1.8.1 Trichilia dregeana Sond.
Trichilia dregeana (Meliaceae), is commonly known as the forest mahogany or umKhuhlu (Zulu) and is indigenous to southern and eastern Africa. The name Trichilia is of Greek origin and refers to the three-lobed fruits which enclose the seeds (Pooley, 1993). Trees are known to reach heights of between 10 - 35 m and, although not common in the coastal forests of KwaZulu-Natal, South Africa, is also cultivated as a street tree in the province (Pooley, 1993; Kioko, 2003). The leaflets are shiny, have an almost hairless undersurface and are pointed at the tips. In southern Africa the plant flowers between October and December and prominent fruits are produced between March and May (and sometimes later). Each fruit capsule yields six black seeds, each almost completely enclosed by a scarlet aril (Pooley, 1993; Figure 1.3). The fruit is eaten by not only birds, but also by people as a milky soup with the addition of spinach (Pooley, 1993).
Products from this tree are used commercially (wood for furniture and oil for soap and cosmetic use), and also have medicinal properties. Preparations of the bark are used in the treatment of backache, stomach problems, kidney ailments and its usage as a fish poison has also been reported (Pooley, 1993; Hutchings et al., 1996; van Wyk and Gericke, 2000). Five limonoids have been chemically isolated from these seeds (Mulholland and Taylor, 1980) including trichilin A and dregeanin, which could contribute to the medicinal properties of this species and/or could have anti-fungal activity as reported for Khaya ivorensis, another species in this family (Abdelgaleil et al., 2005).
The seeds, which contain up to 65% lipid by weight, were reported to be recalcitrant and chilling sensitive (Choinski, 1990). Since then, other in-depth studies have been carried out on seeds of this species to determine strategies for field collection (e.g.
Berjak et al., 2004), the potential for sub-imbibed storage (Drew et al., 2000; Eggers et al., 2007), the effects of dehydration on the nucleoskeleton (Merhar et al., 2002) and to assess if the absence of dehydrin-related molecules contributes to their desiccation sensitivity (Han et al., 1997). Work carried out by Kioko et al. (1998) and Kioko (2003)
showing the lack of shoot development after cryopreservation is of particular interest in the current study, which is aimed at ameliorating this deficiency and perhaps provide information pertaining to the failure of shoot development.
1.8.2 Trichilia emetica Vahl.
This is the second of the two Trichilia spp. found in Africa and is commonly known as the Natal mahogany and shares the same Zulu name with T. dregeana (umKhuhlu). In South Africa, the species occupies a similar habitat as T. dregeana, but does not extend as far south in KwaZulu-Natal. There is a striking superficial similarity in appearance between the two trees in this genus. However, while T. dregeana range between heights of 10 - 35 m, T. emetica trees reach heights of between 5 - 10 m (Pooley, 1993). The leaflets and fruit are also superficially morphologically similar; however, the leaflets of T. emetica are not as shiny as those of T. dregeana, have hairs on the undersurface and have rounded tips. There are also differences between the flowering and fruiting seasons, which are September to November and January to April, respectively, for T. emetica. The fruits have a distinct neck (absent in T. dregeana) and are slightly smaller than those of T. dregeana. The seeds, however, although slightly smaller in T. emetica, are very similar (compare Figures 1.3 and 1.4). Fruits are eaten by baboons, monkeys, antelope, and are also used to make a milky soup similar to that of T.
dregeana (Pooley, 1993).
Preparations of bark, roots, leaves, as well as seed oils, are used for medicinal purposes against stomach, intestinal and kidney ailments, indigestion, fever, parasites and eczema (Hutchings et al., 1996; van Wyk et al., 1997). Resin and tannin is found in the bark (Hutchings et al., 1996) and limonoids such as trichilin A have also been isolated (van Wyk et al., 1997) and may contribute to the medicinal properties of this species.
Few studies have been published on the behaviour of the seeds of this species, but they have been classified as recalcitrant (Maghembe and Msanga, 1988; Kioko et al., 2006).
1.8.3 Strychnos gerrardii N.E. Br.
This species belongs to the family Loganiaceae and is commonly known as the black monkey orange or umGuluguhla (Zulu). The family is widespread throughout the world, with seven species represented in South Africa. Strychnos gerrardii is often confused with S. madagascariensis and also has the same English common name. Trees of S. gerrardii are found along the coastal and dune forests of KwaZulu-Natal and reach heights of 10 - 25 m. The leaves are shiny, hairless, fairly thin and taper at the tip and the base. These trees flower between November and January and fruit from April to November (Pooley, 1993). Fruits contain multiple seeds and have a substantial woody pericarp/exocarp that changes from green to pale yellow upon ripening (Pooley, 1993;
Figure 1.5).
Although seeds of this species may have mildly toxic properties, the fruit pulp is eaten by people and monkeys. The species with toxic seeds, known for producing strychnine (S. nux-vomica) and curare poison (S. toxifera), are found in India and South America, respectively (Pooley, 1993; Philippe et al., 2004).
A few studies have been carried out on the branches and leaves (Itoh et al., 2005 and Hoet et al., 2006, respectively) of another closely related species, S. spinosa to determine its chemical properties. However, very little is known about the post-harvest seed behaviour of any Strychnos spp. indigenous to South Africa. Preliminary studies carried out by Khuzwayo (2002), however, indicated that the seeds of S. gerrardii show recalcitrant behaviour.
Figure 1.3: Three-lobed fruit and seeds of T. dregeana. Bar = 10 mm.
Figure 1.4: Fruit and seeds of T. emetica.
Bar = 10 mm.
2. MATERIALS AND METHODS