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Advances in banana transformation through Agrobacterium tumefaciens in Ecuador: Progress, challenges and perspectives

Abstract:

Black leaf streak greatly affects the productivity of banana in Ecuador. Genetic improvement through conventional methods for disease resistance in banana has several constraints due to high sterility, low seed production rate, polyploidy, and long generation cycle of bananas. Furthermore, a conventional breeding program in banana is not established in Ecuador mainly for the limitations described above. On the other hand, genetic transformation may circumvent many of these limitations. A genetic transformation platform has been established at the Biotech Research Center of the Escuela Superior Politécnica del Litoral, using embryogenic cell suspensions of different banana cultivars in combination with Agrobacterium tumefaciens. Different banana cultivars have been transformed, including Williams (AAA genome, Cavendish subgroup) and Barraganete (AAB genome, Plantain subgroup), with the principal purpose to generate cisgenic or intragenic bananas resistant to black leaf streak. Candidate resistant genes have been identified in a subtractive cDNA library upon inoculation of Mycosphaerella fijiensis conidia to Calcutta-4 in greenhouse conditions. Banana promoter characterization is also established by fusion of promoters to reporter genes including GUS and LUC, which may be useful for the generation of cisgenic or intragenic bananas. Although in Ecuador the National Constitution forbids the importation of transgenic seeds and cultures, a biosafety regulation regarding genetically modified organisms (GMOs) needs to be established for the generation of genetically modified plants in the country. Therefore, an established and practical biosafety regulation should be developed for field trials and cultivation of GMOs in Ecuador. The candidate genes for black leaf streak resistance need to be functionally validated. Next steps will include testing these NBS-LRR genes.