In some situations, polyploid crops are preferred because they are sterile. For example, many seedless fruit varieties are seedless as a result of polyploidy. Such crops are propagated using asexual techniques, such as grafting. Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine. Examples
Triploid crops: some apple varieties (such as Belle de Boskoop, Jonagold, Mutsu, Ribston Pippin), banana, citrus, ginger, watermelon, saffron crocus, white pulp of coconut
Tetraploid crops: very few apple varieties, durum or macaroni wheat, cotton, potato, canola/rapeseed, leek, tobacco, peanut, kinnow, Pelargonium
Hexaploid crops: chrysanthemum, bread wheat, triticale, oat, kiwifruit
Octaploid crops: strawberry, dahlia, pansies, sugar cane, oca (Oxalis tuberosa)
Dodecaploid crops: some sugar cane hybridsSome crops are found in a variety of ploidies: tulips and lilies are commonly found as both diploid and triploid; daylilies (Hemerocallis cultivars) are available as either diploid or tetraploid; apples and kinnow mandarins can be diploid, triploid, or tetraploid. Fungi
Besides plants and animals, the evolutionary history of various fungal species is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 2012 for review). Several examples of polyploids are known:

autopolyploid: the aquatic fungi of genus Allomyces, some Saccharomyces cerevisiae strains used in bakery, etc. allopolyploid: the widespread Cyathus stercoreus, the allotetraploid lager yeast Saccharomyces pastorianus, the allotriploid wine spoilage yeast Dekkera bruxellensis, etc. paleopolyploid: the human pathogen Rhizopus oryzae, the genus Saccharomyces, etc.In addition, polyploidy is frequently associated with hybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa.
The mechanism by which the genome is accurately restored involves RecA-mediated homologous recombination and a process referred to as extended synthesis-dependent strand annealing (SDSA).Azotobacter vinelandii can contain up to 80 chromosome copies per cell. However this is only observed in fast growing cultures, whereas cultures grown in synthetic minimal media are not polyploid. Archaea
The archaeon Halobacterium salinarium is polyploid and, like Deinococcus radiodurans, is highly resistant to X-ray irradiation and desiccation, conditions that induce DNA double-strand breaks. Although chromosomes are shattered into many fragments, complete chromosomes can be regenerated by making use of overlapping fragments. The mechanism employs single-stranded DNA binding protein and is likely homologous recombinational repair. See also
Diploidization
Eukaryote hybrid genome
Ploidy
Polyploid complex
Polysomy
Reciprocal silencing
Sympatry

References
Further reading
External links

Polyploidy on Kimballs Biology Pages
The polyploidy portal a community-editable project with information, research, education, and a bibliography about polyploidy.