Polyethylene Glycol (PEG) And Salicylic Acid As Alternative Stimulants

Stimulants

Stimulants are usually used to increase latex yield. The aim is to optimize the production of rubber trees. Stimulants application is more effective for high response clones (Sumarmadji, 2005). Clone PB 260 is one of the superior clones classified into Quick starter clones with specific properties including high initial production, less responsive to stimulants and susceptible to tapping dry grooves (KAS) (Sumarmadji, 2011).

Currently, stimulants that are widely used are etephon based stimulant (2-chloroethylphosponic acid) which functions to increase endogenous ethylene production in rubber trees and increasing latex yield. Such stimulant application however must be managed carefully because excessive use will disturb tree health which is marked by increasing tapping dry grooves incidence. Therefore, it is necessary to look for alternative stimulants that can increase latex yield, and is feasible to the characteristics of rubber clones and safe for rubber trees.

Polyethylene glycol (PEG)

PEG is one of the potential ingredients to be used as an alternative stimulant. Rahayu, Siregar, Purba, and Tistama (2016) reported that application of PEG 3 % as a stimulant to rubber plants could increase latex yield by 40.42 %. Besides PEG, salicylate is another potential ingredient to be used as a stimulant. Salicylate is a phenolic compound which regulates plant growth especially physiological activities such as photosynthesis, flowering, nitrate metabolism, ethylene production and protection against biotic and abiotic stresses. Ali and Adel (2013) reported that leaf application of salicylates can significantly increased plant height, number of branches, seed pods, seed growth per pod, and weight of 1000 seeds compared to the controls. In addition, Wicaksono, Irwan, Wahyudin, and Setianingrum (2015) also reported that application of salicylic acid and calcium chloride showed the best growth and yield for wheat at 9-day intervals.

Based on previous research findings, it is known that salicylates have the potential to be used as a stimulant to increase the production of latex by increasing stem growth of the rubber trees. Therefore, the purpose of this study is to determine the effect of PEG and salicylic acid in increasing rubber latex yield.

Production of latex

Table 01 shows that PEG application had a significant effect on latex yield. The highest production of latex was found in PEG 6% with 98.92 g/p/s while the lowest is PEG 0% (control) with 89.81 g/p/s. There was an increase in latex yield by 10.14 % with PEG 6 %. Salicylate application also had a very significant effect on latex yield whereby the highest yield was found in 3 g/L salicylic acid with 100.82 g/p/s, whilst the lowest was in 0 g/L salicylic acid (control) with 87.76 g/p/s. Combination of PEG and salicylic acid did not have a significant effect on the latex production.

Total solid content (TSC)

Table 02 shows that the application of PEG did not have a significant effect on TSC value, whilst salicylic acid gave a significant effect. The highest TSC percentage (87.64 %) was found in the treatment of 3 g /L salicylic acid and the lowest (86.36 %) was in 0 g/L salicylic acid (control) treatment.

Flow of latex

Table 03 shows that PEG application had a significant effect on the rate of latex flow. The most rapid was found from PEG 6% at the rate of 17.68 cc/minute whilst the slowest was from PEG 0% (control) at 12.40 cc/minute. In this case there was an increase in the latex flow rate by 42.58 % with PEG 6 %. The treatment of salicylic acid had no significant effect on the rate of latex flow but increased with increased concentration compared to the control.

Plugging index

Table 04 shows that PEG application had a significant effect on plugging index. The lowest percent plugging index was found at PEG 6% which was 7.40 whilst the highest percent was at PEG 0 % with 15.19. Plugging index was inversely proportional to latex production. In such case, there was a decrease in plugging index by 102.7 % with PEG 6 %. The application of salicylic acid however did not significantly affect the plugging index.

Production is the most important response from any treatment given to rubber trees. In this study, the clone used was PB 260 which is characterized by high initial production and limited response to stimulants. Results found that the interaction of PEG and salicylic acid applications did not show any significant effect. On the contrary, individual treatment showed a significant effect on the latex production. This was because PEG was able to maintain the stability of osmotic potential and water content in plant cells (Roohi & Surki, 2011). Water levels in plant cells will increase the turgor pressure, and in turn increase the latex yield because latex flow is influenced by turgor pressure. Rahayu, Siregar, Purba, and Tistama (2017) stated that PEG application could increase the latex yield by 49.96 % at 5 months after application. Andriyanto and Darojat (2016) reported that there was an increase in the volume of latex and dry production with PEG stimulant applications.

Application of salicylic acid also increased the latex yield and total solid content (TSC). This was because salicylic acid is a fatty acid that will be converted into acetyl coenzyme A (acetyl-CoA) to form tricarboxylic acid (TCA) as an energy producer. Acetyl CoA is an important molecule participating in both primary and secondary metabolism whereby in the latter, Acetyl CoA is a precursor to build terpenoid compounds among polyterpenes (latex) (Dewiek, 1979; Rahayu et al., 2016). Therefore, the application of salicylic acid could increase latex yield. Rahayu et al. (2016) also reported an increased latex yield with the application of palmitic acid, a saturated long chain fatty acid.

In addition to latex production, application of PEG also had a significant effect in reducing the plugging index and increasing the rate of latex flow. Sumarmadji (1999) stated that plugging index correlated negatively with the production in which decreased in the plugging index increased the production of latex.