Genetic transformation of the 'W Murcott' tangor: comparison between different techniques

Genetic transformation of citrus has been mainly conducted via Agrobacterium tumefaciens using juvenile tissues of the epicotyl segments obtained from the in vitro germination of seeds. Transformation of the stem segments obtained from the mature material is an alternative to overcome or reduce the juvenile phase reported in perennial species such as citrus. However, some citrus species, including mandarins, are recalcitrant to these methods or have low genetic transformation efficiency. Thus, the alternative is the use of juvenile explants with high regenerative potential, such as cell suspensions obtained from citrus embryogenic callus or direct incorporation of DNA into protoplasts using polyethylene glycol (PEG). The present study aimed to compare these four genetic modification techniques for 'W Murcott', one of the main fresh market mandarin cultivars in the United States. The transgenic plants were obtained by the different techniques using a vector containing the EGFP gene under the control of the CaMV35S promoter. The genetic transformation efficiency was low, utilizing either juvenile epicotyl or mature stem segments, with an average of 1.23% and 0.33%, respectively. The genetic transformation efficiency using cell suspensions and cell suspension-derived protoplast explants were higher, with an average of 29% and 11%, respectively. Our results reveal the importance of utilizing cell suspension-derived cultures for the efficient transformation of 'W Murcott'.