5.3.9
TOWARDS PATHOGEN-DERIVED RESISTANCE TO BANANA BUNCHY TOP VIRUS IN BANANA (MUSA SPP.)

DK BECKER, B DUGDALE, RM HARDING and JL DALE

Centre for Molecular Biotechnology, Queensland University of Technology, Brisbane, Australia

Background and objectives
Bananas and plantains are a major food staple in tropical and subtropical developing countries. World production is estimated at over 85 million tonnes annually. A substantial portion (15%) of this production is for export trade and makes a significant contribution (over 4.5 billion US dollars) to the revenue of many developing countries. The incidence of fungal, viral and bacterial diseases threatens the current level of production. Banana bunchy top virus (BBTV), the major virus infecting bananas, can cause plants to become completely unproductive and continues to spread to new regions. There is no known immunity to BBTV within the Musa gene pool, thus precluding the use of conventional breeding as a means of developing resistant cultivars. Therefore it would be a major advantage to create BBTV-resistant plants by genetic transformation of currently accepted cultivars using pathogen-derived resistance strategies.

Materials and methods
Embryogenic suspension cells of banana were bombarded using the GUS reporter gene and a number of potential resistance constructs, including the two genes from BBTV DNA 1 and the gene from BBTV DNA 5. All transgenes were under the control of the maize polyubiquitin promoter, while the NPT II selectable marker gene was driven by the BBTV DNA 6 promoter. Plants were regenerated on medium containing kanamycin. Southern blot analysis was used to confirm stable integration of NPT II into the banana genome. PCR was used to detect plants which were co-transformed with NPT II and the particular transgene of interest.

Results and conclusions
Southern blot analysis confirmed stable integration of NPT II into the genome of putatively transgenic plants, while no hybridization signal was detected in non-transformed control plants. Plants transformed with the GUS reporter gene showed strong constitutive expression in leaves and roots when histochemically stained. Plants shown by PCR to contain potential virus resistance constructs were multiplied in vitro before placing in the glasshouse. Plants are currently being assessed for BBTV resistance.