Hi Bob
You are most likely to be successful if you cross species with compatible chromosome numbers. The wider the cross the more likely the offspring are to be sterile. Sometimes sterility is not complete though and you may occasionally get a viable seed. If you are interested in crossing Iris species the Species Iris Society, SIGNA would be extremely helpful. They have articles on wide crosses and on chromosome counts. Some of the crosses that are possible and have been done are:
ensata x pseudacorus
versicolor x ensata
versicolor x virginica
PCNs x 40 chromosome siberians such as I. chrysographes
Siberian Iris x I. setosa

The Louisiana Iris group are a group of hybrids from maybe 5 closely related species. The exact number of species is still in dispute.

Same with the Pacific Coast Iris group only more species are involved, but are still very closely related.

Amanda,

Thank you for your informative response. I had to learn the chromosome captability issue when I started with roses so I'm hoping my learning curve with irises will be short. I will look at the SIGNA web site for more information. Thanks again!

Bob

If you appear to have a success from your crosses, be aware that it will most likely be a self. Both pseudacorus and siberians self pollenate very readily, and you need to open the bloom before it unfolds, and remove the anthers, then cover the bloom until and for a day or 2 after you pollenate it.
Much interesting work is still being done with species crosses among irises, but many of the achievements are through converting diploids to tetraploids.
Good luck with your future crosses, Jan

Jan,

Thank you for the additional information and directions. I'm planning on working on experiments to convert diploid roses to tetraploid this year using oryzalin/DMSO and caffeine/DMSO treatments.

Are iries chromosome counts doubled using these or similar chemicals (colchicine)? Thanks again.

Bob

I think so. There is a web page somewhere for Tomas Tamberg in Europe, who has done much work in this direction. You could do a search, or I will try and find it for you.
Are you on the iris-talk list? There is a lot of information archived. Contact me privately if you want the address. These forums don't seem to like that sort of info.
Cheers, Jan

Jan,

Thanks for providing Tomas' name. I'll do an internet search on his name. I think John Curran may have given me information regarding Iris talk but I will check on that. Thanks again for the information.

Bob

This doesn't directly help answer your question, but you may find it interesting. Edgar Anderson's book, 'Introgressive Hybridization', is a wonderful resource that follows iris species in the Mississippi delta and their hybrid progeny in intermediate environments. For years people dug these hybrids because they are very beautiful. Many of these hybrids are quite fertile, but when you make the orginal F1 with neighboring species they are almost sterile. Because of this, people thought the pretty iris they were digging were not hybrids of the neighboring species. Egar proposed repeated generations and backcrossing to each species over time produced these hybrids and those with greater fertility naturally had a selective advantage and grew well in the intermediate environments. Molecular scientists in the early 1990's tried to prove his work wrong, but what happened was that their data supports his hypothesis (Edgars work was published in the late 1940's I think). Dr. Peter Ascher at the U of MN used Edgar's ideas to help develop his congruity backcrossing scheme that opened up the crossing barriers in beans and allows direct sexual introgression of disease resistance genes from scarlet runner bean into common bean.

It's a great book and hopefully you can get it through your library perhaps through interlibrary loan.

Sincerely,
David

Hello David. Thanks for the tip on this book. I'll look into getting a copy.

Regards,

Bob

Just a note on the Oryzalin treatment of your Irises to convert them to tetraploids. It won't be as simple as spraying a bunch of growing plants and hoping to get some conversions. As with your roses I'm guessing you are treating stems or shoots with the chemical. The rose meristems are quite a bit more exposed and accessible to the chemical than irises. With irises you will need to expose the meristem tissue. Since I am starting on working on this myself I have dome some research. There are two methods to achieve direct access to the meristematic tissues. One is to remove all leaf tissue from a rhizome and carefully scoop out the area around the growing point. This is obviously very tedious and would require a lot of plant material for practice and hope of getting some that would suitable for treatment. Plus treatment with oryzalin is no guarantee of conversion.

The other method is to treat fresh seed or seedlings in oryzalin and allow them to grow and select the ones you think have been converted.

There is an article where this discussed and I can't seem to find it at the moment but if you are interested I can email you the link and you can read it over - rather complicated and scientific though.

What I got out of it is that I decided the best method for achieve converted plants was to treat seeds and seedlings with a solution of Oryzalin (0.5 ml in 1 gallon water) overnight. Pretty simple and unmessy.

Or .....even better you can find it yourself on google.com. Type in "iris oryzalin tetraploid" and it's the very first listing.