0148-B4

Gum tapping in Sterculia urens Roxb. (Sterculiaceae) using ethephon

M. N. B. Nair ¹

Abstract

A dry exudate from Sterculia urens known as gum karaya (one of the important non-wood Forest Products, NWFP) is one of the least soluble gums used for many industries such as petroleum and gas, textiles, paper and pulp, pharmaceuticals, medicine and several other products. Besides S. urens, exudate from S. villosa, Coclospermum gossypium Alston (DC) are also included under karaya gum. The commercial tapping of karaya is done by blazing, peeling, or by making deep cuts at the base of the bole using an axe or a cycle. These methods often lead to the death of the tapped trees. On account of crude tapping methods and over exploitation the population of karaya trees has markedly declined. In the absence of cultivation of these trees in regular plantation, there is a grave concern about the loss of wild germplasm of S. urens. As gum karaya is vital for tribal economy and its trade value is substantial, there is a pressing need to develop a scientific and sustainable tapping method to increase the yield and ensure the survival of the tapped trees. A simple and safe technique of tapping with substantial increase in the yield is developed using ethephon to enhance gum yield and wound healing. After 45 days a thick wound tissue has developed at the injured region and nearly replaced the damaged tissue. The wound is completely healed 60 days after tapping. The yield has increased about 20 to 30 times more than the control and about 10 times more than the traditional tapping methods used by the local people. There was a marked difference in the yield among individual trees, presumably due to heterozygosity. The systematic and scientific tapping technique using ethephon as stimulating agent for gummosis or gumresinosis could ensure substantial improvement and sustainable production of these materials. The concentration used for treatment is critical for each species. If it exceeds the optimum amount there will be possibility of die back and death of the plants.

Introduction

Gum Karaya is the dry exudate of Sterculia urens, S. villosa and some species of Cochlospermum. However, in India it is mainly collected from S. urens and S. villosa. Karaya gum was reported to be collected from S. urceolata and S. foetida in Indonesia, S. setigera in Africa and from S. caudata in Australia (Gautami and Bhat 1992). Karaya gum also known by the name Indian tragacanth as it resembles gum tragacanth produced by Astragalus sp. Gum karaya is one of the least soluble gums used for many industries such as petroleum and gas, textile, paper and pulp, leather and allied products, ammunition and explosives, electrical appliances, adhesives, confectionery, medicine, pharmaceuticals and cosmetics (Gautami and Bhat 1992). There is high demand of export of gum karaya from India. Yield of this gum has shown a phenomenal decrease from 6838 Metric tons (MT) in 1975 - 1976 to 461.3 MT in 1990 - 1991, During this period the price has shot up Rs. 7491 per MT to Rs. 83, 361 (Gautami and Bhat 1992).

Sterculia is native of dry deciduous forests of dry rocky hills and tablelands of tropical climate (Fig 1). This genus has about 100 species and India has 8 species present in tropical

Himalayas, West and Central India, Deccan Plateau and throughout Eastern and Western Ghats (Gatami and Bhat 1992). Commercial tapping of gum Karaya is done by blazing, peeling or by making deep cut in the base of the tree trunk with an axe or cycles (Fig 2). These methods are wasteful and injurious to the trees (Fig 3 & 4) often leading to their death, On account of crude tapping method and overexploitation the population of karaya trees has markedly declined. In absence of cultivation of this tree in regular plantation there is grave concern about the loss of wild germplasm of S. urens. The Government of Madhya Pradesh, Rajasthan and Uttar Pradesh has imposed ban on tapping and collection of gum karaya to allow recovery and regeneration of this tree. As gum karaya is vital for the tribal economy and its trade value is substantial there is a pressing need to develop a scientific and sustainable tapping method to increase the yield and to ensure the survival of the tapped trees. Here, I present a simple and safe method for tapping, the gum karaya tree with a substantial increase in the yield.

Material and Methods

A preliminary observation showed that ethephon enhances gum formation and wound healing in Sterculia urens (Nair et al. 1995). I have selected 15 trees in the village of Ghati near Gwalior Highway No.3 for experiments to find out the optimum concentration of ethephon to induce maximum production of gum with minimum injury to the tapped trees. Using a specially devised knife, holes each of 5mm diameter and 2-3.5 cm depth (based on the thickness of the bark) were made on the tree trunk 20 to 30 cm distance at I m above the ground. The holes were angled towards the base of the tree to prevent the backflow of the introduced solutions. One hole in each tree is maintained as the distilled water control and rest of them was treated with ethephon (2-chloroethyl phosphonic acid). One ml of ethephon containing 190/285/390 mg of active substance (one ml of distilled water for controls) was dispensed into each hole. Five trees were used for each concentration. The gum started oozing out after 4 hours in treated holes (Figs 5,6). After couple of weeks the exuded gum appear as stalactic mass (Figs 7, 8). The first collection of gum produced in the control and treated holes were made after 15 days. The succeeding 3 collections were done after every 10 days and the data were pooled (Table 1).

