GRAPE BREEDERS HAVE LONG had a thorny problem. As they germinate seeds from their experimental crosses, breeders don’t know whether flowers of the resulting seedlings will be hermaphroditic (with flowers having both functional sexual organs), female (with flowers that set fruit but have reduced stamens that don’t release viable pollen) or male (with flowers that have functional stamens but don’t set fruit). In grapes, flower sex type cannot be determined until two to four years...