The text features that would be most helpful to support the central idea of the passage are:
1) a map of Alexander the Great's route and the site of the sugar cane discovery: the passage illustrates the places Alexander is conquering and how his close friend Nearchus discovered the sugar cane when sent to explore Asia
2) a timeline showing when Darius I and Alexander the Great learned of sugar cane: the passage explains that Darius I discovered sugar cane when they invaded India in 510 B.C. and then Alexander the Great also discovered it in 326 B.C.