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The aim of study was assessed clonal variability of starch and sugar soluble (SS) in trunk of rubber tree. The two experiments were set up, the first field compared 25 clones tested in an international clone exchange program which is now 30 years old. A second field clone trial was used for 15 years trees, with 18 clones. The results showed that an average starch in wood 71 mgGLUg/SDM and SS wood 21 mgGLU/gSDM recorded 25 clones exchange trial at 30 years were similar to the average obtained the same season in the previous study on standard clone RRIM600 age 11 years, starch 76 mgGLU/gSDM and SS 16 mgGLU/gSDM. However, mean contents SS bark 37 mgGLU/gSDM, and particularly starch in bark 25 mgGLU/gSDM were higher in the 30 years tree than the previous study SS 22 mgGLU/gSDM and starch 11 mgGLU/gSDM. The 15 years trial with 18 clones, mean content in wood were a bit higher for both starch 94 mgGLU/gSDM and SS 28 mgGLU/gSDM than the previous study. The bark SS 22 mgGLU/gSDM was similar as above but starch 41 mgGLU/gSDM was much higher than RRIM 600 age 11 years. Starch and SS in wood seems not much variable with age, However, carbohydrate contents in bark varied widely. The main source of variation may be the status of the bark Nevertheless, there was a negative correlation between cumulative yield and starch content in the bark Carbohydrate contents in clones had a high variability and heritability. Some interesting trends linking contents in the different forms of carbohydrate to clonal origin or to a well known metabolic characteristic were also detected.

After two years of tapping in Chachoengsao province, uprooting of 12 trees (clones RRIM 600, PB 235, GT1, 4 trees per clone) provided estimations of the relations existing between the total dry biomass of rubber trees and their trunk girth. These relations were found linear at least inside the studied range (trunk girth varying from 45 cm to 65 cm), but different between clones. A general model, able to estimate in one location the biomass of all clones might perhaps be set up by taking into account not only the trunk girth but also some other variables describing canopy structure, as the canopy biomass cannot be described by the trunk girth only. Nevertheless, finding and parameterizing such a model requires further survey. Thanks to the linear regression models obtained between biomass and trunk girth, biomass of the trees could be estimated at the moment of opening and after two years of tapping. Biomass partition variables could be calculated, allowing estimation of the harvest index and k factor, accounting for rubber production efficiency. Nevertheless, as these models rely on the uprooting of only 4 trees per clone, an extended survey is required to confirm their accuracy. Competition between growth and production was found linear for all three clones, confirming numerous previous studies. Clone GT1 showed a rather bad behavior regarding the competition between growth and rubber production. Clones PB 235 and RRIM 600 showed much better behaviors with lower competition between growth and production. Moreover, RRIM 600 seemed to maintain a significant growth compared to other clones during the tapping stop period (February to April 2000, dry season), sign of a better water use effectiveness. Rubber breeders in rather dry areas should aim at such a characteristic .and systematic survey of clonal girth increments during the dry season could provide a reliable picture of clonal susceptibility to draught and water stress.