The potato (Solanum tuberosum) is a globally staple starchy tuber. After harvest, this living biological entity undergoes various changes, which include natural life cycle processes and signs of decay or toxicity. These post-harvest transformations fall into three categories: the potato’s attempts at reproduction, a chemical defense response, or colonization by external microbial pathogens. Understanding these growths is important for determining the potato’s edibility and safety.
Signs of Healthy Dormancy and Propagation
Potatoes are vegetatively propagated, meaning a new plant grows directly from the tuber rather than a seed. The small indentations on the surface, called “eyes,” are nodes where new stems or sprouts emerge. After harvest, the tuber enters a period of dormancy, a natural state where growth is inhibited. This dormancy protects the potato from sprouting prematurely.
Once dormancy breaks, the eyes begin to sprout, which is the potato’s method of reproduction. Gardeners sometimes encourage this process, known as “chitting,” by placing tubers in a cool, bright area to promote short, sturdy sprouts. Storage in a dark, warm environment typically produces long, pale, spindly sprouts as the plant attempts to find light. While sprouted potatoes are technically edible once the sprouts are removed, their appearance signals a significant physiological change.
The Danger of Green Potatoes
“Greening” is a distinct change on the potato surface, triggered by light exposure. The visible green color is caused by the synthesis of chlorophyll, the pigment found in leaves. While chlorophyll is harmless, its production marks the buildup of a toxic compound beneath the skin.
This toxic compound is solanine, a glycoalkaloid and natural defense chemical belonging to the nightshade family. Solanine is concentrated in the sprouts and just under the skin, where its presence is indicated by a bitter taste. High levels of solanine can cause poisoning, primarily presenting with gastrointestinal symptoms like nausea, vomiting, and abdominal pain. More severe cases may involve neurological effects such as headaches or confusion. Since cooking does not destroy solanine, any potato with extensive greening or a bitter taste should be discarded. If the green area is small, peeling and trimming away the affected flesh can reduce the risk.
Pathogenic Growths and Storage Decay
Various microorganisms can cause visible decay, which is accelerated by poor storage conditions. These pathogenic growths are classified as either fungal or bacterial rots, often gaining entry through wounds or bruises. Soft rot is a common bacterial infection, often caused by species like Pectobacterium. It transforms the potato tissue into a wet, slimy, mushy mass characterized by a foul odor. This decay can rapidly spread through stored tubers, especially in high-humidity environments.
In contrast, fungal infections often result in dry rots, such as those caused by Fusarium species. Fusarium dry rot manifests as sunken, shriveled patches on the exterior, with the internal tissue turning brown or black and remaining dry and powdery. Visible growths of white, yellow, or pink fuzzy mold may accompany this decay within the cavities. Another fungal condition, Silver Scurf (Helminthosporium solani), is primarily a blemish disease causing tan-to-gray circular lesions that appear shiny when wet. While Silver Scurf mainly affects cosmetic appeal and causes moisture loss, any potato exhibiting microbial decay indicates spoilage and should be discarded to prevent contamination.