d5 6d/7 ET2.5% Pa1(1) 8/y

v S/2 d6 6d/7 ET2.5% Pa1(1) 10/y

Moderate metabolic clones:

v S/2 d3 6d/7 ET2.5% Pa1(1) 6/y

v S/2 d4 6d/7 ET2.5% Pa1(1) 6/y

v S/2 d5 6d/7 ET2.5% Pa1(1) 10/y

v S/2 d6 6d/7 ET2.5% Pa1(1) 12/y

Slow metabolizing clones:

v S/2 d3 6d/7 ET2.5% Pa1(1) 8/y

v S/2 d4 6d/7 ET2.5% Pa1(1) 12/y

v S/2 d5 6d/7 ET2.5% Pa1(1) 15/y

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Diarrassouba Moussa, Tuo Seydou, Camara Brahima, Obouayeba Samuel. Adaptation of Latex Harvesting Technologies to the Three Metabolic Activity Classes of Rubber Clones According to Socio-economic Conditions in Côte d'Ivoire. American Journal of Food and Nutrition. Vol. 10, No. 1, 2022, pp 1-15. http://pubs.sciepub.com/ajfn/10/1/1
MLA Style
Moussa, Diarrassouba, et al. "Adaptation of Latex Harvesting Technologies to the Three Metabolic Activity Classes of Rubber Clones According to Socio-economic Conditions in Côte d'Ivoire." American Journal of Food and Nutrition 10.1 (2022): 1-15.
APA Style
Moussa, D. , Seydou, T. , Brahima, C. , & Samuel, O. (2022). Adaptation of Latex Harvesting Technologies to the Three Metabolic Activity Classes of Rubber Clones According to Socio-economic Conditions in Côte d'Ivoire. American Journal of Food and Nutrition, 10(1), 1-15.
Chicago Style
Moussa, Diarrassouba, Tuo Seydou, Camara Brahima, and Obouayeba Samuel. "Adaptation of Latex Harvesting Technologies to the Three Metabolic Activity Classes of Rubber Clones According to Socio-economic Conditions in Côte d'Ivoire." American Journal of Food and Nutrition 10, no. 1 (2022): 1-15.
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  • Figure 2. Average trunk circumferences of all trees according to treatments for the IRCA 111, IRCA 130 and PB 260 clones after nine years of experimentation in southwestern Côte d'Ivoire (Trait: treatment; Treatment 1: S/2 d2 nil stimulation; Treatment 2: S/2 d3 6d/7 ET2.5 % Pa1(1) 4/y; Treatment 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 4/y; Treatment 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Treatment 3: S/2 d5 6d/7 SD2.5 % Pa1(1) 8/y; Treatment3 : S/2 d6 6d/7 SD2.5 % Pa1(1) 10/y; a, b: results with the same letter are not significantly different (Scheffe test at 5%))
  • Figure 3. Average tapping panel dryness (TPD) rates of trees of the Hevea brasiliensis clones IRCA 111, IRCA 130 and PB 260, of the metabolically active class, in the southwestern region of Côte d'Ivoire after nine years of latex harvesting in downward bleeding on virgin bark of the low panel (Trait treatment, Trait 1: S/2 d2 nil stimulation; Trait 2: S/2 d3 6d/7 ET2.5 % Pa1(1) 4/y; Trait 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 4/y; Process 4: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Process 5: S/2 d5 6d/7 SD2.5 % Pa1(1) 8/y; Process 6: S/2 d6 6d/7 SD2.5 % Pa1(1) 10/y)
  • Figure 4. Average tree trunk circumferences as a function of treatments for the GT 1, RRIC 100 and BPM 24 clones after nine years of experimentation in southwestern Côte d'Ivoire (Trait: treatment; Treatment 1: S/2 d2 nil stimulation; Treatment 2: S/2 d3 6d/7 ET2.5 % Pa1(1) 6/y; Treatment 3: S/2 d4 6d/7 SD2.5 % Pa1(1) 6/y; Process 4: S/2 d4 6d/7 SD2.5 % Pa1(1) 10/y; Process 5: S/2 d5 6d/7 SD2.5 % Pa1(1) 10/y; Process 6: S/2 d6 6d/7 SD2.5 % Pa1(1) 12/y; a, b: mean circumferences assigned the same letter are not significantly different (Scheffe's test at 5%))
  • Figure 5. tapping panel dryness rate of trees in the GT 1, RRIC 100 and BPM 24 clone set of Hevea brasiliensis, from the moderate metabolic class of clones, in the southwestern region of Côte d'Ivoire after nine years of latex harvesting in downward tapping on virgin bark of the lower panel (trait treatment; Trait1: S/2 d2 nil stimulation; Treatment2 : S/2 d3 6d/7 ET2.5 % Pa1(1) 6/y; Trait3: S/2 d4 6d/7 SD2.5 % Pa1(1) 6/y; Process4: S/2 d4 6d/7 SD2.5 % Pa1(1) 10/y; Process5: S/2 d5 6d/7 SD2.5 % Pa1(1) 10/y; Process6: S/2 d6 6d/7 SD2.5 % Pa1(1) 12/y)
  • Figure 6. Average tree trunk circumferences as a function of treatments for the PB 217 and PR 107 clones after nine years of experimentation in southwestern Côte d'Ivoire (Trait: treatment; Treatment1 : S/2 d2 nil stimulation; Treatment2 : S/2 d3 6d/7 ET2.5 % Pa1(1) 8/y; Treatment3: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Process4: S/2 d4 6d/7 SD2.5 % Pa1(1) 12/y; Process5: S/2 d5 6d/7 SD2.5 % Pa1(1) 15/y; Process6: S/2 d6 6d/7 SD2.5 % Pa1(1) 18/y; Process6: S/2 d6 6d/7 AND 2.5 % Pa 1(1) 18/y; a,b, : mean circumferences assigned the same letter are not significantly different (Scheffe's test at 5%))
  • Figure 7. Tapping panel dryness rate of trees in the PB 217 and PR 107 clones of Hevea brasiliensis, from the slow-metabolizing clone class, in the southwestern region of Côte d'Ivoire after nine years of downward bleeding latex harvesting on virgin bark of the lower panel (trait: treatment; Trait1: S/2 d2 nil stimulation; Treatment2 : S/2 d3 6d/7 ET2.5 % Pa1(1) 8/y; Trait3: S/2 d4 6d/7 SD2.5 % Pa1(1) 8/y; Process4: S/2 d4 6d/7 SD2.5 % Pa1(1) 12/y; Process5: S/2 d5 6d/7 SD2.5 % Pa1(1) 15/y; Process6: S/2 d6 6d/7 SD2.5 % Pa1(1) 18/y)
  • Figure 8. Relationship between production g.t-1.t-1 and rubber tree circumference, tapping panel dryness rate and tapping intensity of metabolically active clones (A : Polynomial regression between tree circumferences and production g.t-1.t-1; B : Polynomial regression between TPD rates (%) and production g.t-1.t-1; C: Polynomial regression between tapping intensity and production g.t-1.t-1)
  • Figure 9. Relationships between production g.t-1.t-1 and rubber tree circumference, tapping panel dryness rate and tapping intensity of moderate metabolism clones (A : Polynomial regression between tree circumferences and production g.t-1.t-1, B : Exponential regression between dry notch rates (%) and production g.t-1.t-1, C: Polynomial regression between bleeding intensity and production g.t-1.t-1)
  • Figure 10. Relationship between production g.t-1.t-1and rubber tree circumference, tapping panel dryness rate and tapping intensity of slow metabolism clones (A: Polynomial regression between tree circumferences and production g.t-1.t-1; B: Polynomial regression between dry notch rates (%) and production g.t-1.t-1; C: Linear regression between bleeding intensity and production g.t-1.t-1)
  • Table 1. Physiological and agronomic characteristics of Hevea brasiliensis clones IRCA 111, IRCA 130, PB 260, GT 1, RRIC 100, BPM 24, PB 217 and PR 107 distributed in the three metabolic classes (active, moderate and slow)
  • Table 3. Average annual dry rubber production of all IRCA 111, IRCA 130, PB 260 clones of the metabolically active class, expressed in g.t-1.t-1 ; g.t-1.yr-1 and in kg.ha-1.yr-1 as a function of treatments in the southwest of Côte d'Ivoire after nine years of experimentation
  • Table 4. Average annual dry rubber production of all GT 1, RRIC 100 and BPM 24 clones of the moderate metabolism class, expressed in g.t-1.t-1; g.t-1.yr-1 and in kg.ha-1.yr-1 as a function of treatments in southwestern Côte d'Ivoire after nine years of experimentation
  • Table 5. Average annual dry rubber production of the PR 107 and PB 217 slow-metabolizing clones expressed in g.t-1.t-1; g.t-1.yr-1 and kg.ha-1.yr-1 as a function of treatments in the southwest region of Côte d'Ivoire after nine years of experimentation
  • Table 6. Dry rubber production in kg.ha-1.yr-1, g.t-1.t-1 by metabolic class according to tapping frequency
  • Table 7. Difference in productivity (%) between the group of clones of the active metabolism class and the groups of clones with moderate and slow metabolism under stimulated and unstimulated regimes according to the tappings frequencies
  • Table 8. Average annual girth increase and average tapping panel dryness rate based on active, moderate and slow metabolism clone groups
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