Sarvari Research Trust (SRT) director Dr David Shaw said such a spread was probable. "Most amateurs do not spray and, in a year like this, their crop gets totally blighted and spores drift off to infect healthy potatoes."
But he added: "Professionals do not grow resistant varieties. Why would they do that when you can make a variety resistant if you keep it sprayed? The problem is that continuous wet weather prevents the spray tackle getting on the field every four or five days so chemical control is less than 100 per cent - and some of the newest varieties grown for the supermarkets are very susceptible."
Amateur-gardening supplier Thompson & Morgan said in a statement: "It seems unlikely that the blame can be put on any one set of growers. Ironically, in the past potato farmers were blamed for causing blight problems for gardeners by leaving diseased plants and tubers in or on fields, enabling spores to reproduce and spread."
The firm has urged amateur growers to choose Sarpo and similar blight-resistant varieties bred by the SRT.
Earlier, Potato Council corporate affairs manager Maria Ball blamed gardens and allotments for "a disproportionate amount of overall blight pressure". The group's chairman Allan Stevenson added: "It would be preferable if people bought healthy, well-produced potatoes from their retailer, rather than grow their own."