I have read that actively growing cells of seedlings of woody plants frequently produce polyploids when they are exposed to extreame heat and cold temperatures. Knowing that most (or all) pentaploids and hexaploid roses were discovered in colder climates with moderately warm summers, it makes much sense to me. And now I’m thinking about skipping colchine and getting myself a mini fridge and some type of mini greenhouse heat pad. Anyone else heard about this? I have not seen a written experiment before.
One of the common pretreatments before looking at root tips to get more cells arrested in metaphase (hinder spindle fiber function) is to use an ice bath. Colchicine and 8-Hydroxyquinaline pretreatments are typically far more effective and sometimes are used in conjunction with an ice bath (~12-24 hours usually). Let us know how it goes. I’d imagine that you would have the best results using a very active growing shoot under relatively warm temps (~80F, more cell division) and then plunging it in icewater for a period of time and then bringing it back to the favorable growing temperature. I don’t think extreme heat will do anything except stress your cells out even more. After the action of the cold on the spindle fibers you need those cells to go into cell division again with the new ploidy level and hopefully as soon as possible so you don’t get a blind shoot.
David, is it necessary to use a icewater bath? Or could any cold source would do (as in a mini fridge). Any clue to what are optimal temps? Wish I could find more info about this.
That’s a good question. I assume the colder the better without freezing and ice water gives us that.
Well-- Today I did it. Or I’m doing it. I had a Bishop Darlington to experiment with that had lots of buds. Don’t mind if I kill it, although I think I should try it with something hardier. I uprooted it, washed the soil off the roots, and completely submerged it in water and left it in the fridge. That was at 3pm and I just took it out at 10:30. It did not completly freeze over-- there were pockets of water. I will leave it on the counter until the morning, and return it to the freezer sightly before 7:00, and take it to thaw after 2pm when I return home. I think 3 treatments will be good enough to keep it alive if the ice doesn’t completly chill.
Bishop Darlington is quite hardy. I grow it in zone 5 without protection. With all this weird weather we’re having I’ll know for sure in a couple of months.
Is it supposed to be a diploid? or triploid? I’ve been treating it as a tetraploid based on its appearance. Sure would help my breeding program if I knew for sure. Being a northerner, I’m naturally interested in diploid and other things un-northerly.
Bishop Darlington’s ploidy isn’t given in Modern Roses. Three of its four grandparents are known to be diploid (R. wichurana, William Allen Richardson, Trier) and the fourth is probably diploid (Sulphurea), so Bishop Darlington is probably diploid.
Good luck, Enrique! Bishop Darlington is a great choice for chromosome doubling.
Okay, the last treatment I’ve used a generous amount of coffee. Caffeine in it should stop the spindles. Didn’t know how much-- just poured on a LOT. I leave it for 6 to 8 hours before rinsing it, and returning it to a pot of good soil. So now it is thowing out very slowly in a dark cabinet. Eventually the coffee will mix with the melted ice water. I don’t see any dead growth or damaged growth-- so far, so good. I do hope it will survive.
Bishop Darlington is such an amazing rose when it comes to health, and fragrance. I’ll be doing this again with more specimens. I tried to root a bunch cuttings from a sterile rugosa cultivar (didn’t set hips), but all of them died. Bishop was the only thing I had at hand.
I feel a whole lot better. Pickering rejected my spring order for a China and a Noisette. I’ll be using Bishop Darlington instead.
Okay, a week passes by. Some serious damage to existing leaves. Some buds look slightly damaged. It is in high moisture right now, in serious condition. BUT-- one bud has breaked out of ground level. Hope it survives.
So then, using this type of treatment you can double the chromosomes of a triploid and presumably make it viable as a seed or pollen parent?
I don’t know. It is still alive, and under a plastic milk bottle to keep in moisture. it will be a while for it to produce flowers. If it is a tetraploid, then crosses of this with modern roses such as hybrid teas will produce tetraploids. That is unless someone can examine it under a microscope and count the chromosomes.