Régis Lacote

Tapping panel diagnosis, an innovative on-farm decision support system for rubber tree tapping

Latex is a key product for many tropical countries, of which 80% is produced by smallholders. Latex is produced by the rubber tree (Hevea brasiliensis). Given the 7-year immature unproductive period, establishing a rubber plantation requires considerable investment by smallholders, emphasizing the need for sustainable management. The difficulty of performing an agronomic diagnosis of a tree crop is to obtain an accurate picture of current and past cultivation practices, to be able to assess their impacts on the agro-ecosystem as well as on sustainability. Smallholders do not usually keep records of latex yield or of their technical practices, making it impossible to perform a diagnosis based on productivity. As latex harvesting involves tapping the bark, which leaves scars on the trunk, we hypothesised that these morphological traces would be good indicators of current and past practices and would thus enable a diagnosis based on the economic lifespan of plantation. To this end, we formalised a tapping panel diagnosis that involved reproducing the scars on tapping panel diagrams, and analysing them using two indicators: the amount of virgin bark consumed and the number of tapping years that remained. We validated this tapping panel diagnosis in a sample of 25 smallholder plantations in Cameroon, where we characterised eight tapping management systems reflecting different levels of tapping intensity. The assessment of the respective share of each tapping practice on virgin bark consumption revealed major effects of tapping frequency and of shaving thickness. We showed that the tapping panel diagnosis used as a decision support tool can increase remaining tapping years by 33% to 355%. To conclude, the tapping panel diagnosis formalised here for the first time will be a useful support for the participatory development of innovating tapping management schemes involving both technicians and smallholders.

Carbon isotope composition of latex does not reflect temporal variations of photosynthetic carbon isotope discrimination in rubber trees (Hevea brasiliensis)

Latex, the cytoplasm of laticiferous cells localized in the inner bark of rubber trees (Hevea brasiliensis Müll. Arg.), is collected by tapping the bark. Following tapping, latex flows out of the trunk and is regenerated, whereas in untapped trees, there is no natural exudation. It is still unknown whether the carbohydrates used for latex regeneration in tapped trees is coming from recent photosynthates or from stored carbohydrates, and in the former case, it is expected that latex carbon isotope composition of tapped trees will vary seasonally, whereas latex isotope composition of untapped trees will be more stable. Temporal variations of carbon isotope composition of trunk latex (δ(13)C-L), leaf soluble compounds (δ(13)C-S) and bulk leaf material (δ(13)C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ(13)C-L was observed between tapped and untapped trees whatever the season. Trunk latex from tapped trees was more depleted (1.6‰ on average) with more variable δ(13)C values than those of untapped trees. δ(13)C-L was higher and more stable across seasons than δ(13)C-S and δ(13)C-B, with a maximum seasonal difference of 0.7‰ for tapped trees and 0.3‰ for untapped trees. δ(13)C-B was lower in tapped than in untapped trees, increasing from August (middle of the rainy season) to April (end of the dry season). Differences in δ(13)C-L and δ(13)C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ(13)C-L and δ(13)C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping.

A Comparative Analysis of Smallholders Tapping Practices in Four Rubber Producing Regions of Thailand

Rubber has been grown for long in the South and East of Thailand. Since 2005, rubber plantations have largely spread to new regions, in the North and above all in the Northeast. Tapping is one of the most important practices to optimize the yield of rubber plantations and farmers income [. If tapping practices are well documented in the traditional growing areas [2, , we lack information for the new rubber producing regions. And so far, no study has been done at the level of the country. Therefore, a survey was conducted with 219 rubber farmers from 10 provinces in four rubber producing regions to describe farmers tapping practices. The objective was to compare farmers practices in the different regions and try to identify some standardization or differentiation factors. Results show that tapping systems used by the farmers vary with the region but everywhere, even in the South and Centre east, the real tapping practices are not really intensive. Tapping practices seem to be linked to farmers rubber experience, the size of mature plantation, the rainfall and the length of the leaf-fall period. So finally, tapping days are irregularly distributed throughout the year which probably affects latex physiology and so, the potential yield of rubber plantations.

Starch Synthesis and Mobilization in Wood and Bark of Rubber Tree, in Relation with Latex production, (1) Methodological approach

In rubber tree, starch reserves are necessary for growth and latex regeneration when the demand exceeds supply from photosynthesis. It tends to accumulate in the wood near the tapping cut [1,2] whereas sucrose remains rather stable in the wood and decreases in the latex vessels where it is used to regenerate the exported latex [3].Thus higher starch ability could sustain higher latex yield. However the enzymatic processes driving the dynamics of starch synthesis and hydrolysis as related to tapping are not known. The objective of the study is to analyze the effects of tapping on the enzymes involved in starch and sucrose metabolism in the wood of rubber trees. The first approach of this study was to set up the most adapted methodology on measurement of total nonstructural carbohydrates (NSC) and related enzymes activities. The experiment was conducted in Heveabrasiliensis (rubber tree), clone RRIM600. Treatments include untapped trees (Control) and yielding trees tapped with Ethephon stimulation (ET). Each treatment includes 6 trees. Samples have been collected along the trunk and separated into 2 parts, wood and bark, from both side of the tree tapped and untapped panel. The activity of acid invertase (AI), amylase (AMY), sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) were assessed in the part of soft bark with amethod of sample preparation recoveringmore protein and concentrated enzyme with acetone precipitation. The method has increased enzyme activities of SuSy and SPS. On another hand, starch, sucrose, fructose and glucose concentrations have been enzymatically measured.The results showed that starch was the major component in wood and sucrose was mostly found in bark. There was no difference between the former drainage area and resting area after 2 untapped years before restarting tapping.