Morpho-Physiological and Yield Responses of Stay-green Elite Sorghum (Sorghum Bicolor (L.) Moench) Varieties to Different Irrigation Levels in the Rift Valley of Ethiopia

Morpho-physiological and yield responses of local and improved sorghum (Sorghum bicolor (L.) Moench) varieties with stay green property to deficit irrigation were evaluated. The study was undertaken in split plot designs with three replications in the Ethiopian rift valley during off season in 2011 and 2012. Drought was imposed during pre-flowering with irrigation levels 0%, 25%, 55%, 65% and 80% of TAW and a post-flowering progressive drought stress. The different deficit irrigation levels delayed maturity and reduced third leaf area, culm height and biomass with different degrees. Senescence rate was recorded least in SorColl 163, E 36-1and B 35. Root biomass of E 36-1 and SorColl 163 increased at severe and mild drought stress levels respectively, but diminished in SorColl 60 and SorColl 179 with increasing water deficit levels. Genotypes E 36-1, SorColl 178 and SorColl 163 demonstrated a sharp increase in root-shoot biomass ratio, while SorColl 179 had the least. RLD distribution that was skewed to the first two upper soil depths improved with increasing drought stress in most plants. Highest DTI value was recorded in Abshire, SorColl 178 and SorColl 60; but SorColl 179 demonstrated least. Assimilation rate decreased with increasing drought stress and at 55% water deficit level, SorColl 146 (48.4 mole CO2/m2s), E 36-1 (43.4 mole CO2/m2s) and SorColl 163 (40 mole CO2/m2s) maintained better and significantly (P<0.05) reduced at 65% and 80 % stress levels. Yield in terms of seed weight per panicle was observed highest in the check E 36-1 followed by SorColl 163 and SorColl 60 whereas SorColl 178 performed least. Based on the results obtained SorColl 163 had prominent stay green trait that is found to give high yield under deficit irrigation. SorColl 146 performed in many traits next to SorColl 163 but had reduced yield. Thus, SorColl 146 may be described to have cosmotic stay green trait. The study identied SorColl 163 to be used as stay green trait source concomitant with B 35 and E 36-1. Key words: Sorghum, drought stress, biomass, leaf area, senescence, photosynthesis, RLD, yield, stay green.