Why Pumkin is associated with halloween?

The practice of carving pumpkins and lighting them from within with candles for Halloween originated in Ireland with a folktale about a man named Stingy Jack. Based on the story of the "Jack-o'-lantern," American children began carving their own lanterns out of New World pumpkins. The lanterns became associated with Halloween when the mayor of Atlanta decorated his home with them for a Halloween party.
 According to the folktale, Stingy Jack invited the Devil to have a drink. Not wanting to pay, he convinced the Devil to turn himself into a coin. However, rather than use the coin to pay for the drinks, Jack kept it for himself. Eventually Jack freed the Devil who promised not to take his soul to Hell. Instead, he gave Jack an ember that he placed in a hollowed-out turnip and carried as he walked the Earth forever.
The legend of Stingy Jack and his turnip lantern traveled to the United States with Irish immigrants. It was not long before children began making their own vegetable lanterns using pumpkins, which were plentiful in America. Over the years, children began carving faces into the pumpkin lanterns to frighten each other. Throughout the late 19th century, jack-o'-lanterns became more common as decorations at Halloween until they became part of the holiday itself.