Towards a physiological latex diagnosis of thai rubber plantations : First reference values of latex physiological parameters in a non-traditional rubber growing area (Chachoengsa province, Thailand)

Latex Diagnosis physiological parameters (TSC/DRC, [Suc], [Pi] and [R-SH]) have been investigated during the first two years of tapping of three clones (RRIM 600, PB 235 and GT1) in Chachoengsao Rubber Research Center (CRRC-RRIT-DOA-MOAC). Trees were tapped using a ½ S d/3 6d/7 tapping system and were submitted to different stimulation intensities in order to induce gradients of latex metabolic activity. Comparison of the concurrent evolution of these parameters with the monthly production curves showed that the suitable period to perform such LD analysis was September-October under the particular eco-climatic conditions of this non-traditional rubber growing area (Sanam Chai Khet, Chachoengsao province, Thailand: 1200 mm rainfall/year, 4-5 months of dry season). As a matter of fact, analyses performed before September represented an activating latex metabolism (highly increasing production trend), with very unstable values of metabolic parameters, especially [Suc] and [Pi]. In the contrary, analyses performed in November or later represented a decreasing metabolism, because of the decreasing production trend. Moreover, [Suc] values observed during such late analyses might be artificially increased by start of the canopy defoliation process, possibly inducing release of sugars from leaves parenchyma to phloem sap and therefore to latex. Reference values of TSC/DRC, [Suc], [Pi] and [R-SH] corresponding to an optimal latex metabolic activation of the three clones were calculated, in case of a LD analysis performed in September-October in this area. Results were in accordance with the metabolic characteristics of these clones (clonal typology). Nevertheless, an extended survey is still required to precise these reference values in order to apply them as interpretation keys of a physiological diagnosis of rubber plantations using the latex diagnosis technique. (Résumé d'auteur