chalyse said:Yes, tets came from dips, and have moved forward as tets-only over many generations. Because they have more chromosomes it is easier for them to mutate faster. So, to bring some of those more highly mutated genes (newer patterns, edges, etc) into the dip line, it might be desirable or useful to revert some tets and bump up the dips a bit.
Tetraploids have twice as many chromosomes as diploids and so they do have approximately twice as much DNA that can mutate. But it is much harder to find or see (work with) those mutations in a tetraploid than in a diploid. As a simple example, consider a simple recessive mutation (the majority of new mutations are recessive). In a diploid the mutation will occur and the individual plant that is carrying the mutation will be heterozygous (N = normal and n = mutation) Nn. If we have two individuals carrying the new mutation (for example the plant was self-pollinated) and we cross them then Nn x Nn will produce approximately 3 normal to 1 visibly mutant offspring.
When a new mutation first occurs in a tetraploid then that plant will be NNNn. If we self-pollinate it then the best we can hope for is that some of the offspring will be NNnn and there will not be any visibly mutant offspring. If we somehow have two individuals that are NNnn and we cross them then approximately 1 out of 36 of the offspring of that cross will be nnnn and visibly mutant. Tetraploids genetics can even be much worse - individuals that are NNnn may produce only Nn pollen or ovules so that the cross NNnn x NNnn produces only NNnn offspring (called fixed heterozygosity). There are other complications in tetraploid genetics that affect the numbers of genotypes produced by crosses.
Although I strongly consider that there is no characteristic (phenotype) present in tetraploids that is not or cannot be found in diploids the actual extent of some characteristics in diploids may not be similar to that in tetraploids. Tetraploids on average have cells that are larger in volume than diploids. That size difference and its effect on characteristics may not be directly transferable to diploids. For example, it is possible that larger cells allow larger ruffles and wider and darker (more intensely coloured) picotees in tetraploids.
In the past professional plant breeders working with single gene mutations in tetraploid plant species have preferred to work in the diploid versions and then to double the diploid version to transfer the new mutation to the desired tetraploid version.
Tetraploid daylilies have possibly advanced more than diploids because at some point far more hybridizers started working with tetraploids and made far more crosses than were made with diploids.
Unfortunately the ploidy listed in the AHS registration database cannot be considered to be error-free. Researchers checked the ploidy of 94 cultivars and 6 were incorrect - that is approximately one incorrect ploidy for every 15 registered cultivars. The incorrect ploidies were both diploid and tetraploid and two of the six were triploids registered as diploids.
