Ah found this answer 'Occasionally gardeners are surprised to find small, round, green, tomato-like fruit on their potato plants. These fruit are not the result of cross-pollination with tomatoes. They are the true fruit of the potato plant. The edible tubers are actually enlarged, underground stems. Normally, most potato flowers dry up and fall off the plants without setting fruit. A few flowers do produce fruit. The variety 'Yukon Gold' produces fruit more heavily than most varieties.
The potato fruit are of no value to the gardener. Potato fruit, as well as the plant itself, contain relatively large amounts of solanine. Solanine is a poisonous alkaloid. The small fruit should not be eaten. Since potatoes don't come true from seed, no effort should be made to save the seed.'
Certainly took me by surprise this morning. Thought I was seeing things.
