Edible oil crops and their integration with the major cereals in North Shewa and South Welo, Central Highlands of Ethiopia: an ethnobotanical perspective

摘要

The grain-based farming system in Ethiopia is basically a mixed cropping system where pulses and edible oil crops are integrated with the staple cereal crops both in the farming and in making the cuisine at home. Ethiopia is one of the world centres where crop plant diversity is strikingly high and where some crop species were domesticated de novo (Vavilov 1951; Harlan 1969; Zeven and DeWet 1982). The country takes a unique position in history of domestication of a wide range of crop categories including cereals, legumes, roots and tubers, stimulants, oils and other crops (Harlan 1969, 1975; Westphal 1975; Zeven and DeWet 1982; Hancock 1992).The conditions of the natural environment and the farming system operating together under active involvement of farming communities have produced endemic crops and large number of local farmers’ varieties (landraces); many of them genetically diverse and with peculiar adaptations. The traditional Ethiopian farming systems and the diverse crops/landraces they maintained remained relatively stable for millennia (Harlan 1969; Westphal 1975). At present, alternative strategies for sustainable conservation and use of agrobiodiversity are being sought from surviving traditional systems (Steiner 1982; Altieri and Merrick 1987; Bellon 1996) like those of the present study area. Indigenous knowledge about crop diversity that refers to attributes such as growing habits, seed quality, yield and the like generated by ethnobotanical studies are being called upon to enhance on-farm conservation with continued evolution and diversification of crops as well as adding value to local landraces (Asfaw 2000; Brown 2000).Traditional farming preserves plant genetic resources while simultaneously maintaining processes of evolution and adaptation in conjunction with indigenous knowledge (Brown 2000; Brush 2000; Jarvis et al. 2000); and this operates in the Ethiopian system (Asfaw 2000; Worede et al. 2000). Cropping systems have a direct influence on the performance of genotypes and cause considerable changes in the relative yields of genotypes. As a common traditional agricultural practice, small-scale farmers usually prefer multiple cropping systems as it minimizes economic and environmental risks while fulfilling the goals of subsistence.Oilseeds, which are used for basic dietary requirements, are dual purpose crops providing large quantities of oil and proteins under traditional use regimes. Ethiopia, where oilseeds play an important role in the traditional nutrition (Seegeler 1983), is the centre of origin and/or diversity for many edible oil crops. The place of domestication of noog is Ethiopia (Harlan 1969; Zeven and DeWet 1982) where it has been under cultivation for much longer than any other place (Baag?e 1974; Dagne 1994) and stands first with coverage of about 60?% of the total area and production volume of oil crops. In the course of domestication, the oil content and seed size of noog has increased without a significant change in the fatty acid composition (Dagne and Johnson 1997). Linseed (Linum usitatissimum) is the next most important oil crop in Ethiopia (Teklewold and Alemaw 1993) and is considered an early introduction from Asia (Harlan 1969; Zeven and DeWet 1982; Belayneh 1985, 1991). Ethiopia is generally accepted as a centre of origin/diversity of sesame (Sesamum indicum) and as a secondary centre of variability of safflower (Carthamustinctorius) (Harlan 1969, 1975; Seegeler 1983). The Ethiopian mustard (Brassica carinata) is indigenous to Ethiopia, having its cultivation history in the Ethiopian highlands and north Kenya (Demissie et al. 1991; Teklewold and Alemaw 1993). Many oil crops grown in Ethiopia (e.g. noog, safflower, Ethiopian mustard, sesame and linseed) have wild relatives in Ethiopia (Edwards 1991).Knowledge about in situ conservation can trickle bit-by-bit as ethnobotanically tuned investigations bring up the ways in which farmers perceive and manage the biophysical environment