Hexaploidy is relatively common in grasses, both in cultivated cereals and in wild plants. I couldn't find anything specific on what you wanted, but chromosome doubling with oryzalin or such, I would think would get some fertile hexaploids and allow further breeding, even with the interspecific hybrids.

There is also the possibility that by repeated pollination with diploid and tetraploid pollens that you might someday get a seed or two that's more fertile. It happens in other plants, and succeeding generations can improve fertility further. Probably take an ocean of patience though.

The caution is that these grasses can be extremely weedy and invasive when fertile, so you'd have to be very careful to keep them in bounds. We sure don't need another alien weed!

Vincent

Hi Vincent,
Thanks for your input. I was interested to hear about repeated pollination techniques as a way to restore fertility by sheer dogged determination. I know of that working with Paphiopedilums and triploid Cymbidiums.
There is some evidence that colchicine is more effective than oryzalin (Danish Institute of Agricultural Sciences 2003)) at least in-vitro so will probably go that route Thanks for the flag about fertile grass weeds. My prime interest is to increase breeding possibilities before later selecting of infertile non-breeding forms.
Thanks again.
Alan

Alan,

Did you have any luck doubling the triploid Miscanthus with colchicine to get a fertile hexaploid seed??

Thanks
Gerald