Autopolyploid breeding
Similar to diploid breeding, except for different Mendelian expectations
If the diploid ancestor is known, there is also the possibility of introgression from the the diploid level in two ways:
A new polyploid is made and used directly as a crossing parent with normal autotetraploid germplasm.
A hybrid is made between a diploid and the autopolyploid crop. This is usually male sterile, but it may be possible to backcross it with the crop species.
Yes, it is complicated! Please see the resources given in the beginning of the module for more information.