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Reproductive biology and utilisation of Berchemia discolor (Klotzsch) Hemsley (Rhamnaceae)

Lusepani, Nakwezi Esther (1999-12)

Thesis (M.Sc.) -- University of Stellenbosch, 1999.

Thesis

ENGLISH SUMMARY: Berchemia discolor is an indigenous African fruit tree species with potential in terms of commercialisation and domestication. Indigenous fruit tree species play a role in the socioeconomic well being of small-scale farmers and rural communities. To facilitate the process of domestication and commercialisation of B. discolor, it is important to learn more about the biology of the species, nutritional value of the fruit, and if potential markets exist for the fruit. Fieldwork was carried out in Caprivi and Omusati in northern Namibia in order to study the reproductive phenology and the floral and pollination biology of the species. Analysis of the nutritional value of the fruit was carried out on the dry fruit pulp to assess the nutrients, minerals and vitamins contained in the fruit. In addition to this a socio-economic survey was carried out to assess the current trade in fruit and the utilisation of the tree and its products. The length of the reproductive phase during the 1996-97 season extended from mid October to end of March in Caprivi and from beginning of November to early April in Omusati. Vegetative growth and flower bud formation in Omusati occurred just after the onset of the first rain whereas in Caprivi it occurred two weeks prior to the onset of the rain. The flowers of B. discolor are dichogamous and protandrous. Pollinators are probably attracted to the flowers by olfactory stimuli, however visual stimuli also play a role as the flowers are greenish-yellowish in colour and several flowers are borne together in the inflorescence. Insect visitors to the flowers were identified as belonging to four different orders (Hymenoptera, Diptera, Coleoptera and Heterophera). Three of these orders have genera which may represent potential pollinators of B. discolor. Stigma receptivity probably occurred only after the elongation of the pistil subsequent to the presentation of pollen. The dry fruit pulp of B. ·discolor is rich in carbohydrates, calcium, sodium, iron, magnesium and potassium, but it is not a good source of phosphorus, fat, protein and ascorbic acid. The fruit trade is important for generating income, which is used to acquire other goods and services by the rural people. B. discolor could, subject to improvements on fruit quality and marketing become one of the commercial fruit in northern Namibia.

AFRIKAANSE OPSOMMING: Berchemia discolor is 'n vrugteboom inheems aan Afrika met kommersiele en ander gebruikerspotensiaal. Inheemse vrugtebome speel 'n belangrike rol in die sosio-ekonomiese welvaart van klein-boere en die landelike gemeenskappe. Vir die benutting van B. discolor is dit no dig dat die spesie bestudeer word in terme van die biologie, die voedingswaarde van die vrugte en die bemarkingspotensiaal. Veld studies is in Caprivi en Omsusati in Owamboland in die noorde van Namibie uitgevoer om die voortplantings-fenologie, die blom- en die bestuiwings-biologie van die spesie te bestudeer. Die voedingswaarde van die vrugte is bepaal deur die vlees van die vrugte te verpulp, te droog en te analiseer vir die teenwoordigheid van voedingstowwe, minerale en vitamiene. 'n Sosio-ekonomiese opname is gedoen om die grootte van die verkoopsmark vir die produkte van die boom (hout en vrugte) te bepaal. Die voortplantingsfase van die spesie gedurende die 1996-97 seisoen het gestrek van die middel van Oktober tot die einde van Maart in die Caprivi en van die begin van November tot die begin van April in die Omusati. Vegetatiewe groei en blomknopvorming in Omusati neem in aanvang net na die eerste reens terwyl dit in die Caprivi twee weke voor die eerste reens begin het. Die blomme van B. discolor is digogaam en protandries. Bestuiwers word waarskynlik na die blomme gelok deur reuk stimuli, maar visuele stimuli kan ook 'n rol speel deurdat die blomme, 'n groen-geel kleur het en verskeie blomme saam in 'n bloeiwyse voorkom. Insekte wat moentlik vir die bestuiwings verantwoordelike is, behoort tot vier ordes (Hymenoptera, Diptera, Coleoptera en Heteroptera). Drie van hierdie ordes bevat genera wat kan dien as potensiele bestuiwers vir die spesie. Die stempel word ontvanklik eers nadat die stamper ten volle verleng het en nadat diestuifmeel vrygestel is. Die droe pulp van die vrugte bevat 'n groot hoeveelheid koolhidrate, kalsium, natrium, yster, magnesium en kalium, maar is nie ryk aan fosfate, vette, proteiene en askorbiensuur nie. Die vrugte word deur die plaaslike inwoners versamel en vekoop, wat dien as bron van inkomste vir die verkryging van ander bestaansgoedere en dienste. B. discolor besit die potensiaal om met verbeterings in vrug-kwaliteit en bemarking, een van die belangrikste kommersiele vrugte in die noorde van Namibie te word.

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