Germination Trials and Domestication Potential of Three Native Species with Edible Sprouts: Ruscus aculeatus L., Tamus communis L. and Smilax aspera L

Ruscus aculeatus, Tamus communis and Smilax aspera are wild species whose young spring sprouts are consumed in some areas of Italy. Although sometimes abundant in the natural vegetation, these species are not common on a country basis. Sprouts are therefore only locally commercially available. Cultivation could contribute to make them better known and increase vegetable product differentiation. Seed germination was investigated by applying the following treatments: control, concentrated H2SO4 for 5 or 10 minutes; GA3 at 500 ppm coupled or not with H2SO4, ethrel 1 or 3 mM, KNO3 0.2 or 0.4%, natural stratification. Germination was very low, and of no practical interest, for S. aspera, ranging from 0 to 65% for the two other species. The mean germination time was 140-220 days. KNO3 and ethrel at low dose improved, GA3 and H2SO4 decreased, and stratification had no effect on germination. Germination time was shorter at higher germination rates. Domestication opportunities are discussed, considering growth habit, cultural traits and consumer acceptance. INTRODUCTION The present tendency towards the recovery of food traditions and the need for product diversification may offer opportunities for new crop domestication. This, however, should rely on a minimum basic knowledge. Ruscus aculeatus L., Smilax aspera L. and Tamus communis L., although mainly known for other characteristics, are used as edible plants in some areas of Italy, where young sprouts are consumed cooked as vegetables. Ruscus aculeatus (Liliaceae) is a well known bushy plant (chamaephyte), rather common in the underwood layer of sub-mediterranean forests. The aerial part generally lives for several years, flowering and fruiting, whereas vegetative growth generally ends in the first year. The growth habit has therefore also geophytic traits, since new shoots are produced yearly from underground buds. The plant produces a dense net of rhizomes, suitable for vegetative propagation. The rhizomes and roots have been extensively studied for their active principles (mainly steroidal saponins; Elsohly et al., 1975), in pharmaceutical preparations and clinical trials. Traditional use in anti-inflammatory treatment has recently been exploited, making R. aculeatus a primary plant remedy for vein ailment and haemorrhoids (Oulad-Ali et al., 1996; Dunouau et al., 1996; Jager et al., 1999). R. aculeatus and other Ruscus are used as ornamentals for shaded places, and as a source of cut foliage. Fertilisers, shading, weed control and climate were studied as critical growing factors (Rumine and Bellandi, 1984; Baum and Biran, 1982; Stamps and Boone, 1992). Seed propagation has not been investigated, whereas some work was done on in vitro propagation of other Ruscus species (Curir et al., 1988). The use of spring sprouts as food is known in many places of Italy (Corsi and Pagni, 1979; Lonardoni and Lazzarini, 1992). Smilax aspera (Liliaceae) is a climbing spiny shrub, occurring in clearings and forest margins of typical Mediterranean woodlands. It has a phanerophytic growth habit, with aerial branches elongating several meters, bearing both flower and vegetative buds, from which sprouts develop in spring. Vigorous root suckers are produced from rhizome buds as well, so that the species may occasionally behave as a geophyte (e.g. after fires or Proc. IS on Sust. Use Of Plant Biodiv. Eds. E. Düzyaman &Y.Tüzel Acta Hort. 598, ISHS 2003 212 when the aerial part is killed by frost). Many Smilax species of Central and South America, collectively referred to as sarsaparilla, as well as east Asian species, have been investigated for the active principles and medicinal uses of their rhizomes. Food uses of S. aspera have been reported for Turkey (Syamoglu, 1984; Ertug, pers. commun.) and other middle-eastern countries, already since long ago (Ridolfi, 1881). In Italy, it is used in some areas and sometimes commercially harvested in Sicily (Arcidiacono et al., 1996). Uses as vegetables have been reported for two other Smilax species in Japan (Tazawa et al., 1990). Tamus communis (Dioscoreaceae) is a climbing vine growing in forest margins, hedges and clearings in sub-mediterranean vegetation types. It is a typical geophyte, whose aerial parts die every year and regenerate in spring from the big tubers; spring sprouts of mature plants are very vigorous. The plant is toxic because of saponins and oxalic acid, in which the fruits are particularly rich. The tuber has been studied for its anti-inflammatory properties (Capasso et al., 1983; Mascolo et al., 1987), and as a potential source of diosgenin (Aquino et al., 1984). The plant is rather popular in some areas as a potent external remedy for traumas and distortions, having, however, a strong skin-irritating side effect. The sprouts are very popular ingredients of soups and side dishes of meat courses in central Italy. Their use is also reported for north-western France (Lieutaghi, 1974; Peyron, pers. commun.). Documented cases of toxicity have not been reported. All three species are often abundant in their natural habitat, but typical of vegetation types not very common on a country basis, and prone to human disturbance. Cultivation may therefore represent a means of reducing the pressure on natural stands. These species can be vegetatively propagated by means of rhizomes (Ruscus, Smilax), tubers (Tamus) and perhaps cuttings. However, seeds would assure faster and easier multiplication. Additionally, as indicated for Dioscorea rotundata (Sadik and Okereke, 1975), seed propagation is more efficient to explore and exploit biodiversity. Experiments on seed germination are almost absent, as is information on cultivation. This paper reports the results of germination trials with seeds from Italian natural populations of the three species, and observations on early seedling growth, aimed at collecting preliminary information on cultivation and domestication opportunities. MATERIALS AND METHODS Ripe fruits were collected in October, 1997. Tamus and Smilax fruits were harvested in the coastal area of Montemarcello, Liguria region, northern Italy. R. aculeatus fruits were harvested on the western slopes of the Cimini mountains, province of Viterbo, central Italy. For the preliminary trials of 1996, fruits of all three species were harvested in the Montemarcello area. The seeds were manually extracted from the fruits, washed with water, dried with air flow at 25 °C for one week, selected for the elimination of all defective seeds, and stored in air-tight containers at 18 °C until the start of germination trials. In 1996, 50 seeds per species were subjected to the tetrazolium test. Germination trials started in December in both years, and were carried out in three replications of 50 seeds, using sterile sand as substrate, in a climatised chamber at 20 °C and 90-95% relative humidity. No differentiated theses were compared in 1996, whereas in 1997 the following treatments were given, plus an untreated control: a) chemical scarification with concentrated H2SO4 for 5 or 10 minutes; b) treatment with gibberellic acid (GA3) at 500 ppm for 1 hour; c) factorial combinations of the previous two treatments; d) treatment with ethylene (ethrel, 1 and 3 mM) for 1 hour; e) osmotic treatment with KNO3 at 2 and 4 mg l for 6 hours; f) stratification in humid sand under plastic tunnel for 120 days. The seedlings were counted each 2-4 days from the beginning of germination. A seed was considered germinated when the coleoptile was fully developed. Mean germination time was calculated as: MGT=Σ(d*n)/N, where d = day from sowing; n = number of germinated seeds in each counting; N = total number of germinated seeds. The data were subjected to the analysis of variance after angular transformation.