Table 1: Showing yield of gum when treated with distilled water, 190mg., 285 mg. and 390 mg active substance.

It was noticed that the trees treated with 285 mg of active substance of ethephon have yielded highest amount of gum and therefore this concentration was used for further experiments. The tapping experiments were repeated at Ghati in Madhya Pradesh and Cheedipalem in Andhra Pradesh. 15 trees of various sizes and ages were selected for the study in both the sites. The trees were tapped in March, May and November 1995 in Ghati using 285 mg of active substance to understand the seasonal variation in the yield. The Tapping of trees at Cheedipalem were done in February and May in 1996. In Andhra Pradesh the Karaya trees are tapped and the tribal people with the help of Girijan Cooperative Corporation (GCC) collect the gum. The yields from the traditional tapping method and the method using ethephon were also compared. The tribal people remove 50 to 55 cm length of bark across the trunk with a cycle and collect the gum as tears or as irregular fragments (Fig. 14). The tapped trees often fails to regenerate after some years (Fig. 3). The trees were tapped throughout the year except in the rainy season,

Results

The gum produced in the control and treated holes were shown in the table 1. The ethephon treatment has resulted in the increase of about 40 to 85 times more than the control. The harvest from the ethephon treated trees was of high quality gum. Histological examination of the unwounded trees absence of any special tissue, which produces gum in Sterculia (Fig.13). Tangential bands of gum cavities were present in the bark of the treated bark. The elongated cavities are parallel to the longitudinal axis of the stem and anastomose tangentially (Fig. 12). Multiseriate rays are observed amidst the anastomosing cavity system (Fig.12). The gum cavity is formed lysigenously.

The gum started oozing out of the holes within 4 hours and gets hardened when comes in contact with air (Figs 5,6). After 15 days the gum can be hand picked as large stalactic mass (Fig.7, 8). The control holes were completely dry after 30 days. In many cases the control holes produced negligible amount of gum. It was found that the damaged tissues of the ethephon treated holes were nearly replaced with wound tissue after 45 days (Figs 10, 11). The injury was completely healed after 2 months.

Table 2: Tapping experiments conducted in March, May and November 1995 at Ghatti (Madhya Pradesh) showing the yield of gum karaya when treated with ethephon (285 mg of active substance)

The result of the tapping done at Ghati Madhya Pradesh, in March, May and November 1995 is shown in Table 2. The highest amount of gum is produced in May and least amounts in November. The tapping experiments conducted in Cheedipalem also shows copious gum production in the summer months (Table 3). The yield of gum when tapped using ethephon is about 10 times more than the yield when tapped using traditional method. The injury made by the traditional tapping is very large (50 to 55 cm long). The gum produced by the tapping using ethephon was high quality gum of the first grade.

Table 3: Tapping experiments conducted in February-March and April - May 1996 at Cheedipalem ( Andhra Pradesh) showing the yield of gum karaya when treated with Ethephone (285 mg of active substance)

Discussion

International trade of gum karaya is exclusively indigenous to India and is vital for the tribal economy. It has now become one of the important sources of income for the state from the forest as a non-wood forest product (NWFP) because the commercial extraction of wood from the forest has become limited. Owing to the lack of scientific tapping technique and post harvest processing it has become difficult to utilize this product optimally. In the present study, the gum production was increased substantially as a result of using ethephon. It also ensures minimum injury to the trees so that the tree is regenerated easily, thus guarantee sustainable production of this gum.

In S. urens lysigenously formed gum ducts are present in the pith and cortex of the young stem (Shah and Setia 1976) but they are absent in the secondary phloem. The gum cavities are induced upon ethephon treatment. According Abeles (1973) ethylene may cause formation of gum cavities of pocket or cyst in plants. Ethephon is used to stimulate latex flow in para rubber (Hevea brasiliensis), resin enhancement in pines (Peters et.al.1978), gum production in Acacia senegal (Bhatt and Mohan Ram 1990), Anogeissus latifolia (Bhatt 1987), Azadirachta indica (Nair et al, 1980, 1985). It also increases gumresinosis in Mangifera indica (Bhatt and shah 1985) and Commiphora wightii (Bhatt et al. 1989). Ethephon is a nontoxic, environment-friendly, inexpensive and easily available plant growth regulator (PGR) manufactured in India and used extensively in agriculture and horticulture.

