Agronomic and physiological assessments of genotypic variation for drought resistance in sorghum

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Abstract
This study was designed to assess genotypic variability for drought resistance in sorghum (Sorghum bicolor [L.] Moench) and to conclude on the possible physiological differences between drought resistant and drought susceptible genotypes.Grain yield under drought stress ranged from 184 to 943 g m-2 and relative yield ranged from 35.8 to 103.5% among genotypes. Yield (but not relative yield) under stress was decreased (r= -0.89**) with a longer growth duration of gentoypes. Both stover yield and total biomass under stress increased (r = 0.69** and r = 0.72**, respectively), while harvest index decreased (r = 0.80**) with longer growth duration. Genotypes differed significantly in leaf water potential (LWP), canopy temperature, leaf rolling, leaf carbon exchange rate (CER), stomatal conductance and osmotic adjustment. These data were averaged for the four best ('drought resistant'-R) and the two poorest ('drought susceptible'-S) genotypes in terms of their absolute and relative yields under stress. Compared with S, the R genotypes were earlier in heading and had higher LWP, lower canopy temperature and higher stomatal conductance. While leaf rolling was similar in R and S genotypes, it was found to increase as LWP decreased across all genotypes. Under these stress conditions variations in CER among genotypes on given dates appeared to be affected more by phenology than by plant water status.