I have planted some of the usual diploid zinnias (Burpeanna, Burpee hybrids, Whirligig, Scabiosa flowered, etc) and some tetraploid State Fair zinnias. I would like to cross the diploids and tetraploids to get some triploid seeds, which hopefully would grow plants that were sterile and not need deadheading. Any hints on how to do this successfully? I have had some experience breeding diploid zinnias, so I know about the mechanics of pollen transfer.

In particular, should I use any kind of hormone to make the female stigma more receptive? And is it better for the female plant to be the tetraploid or the diploid?

MM

I don't know about zinnias, but in breeding seedless watermelons the tetraploid has to be the female plant. In the linked page scroll way down to the section "Seedless Variety Development."

Thanks for that information. This last year, I tried the cross both ways and hopefully will have some results this year. This coming year I will also be using some of the tetra zinnias from Burpee. This last year I used only "State Fair."

Tetra zinnias have their own special "look", which I am not particularly fond of. The petals all tend to be cupped like spoons, which exposes to view some of their bottom surface, which doesn't look very good.

So I am a bit skeptical about whether I will like any triploid zinnias, even if I am successful in producing them. But I plan to continue the experiments in a kind of low priority way. I expect better results from my crosses between various diploid zinnias.

MM