Could be blight, but see what other responses you get, Bob.

Look for white fungal threads appearing anywhere on the plant, most likely near the blackening stems. If they appear, bin the plants - up to you whether you risk saving and ripening the fruit (I wouldn't, but I'm mould sensitive) - its a fungal infection that spreads through the plant. Sterilize the pots and don't reuse the compost. Otherwise, could be the first hint of late blight, though usually you'd expect to see symptoms on the leaves as well, or even before any blackening like you're describing.

Thank you both .It is blight.Bo

Sorry about that, Bob.