Abstract:
Cassava (Manihot esculenta Crantz) is one of the most cultivated tuberous crops as a sustainable
source of food security and family income among the poor in the developing world. Despite this economic
significance, cassava’s tuber yield is significantly reduced by viral diseases and pests among them cassava
mosaic disease (CMD), cassava brown streak disease (CBSD) and cassava green mites (CGM). CMD and
CBSD are respectively caused by cassava mosaic begomoviruses (CMBs) and cassava brown streak viruses
(CBSVs) which often result in 100% yield losses in susceptible cultivars. Through a field-based randomized
complete block designed experiment, the present study screened fifteen cassava genotypes sourced from
different breeding programs and local landraces in Kenya for resistance against CMD, CBSD and CGM.
Genotypic differences for either diseases incidence (INC) or severity (SVY) and marketable root yield (MRY)
was significant (P≤0.05. Both disease and pest incidences were generally low (0-15%) indicating potential
suppression. Genotypes were grouped into disease tolerant (DT) and disease susceptible (DS) classes with
significantly higher MRY of 23.8 t/ha bulked by a DT genotype TME-419 and least MRY of 2.1 t/ha recorded in
a DS cultivar Thika2. The negative correlation observed between MRY and both disease incidence and severity
indicated the inhibitory role of CMD and CBSD on cassava production. Molecular diagnostics two CMB
species, African cassava mosaic virus (ACMV) and East Africa cassava mosaic virus (EACMV) and CBSVs in
some tolerant and all susceptible genotypes. Four (990005, TC4, TC14 & TME419) high yielding and DT
cassava genotypes identified in the current study could potentially be used as parents in future breeding
programs for introgression of tolerance traits in farmer preferred but susceptible local landraces.