Oligo-FISH-Based Analysis of the Mechanisms Underlying Chromosome Number Variation in Saccharum spontaneum

Interspecific hybridization serves as a crucial strategy for innovating sugarcane germplasms. Currently, nearly all modern sugarcane varieties that incorporate genetic material are derived from <i>Saccharum spontaneum</i>. The number of chromosomes in <i>S. spontaneum</i> ranges from 40 to 128, contributing significantly to the diversity of its genetic resources. However, the genetic mechanisms driving chromosome number variation in <i>S. spontaneum</i> remain to be fully elucidated. Here, oligonucleotide fluorescence in situ hybridization (Oligo-FISH) was conducted to identify individual chromosomes and explore chromosome transmission during the intraspecific hybridization of <i>S. spontaneum</i>. The results indicate that from the progenies generated from <i>S. spontaneum</i> Yunnan2017-22 (2<i>n</i> = 8<i>x</i> = 64) and Yunnan82-1 (2<i>n</i> = 8<i>x</i> = 64) emerged two distinct karyotypes, 2<i>n</i> = 12<i>x</i> = 96 (A1) and 2<i>n</i> = 8<i>x</i> = 64 (A2, A33-1, A18). This implies that the chromosome inheritances were 2<i>n</i> + <i>n</i> and <i>n</i> + <i>n</i> in the progenies. However, self-pollinated samples of A1 (2<i>n</i> = 12<i>x</i> = 96) produced normal offspring C1 (2<i>n</i> = 94) and C2 (2<i>n</i> = 96). The 2<i>n</i> + <i>n</i> inheritance pattern did not continue. In another cross, the progenies derived from <i>S. spontaneum</i> Yunnan2017-41 (2<i>n</i> = 8<i>x</i> = 64) and Yunnan8 (2<i>n</i> = 10<i>x</i> = 80) carried a karyotype of 2<i>n</i> = 9<i>x</i> = 72, with <i>n</i> + <i>n</i> inheritance mode. These findings highlight the existence of two chromosome inheritance modes, 2<i>n</i> + <i>n</i> and <i>n</i> + <i>n</i>, in the context of the intraspecific hybridization of <i>S. spontaneum</i>. Additionally, hybridization between different ploidy <i>S. spontaneum</i> was also accompanied by chromosomal translocations (A1, A2, A18, A18) and loss (A2, A33-1, AA-4, and C2) that further resulted in the complexity of the <i>S. spontaneum</i> genome. Together, these findings highlight diverse chromosome inheritance in <i>S. spontaneum</i> hybridization, and provide a theoretical foundation for the further utilization of <i>S. spontaneum</i> germplasm in sugarcane breeding.