Relationships among the founding ancestral genomes involved in the origin of sugarcane (Saccharum spp.) based on FISH and GISH comparative analysis

Saccharum spontaneum, S. robustum and S. officinarum are the founding polyploid genomes of the modern varieties of sugarcane (Saccharum spp.). The crop is one of the world's major sugar and biomass-producing crops, potential sources of renewable energy. Understanding the genomic relationships among the founding genomes is crucial if we are to develop disease/drought-resistant varieties to counter the threat posed by climate change. Saccharum cytogenetics is a growing field, and significant progress has been achieved particularly in S. spontaneum (x = 8, 2n = 5 – 16x = 40 – 128, commonly 2n = 8x = 64) and S. officinarum (x = 10, 2n = 8x = 80). However, only a few studies on S. robustum (x = 10, 2n = 6 − 20x = 60 − 200) have been conducted, which is thought to be the wild ancestor of S. officinarum, a legitimate species, commonly known as noble cane. Herein, using fluorescent in situ hybridization with centromeric probes we found clear evidence that S. robustum meiosis is regular (2n = 100), exhibiting 50 bivalents, with no univalents or multivalent associations. In addition, using genomic in situ hybridization, we found a close relationship between S. robustum and S. officinarum and divergence from S. spontaneum.