Evaluation of transgenic oranges expressing the stx IA gene for resistance to Citrus Canker

Citrus Canker caused by Xanthomonas citri subsp. citri (Xcc) is an important disease for citrus production around the world. Several highly valuable commercial citrus cultivars are moderately to highly susceptible to this disease. Development of transgenic plants for disease resistance in economically important citrus cultivars may represent a unique and efficient strategy for control of Citrus Canker. In this work, we report the reaction to Citrus Canker of five independent events (STX-3, STX-5, STX-11, STX-12 and STX-13) of sweet orange cv. ‘Pera’ (Citrus sinensis), transformed with the vector pST10 containing the antibacterial peptide gene stx IA under control of CaMV 35S promoter and the signal peptide from tobacco PR 1a. For inoculation, young expanded citrus leaves were injection-infiltrated or sprayed with a suspension of strain 306 of Xcc. Reduction in disease incidence was observed for the transgenic events as compared with the non-transformed control citrus plants. The lowest levels of disease incidence were observed for the events STX-3 and STX-5. Furthermore, significant differences were also observed in disease severity between the transgenic plants and the non-transformed control plants. The events STX-3 and STX-12 showed the lowest populations of Xcc in the leaf tissue. A slower growth of Xcc was observed in the stx IA transgenic plants, with differences of up to 2 log units in bacterial populations between transgenic plants and non-transformed control plants.