1248 AJCS 8(8):1248-1256 (2014) ISSN:1835-2707 Assessment of genetic diversity in sorghum (Sorghum bicolor (L.) Moench) for reactions to Striga hermonthica (Del.) Benth. Mesfin Abate 1*,4 , Firew Mekbib 1 , Temam Hussien 1 , Wondimu Bayu 2 , and Fasil Reda 3 1 Department of Plant Sciences, College of Agriculture and Environmental Sciences, Haramaya University, P. O. Box 138, Dire Dawa, Ethiopia 2 International Center for Agricultural Research in the Dry Areas (ICARDA), Bahir Dar, Ethiopia 3 Agricultural Transformation Agency (ATA), P. O. Box-708, Addis Ababa, Ethiopia 4 Department of plant sciences, College of Agriculture and Natural Resource, Debre Markos University, P.O. Box 269, Debre Markos, Ethiopia *Corresponding author: mesfin197306@yahoo.com Abstract Striga is the largest biological barrier to sorghum production in several sorghum growing areas in Africa and Asia. Field experiments were conducted to assess the diversity of 49 sorghum genotypes for their reaction to Striga hermonthica and grouped them. Different multivariate analysis, including principal component and cluster analysis, were made on 15 ( for Striga-infested) and 6 (for non- infested) yield, yield attributes and Striga resistance/tolerance parameters. The result showed that the first four and three PCs explained 77 and 73 % of the total variation under Striga infested and non-infested conditions, respectively. Emerged Striga counts at 17 and 20 weeks after planting, Striga severity , Striga vigor, area under Striga number progress curve and area under Striga severity progress curve were the most important traits in the first PC. However, grain yield and dry weight had strong association and were loaded on the second PC. Scatter plot of PC1 and PC2 revealed sufficient diversity among genotypes and separated them with those field resistant and tolerant to Striga from the susceptible ones. The Ward’s minimum variance cluster analysis grouped the 49 sorghum genotypes in to four and three distinct clusters under Striga infested and non-infested conditions, respectively. Under Striga infested condition, most members of cluster I and III showed adequate degree of Striga resistance and tolerance, while cluster II and IV exhibited susceptibility to Striga. From these observations, it could be suggested that rich genetic sources of resistance and tolerance are available in a range of landrace, which could be utilized for future breeding and germplasm conservation programs aimed at improving Striga resistance and tolerance in sorghum. Keywords: Genotypes; Non-infested; Sorghum; Striga hermonthica; Striga-infested. Abbreviations: ASNPC_ area under Striga number progress curve; ASVPC_ area under Striga severity progress curve; DSE_days to Striga emergence; DSF_days to sorghum flowering; GY_ grain yield; IBPGR_institute of biodiversity and plant genetic resources; ICRISAT_international crop research institute for semi-arid tropics; IITA_international institute of tropical agriculture; PAL_ panicle length; PH_ plant height; PCA_ principal component analysis; SDW_sorghum biomass dry weight; SC_Striga emergence count; SH_Striga height; SSEV_ Striga severity; SV_ Striga vigor; STW_Striga weight; TIL_tillering; WAP_weeks after planting. Introduction Sorghum is an important cereal crop globally next to maize, wheat rice and barely. Over 80% of the sorghum production comes from Africa and Asia (FAO, 2010). In Ethiopia, sorghum is the principal food crop for people living in marginal areas where erratic rainfall, high temperatures, poor soil fertility and Striga infestation are major production problems. The parasitic weed (Striga hermonthica) infestation is gravely limiting sorghum production in Africa in general and in Ethiopia in particular. In Africa the weed has infested about 50 million hectares of crop lands which has negatively affected nearly 300 million people (Ejeta, 2007). The yield loss accounted to Striga infestation is immense, reaching up to 65% on average. In countries like Ethiopia and Sudan the damage is worse, reaching up to 100% yield loss, especially when it comes to drone prone (Ejeta et al., 2002). According to Reda and Parker (1994), in some areas in Ethiopia because of heavy infestation it is common to get farmers who have either abandoned their land or switched to other less important crops. Different researchers ( Bayu et al., 2001; Omanya et al., 2004; Rodenburg et al., 2005) have reported variability in sorghum responses to Striga infestation. Some sorghum genotypes support significantly fewer Striga plants and give higher grain yield than others. Some other genotypes show smaller yield reductions than others under the same level of infestation. Some are highly susceptible and would not give yield at all. The presence of this wide range of variability in Striga resistance and tolerance traits among sorghum genotypes suggests an opportunity to develop high yielding and resistant/tolerant genotypes through hybridization. Though there is no single effective method to control Striga, developing Striga resistant and tolerant genotypes is the most promising, practical, and cost effective approach to reduce the debilitating effects of Striga in small holding farming systems in Africa ( Ejeta and Butler, 1993).