Odd R. multiflora leaf.

I was walking around, looking at some of the wild growing R. multiflora bushes, and a particular new cane of growth caught my eye. They leaves were larger than any around them. I scanned a picture (which I HOPE I mannaged to include in this post) of the odd leaf next to a normal one. The normal one is on the right, and if you look at the base, you can see it was taken from a new cane nearly twice the size of the one the leaf on the left came from, and yet the left-hand one is still significantly larger. The leaflets of the larger leaf also felt significantly thicker than the normal leaves. I can’t help but hope that this is a tetraploid sport, but it is hard to say for sure. Any thoughts?

Can roses spontaneously sport from diploid to tetraploid? That seems unlikely. Maybe it is a hybrid with some other rose…

Mike

GeoCities doesn’t allow people to link to pictures on their site from other sites. You can see the picture at this address:

R. multiflora is an extremely variable species. Having grown large numbers of this species from seed, I can tell you that you will get a WIDE variety of leaf sizes and types. They are all clearly multiflora, but the leaf characteristics vary a lot.

Consider this: R. bracteata is a diploid. Ralph Moore started a bracteata line by crossing R. bracteata X ‘Guinee’, resulting in ‘Muriel’. Since then, he has an entire line of Hybrid Bracteatas made by crossing ‘Muriel’ with other roses. Beyond doubt, the line is now tetraploid, as it crosses freely with modern roses. What this illustrates (and what has been said before by many breeders) is that tetraploidy arises as a natural result of crossing lines of mixed ploidy; roses want to remain fertile, and so they strive to return to a fertile gene count. In any mixed line of breeding, (even fertile triploids) there will be a certain number of gametes that revert to 7’s or 14’s, resulting in some tetraploid offspring. Selecting for the strongest, best offspring tends to select for tetraploidy.

That being said, if you want to work with R. multiflora, then go for it and ignore the gene count issue. It will even out in the results.

Paul

Paul, yes, I am well aware of R. multiflora’s variability – it grows itself from seed all over the place around here, and there are a lot of differences. If the whole plant had shown the larger than usual foliage, I wouldn’t have thought about it twice, but it is just the one cane. So it seems to be a sport of some kind, and I was just curious.

And yes, a tetraploid multiflora wouldn’t be a whole lot more useful than a diploid one. Looking at rose breeding history, it seems to be one of those species which crosses ploidy barriers pretty easily (unlike, say, rugosa which seems to always produce stubornly steril triploids.)