"Blight-proof" potatoes -
Pentland Dell and others
Previously blight only reproduced asexually. It still managed to evolve enough to overcome blight resistance in some new varieties within a few years. Now there is a second breeding type which arrived in Europe in some imported potatoes - and it now reproduces sexually, too. This has increased the speed at which it can overcome blight resistance; sexual reproduction gives more diversity.
In his book "A Scottish Potato Breeder's Harvest", Jack Dunnett sums up the blight situation like this: Phytophthera Infestans produces astronomical numbers or airborne spores, only one of which needs to mutate to initiate an epidemic due to a new resistance-breaking race, which has happened time after time and still happens.
"Within two years of the first observed breakdown of resistance, all the British crops of Pentland Dell, which incorporated a stack of three different major resistance genes, were blighted....after that, at Pentlandfield where Pentland Dell was bred, we gave up, but others persisted, in a triumph of optimism over experience".
Alan Romans says in his potato booklet (a must-buy for all potato enthusiasts and growers) that blight resistance assessments need to be updated frequently, and that old figures can be misleading.
In bad blight years in Leicestershire I've found that many potatoes rated at 6 or below are unable to prosper. The plants stop growing mid-July; second cropping is poor.
The current blight-resistant types are as follows: (blight susceptibility on scale 1-9; 9 = most resistant)
Almost immune; foliage doesn't die off:
9 SARPO MIRA (Hungarian lineage)
9 SARPO AXONA (ditto)
Very resistant:
8 VERITY (released by Jack Dunnett, 1998. Red eyed, tubers similar to King Edward, short foliage.)
8 MIDAS (1996; similar to Maris Piper; English)
Resistant:
7 ORLA (Irish)
7 LADY BALFOUR (2001, Scottish)
7 STIRLING (SCRI variety, 1990. Prone to spraing.)
7 REMARKA (Dutch, 1992.)
7 ROBINTA (Dutch, 1992, red)
7 CARA (1976, Irish)
7 RED CARA (1976, Irish)
7 AVONDALE (1982, all-white CARA sport with similar blight resistance)
7 POMEROY (2001, Northern Ireland)
7 COSMOS (1973, Dutch)
------------------------------------------------------------------
Partially resistant:
6 PICASSO (1992, Dutch)
6 WHITE LADY (Hungarian, 1999)
6 VALOR (Jack Dunnett, 1998, waxy, good on poor soil)
6 ROMANO (1978, Dutch; parent is Desiree)
6 RIOJA (1999, Hungarian, red)
6 KARLENA (1993, German, dry and floury)
6 COLLEEN (1993, first early, Irish)
6 CLARET (1996, SCRI attempt at improved Desiree type, darker in colour)
6 ARRAN VICTORY (1918, blue-purple, floury, good for mashing)
6 ADMIRAL (1998, English, large waxy tubers)
6 GOLDEN WONDER (1906, Scottish / English; very dry, floury; excellent flavour)
For the record, PENTLAND DELL (1961) is now rated at 5.
Nigel Deacon, Diversity website, April 2005
