Abstract
This study was carried out to assess genotypic variability in abscisic acid content, carbon isotope ratio, and their
relationship to storage root yield and yield components in cassava under irrigation and moisture stress. The study involved 20
cassava genotypes arranged in randomized complete block design with three replications. Irrigation water was applied using a
drip irrigation system with a discharge rate of approximately 5.33 L m-2 hr-1. Significant (P < 0.05) genotypic variability was
observed for all physiological, growth, and yield traits assessed. Abscisic acid content was higher under stress than irrigation
and negatively correlated with root yield (r = -0.45), harvest index (r = -0.43), and above-ground biomass yield (r = -0.20)
indicating that it can be used as indirect selection criteria against unproductive genotypes. Carbon isotope ratio was
significantly and positively correlated with above-ground biomass yield (r = 0.20) but not root yield (r = 0.09). Estimates of
genotypic variability indicated high values for most of the growth and yield components but low heritability values for
abscisic acid content, carbon isotope ratio, stomatal conductance, and root yield under stress conditions. However, higher
estimates were recorded under irrigation and in the combined analysis. It was also found from this study that carbon isotope
ratio influences above-ground biomass but not storage root yield under stress conditions. The results from this study provide
useful information on the relationship between abscisic acid content, carbon isotope discrimination, and storage root yield in
field-grown cassava.
Genotypic Variation in Abscisic Acid Content, Carbon Isotope Ratio and Their Relationship with Cassava Growth and Yield Under Moisture Stress and Irrigation