FIELD PERFORMANCE OF TRANSGENIC POTATOES

Field performance was assessed in 13 transgenic potato (Solanum tubero sum L.) lines from three cultivars expressing a selectable marker gene conferring kanamycin resistance. All lines developed unexpected chang es in the phenotypic appearance of shoots, and/or poor tuber yield gen erally involving a reduced number of small tubers. Each independently selected transgenic line showed distinctly different changes in phenot ypic appearance or yield performance. The observed changes were very u niform within each clonally propagated transgenic line, and were consi stent in appearance over two seasons in the field. These changes were attributed to either epigenetic or genetic events occurring during the tissue culture phase of transformation. Efficient systems for the rap id selection and regeneration of transformed plant cells are therefore required to minimise the frequency of tissue culture induced variatio n in plant performance.