Rubber industry plays an important role in Sri Lankan economy being a major source of export earning and by providing the livelihood for people, particularly in the rural sector. With no success in all attempts taken to remove the skill factor in tapping, stimulation based Low Intensity Tapping (LIT) systems are found to be the only option available to reduce the number of tappers required, bark consumption and cost on tapping.
The response in terms of latex yield of the rubber tree to stimulation would vary with the genotype and, no studies to-date has been conducted to assess the effects of stimulation on latex and raw rubber properties. Therefore, the study reported here aimed to assess these responses with four major Hevea genotypes grown in Sri Lanka.
Mono clonal mature rubber fields with four major genotypes (i.e. RRIC 100, RRIC 102, RRIC 121 & RRIC 130) tapped on the renewed bark, was selected for the study. Four tapping frequencies, d/2, d/3, d/4 and d/6 (i.e. tapping once in two days, three days, four days and six days, respectively) were imposed on each clone keeping three replicate (each with 25 trees) plots to each frequency. No stimulants were used in the traditional system of d/2. In d/3, d/4 and d/6 tapping, trees were stimulated 5, 9 and 12 times per year, respectively with Ehtephon i.e. 2-Chloroethylphosphonic acid. In d/3 and d/4 tapping Ethephon was used at 2.5 % concentration whilst 5% was used in d/6 tapping. On average, 1.6g of Ethephon mixture was applied per tree per application.
Latex samples were collected monthly from each treatment plot and initially assessed for latex properties such as Dry Rubber Content (%DRC), Total Solid Content (%TSC), and acetone extractable non rubber. Then, samples were processed to lace crepe and assessed for raw rubber properties i.e. colour and ash content.
The %DRC and %TSC varied with the genotype and those values were highest in RRIC 130 and lowest in RRIC 121. Nevertheless, % acetone extractable non rubber was highest in RRIC 100 and lowest in RRIC 130. The %DRC and %TSC increased with decrease in tapping frequency with that highest values were recorded in the d/6 system. However, % acetone extractable non rubber remained same across the different tapping frequency with a mean value of 2.16%. The raw rubber properties i.e colour and %ash did not vary with the tapping system. However, the lowest ash content was recorded in the RRIC 130 and those of other clones was comparable. The colour was highest in RRIC 102 whilst it was lowest in RRIC 121.