614

16: Stimulants

Piper methysticum G. Forster

Pl. escul.: 76 (1786).

PIPERACEAE

2n = 130

Macropiper methysticum (G. Forster) Hooker & Arnott (1840), Macropiper latifolium Miquel (1847).

Kava, kava-kava (En). Kava, kawa-kawa, ava (Fr). Indonesia: waghi, wati, bari (Irian Jaya). Papua New Guinea: koniak, keu, oyo.

Piper methysticum probably originated in Vanuatu, since its greatest diversity occurs there. It is cultivated all over Melanesia and Polynesia, especially in Vanuatu, Fiji, Samoa, Tonga and Micronesia. In South-East Asia, Piper methysticum occurs mainly in the southern part of New Guinea, both in the wild and in occasional cultivation. Its cultivation and use in New Guinea have declined considerably due to discouragement from former colonial and religious authorities.

The main use of kava over the centuries has been as a traditional ethnic beverage. The beverage is prepared from the roots and basal stem, which are the plant parts containing the desired kavalactones that confer psychoactive properties to the beverage. To prepare the beverage, the plant parts are pulverized by grinding or mastication, suspended in water and then sieved to remove the residue. The resulting milky-brown liquid is the beverage. Considerable social and cultural rituals accompany its consumption. Kava is also used as a medicinal plant in both folk and modern medicine. In folk medicine, the roots and even the leaves are used to treat a range of maladies, including rheumatism, respiratory tract infections, tuberculosis, gonorrhoea, chills and headaches. In these cases, the pulverized plant material is drunk or applied topically. The pharmaceutical use of kava in modern mainstream and alternative medicine relies on the psychoactive properties of the kavalactones contained in the roots and stembase. Because of this, kava has become a valuable cash crop, supplying the growing international demand for pharmaceutical use of the plant. A less tangible but equally important use of kava is that it is often a medium of social and religious interaction. In kava-utilizing cultures, the plant is an important and indispensable item of gift-giving to other people, or for religious offerings to the spirits.

Total world production of kava is difficult to estimate, mainly because so much of what is produced is consumed locally, especially in Vanuatu, Fiji and Tonga. In 1994, over 420 t of kava entered into international trade, with the major exporters being Fiji (329 t), Vanuatu (89 t) and Tonga (5 t). The main importers are Germany, France, Australia and New Zealand. The price was about US$ 15 per kg. Kava production in Papua New Guinea occurs in isolated communities and is extremely informal; there is no export of kava from the country.

The freshly-harvested used plant parts contain 80% water, but after drying, the water content is 12—15%. The composition per 100 g of the dry product is: water 12 g, protein 3.6 g, starch 43 g, sugar 3.2 g, fibre 20 g, ash 3.2 g, kavalactones 3—20 g. The kavalactones are the main active ingredient of kava, and the ones that are present in the highest concentration are yangonin, methysticin, dihydromethysticin, kavain, dihydrokavain and demethoxy-yangonin. Alone or in combination, these kavalactones are able to act as sleep inducers, painkillers, antibiotics, anaesthetics or muscle relaxers. These properties form the basis of the pharmaceutical use of kava. The effects of kava are likened to those of diazepam (valium). Overconsumption produces slight paralysis and skin lesions.

Kava powder made from the roots is often adulterated with similar looking powders that do not have the same effect. On several Pacific Islands (particularly the French-speaking islands) the traditional kava drink has largely been replaced by alcoholic drinks. In South-East Asia and the South Pacific kava can be substituted by Piper subbullatum K. Schum. & Lauterb.(synonym Piper torricellense Lauterb.). In tropical central America the roots of Piper medium Jacq. are used to prepare a drink similar to kava.

A dioecious, woody, perennial shrub, 2—4 m tall, with a massive base at or just below the ground (crown or short rootstock) from which several shoots arise, giving the plant an overall rosette appearance. Each main stem is erect, 1—3 cm in diameter, green, red-brown or dark purple and looks jointed due to the swollen nodes and prominent scars left by abscission of leaves and branches. Leaves alternate, deciduous; stipules large, persistent; petiole 2—7 cm long; blade cordate, 10—30 cm x 8—23 cm, base cordate, margin entire, apex acute, glabrous to finely pubescent, palmately veined, principal veins 9—13, all except the 3 uppermost spreading from base. Inflorescence a spike, axillary or opposite the leaves but much smaller; peduncle 1.5 cm long; spike 3—9 cm long, with small unisexual flowers without sepals or petals; the male spike bears numerous flowers with 2 short stamens; the female spike bears flowers with a single basal ovule in an unilocular ovary topped by a stigma. The fruit is seldom produced; it is a berry, containing one seed.

