Effect of cassava brown streak disease on cassava root storage components were studied on four Ugandan varieties with varying levels of tolerance. Significant differences (P<0.05) were observed with reductions of 30% in amylose content and 50% in amylopectin content of diseased compared to healthy plots. Average dry matter content of diseased plots was 25% higher as much as starch yield and starch content reduced by 40 and 15% respectively in diseased plots compared to healthy plots. Susceptible varieties had lower protein and higher cyanide contents in diseased state compared to tolerant varieties. On pasting, mixed reactions were observed but importantly there were significant differences (P<0.05) in the starch pasting properties of starch from diseased compared to healthy plots. Plants with similar reactions to viral attack at the phenotypic level had different reactions when the levels of particular metabolite components (especially cyanide and starch constituents) were quantified. The results point to hijacking of plant carbohydrate and nitrogen metabolic processes for viral metabolic gains. In turn, this affects the use of cassava for food and other applications but also points to possible use of metabolite based selections for tolerant varieties rather than mere root and stem phenotypic observations.
Key words: Brown streak disease, Cassava, metabolism, starch, plant virus.