The tomato is also known as the love apple. When tomatoes, which are native to the New World, were brought to Europe in the 16th century, they were at first considered to be poisonous. As time passed, the fruit's allegedly poisonous attributes began to be linked with supposed aphrodisiacal qualities.
Another theory on how the tomato got its moniker is its association with the Moors, who ruled Spain for a time. When the Moors eventually returned to Morocco, they brought the tomato with them. The fruit was then known as the pomi dei mori, or the fruit of the Moors.
It's possible that the French misinterpreted this and started calling the tomato the pomme d'amour, or apple of love.