Diploid to tetraploid in Clematis vs. Rosa genus

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I’m an amateur Clematis breeder who, given the dearth of good information on breeding in this genus, find myself digging into articles and discussions about breeding other genera (like roses!). Over the past decade common ideas emerge that have been helpful to me that I can then apply to Clematis.

This forum has been a favorite of mine for information on ploidy level discussion and I’m wondering if anyone could give me some general feedback on two things I’m trying.

The Clematis genus is for the most part 2n = 2x = 16, though making crosses across species still comes with many barriers. There are around 300 Clematis species and much of the germplasm has never been introgressed into the more ornamental species and hybrids.

I’ve been experimenting with converting Clematis diploids (most species and hybrids) to tetraploid and am wondering if any of you rose breeders could weigh in on my issues below. There just aren’t communities on the web focused on Clematis breeding, but I imagine there are analogous issues.

I’d like to be able to do two things:

1. Convert species from diploid (most Clematis species) to tetraploid. To do this I’m using 7-10 day old seedlings.

2. Convert existing hybrids from diploid to tetraploid. To do this I’m using dormant cuttings so that I can treat the visible, not-yet-growing buds.

I’m currently using Oryzalin (still have an old bottle of Surflan) and have not tried Treflan/Trifluralin or colchicine. I’ve also not tried in vitro/TC, though I do have experience rooting Clematis in vitro. Here are my methods and my problems.

To covert young seedlings using Oryzalin there seem to be three methods:

  • misting anti-mitotic on seedlings over a multiple-day period (pros: easy, cons: you don’t then rinse it off afterward)

  • submerging the young seedling in solution for a period of time (pros: you can control dilution and time period, cons: seedling being submerged is stressful, seedlings fragile and hard to work with)

  • Drops of agar-solified mitotic inhibitor placed on meristem, then removed (this doesn’t work with Clematis - they’re too fragile when young to support this very well).

I’ve been submerging the entire seedling into various dilutions of Surflan, although sometimes I’ve tried submerging just the meristem. Either method produces the same results, which is that no matter what the % of dilution or the contact time, the seedlings all show conversion early on. Then the growing tips gradually start showing blackening on the slowly emerging bud. Eventually they die, having the bud entirely blacken over the course of a year or so.

Some seedlings have produced new stems from that single growth point, but these seem to be diploid because the mix of cells was not entirely converted.

I’ve been using dilutions of the straight Surflan:water at 1:100 through 1:300 in intervals of 25 (1:125, 1:150…) and times of 12 hours through 24 hours. My feeling here is that since they are converting I need to find the weakest solution and the shortest time to convert, right? The black spots/blackening is my big question here: is this something anyone has seen in roses?

The second thing I’m trying to do is convert existing plants by taking cuttings, getting them to go dormant, then treating the dormant buds. Here I’ve tried stronger solutions with 2-3 treatments, so the buds get submerged in Surflan at various dilutions for 12-24 hours, rinsed off, then this happens again 4 days later, then a third time 4 days after that.

Here I’m assuming I need a stronger solution to get the anti-mitotic into those buds, or to use DMSO (have not used yet) or Tween (have used dish soap only). With Clematis there are so many growth points on the dormant crown that the strong unconverted diploid buds take over quite quickly.

I’m using straight Surflan:water at 1:100 through 1:200 for these different treatments. My gut says I need to get some DMSO in there to help absorption. Or to get some agar/Surflan to sit on the buds for a longer period of time?

I can’t find many specific posts on this, though I know it’s commonly done. Any advice on this from those who have converted before?

Thanks,

Mike

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In the breeding of Crimean roses,radiation was used to change the genetic structure of rose seeds and produce brighter colours.
Clematis breeder Alla Olkhovska works in Ukraine even now,under war conditions.A few photos about her.Sche wrote the book “Clematis”.

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Thank you for this reminder. I do know her through a Facebook group focused on Clematis. Some very interesting breeding work in this genus has been done in the former Soviet Union countries through today.

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Hi, I’m interested in growing clematis from seed.
I have a beautiful one that produces seeds. Do you stratify them?

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Hi, Heather! There are a few different Clematis species that are commonly grown, though when most say “I have a Clematis” it’s usually one of the large flowered Asian hybrids like ‘Jackmanii’ or similar. Is this what you have?

If so then yes, many of those larger flowered seeds will germinate more readily if you give them a moist warm/cold/warm cycle. Some of the seed batch could germinate within the warm cycle and most will germinate in the second warm cycle. Depending on your hybrid, they can also germinate a radicle, then want the cold cycle.

Let me know which one you have and I could give you more details!

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Thanks, Mike! Don’t know what kind it is, I’ve had it for many seasons. Dark purple flowers, 4 petals.

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Likely a large flowered variety. Just sow the seed lightly covered in grit, give it a few months and if no germination, allow it 8 weeks in the fridge.

Alternately, sow them in bags of barely damp vermiculite so you can see the radicle germinate more easily.

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Thanks for the details!

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