370 AJCS 10(3):370-376 (2016) ISSN:1835-2707 DOI: 10.21475/ajcs.2016.10.03.p7230 Performance of Ethiopian bread wheat (Tritium aestivum L.) genotypes under contrasting water regimes: potential sources of variability for drought resistance breeding Habtamu Ayalew 1,2 , Tadesse Dessalegn 3 , Hui Liu 1 , Guijun Yan 1* 1 School of Plant Biology, Faculty of Science and the UWA Institute of Agriculture, The University of Western Australia, Crawley, WA 6009, Australia 2 Department of Horticulture, College of Agriculture and Natural Resources, Debre Markos University, PO Box 269 Debre Markos, Ethiopia 3 East African Agricultural Productivity Project, Wheat Regional Centre of Excellence, Kulumsa Agricultural Research Centre, PO Box 439, Assela, Ethiopia *Corresponding author: guijun.yan@uwa.edu.au Abstract Drought is a common abiotic stress in Ethiopian agriculture. Crop yield is at risk due to drought that happens at various developmental stages of the crop. This experiment evaluated 248 Ethiopian bread wheat genotypes under water stress and non-stress growing conditions. Augmented complete block design with three blocks and eight replicated entries was used. Analysis of variance showed significant diversity among the genotypes in reaction to water stress. The average root and shoot lengths were reduced by 33.4% and 28.8%, respectively, due to water stress. The average fresh biomass per plant was 192 mg for non-stressed and 116 mg for stressed treatments, suffering a 40.5% reduction due to stress. Accessions 8314, 204463, 204454 and 204521 showed the longest roots while accessions 222381, 222405, 222439 and 204586 showed the shortest roots under stress conditions. Drought tolerance indices were calculated based on root length. Geometric mean performance (GMP) index was found helpful in identifying the relatively stable genotypes across the two water regimes. High GMP indices were observed for genotypes 8314, 204521, 231614, and KSN81 which were long rooting genotypes under both stress and non-stress conditions. ANOVA based on region of collection showed that genotypes from Southern Nations Nationalities and Peoples Region had the longest roots. Elevation of origin did not show any significant difference for any of the traits measured. This study demonstrated the presence of large variations for water stress response in the Ethiopian bread wheat germplasm. The identified stress resistant genotypes can be used as potential breeding stocks to develop drought resistant cultivars. Keywords: hydroponics; osmotic stress; seedling resistance; wheat collections. Abbreviations: DRI_Relative drought resistance index; GMP_Geometric mean performance; KSN_Kulumsa screening nursery; PEG_Polyethylene glycol; SSI_Stress susceptibility index; STI_Stress tolerance index. Introduction Agriculture is the largest sector of employment and main source of livelihood in Ethiopia. Nearly 85% of the population depends directly on farming. Grain production constitutes the major share of the domestic agricultural production. Nearly 98% of cereals are produced by small holder farmers (USDA, 2014). Ethiopia is the largest wheat producing country in Sub-Saharan Africa, with annual production of more than 4 million tons of grain on 1.6 million hectares of land which accounted for 13% of total land allotted to cereals (CSA, 2014; USAID, 2014). Wheat is mainly grown in the central and south eastern highlands during the main rainy season (June to September) (Hailu et al., 1991). The Ethiopian agriculture is mainly rain-fed in that its performance is highly dependent on the timing, amount and distribution of rainfall (Cheung et al., 2008). This makes the sector vulnerable to drought and other natural calamities. Due to the changing global climate, the rain fall trend is also changing (Funk et al., 2012; Hellin et al., 2012; Schlenker and Lobell, 2010; Stroosnijder et al., 2012). The rains are becoming more erratic with a trend of starting late and ceasing early in the season. This has posed an eminent danger for crop production. The production loss due to both biotic and abiotic factors coupled with the increasing population has made it difficult to attain food security in the country. Improving the adaptability of crop varieties to a changing environment supported by appropriate crop management strategies is the working principle worldwide in ensuring crop productivity (Blum, 2011a; Farooq et al., 2015; Stroosnijder et al., 2012; Wasson et al., 2012). However, crop improvement for water stress is a much complicated task as drought damage is manifested in various forms at various crop growing stages making breeding for drought resistance uneasy (Blum, 2005; Fischer et al., 2012; Szira et al., 2008; Tuberosa, 2012). Therefore, breeding for drought resistance has to integrate all methodologies that help in genotype evaluation and selection at all stages of the crop instead of one final stage (Qu et al., 2008). Seedling or early vigour, and deep root system are believed to contribute for better drought resistance (Al-Karaki, 1998; Atkinson et al., 2015; Chloupek et al., 2010; Comas et al., 2013; Lilley and Kirkegaard, 2011). Some genes that contribute to seedling drought resistance may also contribute to later stage resistance