I do not understand why we would want to go from tet to dip when the tets came from dips in the first place. Here's an article on the subject.
Plants with more chromosomes tend to have more substance than their diploid cousins. Tetraploid daylilies have larger and thicker leaves and flowers, stronger flower scapes, more intense coloration and increased vigor. Because of the difference in the number of chromosomes, diploid and tetraploid daylilies cannot be crossbred to produce new types. While most of the major daylily awards have gone to diploid selections, much of the excitement among daylily enthusiasts in the last few years has been about tets.
Artificial manipulation of chromosome numbers began in 1937 when it was discovered that a potent alkaloid drug called colchicine, extracted from the bulbs of the autumn crocus, caused chromosome doubling in a wide array of plants. By the late 1940's this discovery was being used as a topic of research projects for several students pursuing advanced degrees in plant breeding. Either established plants or seedlings can be transformed to tetraploids using colchicine.
The first tetraploid daylilies bloomed in California in 1947, but they were a far cry from what breeders have been able to develop in the subsequent decades. The first tetraploid daylily to win the Stout Award, the highest award given by the American Hemerocallis Society, was a yellow flowered cultivar called ‘Mary Todd’ that won in 1978. Since 1996 all of the Stout Award winners have been tetraploids.
