Postharvest root deterioration or vascular streaking of cassava clones (accessions and breeding lines) was evaluated with harvests at different ages (8 and 12 mo.), seasons (beginning and end of wet season), and locations (CIAT-Palmira, Carimagua,…

Several species of double-stranded RNA (dsRNA) were found to occur in the cassava clone Secundina, which was thought to be virus- free. A large dsRNA molecule (6.6 x 106 Mr = relative molecular mass)(L-dsRNA) was shown to be graft, but not mechanically transmitted and occurred primarily in a nuclear-rich fraction isolated from dsRNA-containing Secundina plants. Viruslike particles were not detected in plants containing the L-dsRNA using a var. of purification procedures. L-dsRNA was also found in 2 non- Secundina cassava introductions. Smaller dsRNAs(S-dsRNAs), ranging mainly between 0.61-0.41 x 106 Mr, were also detected in some Secundina plants containing the L-dsRNA. The S-dsRNAs were not transmissible by mechanical inoculation or grafting. All dsRNAs could be eliminated by meristem-tip culture of infected plants. DsRNA analysis is recommended for indexing cassava for this latent viruslike agent. (AS)