If this has been posted before, sorry for the duplicate. I found this article helpful in understanding interploidy crosses and what ploidy counts can be expected. Hopefully things are similar in Rosa. The PDF version is full-text.
Fecundity and offspring ploidy in matings among diploid, triploid and tetraploid Chamerion angustifolium (Onagraceae): consequences for tetraploid establishment
http://www.nature.com/hdy/journal/v87/n5/full/6889550a.html#top
I found the very low set rates for triploid x triploid and triploid x diploid crosses to be instructive. I hadn’t knowingly tried any before, and those numbers don’t make me want to try them in the future.
Roses ignore dogma to the point where you’d be foolish to not try a cross that would otherwise be interesting to do. For one thing, some triploid roses make lots of diploid pollen and (less) tetraploid pollen. Triploids as mothers work out less often but every once in a while a cross pays off.
A lot of the bloomalot hedgeclipper roses are triploid yet are worth working with in a breeding program targeting disease resistance.
I agree with Don. I have used Rainbow KO on Silver Moon and New Dawn with results (few and far between maybe, but still doable.) I was just counting up some stuff the other night and saw that I got an average of 1 seed per pollination on Silver Moon. Many failed, but some made 2 or 3 seeds. If you have lots of pollen like RKO, and a profuse bloomer like SM, it’s not difficult- 500 blooms is 500 seeds. ND is more resistant. For you who’d like to do something outrageous, RKO on Dr Huey works nearly as well as on SM. SM at least throws some rebloomers, but so far Dr. H hasn’t. But they are really vigorous, prickly and some are disease resistant. If they are winter hardy they’ll be really mean rootstock.
Long ago (and far away) I read an article on crossing between ploidy levels in Rosa. The author(s?) found that in general the most successful crosses were lower x higher. The one notable exception (as I recall) was R. gallica (tetraploid), which happily accepted pollen from diploids.
The irregular polyploids of the Caninae section are different, of course. Schoener raised hybrids from Rosa pomifera pollinated by the Spitzenberg apple. They were fruitful, but I don’t know how fertile.
http://bulbnrose.x10.mx/Roses/breeding/Schoener/SchoenerCD1938.html
I read somewhere that the gametes of triploids don’t always have full sets of chromosomes. There is a high percentage where one or more of the chromosomes are missing and that is a contributing factor in a triploids lower fertility.
I have done some work with triploids mostly as the pollen parent but I have tried a few as the seed parent. Two that have some female fertility are Bonica and Prairie Joy. I used two diploid pollens on Bonica several years ago but got few seeds and no seedlings where Bonica sets OP hips quite readily. These diploid pollens were a pretty wide cross and I’m sure that was a contributing factor. If I had used something genetically closer to Bonica the crosses may have taken. I’ve had better luck using triploids as the pollen parent. This year I used three different triploids (Double Knock Out, Belinda’s Dream and Prairie Joy) on a diploid (Showy Pavement x R.blanda). I did (6) pollinations with each pollen and I got (10) seeds from BD, (15) seeds from DKO and (147) seeds from PJ. I don’t know if PJ pollen is more fertile or if it is just closer genetically to SPxRb to get so many more seeds.
Softee is a triploid that had been very fertile for me when I was using it.
And of course there is Lynnie who is triploid and produces seeds if there is any rose pollen within 10 miles of her.
With each seed producing multiple seedlings! That one definitely read the verse to “go forth and multiply”!
Pg , Bonica is receptive to tetraploid pollen, you don’t need the pollinators to be genetically close . I did this cross a while ago, Bonica X Elara, Elara is a Wendy X Abraham Darby, and the results were very good. This seedling later became White Shadows. I think Bonica still has a lot to give. I have noticed over various seasons some Triploids become more fertile, sometimes in the pollen or both seed and pollen. This is a pic of White Shadows, shrub rose growing to the height of just over 3 feet.
There are considerable differences among triploids. I have a couple of reports:
Wulff (1959)
http://bulbnrose.x10.mx/Roses/breeding/Wulff/Wulff_triploid.html
Rowley (1960)
http://bulbnrose.x10.mx/Roses/breeding/Rowley/Rowley_Triploids.html
Rowley (1960b) also dealt with aneuploids that have non-standard chromosome counts.
http://bulbnrose.x10.mx/Roses/breeding/Rowley/RowleyAneuploidy1960.html
Very nice Warren, White Shadows is a great looking rose. I have only used Bonica as the seed parent with the two diploids mentioned earlier but I have used it as the pollen parent five times including twice this year. Your success with it as the seed parent gives me incentive to try it again in crosses with plants that are poor seed parents.
Karl,
I think you’re right about that, there probably is quite a bit of variation among different triploids. The source I read discussed triploid spinach which has n=6. It gives a formula where gametes are formed with (6) and (12) chromosomes only 2/64th of the time. The rest of the gametes formed had 7 thru 11 chromosomes. I don’t know if they came up with those numbers by observation or what, but the number of viable gametes sounds quite low to me.