Since my last posting on this subject I now find that I have to throw a very large spanner in the works by advancing a hitherto undiscussed theory. This is as a result of a suggestion, made to me by someone with far greater knowledge than mine, that I should consider Internal Heat Necrosis as a possible cause. I had never heard of Internal Heat Necrosis before then, neither (apparently) has it come to the notice of the RHS or HDRA, and there do not appear to have been any recorded cases in Britain.
Inner Heat Necrosis is a purely physiological disorder of the tuber which causes damage similar to that shown in Rhys`s picture, and is a disorder well known in countries where summer temperatures are somewhat higher than we are normally accustomed to.
The disorder is caused by a period of high temperatures during the period between tuber initiation and harvesting of the plant, usually in conjunction with dryness of the soil resulting from such temperatures. Analysis of tubers so affected usually indicates a low calcium concentration in the tuber, the perception being that the effect of the high temperature and the dry soil together is to restrict the ability of the plant to take up the necessary amount of calcium even though it is present in the soil. The disorder is further exacerbated by harvesting during high temperatures.
Rhys`s potatoes (Maris Peer), as second earlies would indeed have spent at least part of the tuber growing stage in the very hot weather, and she has confirmed that she harvested them also in the hot weather.
It is impossible to say definitely that IHN was the cause of the damage in this case, or to rule out my earlier suggestion of induced boron deficiency, but after considerable research among transatlantic websites I now consider IHN to be the more likely cause.
The disorder is purely physiological, and so cannot be spread from plant to plant or persist in any way in the soil, and is only likely to appear with the sort of weather conditions (heatwave and drought combined) that we experienced this summer. However, this may well be yet another instance of the effects of climate change, and one which potato growers should take note of for the future.
Resistance to the disorder varies with different varieties of potato – research in the USA indicates that immune or resistant varieties have higher tuber concentrations of magnesium, sulphur, manganese and calcium, and lower levels of potassium. Unfortunately we do not have the US varieties in this country, and no research appears to have been done yet on our own varieties in this respect.
