Potato transformation

The traditional method of potato genetic transformation employs Agrobacterium-mediated systems. Whilst transgenic potato is often used as a model system to assess the roles of specific gene(s), cultivars such as Desirée tend to dominate the ‘transgenic’ literature as transformation efficiencies are high. However, Dale and Hampson (1995) examined transformation efficiencies in 34 potato varieties using a tuber disc protocol, showing that only half of the cultivars regenerated. From those that could be regenerated all but one produced transgenic plants. Some cultivars which did not regenerate from tuber discs did so from leaf and internode segments. It follows, then, that to deliver a commercial product which is true-to-type but which has the desired level of transgene expression and trait modification may not yet be a facile operation with some genotypes.

Belknap et al. (1994) transformed Lemhi Russet and Russet Burbank with constructs containing GUS, ClaSP (tyrosine-rich arylphorin) or a gene encoding a bacterial lytic peptide and showed that the highest potential for deviation from typical performance occurred in yield and tuber size gradings. The frequency of off-types varied between 15 and 80%, depending on cultivar, but off-types were not always apparent until plants were grown in the field. Of the lines transformed with GUS, less than 50% produced seed tubers under field conditions. Field trialling is clearly imperative to gain a real insight into compositional, biochemical, phenotypic and agronomic performance.