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WASHINGTON -- Michelle Obama took a turn on David Letterman's "Late Show" on Tuesday to give us a few Top 10 "fun facts" about gardening.

A sampling, according to a CBS preview of the program:

"No. 7: In his lifetime, the average American will eat half a radish," she said, speaking from the White House Map Room.

"No. 6: The largest zucchini ever grown contained a Starbucks."

"No. 5: Later this year the Supreme Court will finally rule on 'tomato' vs. 'tomahto.'"

The network said Mrs. Obama's list was related to her new book, "American Grown: The Story of the White House Kitchen Garden and Gardens Across America."

The first lady last appeared on the Letterman show in March. She has been making the rounds of other talk shows in recent weeks to promote her book.

Mrs. Obama's turn in the spotlight comes as President Barack Obama's campaign seeks to use his wife's popularity to help him get re-elected.