Wish this forum had a little more traffic. I'm just posting so this will drop...eventually.

Christie,
I think the lack of response may be due to a lack of knowledge, especially in reference to the Cornus kousa x C. mas. That would be an interesting cross, and I've wondered about that myself, but I don't know how sexually compatible they are. They are grouped in different subgroups (C. kousa and C. florida are in the same subgroup) and they have different fruit structure. So while it may not be impossible, I can't find evidence of anyone having made the cross before. It may require some extra effort, like embryo rescue or ovule culture. I think it would be cool, but I'm not going to do it.

In regard to the seedlessness of interspecific hybrids, I don't think you can make a general claim one way or the other as several factors can affect that. I assume you are just talking about interspecific hybrids in general? Many are fertile and have been used in different breeding programs. Things that can affect seedlessness are things like ploidy level or perhaps some kind of genetic barrier. For example, in citrus you can have seedless triploids or there are known genes that cause seedlessness. In persimmons you can get fruit formation without seeds, but in some species if you don't have seed formation then you don't get fruit. I don't know how that works in Cornus species. Do you have or know of a plant that is producing seedless fruit?

As to know whether a C. kousa x C. mas would produce seedless fruit--You would just have to make the cross!

Thank you Ethane! I haven't tried to cross them. I have c. kousa trees but not c. mas. I was thinking about ordering one but someone mentioned that the seed was large in them and it just got me thinking that it would be nice if there was a seedless variety available.

Stellar Hybrids: "Results of crosses made between Cornus florida and Cornus kousa; highly resistant to dogwood borers"

More on dogwoods and hybrids
http://www4.ncsu.edu/~qyxiang/cornushorticulture.html

I'm interested in the red-twig types, Cornus alba (Siberia, China), sericea/stolonifera (U.S.) and sanguinea (Europe). They are somewhat similar, but I can't find any info on crosses among them. C. sericea/stolonifera has been crossed with other American species, though.

Karl

Here is a link that might be useful: Dogwood, Stellar hybrids