Hi Teresa,
" So is there any advantage at all to growing tetraploid zinnias? Are they larger, produce better or more clearer colors? "
The following is a quote from page 347 of the book Flower Breeding and Genetics, edited by Neil O. Anderson. The quote is in Chapter 12,
Zinnia by Dennis Stimart and Thomas Boyle.
" Relative to diploids, tetraploid zinnias have larger flowers and thicker, stronger stems but also have poorer seed germination, less branching, delayed flowering, and fewer capitula. Difficulties also occur with producing autotetraploid lines with a uniform phenotype due to additional alleles affecting ligule color and plant habit. "
By way of explanation, capitula = bloom and ligule = petal. My own experience growing both tetraploid zinnias and diploid zinnias is that I prefer the diploid zinnias. Those "larger flowers" and "thicker, stronger stems" advantages didn't seem that significant.
In my opinion, the main reason for growing tetraploid zinnias would be that you wish to use them to cross with diploid zinnias to produce triploid zinnias. I will go into the advantages and disadvantages of triploid zinnias in a subsequent message. More later.
ZM
