Bittersweet and brown rot in potatoes

Bittersweet (Solanum dulcamara) is often found twining amongst brambles. Its fruits are attractive, gleaming like jewels, but don’t be tempted by them: they’re poisonous.

Another name for bittersweet is woody nightshade. This provides a clue to bittersweet’s toxic qualities, as nightshades are plants of the Solanaceae family: a group of plants renowned for producing alkaloids, which can be toxic. The group includes other poisonous wild plants, like deadly nightshade and mandrake; as well as import edible crops like potatoes, tomatoes, aubergines, etc. The blossoms of bittersweet are reminiscent of potato flowers, providing another pointer to their family association.

The flowers of bittersweet (Solanum dulcamara) are reminiscent of potato flowers
The flowers of bittersweet (Solanum dulcamara) are reminiscent of potato flowers

Happily, poisoning from eating bittersweet berries is quite rare. Also, the berries apparently taste very bitter which means if somebody does try them, they’re unlikely to eat them, or not many anyway.

Bittersweet fruits ripening in a bramble thicket
Bittersweet fruits ripening in a bramble thicket

For potato growers, bittersweet is of interest for an altogether different reason: it can play host to the bacteria that cause brown rot in potatoes. In the UK, brown rot is uncommon and when it has occurred it is usually linked to contaminated seed potatoes.

However, on the continent, brown rot has been linked to bittersweet. This is particularly so when river water is used for irrigation. Bittersweet often grows on river banks and can then, apparently, contaminate the water and, via irrigation, contaminate the potato crop.

It’s not all bad news in relation to bittersweet: it has many beneficial properties and has been used for centuries by herbalists. These days, one of the things scientists are interested in is its ability to inhibit bacterial growth, particularly E. Coli and Staphyloccocus aureus.

The name bittersweet is said to have come about because if you chewed twigs of the plants (don’t try it!) they taste bitter at first and then become sweet…

Culpeper said that bittersweet, then known as Amara Dulcis (sweet bitter),  was “excellently good to remove witchcraft both in men and beasts”.

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