Association between morphological traits and yield components in the durra sorghums of Ethiopia

摘要

The northeast quadrant of Africa is considered the center of origin and domestication for cultivated sorghum (Doggett 1965; Dillon et al. 2007). This can be recognized from abundant feral relatives in the region occurring in sympatry with cultivated forms (Ayana et al. 2000a; Tesso et al. 2008). Ethiopia, one of Vavilov's centers of origin for several crop species, hosts wide genetic variability for sorghum; all races of sorghum occur in the country's major sorghum-growing areas (Stemler et al. 1977; Doggett 1988). Sorghum is grown by almost all of the more than 80 ethnic nationalities of the country stretching from the hot, dry lowlands with a typical semiarid climate to the cool highlands with temperate weather. This assortment of environments along with the ethnic, social, and cultural diversity of the population have contributed to the development of diverse and distinct pool of sorghum germplasm, many of which are represented in international gene banks and the USDA/GRIN database (Gebrekidan 1973; ).Besides the diverse growing conditions and complex ethno-cultural settings, the different cropping systems practiced throughout Ethiopia (Davis and Woolley 1993; O'Leary and Smith 1999; Tamado and Eshetu 2000; Santalla et al. 2001) and the diverse uses of the crop (Osafo et al. 1993, Reed et al. 1986) may have also contributed to the evolution, cultivation, and maintenance of unique types of sorghum. For example as a result of years of cultivation under multiple cropping systems (Georgis et al. 1990), farmers in eastern Ethiopia have identified unique variants of the crop suited for intercropping with both legume and non-legume species. Likewise, continued use of the crop as a major ingredient for local brew in the north and as a chief source of energy and protein throughout the country has led to selection and maintenance of sorghum types with high fermentation efficiency and others with improved grain and nutritional quality (Singh and Axtell 1973; Gebrekidan and Kebede 1979). Moreover, the need for sorghum biomass as source of fuel, animal feed, and construction material has resulted not only in sustained cultivation of the tall, crook-necked durra but also in selective adaptation and production of sweet and high biomass types used as dual-purpose crops. The value of these traits is well recognized in modern plant breeding, which seeks to improve sorghum for use as a major food, feed, and bioenergy crop.The wealth of genetic variability in the Ethiopian sorghum germplasm sources has always attracted the attention of regional and international sorghum breeding programs. Several accessions possessing traits of economic importance have been identified among Ethiopian sorghums. These include sources of post-flowering drought tolerance (Haussmann et al. 2002; Kebede et al. 2001, Xu et al. 2000; Tao et al. 2000), high grain quality and high yield potential (Prasada Rao and Mengesha 1981), and sources of high lysine and high protein digestibility (Singh and Axtell 1973). Over the past 30 yr, the Ethiopian Inst. of Biodiversity Conservation (IBC) has collected and maintained more than 5000 sorghum accessions. However, although Ethiopia's diverse sorghum-growing environments are presumed to harbor wide genetic variability, many of these areas are inaccessible for germplasm collection. Thus, the accessions in the gene bank represent only a fraction of the existing in situ variability. Regardless, these are valuable resources and have already rendered service to the international sorghum research community in many ways.Attempts have been made to document the extent of genetic variability among these accessions (Teshome et al. 1997, 1999; Ayana et al. 2000b; Tunstall et al. 2001; Ayana and Bekele 2004; Mamo et al. 2007). But the efforts were fragmented in that they focused either on accessions originated only from specific localities or on a narrow set of samples too small to fully reflect the breadth of genetic variability that exists