Physiological responses to tapping and ethrel stimulation in latex producing bark of Hevea brasiliensis : Distribution pattern of latex sucrose content and concurrent metabolic activity at the trunk level

Four RRIM600 rubber trees, planted in 1992 and opened in May 1999 using the tapping system ½ S d/3 6d/7, with or without Ethrel® stimulation (two trees each), were used to map the latex metabolic status from different heights on both tapped (A) and untapped (B) panels. Latex was collected from puncturing at various positions of trunks and was analyzed using Latex Diagnosis technique (LD). The concurrent comparison of latex sucrose and inorganic phosphorus concentrations for every sampling position allowed estimating the size and shape of the actual latex regeneration area. Regular tapping induced latex sucrose depletion in tapped panel bark. This sucrose depletion was enhanced by the use of stimulation, as a consequence of an increased production and therefore a higher latex regeneration metabolism. Use of Ethrel® stimulation also induced a huge sucrose sink effect inside untapped panel bark and therefore even outside the metabolically active area, where sucrose concentration was about doubled. As a consequence, although obtaining a higher rubber production, the average latex sucrose concentration in the whole trunk was found higher in stimulated trees than in unstimulated ones. This might explain why a very local metabolism (the latex regeneration metabolism) has so much negative effect on the growth and biomass creation of the rubber tree: As a matter of fact, all carbohydrates stored inside latex cells, even in bark regions outside the latex regeneration area, are not available anymore for any other metabolism and in particular for growth. Many authors mentioned that the biomass loss due to the rubber production could not be accounted by this only rubber production. Latex diagnosis technique is here proved to be a powerful tool in order to study the physiology of the latex producing bark of Hevea brasiliensis and the impact of tapping systems on the latex physiology at the trunk scale. It is much simpler compared to the methods previously used to study the delimitation of the latex regeneration area, using radio-labeled isotopes or latex turgor pressure measurements. It seems also a more informative method, as it allows a concurrent description of the size and shape of the latex regeneration area as well as quantification of the metabolic activity of the different bark areas involved or affected by the latex regeneration process. (Résumé d'auteur)