Abstract:
Cassava is an important source of food security
and livelihoods for millions of consumers daily. Water
deficit conditions are one of the major factors that affect
the development of root system architecture (RSA) and
consequently, crop productivity, and yet, due to its long
maturity periods and bulky storage root systems, RSA
studies in cassava are uncommon. The objective of this
study was to identify traits that are responsible for the
variability and plastic responses of cassava in response to
drought at the juvenile stage of growth. Eight cassava
genotypes were grown in soil-filled pots under well-watered and droughted conditions for up to 45 days and
multivariate analyses employed to determine the major
contributory traits to variability and the relative distance
plasticity index (RDPI) was computed to evaluate plasticity. There were significant genotypic variations for most of
the traits measured. Drought generally inhibited root production and development and the degree of inhibition was
between 2 and 22%. Regardless of the soil moisture condition, traits which differentiated the RSA included root
biomass, root numbers, root branching density, and total
root length, and these were also the important contributory
traits to variability under well-watered soil conditions.
Important contributory traits to variability traits under
drought were shoot-related traits such as leaf area and shoot biomass, and also root system traits such as nodal
root number, root biomass, diameter and branching density.
Phenotypic plasticity was found in most traits where the
number, branching density and diameter of upper nodal
roots presented the highest RDPI. These traits corresponded with the traits contributing greatly to variation.
Plastic responses of cassava to drought were dependent on
trait and genotype. It is concluded that upper nodal rootsrelated traits could have importance in breeding cassava to
better tolerate water deficit conditions. The secondary
growth and ability to maintain or increase the upper nodal
root count or density under limited soil moisture may be
related to good growth and yield performance of cassava
under drought conditions. Upper nodal roots could be used
to screen and select cassava genotypes adapted to drought
at the juvenile stage but as a potential indirect selection
strategy, the persistence and pertinence of these traits and
their relationship with yield and yield components under
drought conditions in the field must be confirmed
