There is an excellent book on food plants cultivated by Incas: Lost crops of the Incas : little-known plants of the Andes with promise for worldwide cultivation / report of an ad hoc panel of the Advisory Committee on Technology Innovation, Board on Science and Technology for... Washington, D.C. : National Academy Press, 1989. I hope you can find it in a library. Adolf Ceska aceska@freenet.victoria.bc.ca