Field selection of elite events of East African highland bananas expressing elevated levels of pro-vitamin A.

Biofortification of staple crops is a sustainable strategy to deliver essential micronutrients to impoverished populations in developing countries. Banana is a highly valued crop consumed by over 75% of Ugandans. However, the starchy green cooking bananas have very low levels of pro-vitamin A (PVA) and heavy dietary reliance on them has been associated with vitamin A deficiency (VAD). Two banana cultivars, hybrid M9 and Nakitembe, were selected for PVA biofortification. A phytoene synthase 2a (MtPsy2a) gene was transformed into the selected cultivars under the control of the constitutive maize polyubiquitin1 promoter or the banana fruit-preferred ACC oxidase (ACO) promoter. Plants were regenerated on selective media and putatively transgenic plants confirmed by PCR. A total of 356 and 162 transgenic events for M9 and Nakitembe, respectively, were planted in a confined field trial (CFT). Transgenic plants were assessed against non-transformed controls. Selection was based on phenotype, cycle time, yield, β-carotene equivalents (β-CE) and transgene copy number. There were no significant variations in cycle time, but some phenotypic differences were observed between transgenic and non-transgenic controls. Transgenic fruits had yellow to orange fruit pulps, unlike pulp from non-transgenic controls that were paler. On average, fruit from transgenic M9 and Nakitembe accumulated fourfold and threefold more β-CE than non-transgenic controls, respectively. Five elite lines each of M9 and Nakitembe have been selected for national agronomic performance trials that will aid the selection of lead events to be considered for environmental release.