Physiology of the Rubber Tree Linked to Yield : A Case Study ; Impact of Reduced Tapping Frequency on Potential Latex Yield of Clone RRIM 600

Abstract

Rubber smallholders face both rubber price fluctuation and labour shortage. Low frequency tapping (LFT) systems may be interesting in such context as they can increase yield per tapping day. Then, LFT systems (tapping every 3 days, d3) were tested in S/2 and S/3 compensated by different levels of ethylene (ET) stimulation in southern Thailand. An experiment was established at the Thepa Research Station, Songkhla province. There were three parts of investigation. The first study was used 8- year-old trees of RRIM600 clone, it was designed as a randomized complete block design with five treatments (T1: S/3 dl 2d/3 (usual system for Thai smallholders), T2: S/2 d2 (standard for RRIT), T3: S/2 d3 ET 2.5% Pal(1) 8/y (m), T4: S/3 d2 ET 2.5% Pal(1) 4/y (m) (standard for RRIT) and T5: S/3 d3 ET 2.5% Pal(1) 12/y (m)) with three replications (elementary plot). There were ten trees per treatment in each elementary plot. The results showed that the so-called LFT system (S/2 d3) with stimulation 8 times per year efficiently gave the yield per tapping able to compensate the cumulative yield in kg/t comparing with the conventional tapping system (S/3 2d/3). The higher yield per tapping affected latex biochemistry was leading to decrease in sucrose (Suc) and reduced thiol (RSH) contents. Although LFT system with stimulation expressed less bark consumption with no prominent effect on girth increment, it still slightly increased of TPD (tapping panel dryness). The second study was used 9-year-old trees of RRIM600 clone, it was designed as one tree plot design with five treatments (T1: S/3 d1 2d/3 (usual system for Thai smallholders), T2: S/2 d2 (standard for RRIT), T3: S/2 d3 ET 2.5% Pal(1) 8/y (m), T4: S/3 d2 ET 2.5% Pal(1) 4/y (m) (standard for RRIT) and T5: S/3 d3 ET 2.5% Pal(1) 12/y (m)) with three trees per treatment. The results showed that the response to stimulation was dependent on the physiological status of the tree according to the seasonal variation of the tree metabolism in both periods (high yield and low yield period). However, the yield was always higher in the high yield period than in the low yield period, even the relative higher response to stimulation on initial flow rate (IFR), plugging index (PI) and sucrose content (Suc) were found in the low yield period. The third study was used 10-year-old trees of RRIM600 clone, it was designed as one tree plot design with six treatments (T1: S/3 d1 2d/3 (usual system for Thai smallholders), T2: S/2 d2 (standard for RRIT), T3: S/2 d3 ET 2.5% Pal(1) 8/y (m), T4: S/3 d2 ET 2.5% Pal(1) 4/y (m) (standard for RRIT), T5: S/3 d3 ET 2.5% Pal(1) 12/y (m) and T6: untapped trees) with six trees per treatment. It was found that the expression of potential yield under the LFT system was slightly leading to a relatively lower storage of the TNC (total nonstructural carbohydrate) content in wood and bark comparing with the conventional tapping system, but it was still accumulated in the drainage area of wood. In overview of three experiments, LFT system (S/2 d3) with stimulation 8 times per year could efficiently give the yield per tapping leading to compensate the cumulative yield in kg/t for the clone RRIM 600. It is remarkable, under the climate variability of southern Thailand, it is possible of using ethylene stimulation to increase the potential yield of the rubber tree at each tapping under LFT system. This suggests that rubber smallholders in southern Thailand possibly apply LFT systems with stimulation under rubber price fluctuation and tapping labour shortage.