First, the effects of polyploidy (a more general term for whole genome duplication) are easily observed with a microscope, and paleopolyploidy has been confirmed by recent analysis of genome sequences. There is no controversy about it having occurred.
If you want to learn more, you can do searches on terms like "polyploidy", "induced polyploidy", "colchicine polyploidy", "crops polyploidy", and "paleopolyploidy".
A lot of crops are polyploid.
* Triploid crops: banana, apple, ginger, watermelon, citrus
* Tetraploid crops: durum or macaroni wheat, maize, cotton, potato, cabbage, leek, tobacco, peanut, kinnow, Pelargonium
* Hexaploid crops: chrysanthemum, bread wheat, triticale, oat, kiwifruit
* Octaploid crops: strawberry, dahlia, pansies, sugar cane