I have a half wine barrel planter in which I planted 4 Matamoro Beefsteak plants and one Celebrity Beefsteak. Within two weeks the plants a strong, green and two feet high. The picture of health. In fact the Celebrity has four

ping pong ball sized fruits! All is well until a week later the Celebrity leaves all begin to shrivel and the the fruit

turns "leathery". At the soil level the main stalk has developed a brownish powdery look and small bumps breaking out around it. All the other plants look hale and hearty and continue to grow. What is this condition? Can I save my Celebrity and will it spread to my other plants? Greatly appreciate any help.