Cytogenetic analyses of intergeneric hybrids between barley and nine species of Elymus

Chromosome behavior during meiosis in pollen mother cells from Saccharum officinarum × Erianthus arundinaceus F1 hybrids

BACKGROUND

In recent years, sugarcane has attracted increasing attention as an energy crop. Wild resources are widely used to improve the narrow genetic base of sugarcane. However, the infertility of F₁ hybrids between Saccharum officinarum (S. officinarum) and Erianthus arundinaceus (E. arundinaceus) has hindered sugarcane breeding efforts. To discover the cause of this infertility, we studied the hybridization process from a cytological perspective.

RESULTS

We examined the meiotic process of pollen mother cells (PMCs) in three F₁ hybrids between S. officinarum and E. arundinaceus. Cytological analysis showed that the male parents, Hainan 92-77 and Hainan 92-105, had normal meiosis. However, the meiosis process in F₁ hybrids showed various abnormal phenomena, including lagging chromosomes, micronuclei, uneven segregation, chromosome bridges, and inability to form cell plates. Genomic in situ hybridization (GISH) showed unequal chromatin distribution during cell division. Interestingly, 96.70% of lagging chromosomes were from E. arundinaceus. Furthermore, fluorescence in situ hybridization (FISH) was performed using 45S rDNA and 5S rDNA as probes. Either 45S rDNA or 5S rDNA sites were lost during abnormal meiosis, and results of unequal chromosomal separation were also clearly observed in tetrads.

CONCLUSIONS

Using cytogenetic analysis, a large number of meiotic abnormalities were observed in F₁. GISH further confirmed that 96.70% of the lagging chromosomes were from E. arundinaceus. Chromosome loss was found by further investigation of repeat sequences. Our findings provide insight into sugarcane chromosome inheritance to aid innovation and utilization in sugarcane germplasm resources.

GISH characterization of Erianthus arundinaceus chromosomes in three generations of sugarcane intergeneric hybrids

Within Erianthus, a genus close to Saccharum, the species E. arundinaceus has the potential to contribute valuable traits to sugarcane, including adaptation to biotic and abiotic stresses and ratooning ability. Sugarcane breeders have tried for a long time to use Erianthus species in their breeding programs but until recently were constrained by a lack of fertile Saccharum x Erianthus hybrids. We report here for the first time the chromosome composition of fertile Saccharum officinarum x E. arundinaceus F1, BC1 (F1 x sugarcane cultivar), and BC2 (BC1 x sugarcane cultivar) hybrids. The F1 and BC2 resulted from n + n chromosome transmission, while the BC1 resulted from 2n + n transmission. In the BC1 clones, the number of E. arundinaceus chromosomes ranged from 21 to 30, and in the BC2 clones, the number ranged from 14 to 15, revealing cases of chromosome loss. No recombination events between Saccharum and Erianthus chromosomes were observed in either the BC1 or BC2 clones. The implications of these results for introgression of genes from E. arundinaceus in sugarcane breeding programs are discussed. We propose a strategy to identify the agronomic value of chromosomes from E. arundinaceus and to conduct targeted breeding based on this information.