Tropical plants with sweetening properties physiological and agronomic problems of protected cropping 2.Tha uma tococcus daniellii

Abstract

An acceptable, non-toxic, non-caloric 'natural' sweetener has great potential as an alternative to 'synthetic' sweeteners, some of which have taste-limiting properties (Radar et al., 1967), or to sucrose, which may be dietetically unacceptable. It has long been known that certain plants indigenous to tropical West Africa produce fruits which are intensely sweet or have taste-modifying properties (e.g., Inglett and May, 1968). The discovery of intense sweetness in proteinaceous form in fruits of Thaumatococcus daniellii (Van der Wel and Loeve, 1972) came at an opportune time when alternatives were sought to the organic synthesis of analogues of sugar substitutes such as cyclamates and saccharin (Cagan, 1973a, b). Thaumatococcus daniellii (Family Marantaceae) is a tropical, rhizomatous, perennial herb with a characteristic pulvinus at the distal end of each petiole. The large leaves are ovate-elliptical (up to 60 cm long and 40 cm wide) and are borne individually on petioles up to 3 m long. Inflorescences are inconspicuous, single or simply branched spikes and emerge from swollen petiole bases at ground level (Tomlinson, 1961 ). Each inflorescence generally produces between one and three fleshy, trigonal fruits which mature to a dark red/brown colour. At maturity, the three seeds in each fruit are black, extremely hard, with a pale yellow basal aril. T. daniellii is common throughout the West African rain forest zone from Sierra Leone to Zaire ( 1300 to 2000 mm rainfall per annum ), and at altitudes up to 1300 m OD. Vegetative growth is seasonal with flowering and subsequent fruit-set occurring throughout two distinct periods, viz., February to June and August to October, respectively. There are limited qualitative botanical data on this species (e.g., Tomlinson, 1961 ) but, to our knowledge, nothing is known of the factors affecting growth and reproductive development. This paper describes results from a collaborative research project directed towards the potential production of T. daniellii in protected cropping systems in the U.K. Information gained with respect to seed germination, methods of vegetative propagation and effects of population density on vegetative and reproductive growth would also be relevant to agronomic situations in West Africa.