Transgenic RNA interference (RNAi)‐derived field resistance to cassava brown streak disease
Cassava brown streak disease (CBSD), caused by the Ipomoviruses Cassava brown streak virus (CBSV) and Ugandan Cassava brown streak virus (UCBSV), is considered to be an imminent threat to food security in tropical Africa. Cassava plants were transgenically modified to generate small interfering RNAs (siRNAs) from truncated full‐length (894‐bp) and N‐terminal (402‐bp) portions of the UCBSV coat protein (ΔCP) sequence. Seven siRNA‐producing lines from each gene construct were tested under confined field trials at Namulonge, Uganda. All nontransgenic control plants (n = 60) developed CBSD symptoms on aerial tissues by 6 months after planting, whereas plants transgenic for the full‐length ΔCP sequence showed a 3‐month delay in disease development, with 98% of clonal replicates within line 718‐001 remaining symptom free over the 11‐month trial.