Enhanced Resistance to Canker Disease and Tolerances to Biotic and Abiotic Stresses in terf1 Transgenic Sweet Orange

The transcription factors TERF1 gene was transferred into 'Succari' sweet orange [Citrus sinensis (L.) Osbeck] via Agrobacterium infection and 7 transgenic clones were obtained. Three transgenic clones were further tested for tolerance to water deficiency, low temperature and their resistance to citrus canker disease (Xanthomonas axonopodis pv. citri). Under 10% of soil relative water content (SRWC), transgenic clones showed stronger tolerance than the wild type, with normal growing, leas leaf chlorophyll content decrease, higher Proline (Pro) accumulation and activity of the protective enzymes (CAT, POD and SOD). Simultaneously, transgenic clones showed stronger tolerance to low temperature stress. When plants being treated at -10 degrees C for 30 min, all the wild type plants completely died within 5 days, while the transgenic plants merely revealed severe damages on the shoots and leaves, the main stem and the roots were still alive. The terf1 transgenic clones displayed resistance to citrus canker disease. In the in vitro assay and vivo assay, transgenic clones obviously decreased the disease incidence rate. When the transgenic clones were inoculated with 104 and 105 cfu/ml of citrus bacterial canker pathogen, no symptom occurred. The results indicated that the tested transgenic clones showed obvious tolerance to abiotic stresses and resistance to canker disease. Further investigation in field is going on.