In sub-Saharan Africa, sweetpotato (Impomoea batatas L.) production is greatly constrained by sweetpotato virus disease (SPVD) complex. This study was conducted to assess the incidence of viruses in healthy-looking sweetpotato in Uganda and to optimise modern technologies for virus diagnosis. A collection of healthy-looking sweetpotato vines from central Uganda were serologically assayed for sweetpotato viruses and the positive samples were confirmed by RT-PCR. A multiplex RT-PCR assay was optimised for simultaneous detection of Sweet potato chlorotic stunt virus (SPCSV), Sweet potato feathery mottle virus (SPFMV) and Sweet potato mild mottle virus (SPMMV). The use of in vitro thermotherapy was also investigated as a means of eliminating sweetpotato viruses. Four viruses namely SPCSV, SPFMV, SPMMV and SPCFV were detected mostly as single infections in the healthy looking plants. SPCSV (70. 6%) recorded highest incidence followed by co-infection of SPFMV and SPCSV (8.3%). Based on shoot survival and effectiveness of virus elimination, the best results were obtained by exposing plantlets to daily temperature regime of 32 RÉSUMÉEn Afrique sub saharienne, la production de la patate douce (Impomoea batatas L.) est grandement affectée par un complexe de maladies de virus (SPVD). Cette étude était conduite pour évaluer l'incidence maladie des virus sur des boutures apparemment saines de la patate douce en Ouganda et optimiser les technologies pour diagnostic de virus. Des boutures apparemment saines de patate douce collectées au centre de l'Ouganda étaient sérologiquement testées et les échantillons infectés étaient confirmés par RT-PCR. Un essai multiplexe RT-PCR était optimisé pour la detection simultanée du virus du rabougrissement chlorotique de la patate douce (SPCSV), le virus de la marbrure duveteuse de la patate (SPSMV) et le virus de marbrure modérée de la patate douce (SPMMV). L'usage de la thermothérapie in vitro était aussi testé comme moyen d'élimination des virus de la patate. Quatre virus dont SPCSV, SPFMV, SPMMV et SPCFV étaient detectés surtout comme seules infections des plantes apparemment saines. Le SPCSV (70. 6%) avait présenté une incidence élevée, suivi de SPFMV et SPCSV dont le niveau d'infection était le même (8.3%). Basé sur la survie des pousses et l'efficacité de l'élimination de virus, les meilleurs résultats étaient obtenus en exposant les plantules à un regime de température de 32 o C pendant 8 heures sous obscurité et 36 o C pendant 16 heures sous lumière durant quatre semaines. La culture du bout du méristème combinée à la thermothérapie a perimis l'élimination de SPFMV et SPMMV dans 77 % des plants qui étaient au départ infectés avec des virus respectifs. Par ailleurs, l'élimination de SPCSV avait échoué.

Assessment of the impact of transgenic crops on non-target organisms (NTO) is a prerequisite to their release into the target environment for commercial use. Transgenic sweetpotato varieties expressing Cry proteins (Bt sweetpotato) are under development to provide effective protection against sweetpotato weevils (Coleoptera) which cause severe economic losses in sub-Saharan Africa. Like any other pest control technologies, genetically engineered crops expressing insecticidal proteins need to be evaluated to assess potential negative effects on non-target organisms that provide important services to the ecosystem. Beneficial arthropods in sweetpotato production systems can include pollinators, decomposers, and predators and parasitoids of the target insect pest(s). Non-target arthropod species commonly found in sweetpotato fields that are related taxonomically to the target pests were identified through expert consultation and literature review in Uganda where Bt sweetpotato is expected to be initially evaluated. Results indicate the presence of few relevant non-target Coleopterans that could be affected by Coleopteran Bt sweetpotato varieties: ground, rove and ladybird beetles. These insects are important predators in sweetpotato fields. Additionally, honeybee (hymenoptera) is the main pollinator of sweetpotato and used for honey production. Numerous studies have shown that honeybees are unaffected by the Cry proteins currently deployed which are homologous to those of the weevil-resistant Bt sweetpotato. However, because of their feeding behaviour, Bt sweetpotato represents an extremely low hazard due to negligible exposure. Hence, we conclude that there is good evidence from literature and expert opinion that relevant NTOs in sweetpotato fields are unlikely to be affected by the introduction of Bt sweetpotato in Uganda.

Weevils damage about a quarter of the sweetpotato harvest in Uganda and induce the accumulation of toxic compounds in the healthy-looking parts of damaged storage roots. We have introduced new genes that produce anti-weevil proteins in the sweetpotato storage root through biotechnology. We may have found few with some resistance to weevils. In parallel, we are testing a new strategy to weaken specific genes of the weevils to block their development. These two strategies will eventually be combined into widely-cultivated sweetpotato varieties in SSA.

Sweetpotato weevils are the most devastating pests of sweetpotato causing yield losses ranging from 60 to 100%. Their cryptic nature, where the larvae is found within plant tissues render them difficult to manage especially using chemicals control. Development of weevil resistant sweetpotato was conducted by crossing a transgenic event CIP410008.7 as a female parent with three Ugandan cultivars as male parents. Crossing event CIP410008.7 with New Kawogo, Tanzania and NASPOT1 gave 57, 32 and 19 seeds respectively. A total of 86 F1 progenies were analysed for the presence of cry7Aa1 using polymerase chain reaction (PCR). Expected 608 bp bands were amplified in progenies that contained the cry gene. The gene was integrated at different frequencies in the F1 progenies of different families: CIP410008.7 x New Kawogo (47.2%), CIP410008.7 x Tanzania (52%) and CIP410008.7 x NASPOT1 (44.4%). Chi-square test showed that all the three families followed a 1:1 segregation cry7Aa1 gene ratio. This study shows the transfer of a transgene from genetically modified event into elite sweetpotato lines.

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