Response of sweet pepper (Capsicum annuum L.) genotypes to Agrobacterium tumefaciens as a means of selecting proper vectors for genetic transformation

Sweet pepper has been considered recalcitrant to genetic transformation. As a first step for the development of a transformation system for pepper, we investigated the suitability of five Agrobacterium tumefaciens strains for inducing tumours in nine different varieties. A. tumefaciens wild-type strains A281, Ach5, C58, 42CNBP and 1102 were used for inoculation of plants of the nine pepper cultivars Lamuyo, Dulce Italiano, Yolo Wonder, Negral, Luesia, Toledo, Piquillo, Agridulce and Yatsufusa. Different responses to bacterial infection were found among the pepper varieties tested. `Yatsufusaʹ and `Piquilloʹ had a low response to Agrobacterium infection while for the other seven varieties at least one and usually two strains produced tumours at 80-100% frequency. Furthermore, C58 and 1102 strains showed significantly greater virulence and also induced more tumours per wound than Ach5, 42 CNBP and A281. To investigate any correlation between Agrobacterium virulence and transformation ability, sweet pepper cotyledon explants were co-cultivated in vitro with disarmed derivatives of C58 and A281 carrying the binary plasmid pBin19-sgfp. It was shown that genotypes with poor tumourigenic responses also were recalcitrant to genetic transformation in vitro. For those cultivars highly responsive to Agrobacterium infection, the C58 disarmed strain induced 6-14-fold higher stable transformation frequency than the A281 derivative, suggesting that C58 disarmed derivatives would be the most appropriate to genetically transform these sweet pepper cultivars.