Enhanced Disease Resistance in Transgenic Grapefruit (Citrus paradisi) Following Over Expression of Antimicrobial Lytic Peptide Genes

Florida is the world’s third largest producer of citrus, behind Brazil and China. Several diseases, both bacterial and fungal affect this important crop and some like Huanglongbing (HLB) and Citrus canker have the potential to wipe out the entire industry due to the unavailability of resistance in commercial cultivars.  Transgenic citrus plants offer the potential to provide resistance to one or more of the diseases affecting citrus. The aim of our current research was to evaluate transgenic grapefruit plants containing either LIMA, CEME or TempA synthetic antimicrobial peptide genes or a natural AttacinE gene from the Hyalophora cecropia moth for resistance to either citrus scab, caused by the fungus Elsinoë fawcetti or to citrus bacterial spot caused by the bacterium Xanthomonas alfalfae subsp. citrumelonis. We screened a large population of transgenic lines and isolated several that provided increased resistance to each of these pathogens. Such results are important since randomness of Agrobacterium mediated gene integration can lead to considerable variation in the incorporation, position and structure of transgene locus among independent transgenic lines. These factors can subsequently have an effect on the level and stability of transgene expression. Our results enabled us to isolate potential transgenic lines that will subsequently be screened for resistance to HLB and canker.