EVALUATION OF TRANSGENIC CITRUS FOR DISEASE RESISTANCE TO HLB AND CANKER

Sweet orange and grapefruit cultivars were transformed with gene(s) encoding antimicrobial peptides or systemic acquired resistance (SAR) proteins. Each gene was under control of an enhanced CaMV 35S promoter. Several genes were also under control of a phloem specific Arabidopsis SUC2 (AtSUC2) promoter. A number of clones of each transgenic line were evaluated for resistance to Huanglongbing (HLB, caused by Candidatus Liberibacter asiaticus) and citrus canker (caused by Xanthomonas citri ssp. citri). Six hundred trees planted in spring 2009 in a heavily HLB and canker infected Martin County, FL grove were tested using qPCR for HLB after 30 months in the field. Three hundred ninety-six trees tested negative for the HLB bacterium. Approximately 200 PCR negative trees were observed to be healthy and flushing after 40 months in the field and were again evaluated using qPCR. In addition, we observed several trees containing one of our antimicrobial constructs to be tolerant to citrus canker. These results suggested that some of the antimicrobial peptides/SAR inducing genes could provide varying levels of resistance against both HLB and canker.