One row of spuds died suddenly

[monica119]

Hi, I have a number of potatoes all doing fine with one dramatic exception. In  one bed by themselves I planted just one row of purple fleshed potatoes that I had originally grown last year from a supermarket bag of spuds, and these were the offspring of those. They started out fine. Quite attractive, even the leaves have a purple tinge. I covered them up from time to time just as I did the rest. Last time I covered them up was 5th May and on 11th May I made a note that there was no sign of them, the leaves were not breaking through the soil as all the rest had. I waited and waited ..... nothing. Yesterday I dug down to see what was happenning, found a baby peanut sized spud looking fine and healthy, but the stem of the plant purple and fleshy had no leaves on it. What raises my alarm is that the whole row has suffered the same fate. My first thought was that I had covered them up too much, but I don't think that would effect the whole row. Would appreciate any suggestions as to what has happenned and what I should do now. Has similar happenned to anyone else? My current plan is to prepare the bed for a different type of crop and stay clear of spuds for the forseeable future in that bed.