Conventional breeding is slow, expensive and uncertain – and it is near impossible
to combine effective resistance to the most significant diseases and pests with the
other features demanded by farmers, processors and consumers.
Breeding varieties with durable resistance to late blight has proved extremely difficult.
At least half a dozen resistance genes have been identified in wild potato species
which give resistance to at least some races of the pathogen. But varieties such
as Cara, Valor, Remarka and Lady Balfour, once considered relatively blight resistance,
have succumbed – in particular to a virulent recently-evolved race, 13_A2 (Blue 13).
The Hungarian Sarpo varieties resist all currently known races but have not proved
acceptable to commercial growers and processors.
In contrast, the GM approach now allows a whole array of useful genes to be stacked
in the best existing varieties. With recent major advances in transformation technology
the GM process offers speed, precision and relatively low costs.
Why GM varieties are essential
Devastation caused by late blight
Late blight resistance based on only one gene is also liable to break down sooner
or later, so it is very desirable to stack two or more complementary genes both to
enhance resistance and extend its life. Such resistance should greatly reduce the
need for expensive fungicides, some of which are likely to be banned by the EU.
Potato growers’ other big need today is for varieties with effective and robust nematode
resistance, and again genes giving protection to all significant nematodes have been
discovered and field-tested. Genes that give resistance to Colorado beetle, aphids
and potato tuber moth also exist.
Other production genes
There is clear scope to develop GM varieties with other valuable yield-enhancing
traits. Potatoes are highly vulnerable to drought stress. Genes have been identified
that provide drought tolerance. There also appears to be real scope for enhanced