Chascoda,

I don't think that Marigolds and Dandelions are related closely enough to make sexual cross-breeding possible. Asexual cross-breeding could possibly produce plants, but that would involve some advanced somatic hybridization using protoplast technology, and that is beyond the scope of amateur plant breeding.

I agree with you that it would be a good cross to make, and could produce some very interesting results. When I was a kid, I tried repeatedly to cross marigolds and zinnias, with no success at all. I didn't know it at that time, but such a cross would also require somatic hybridization, and the resulting hybrids would probably be sterile.

In recent years I have taken up zinnia breeding, strictly as an amateur, but I have had some interesting results working with just zinnias. This zinnia reminds me of a dandelion.

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I have also had several zinnias that resembled marigolds, like this one.

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I can hardly wait to see the results of that cross. Zinnias have a much wider color range than dandelions or marigolds, and, in my opinion, offer more opportunities for the amateur plant breeder.

ZM

Some of the dandelions are apomictic, setting seed without pollination. This would make crossing of any kind more difficult. Besides, dandelion and marigold are WAY too far apart to cross.

Another difficulty involves storage nutrients, which even limits grafting.

Comptes Rendus, 21st September, 1891
Incompatibility in Grafts
Lucien Daniel

"It seems strange to see plants similarly closely related to the genus Taraxacum, such as Barkansia [Crepis], Lettuce, and Chicory, behave differently; the first grafting successfully, the two other knitting well, but dying if their adventive roots are removed.

"Anatomical studies may explain this anomaly. The roots of the Taraxacum are gorged with inuline; this substance passes through the membranes of the Barkansia, which assimilates it, as may be ascertained by microscopical examination of tranverse and longitudinal sections of the graft; both stock and scion contain inuline.

"But inuline does not penetrate the scions of Lettuce or Chicory; it has never been detected in them. Therefore, they wither or die, if supplementary food is not given to them through their adventive roots. This is not an isolated case. We may understand that the membranes of some scions are impermeable to certain matters elaborated by the stock, in the same way as Lettuce and Chicory are impermeable to inuline. The failure of many grafts may thus be easily explained by a phenomenon of insufficient nutrition, without having recourse to problematic affinities between genera and species."

Graftability does not guaranty crossability, but graft incompatibility suggests that crossing could also be a problem.

The link below includes the Tageteae tribe (page 22-23) and the presumed relationships among the genera Tagetes, Adenopappus, Adenophyllum, Dyssodia, Gymnolaena, and Schizotrichia.

Intergeneric hybrids among these would certainly be more likely than a cross between Tagetes and Taraxacum.

Karl

Here is a link that might be useful: Chromosome Numbers in Compositae, XII: Heliantheae