The Grapes of Wrath had been made into a big screen classic starring Henry Fonda in 1940, and East of Eden starring James Dean came out in 1955.

More than half a century later Hollywood was keen on a big screen version of Of Mice and Men starring Jennifer Lawrence, and a remake of The Grapes of Wrath to be directed by Steven Spielberg.

But Mrs Kaffaga claimed every time she was close to a deal with major studios Mrs Steinbeck intervened and threatened legal action, forcing the studios to back off.

Mrs Kaffaga is seeking at least $6.5 million in damages from Mrs Steinbeck, and the case is being considered by a judge and a jury of six.

The jury was given a detailed explanation of the Steinbeck family tree so they could understand how the two women are related to the author.

Taking the witness stand the elderly Mrs Kaffaga, dressed in a scarf and spectacles, described her stepfather as a man who "wrote quite a few books," and said she was 12 when she first met him. Her mother Elaine Steinbeck, a stage manager, was married to him for 18 years until his death in 1968.

Explaining her enthusiasm for film versions of the books Mrs Kaffaga said: "She (my mother) felt it was important that John not be forgotten. I haven't been able to do what my mother wanted me to do, what John would have wanted me to do."