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Saccharum spp.


An outstanding polyploid grass

Sugarcane (Saccharum spp.) is an important crop that contributes 70% of the raw sugar produced worldwide and it has a high bio-fuel production potential. It presents a C4 carbohydrate metabolism, which allied with its perennial nature, turns it into one of the most productive cultivated plants. Sugarcane belongs to the Poaceae family and to the Andropogoneae tribe like sorghum and maize. It probably has the most complex of all crop genomes studied to date, mainly due to the very high degree of polyploidy (>10x), together with an interspecific origin.

Modern sugarcane cultivars derive from the combination of the species S. officinarum, the domesticated sugar-producing species with x=10 and 2n=8x=80, and S. spontaneum, a vigorous wild species with x=8 and 2n=5x=40 to 16x=128 and many aneuploid forms. Breeders combined both genomes a century ago. S. officinarum was backcrossed to recover the thick sugar-containing stalks of this species and this process was accelerated through the selection of hybrids derived from 2n transmission of S. officinarum chromosomes. Modern cultivars are highly polyploid (more than decaploid) and aneuploid, with around 120 chromosomes, a total genome size of around 10 000 Mb and a monoploid genome size of around 900Mb (close to sorghum 760Mb). The meiosis of modern sugarcane cultivars mainly involves bivalent pairing and chromosome assortment results from a combination of polysomy and preferential pairing. Molecular cytogenetics and genetic mapping studies have shown that modern cultivars typically display 70 to 80% of chromosomes entirely derived from S. officinarum, 10 to 20% from S. spontaneum and a few chromosomes derived from interspecific recombinations.

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