Figure 1.

Diverse outcomes of polyploidy in crop species. Three examples of the consequences of allopolyploidy (in which hybrids have sets of chromosomes derived from different species) in important crop species are shown. (a) Oilseed rape (canola) is derived from a recent hybridization of Brassica rapa (Chinese cabbage, turnip) and Brassica oleraceae (broccoli, cauliflower, cabbage). The progenitor of these Brassica species was hexaploid (compared to Arabidopsis) after two rounds of whole-genome duplication. Extensive gene loss, possibly via deletion mechanisms [18], has occurred in these species. Upon hybridization to form allotetraploid Brassica napus, gene loss is accelerated, producing novel patterns of allelic diversity [19]. (b) Bread wheat is an allohexaploid derived from the relatively recent hybridization of allotetraploid durum (pasta) wheat and wild goat grass, Aeglilops tauschii. The Ph1 locus in the B genome [37] prevents pairing between the A, B and D genomes, leading to diploid meiosis and genome stability. This maintains the extensive genetic diversity from the three progenitor Triticeae genomes that underpins wheat crop productivity. (c) Sugarcane (Saccharum sp.) is a complex and unstable polyploid that is cultivated by cuttings. Hybrids between S. officinarum, which has high sugar content, and S. spontaneum, a vigorous wild relative, have variable chromosomal content from each parent. The genomes are closely related to the ancestral diploid Sorghum [42].