Partitioning index and non-structural carbohydrate dynamics among contrasting cassava genotypes under early terminal water stress

Cassava (Manihot esculenta Crantz.) is a storage root crop of importance in tropical regions where periodic dry season and drought affect performance. Cassava genotypes that differ in performance in ecosystems with various water regimes were subjected to water stress during storage-root initiation and early development. Plants were grown in 50 kg pots in a screen house environment under well-watered and water stress conditions for a 120-day period. Water stress had a significant effect on most traits analyzed. However, relative water content, partitioning index and non-structural carbohydrates were unaffected. Tolerant genotypes had a higher partitioning index than susceptible genotypes during water stress, associated with a larger number of storage roots initiated and larger storage root biomass, while they were shorter and had less fibrous root biomass. Tolerant lines were indistinguishable from susceptible lines in above ground biomass under stress. These findings suggest that early evaluation of storage root number, partitioning index, and associated traits at an early stage of cassava storage-root development could be an effective approach by which cassava genotypes are screened for favorable drought tolerance response.