Evaluation of cassava genotypes (Manihot esculenta Crantz) for drought tolerance and susceptibility under water deficit conditions

Drought stress detriments crop yields and exacerbates food insecurity.Cassava, an inherently drought tolerant crop, is a sustainable solution.This study evaluated cassava genotypes' varied responses to drought enabling selection of superior candidates with improved performance.Field-assessed drought tolerant (DT) and drought susceptible (DS) genotypes varied in leaf wilting, abscission, staygreen, root development and bulking.Under greenhouse experiments, well-watered (WW) plants showed significantly (P 0.001) higher vegetative growth and physiological response than plants exposed to water deficit (WD).Relative to WW treatment, WD reduced total leaves formed by ~20%, leaf retention by ~67%, plant height by ~26%, shoot fresh weight by ~62%, shoot dry weight by ~41% and shoot water content by ~49%.These generally implied negative effects of water deficit on cassava growth and development.Amongst genotypes, DT candidates (98/0002, 95/0306, M98/0068, I92/0067 & 94/0039) exhibited the least decline for most of these traits compared to DS counterparts (92/0427, TME-419 & I96/1439) under WD treatments.Physiologically, significantly (P 0.001) higher leaf stomatal conductance (Gs) was measured from WW plants than WD-plants.Genotypically, a decrease in higher, moderate and lower Gs was recorded between the DT and DS genotypes.Cessation of leaf Gs after 10 days of WD and increased Gs rates after a day of re-watering respectively, mimicked drought-induced stomatal closure and stomatal re-opening.These results imply the potential use of either parameter(s) for rapid screening for drought stress tolerance in cassava genotypes and thus benefit breeding programs for drought-tolerant cassava.Selected morpho-physiologically superior genotypes such as 98/0002, 95/0306, M98/0068, I92/0067 and 94/0039 could be cultivated for better cassava productivity under drought stress.