THE DEVELOPMENT OF POTATO SKIN-SPOT DISEASE

A study of the development of skin spot in the potato variety Kerr's Pink has shown that humid conditions, both before and after infection by Oospora pustulans, increase the incidence of the disease. The results of inoculation experiments have indicated that infection of the tuber does not take place much before the normal time of lifting. It has been found that the pathogen may enter the tuber by way of the lenticels, and that invasion of the cortex and the production of a cork cambium takes place shortly after infection. Some damage to buds was observed within 16 days of inoculation. Although the affected pocket of cortical tissue soon dies, discoloration of the periderm is not apparent until much later. It is suggested that this may be the reason for the comparatively long period which elapses between infection and the appearance of skin-spot symptoms.