Ploidy level and reproductive organ abnormality in interspecific hybrids between tetraploid Miscanthus sacchariflorus and diploid M. sinensis bred from a single cross

Abstract

M. × giganteus, a hybrid of tetraploid M. sacchariflorus and diploid M. sinensis, is a good bioenergy crop because of its high biomass yield and non-invasiveness in non-native countries. However, this species has a single cultivar that was derived from the same clone, and would, therefore, have higher susceptibility to biotic and abiotic stress. To breed M. × giganteus cultivars, we developed an interspecific crossing method and assessed the breeding efficiency of this method. From the hybrid seeds of 14 crossing combinations, we obtained 323 young plants, of which 290 plants became necrotized during the seedling stage. Of the surviving 33 plants, 12 were assumed to be triploid based on their stomatal length, relative fluorescence intensity values, rhizome elongation, and growth habit, which were similar to those of ‘legacy M. × giganteus’ but were different from M. sacchariflorus and M. sinensis. In the first planting year, four plants headed during the first 10 days of October. Pollen grain size in some hybrid plants was not different from that in the fertile, diploid M. sinensis. The percentage of abnormal pollen and the coefficient of variation of pollen size in all hybrid plants and legacy M. × giganteus were different from those in tetraploid M. sacchariflorus and diploid M. sinensis. At 10 days after flowering, ovules were viable in diploid M. sinensis and tetraploid M. sacchariflorus but aborted in the interspecific hybrid and legacy M. × giganteus. Owing to its sterility, the newly bred Miscanthus interspecific hybrid has low invasion potential, posing minimal threat to the native flora, and is, therefore, suitable for cultivation in non-native countries. These results can be applied to future Miscanthus breeding programs designed to secure the genetic diversity of M. × giganteus and to develop a range of Miscanthus cultivars that can produce high biomass yield under diverse biotic and/or abiotic conditions.