The 2012 ASHS Annual Conference

Miscanthus ×giganteus is a highly infertile allotriploid (2n = 3x = 57) hybrid between a tetraploid Miscanthus sacchariflorus (2n = 4x = 76) and a diploid Miscanthus sinensis (2n = 2x = 38).  This hybrid has considerable potential as a bioenergy crop; however, the lack of fertility has restricted the use of M. ×giganteus for crop improvement through conventional breeding approaches.  Chromosome doubling can be a viable approach for restoring fertility in interspecific hybrids.  In the current study, oryzalin-mediate in vitro chromosome doubling was used to develop hexaploid M. ×giganteus cytotypes which were assessed for fertility.  Pollen viability staining increased up to 88% in the hexaploid cytotypes compared to 34% for triploid M. ×giganteus. To further test fertility, reciprocal crosses between hexaploid M. ×giganteus and diploid M. sinensis were conducted.  A total of 466 seed were obtained from approximately 4,000 individual florets from 8 hexaploid M. ×giganteus inflorescences.  Many seeds appeared to abort and contained little or no endosperm.  Therefore in vitro embryo culture was utilized on MS media supplemented with 20 µM 6-benzylamino purine.  Forty six embryos germinated, however, only 9 developed into plantlets that could be transferred to the greenhouse. Using flow cytometry, all recovered plants were determined to be tetraploid representing hybridization events between hexaploid M. ×giganteus and diploid M. sinensis.  In contrast, all progeny from diploid M. sinensis were diploid, most likely arising from selfing.  The restoration of fertility to M. ×giganteus may allow this valuable germplasm to be incorporated into future breeding programs for bioenergy crop improvement.