Body of Abstract: The presentation will illustrate the steps, processes and hurdles encountered to develop and deliver a modified orphan crop to smallholder farmers in Africa. Food and economic security for farmers in sub Saharan Africa is threatened by Cassava brown streak disease (CBSD). CBSD is caused by the two Ipomoviruses, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) and transmitted by the African cassava whitefly Bemisia tabaci, and by farmers who plant infected stem cuttings. Plants infected with CBSD produce brown necrotic tissues within their storage roots, rendering them inedible and with no market value. RNAi technology was applied to develop cassava with high-level resistance to CBSD. Sequences c. 900 bp in length from the coat proteins (CP) of CBSV and UCBSV were fused to produce an inverted repeat construct. Transgenic plants were generated and tested in the greenhouse and under field conditions in East Africa. Resistance to CBSD was correlated with the level of CP-specific siRNAs accumulated, with the best performing lines remaining disease free, and producing usable yields up to 20-fold greater than the non-modified controls. High expressing events underwent breeding programs, with F1 progeny inheriting the transgenic T-DNA and expressed CP-specific siRNAs in the predicted 1:1 ratio. Fi lines were cultivated over five consecutive, 12-month growing cycles across six locations in Kenya and Uganda and selected for resistance to Cassava mosaic disease and CBSD plus other farmer-required traits including storage root weight, dry matter content, high starch and low cyanogenic content. Regulatory data was collected and an application submitted to, and approved by the Kenyan National Regulatory Authority, for advancement of elite F1 lines into National Performance Trials. Parallel work has been initiated to develop the seed systems required to multiply and distribute CBSD resistant RNAi cassava to smallholder farmers in East Africa.