Abstract:

Cassava Brown Streak disease (CBSD) has 3nd continues to be a major threat to the cassava
industry in Uganda. The most economically damaging symptom of CBSD occurs on the roots as
a yellow/brown, corky necrosis. However, the onset and development of this necrosis is not known.
Therefore, this study was conducted to understand the progression of CBSD root necrosis.The
experiment was conducted at Namulongc (centra! Uganda), where the CBSD pressure and whitcfly
population is high. Four CBSD susceptible genotypes (TME204,
S592/0067, MH97/2961, and
Bamunanika) and five CBSD tolerant genotypes (TME14, NASE 3, NASE I, MM96/0686 and 28-
TME 14) were used. The experiment was laid out in a split-plot factorial experiment with three
replicates. CBSD root necrosis was assessed at 4 months after planting (MAP) and, thereafter, at
monthly intervals until 12 MAP. Results indicated significant differences (P<0.001)among reaction
grades (susceptible and tolerant), genotypes and sampling times. CBSD root necrosis commences
as early as 4 MAP in susceptible genotypes with a severity of 2 and incidence of 16.67%. These
findings have important implications for CBSD breeding particularly when evaluating seedlings
and/or clonal plants that often have different number of roots