The gum exudation in Karaya tree is highest in April-May, the exudation is about 10 times more than the production in November. Therefore it is suggested that the gum karaya tapping for commercial purpose be done only during March to May and the trees may be given rest in the remaining part of the year. This will ensure the regeneration of the tapped trees, sustainable supply of this gum and good economic return. This technique is simple, needs no specialized skills and can be taught to unskilled tribal living in the forest fringes.

Conclusion

The future of natural gum and resin industry is uncertain and therefore, a thorough economic study of the national and international trade is necessary. Synthetic products are preferred by the industry because of the uncertain supply and cost of natural gums and resins. However, unstable oil prices, decreased production and high costs of the synthetic material create a promising future for natural gums and resins. In spite of the competition from synthetic products, natural gum and resins are preferred in certain industries as they are superior.

The tapping methods used are brutal and injurious to the plants, often leading to their death. The technology available is old and the innovations are essential for sustainable yield and quality control. A concerted effort by researches and agencies such as research institution, Universities and non-governmental agencies is urgently needed to improve all aspects of the industry such as tapping, collection, processing, grading, classification and marketing. R and D are completely lacking in the area of utilization of natural gums and resins. The industry completely depends on traditional and certain adhoc investigations by individuals. Research into genetic improvement and selection of species for production of gums and resins should be initiated which may lead to establishment of plantation of these species. Gum and resin industry can provide employment and a steady additional income to rural people and thereby stop their migration into the towns and cities.

Literature cited

Abeles, F. B. 1973. Ethylene in plant biology, Academic Press, New York,.271 p

Bhatt, J. R. 1987. Gum tapping in Anogeissus latifolia (Combretaceae) using ethephon. Current Science 56: 936-940.

Bhatt, J. R. and H.Y. Mohan Ram 1990. Ethephon induced gum production in Acacia senegal and its potential value in the semi-arid regions of India. Current science 59: 1247-1250.

Bhatt, J. R. and J. J. Shah 1885. Ethephon (2-chloroethyl phosphonic acid) enhanced gumresinosis in mango, Mangifera indica L. Indian Journal of Experimental Biology 23: 330-339.

Bhatt, J. R. , M. N. B. Nair and H. Y. Mohan Ram 1989. Enhancement of oleo-gumresin production in Commiphora wightii by improved tapping technique. Current Science 58: 349-357.

Gautami, S. and R. V. Bhat 1992. A monograph of gum Karaya, National Institute of Nutrition, ICMR, Hyderabad, India.

Nair, M. N. B., J. R. Bhatt and J. J. Shah 1985. Induction of traumatic gum cavities in sapwood of neem (Azadirachta indica A.Juss.) by ethephon and paraquat. Indian Journal of Experimental Biology 23: 60-62.

Nair, M. N. B., K. R. Patel, J. J. Shah, and R. C. Pandalai 1980. Effect of ethephon (2 Chloroethyl phosphonic acid) on gummosis in the bark of Azadirachta indica. Indian Journal of Experimental Biology 18: 500-503.

Nair, M. N. B., K. R. Shivanna and H.Y. Mohan Ram 1995. Ethephon enhances karaya gum yield and wound healing response: A preliminary report. Current Science 69: 809-810.

Peters, W. J., D. R. Roberts, and J. W. Munson 1978. Ethrel, diquat, paraquat interaction in lightwood formation. Proceedings of the Lightwood Research Coordination Council Annual Meeting, Atlanta, Georgia. 31-39.p

Shah, J. J. and Setia, R. C. 1976. Histological and histochemical changes during the development of gum canals in Sterculia urens. Phytomorphology 26: 151- 158.

Explanation of figures

Fig 1. Sterculia urens growing in Shivapuri, Madhya Pradesh.

Fig, 2. Illegally tapped trees in Ghati village, The injury made on the tree with axe,

Fig. 3 & 4. Highly injured trees due to tapping which are on the verge of death.

Fig. 4 & 5. Ethephone treated holes, note the exudation of gum.

Fig. 7 & 8. Stalatic mass of gum dried on the trunk after 15 days of tapping.

Fig. 9. Comparison of amount of gum produced from the control hole and the treated hole.

Fig. 10 & 11. Tapping of gum karaya trees. The holes made are almost healed.

Fig. 12. Tangential longitudinal section of the bark showing the gum cavities.

Fig. 13. Cross section of the bark showing absence of gum cavity in the untreated secondary phloem and presence of cavity in the secondary phloem treated with ethephon.

Fig. 14. A sample of First and second grade of gum Karaya.

¹ Environment Resource Research Centre, Thekkepulikkootil, Nechipuzhoor, P.O.
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