Leak – Pythium spp., fungus
Infection by this common soil–inhabiting fungus usually takes place at harvest through wounds or bruises, often during hot and (or) wet weather. External symptoms consist of gray to brownish lesions with a water–soaked appearance around wounds or near the stem end. A freshly cut affected tuber is grayish cream, but with exposure to air the tissue turns reddish tan, then brown, and finally black. A distinct dark brown margin may separate diseased from healthy tissue. Tuber flesh is usually granular, and frequently water is freely released upon cutting an infected tuber. Cavities may be formed in the flesh. Blackened tissue may resemble blackheart, but there is no watery exudate from blackheart. The cream–colored tissue bordered by a dark margin is suggestive of blackleg, but again, the firm tissue associated with leak is very different from the slimy rot that occurs with blackleg. To control this disease, avoid injury to tubers during harvest, especially under hot, dry conditions. Tubers should not be harvested until the periderm is mature. If this disease is detected in storage, the temperature should be maintained at 40°–45° F, and the tubers should be kept dry.