Morpho-physiological and biochemical investigations were conducted on five selectedrnsorghum (Sorghum bicolor (L.) Moench) landraces (SorColl 60, SorColl 146, SorCollrn163, SorColl 178 and SorColl 179) and three cultivars (Abshir, E 36-1 and B 35) tornevaluate and screen for drought resistant and stay green potential landraces. The mainrnobjective of the study was to enrich parental lines with stay green trait. The study wasrnundertaken both at field (Melkassa Research Station, Melkassa) and greenhouse (Collegernof Natural Science, Addis Ababa University) conditions in 2011 and 2012. A split plotrnand randomized complete block designs with three replications were used for the fieldrnand greenhouse experiments, respectively. Irrigation levels 0%, 25%, 55%, 65% andrn80% of total available water (TAW)at field and FC at green house during pre-floweringrnand a post-flowering progressive drought stress during the field study were applied.rnResults demonstrated that all sorghum varieties exhibited different values of thernphenotypic traits considered at non stress level except proline content analysis,rnindicating genetic variation among landraces. Moreover, all traits examined were withrndifferent varieties scoring highest value, and high performance at full irrigation had nornsynchronization with stay green trait. Imposing different irrigation level at pre-floweringrnresulted in delayed reproductive stage occurrence in the field study. Culm height wasrnmore affected by pre-flowering drought stress than by post-flowering. Culm height wasrnrelatively more resistant to pre-flowering drought effect in varieties E 36-1, SorColl 163rnand Abshir. SorColl 60, E 36-1 and SorColl 163 demonstrated an improvement in culmrnheight over other varieties.Third leaf area, biomass, senescence rate, assimilation raternresponses were more sensitive to drought, but SPADR was not. SorColl 60, Abshirrnfollowed by SorColl 163 third leaf area decreased least relative to other varieties.rnSenescence rate evaluation after grain filling revealed an increasing rate with increasing drought stress. SorColl 163, SorColl 146 and E 36-1were with least senescence rate inrnpost grain filling stage. At 80% water deficit level, the maximum per cent shoot weightrnloss from the controls was recorded for SorColl 179 (60%) followed by Abshir and E 36-rn1. SorColl 146 had the lowest percent shoot weight loss (36%) as compared to otherrnvarieties. Root biomass of E 36-1 and SorColl 163 increased at severe and mild droughtrnstress levels respectively, while root biomass of SorColl 60 and SorColl 179 wentrndiminishing with increasing water deficit levels. E 36-1, SorColl 178 and SorColl 163rndemonstrated a sharp increase in root-shoot biomass ratio indicating relatively a higherrndry mater partitioning to roots, while SorColl 179 had the least. In all sorghum varietiesrnunder non stress condition /full irrigation/, root length density (RLD) distribution wasrnskewed (greater than 50%) to the first two upper soil depths. The skewed RLDrndistribution was improved with increasing drought stress from 70-60% in non stressrncondition to 55-47.5% at 80% on the upper depth. High drought tolerance index (DTI)rnvalue was recorded in Abshire, SorColl 178 and SorColl 60. Abshir had high DTI thatrnincreased with increasing drought effect; while SorColl 179 demonstrated least indexrnvalue that further declined with increasing drought stress. Assimilation rate decreasedrnwith increasing drought stress and at 55% water deficit level, SorColl 146 (48.4 ïmolernCO2/m2s), E 36-1(43.4 ïmole CO2/m2s) and SorColl 163 (40 ïmole CO2/m2s) maintainedrnrate of assimilation better than others and at both 65% and 80 % levels AN wasrninsignificantly affected by the drought stress.Yield in terms of seed weight per paniclernwas observed highest in the check E 36-1 followed by SorColl 163 and SorColl 60rnwhereas SorColl 178 performed least. The study on interrupted drought in the phases ofrnthe reproductive stage revealed that yield loss was due to different factors in thernreproductive phases considered. Higher yield loss was found due to drought imposed atrnpanicle initiation and seed filling. Loss in seed count had least contribution in E 36-1,rnSorColl 146 and SorColl 163.Seedlings of Sorghum varieties were found decreasing inrnheight, biomass, assimilation rate but increasing in Chlorophyll a and b and prolinerncontent with increasing drought stress. Sorghum landraces SorColl 146, SorColl163,rnSorColl 60 relatively performed better, whereas SorColl 179, E 36-1, SorColl 178,rnAbshir, and B 35 were negatively affected by the drought stress. Green house root-shoot ratio of SorColl 146, SorColl 178, SorColl 179 and SorColl 163 were higher than othersrnat the most severe drought stress (65%). Third Leaf area of SorColl 179, SorColl 163,rnand E 36-1 SorColl 178 was less affected over other genotypes. Unlike the results fromrnthe field condition, assimilation rate of SorColl 163 and SorColl 146 including the checksrnwere affected highest at seedling and greenhouse condition. A gentle increase in Chl arnand Chl b content was recorded with increasing drought but concentrations at 65% werernrelatively lower than 25% and 55% irrigation levels. The highest reading of Chl arncontent was recorded in B 35, SorColl 163 and SorColl 60 but SorColl 146 and SorCollrn179 had least content and with a sharp decrease in Chl a. On the other hand, Chl brncontent in SorColl 179, SorColl 146 and B 35 was highest but SorColl 146, SorColl 163,rnE 36-1 had least and values decreased up to 55% field capacity. Proline content alsornincreased with increasing drought stress in the extracts of all the three organs fromrncontrol plants. In all organs, there was small amount (about 2-5 ïgm/gm) andrninsignificant variation among the varieties (except SorColl 60 (14.17ïgm/gm) andrnSorColl 146 (8.95ïgm/gm) in root) at non stress condition and slow induction in prolinernwas recorded in the mild drought stress. With increasing drought stress, proline contentrnincreased sharply in the stem followed by root extract. E 36-1, SorColl 163, B 35 andrnAbshir demonstrated the highest content in all the organs at the severe drought stressrnlevels, indicating that all the check varieties had active response. It is concluded that ofrnthe grain sorghum landraces studied, SorColl 163 had a stay green trait that is found torngive high yield under both deficit irrigation before flowering and progressive droughtrnstress in post-flowering period. SorColl 146 performed in many traits next to SorColl 163rnbut with reduced yield. Thus, SorColl 146 may be described to have cosmetic stay greenrntrait under drought stress. SorColl 60 had inconsistent responses but had better yieldrnthan SorColl 146 under severe drought stress. The study recomends that SorColl 163 bernused to transfer drought resistant traits to other sorghum lines along with the currentlyrnused lines, B 35 and E 36-1.rnKey words: grain sorghum, stay green, pre-flowering drought stress, post-floweringrndrought stress, biomass, leaf area, senescence, photosynthesis, SPAD, RLD, yield,rnproline, chlorophyll content, drought tolerance.