Once a kava plant has established the older stolons enlarge to form a crown (short rootstock), from which new shoots grow. Additional shoots continue to arise at the periphery of the crown throughout the life of a plant. Although Piper methysticum is dioecious, most plants are male; female plants appear to be very rare. Occasionally monoecious plants have been found. Natural senescence occurs at 15—30 years after planting.

Because kava has been known and used for centuries over a rather large area, variability is great. More than 120 cultivars exist. Some botanists believe that Piper methysticum was derived from Piper wichmannii C. DC. as a result of human selection of somatic mutants of the latter. Others believe that the ancestor of kava is Piper subbullatum, which occurs in the Philippines, New Guinea and South-West Pacific Islands.

Kava is a shade-loving plant, especially in the first year of growth. It does best in the per-humid tropics with temperatures of 20—35°C, rainfall above 2000 mm, and high relative humidity. It requires deep well-drained soils with high organic matter content and pH 5.5—6.5. It is susceptible to damage by moderate to strong winds.

Since fruits are seldom produced, kava is exclusively propagated by stem cuttings or suckers. Cuttings 15—20 cm long are planted directly in the field. Shorter cuttings of 2—4 nodes are first sprouted in a nursery before transplanting to the field. Intercropping is the rule, with the other crops (e.g. taro, bananas or maize) providing the necessary shade and wind shelter for the young kava. Field spacing varies widely, depending on the nature and intensity of the other crops, but 2 m x 2 m (2500 plants/ha) is considered adequate.

If kava is correctly spaced, weed control is necessary in the first 2 years only. Weeding with hand tools is the most common practice. Earthing up is essential to ensure massive proliferation of the rootstock. The crop requires a high nutrient supply. Manures and composts are most frequently used, but compound inorganic NPK fertilizer (12-12-20) or urea (with 46% N) are also used.

Kava suffers from dieback disease caused by the cucumber mosaic cucumovirus transmitted by aphids. The symptoms are wilting and dieback of the shoot. There is no effective control measure, but intercropping and adequate field sanitation are helpful. Another disease of kava is anthracnose caused by Glomerella species which can be controlled with fungicides. The kava weevil borer is the most serious pest; it can be controlled with insecticides. Nematodes are controlled by careful field sanitation and hot water treatment of planting material.

Kava is best harvested when 2—4 years old, but may be allowed to stand for up to a decade. Harvesting can be done any time of the year. It involves cutting off the stems and digging up the rootstock.

Kava yields vary with age and cultivar. Fresh weight yields are 10—60 kg/plant, and 6.6 t/ha for kava intercropped with coconut.

After harvesting, the kava rootstock is washed, chipped or peeled, dried, powdered, sieved and packed. Highest market value is for peels from the root and crown, followed by chips from the root and crown. These constitute the main commodities for export for pharmaceutical use. Chips from the bases of the stems are of much lower value. Kava for use as a recreational beverage (domestic or export) is usually pounded into powder and packaged. Adulteration is a frequent problem in the powdered product, and quality control is poor. In Vanuatu, the beverage is often made from the fresh root.

Collections of kava cultivars can be found at the Tagabe Research Station in Vanuatu, the Kerevat Experiment Station in Papua New Guinea, the Kauai Experiment Station in Hawaii and at various locations in Fiji and Samoa.

The main selection and breeding objectives should be for resistance to diseases and pests, especially the kava dieback disease, and for a higher content of the kavalactones.

With its emerging use in the modern pharmaceutical industry, the prospects for kava are bright. It is already a cash crop in several countries, and its importance is expected to increase. Research is needed to develop disease-resistant cultivars with a high kavalactone content, and to standardize the product.

Davis, R.I. & Brown, J.F., 1996. Epidemiology and management of kava dieback caused by cucumber mosaic cucumovirus. Plant Disease 80(8): 917—921.
Lebot, V. & Levesque, J., 1989. The origin and distribution of kava (Piper methysticum Forst.f. and Piper wichmannii C. DC., Piperaceae): A phytochemical approach. Allertonia 5: 223—280.
Lebot, V., Merlin, M. & Linstrom, L., 1992. Kava, the Pacific drug. Yale University Press, New Haven, United States. 255 pp.
Leung, A.Y. & Foster, S., 1996. Encyclopedia of common natural ingredients used in food, drugs and cosmetics. 2nd edition. John Wiley & Sons, New York, United States. pp. 330—331.
Onwueme, I.C. & Papademetriou, M., 1997. The kava crop and its potential. RAP Publication 1997/12. Food and Agriculture Organization of the United Nations, Regional Office for Asia and the Pacific (RAP), Bangkok, Thailand. 46 pp.

I.C. Onwueme

Onwueme, I.C., 2000. Piper methysticum G. Forster. In: van der Vossen, H.A.M. and Wessel, M. (Editors): Plant Resources of South-East Asia No 16: Stimulants. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea