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It is well known that the productivity and the susceptibility to the tapping panel dryness (TPD) of Hevea brasiliensis are determined by the intrinsic feature of each clone but also by the tapping system. Thus, in order to establish the tapping system that minimizes the TDP occurrence an experiment was carried out in Côte d'Ivoire with four high yielding clones including, PB 235, PB 255, IRCA 18 and IRCA 111. Five tapping systems (d2 6d/7 0/y, d3 6d/7 4/y, d4 6d/7 6/y, d5 6d/7 8/y, d6 6d/7 10/y) were applied to these clones, corresponding to a range of 100 % to 30 % of tapping intensities. The results show that the occurrence of TPD is closely related to the tapping intensity and the tapping system which consists in tapping twice per week with one day rest (S/2 d3 6d/7 4/y), was found to be the best tapping system. A quadratic relation was found between the rate of the TPD and the tapping intensity. Thus the clones IRCA 18 and IRCA 111, like PB 235 and PB 255, belong to the active metabolism clones. These clones also showed their adherence to the group of high rubber producer clones. This experiment also gave further evidence that the production of a tree for the tapping strongly depends on the intensity of tapping. It has also indicated that the intensity of tapping governed the tapping panel dryness rate among the clones having active metabolism, such as IRCA 18, IRCA 111, PB 235 and PB 255.

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The cultivation of Hevea brasiliensis, main source of natural rubber, is facing a problem of scarcity and/or high cost of skilled labour. One of the means to remedy this constraint is to reduce the intensity of tapping. This work aims at studying in clone PR 107 of Hevea brasiliensis, in south-eastern Côte d'Ivoire, according to the nature of bark and the orientation of tapping, low intensity tapping systems but highly stimulated (S/4U d3 6d/7 . ET5.0% Pa1(1) 8-10/y(m) and S/2 d6 6d/7 . ET2.5% Pa1(1) 8-10/y(m)) enabling to reduce the need for tappers by 10 and 50% compared to a traditional tapping system (S/2 d3 6d/7 . ET5.0% Ba2(2) 4/y(3m) control). This study was carried out on the basis of agronomic and physiological criteria. The results of 21 years of exploitation have shown that reductions in the intensity of tapping were compensated for partially or totally, in terms of yield, by the strong stimulations without causing damage to the vegetative, physiological and health status of trees. The best low intensity tapping systems can be alternatives to the traditional exploitation system in order to reduce the need for tappers and thus make up for a deficit and/or a high cost of labour. These tapping systems are, on downward tapping on BI, S/2 d6 6d/7 . ET2.5% Pa1(1) 10/y(m); on upward tapping on HO, S/4 U d3 6d/7 . ET5.0% Pa1(1) 10/y(m) and on downward tapping on HO, S/4U d3 6d/7 . ET2.5% Pa1(1) 10/y(m).

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RESUMELes technologies de récolte du latex de l'hévéa peuvent être ajustées selon le clone et la disponibilité de la main-d'oeuvre saigneur. Cette étude vise à déterminer une technologie adaptée à la saignée descendante du clone PB 235 d'hévéa en conditions de faibles régimes de stimulation hormonale. Les hévéas ont été plantés selon un dispositif en blocs complètement randomisés. La fréquence de saignées d3, avec deux stimulations, et celles en d4 et d6, avec quatre stimulations ont été comparées. Les résultats ont montré que la fréquence de saignées d4 a favorisé une production de caoutchouc importante et un taux d'encoche sèche plus faible par rapport au témoin d3. Les saignées en d4 et d6 permettent de réduire le besoin en main-d'oeuvre saigneur respectivement de 25% et 50% et d'allonger la durée de saignée sur panneau bas de trois et huit ans. La d6 a enregistré une production de caoutchouc moins élevée avec un taux d'encoche sèche identique à celui de la d4. La saignée descendante en d4, plus productive, permet en outre une préservation de l'état physiologique des hévéas et, est donc plus adaptée au clone PB 235. La d6 ne peut être pratiquée qu'en situation de manque de saigneurs. © 2017 International Formulae Group. All rights reserved.Mots clés : Caoutchouc, latex, production, récolte, saigneur, technologie.Effect of latex harvesting technologies d3, d4 and d6 at lower hormonal stimulation on downward tapping of rubber tree clone PB 235 in Côte d'Ivoire ABSTRACT Latex harvesting technologies of rubber tree can be adjusted according to clone and availability of tapping manpower. This study aims at determining a technology adapted to the downward tapping of clone PB L. F. COULIBALY et al / Int. J. Biol. Chem. Sci. 11(4): 1655-1668, 2017 1656 235 in case of lower frequencies of hormonal stimulation. Rubber trees were planted according to completely randomized blocks. Tapping frequency in d3, with two stimulations, was compared with tapping in d4 and d6 both with 4 stimulations. The results showed that tapping at d4 frequency supported significant rubber production and lower rate of panel dryness compared with d3. Tapping frequencies at d4 and d6 allow reduction of the need for tapping manpower by 25% and 50% and stretch the tapping time on downward panel of three and eight years with respect to d3. The d6 recorded a lower rubber production with an identical rate of panel dryness of that of d4. Downward tapping at d4 frequency, more productive, allows besides preservation of physiological state of rubber trees and is thus more adapted to clone PB 235. The d6 is only appropriate in case of lack of tappers.

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In order to test the agronomic performance of the newly developed clones, a Large-Scale Clone Trial (LSCT) comprising Hevea brasiliensis clones GT 1, IRCA 202, IRCA 331, IRCA 707, PB 280 and PB 310 was established in southwestern Côte d'Ivoire. They were planted in completely randomized blocks with six clone treatments and four replications of 112 trees per clone. The measured parameters included isodiametric growth of the trunk, rubber yield, trees stand, latex physiological parameters and sensitivity to tapping panel dryness (TPD). Collected data was analyzed using Statistica 7.0 statistical software. After ten years of downward tapping and four years of upward tapping, clone IRCA 331 showed significantly higher rubber productivity than all other clones. Its productivity gain, relative to the reference control GT 1, was 63% in downward tapping and 80% in upward tapping. Despite its high level of productivity, the annual rate of isodiametric growth of clone IRCA 331 tree trunks (2.56 cm/year) remained statistically equivalent to that of clone GT 1 (2.62 cm/year) at latex harvesting stage. In addition, the physiological profile of clone IRCA 331 was good and similar to that of the control. Clones IRCA 331, GT1 and PB 280 got the lowest sensitivity to TPD. However, only clones GT1 and IRCA 331 maintained a good stand of tappable trees throughout the experimental period. This experiment highlighted the agronomic performance of the clone IRCA331 and allowed to put it in class 1. Clone IRCA 331 can therefore be used as a clone of first choice to improve national productivity.