Evaluation of resistance in Osteospermum ecklonis (DC.) Norl. plants transgenic for the N protein gene of tomato spotted wilt virus

The nucleocapsid protein (N) gene of tomato spotted wilt virus (TSWV) was inserted into Osteospermum ecklonis via Agrobacterium tumefaciens leaf strips co-cultivation. Sixteen primary transformant clones of two O. ecklonis genotypes were analysed. Southern blots of restricted genomic DNA demonstrated integration of the transgene and indicated the number of integrated copies. Expression of the transgene was estimated by DAS-ELISA and Western and Northern blotting. Plants were challenged with TSWV inoculation, either mechanically or by the thrips Frankliniella occidentalis; they were then monitored for symptom appearance and tested by TAS-ELISA for infection. Inoculation of the transgenic clones via the natural TSWV vector was more efficient and led to the identification of 1 clone, characterised by multiple transgene integration and no transgene expression, with improved resistance to TSWV.