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Spatial distribution of sucrose and metabolic activity in the laticiferous tissue of three Hevea brasiliensis clones : Effects of tapping and ethephon stimulation at trunk scale

This study aims at describing the sucrose balance between supply and utilization in the latex producing bark of the tubber tree, as well as the concurrent latex metabolic activity. Experiments were set up on 3 Hevea brasiliensis clones (PB235, RRIM 600 and GT1) on the same polyclonal plot of Chachoengsao Rubber Research Center (CRRC-DOA). Treatments included untapped trees (growth potential control), trees tapped without stimulation (½ S d/3 6d/7 9m/12, physiological control) and trees tapped with Ethephon stimulation (½ S d/3 6d/7 9m/12 ET 2.5% 5/y and 12/y). The results confirmed the significant effect of tapping on whole trunk latex physiology. A huge depletion of the latex sucrose concentration was demonstrated. The Latex Diagnosis Mapping method (LDM) allowed a rather precise description of the shape and the size of the latex regeneration area and the metabolically active bark area. A multi-clonal linear relation between rubber production and estimated latex regeneration area indicates that the regeneration of 1 g of dry rubber requires an average of ca. 100 cm2 latex regeneration area. By assessing the impact of any tapping system on whole trunk latex physiology, the LDM method could be used successfully in order to provide new ideas for imagination and/or optimization of new tapping systems like ethylene gas stimulated systems, micro-tapping cut systems and multi-tapping cut systems, as based on a better physiological knowledge of the whole rubber tree functioning. In Thailand, the rubber tree (Revea brasiliensis Muell. Arg.) is one of the major economic crops, as it directly or indirectly supports around 10 % of the country population. Concerning on economic value, not only latex production, but also wood timber brings about a significant income to the farmers. Both rubber production and growth require assimilates from photosynthesis, mainly in the form of sucrose. As farmers' benefit relies on a suitable management in order to keep a suitable balance between rubber production and plant growth, it is worth understanding the influence of regular tapping or stimulation on the growth of the tree. As a matter of fact, a negative relation exists between latex production and wood biomass creation (Templeton 1968, Wycherley 1976, Sethuraj 1981, 1985, Gohet 1996, Gohet et al. 1996). The aim of this study is to describe but also to quantify the sucrose balance between supply and utilization in the latex producing bark of the rubber tree, as well as the concurrent latex metabolic activity. Such a study cannot be restricted to the only tapped panel, as some other bark areas may be likewise involved or at least affected by the latex regeneration process. Physiological analyses are therefore carried out as well on the untapped bark area, in order to map the latex metabolic activity and the concurrent latex sucrose availability at the trunk level. Ethephon stimulation is used as a physiological tool in order to study the influence of an increased rubber production, and therefore an enhanced latex regeneration, on the metabolic characteristics of the latex sink. Former authors already worked this subject in the past. Lustinec and Resing (1965) found, using radio-labeled isotopes, that the flow area of recently opened rubber tree was distributed about 40-50 cm above and below the tapping cut. On. older trees, these authors showed that this area could extend up to 70 cm above the cut and to the whole area below the tapping cut. Buttery and Boatman (1966), using turgor pressure measurements to determine drained area, reported a pressure drop down to 1.20 m below the trapping cut. Pakianathan et al. (1975) termed "Potential displacement area" a bark area where rapid movement of latex near the region of the tapping cut could occur. Tupy (1973 a) showed that sucrose latex content was depleted below and above the tapping cut as a consequence of latex regeneration process. Nevertheless, none of these studies concurrently described the sucros