Giberellic acid for juvenile bloom?

General Discussion
1

Hi everyone,
I have a lot of rugosa seeds this year(by my standards) and limited space. As I’ve mentioned elsewhere, juvenile bloom is important to me and I will be preferentially keeping the few that do.
However, it’s obviously a shame if this means that I might be throwing out seedlings that might have given better blooms in 2 or 3 years, just because I don’t have room to grow all of them out.
In an old thread on here about remontancy, there was a suggestion of treating axial buds with GA to induce rebloom.
This leads me to wonder if GA can also be used to induce juvenile bloom in rugosa hybrid seedlings.
My plan would be to let the seedlings express naturally for about six months to select the ones that carry the gene, then treat the non juvenile bloomers with GA to hopefully induce blooms.
Has anyone here tried this or is there any conclusive research on this topic?
If it can work, what is the recommended protocol for application?

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Hello SeasideRooftop,
unfortunately, I cannot give you an answer to your specific question, because I have never worked with Gibberellins, the synthetic hormones. The reason is that a matched application of Gibberellic Acid is difficult and not entirely unproblematic. In the wrong dosage or application, it often has the opposite effect. Nevertheless, the matter is interesting of course, which is why I have done several research and attached some links for you. I would appreciate if you could draw some conclusions from the sources. Have much fun reading through!

The Effect of Gibberellins on Flowering in Roses

AV Roberts 1 , PS Blake, R Lewis, JM Taylor, DI Dunstan

Abstract

The gibberellins A(1), A(3), A(5), A(8), A(19), A(20), and A(29) were identified in vegetative shoot tips of Rosa canina by comparing their mass spectra and Kovats retention indices with those of standards. Most wild roses have a short flowering season of 2-4 weeks in spring, whereas most modern cultivars flower recurrently. ‘Félicité et Perpétue’ is a short-season hybrid from a cross between a wild rose and a recurrent-flowering rose, whereas its sport, ‘Little White Pet,’ flowers recurrently. The concentrations of gibberellins (GAs) were measured in shoot apices of both cultivars. In March (before floral initiation in spring) the concentrations of GA(1) and GA(3) were respectively threefold and twofold higher in ‘Félicité et Perpétue’ than in ‘Little White Pet.’ In April (after floral initiation) the concentrations of both gibberellins were substantially greater than in March, and concentrations of GA(1) and GA(3) were, respectively, 17-fold and 12-fold greater in ‘Félicité et Perpétue’ than in ‘Little White Pet.’ It is postulated that, in ‘Félicité et Perpétue,’ floral initiation occurs when concentrations of GAs are low and is inhibited when concentrations of GAs are high, whereas in ‘Little White Pet’ concentrations of GAs remain at permissive levels throughout the growing season. Applications of GA(1) and GA(3) to axillary shoots in March inhibited floral development in ‘Félicité et Perpétue’ but not in ‘Little White Pet.’ This suggests that the combined concentration of exogenous and endogenous gibberellins might have been raised to inhibitory levels in the former but not in the latter cultivar.

Recipe for general application without warranty:
GA is a white powder and is dissolved in water for application. To accelerate growth gibberellic acid is sprayed once 7 - 10 days and once 14 - 20 days after potting. The concentration should be about 1 g per 10 liters of water. To accelerate the solution in water, GA can first be dissolved in a little alcohol and then added to the water.

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Thank you so much for the link to this article Roseus!
It looks like the GA would probably have the exact opposite effect of what I was hoping for, or at best, no effect at all like it did in repeat bloomer Little White Pet.
From what I understand juvenile bloom is toggled by some secondary genetics along with the repeat bloom gene, especially in rugosas which have repeat but usually not juvenile bloom, but that shouldn’t give me any hope since overall bloom seems inhibited by GA.
Also, it was interesting to note that the article mentioned an experiment with the giberellin suppressor PCB, which didn’t seem to have an effect on bloom induction either and only caused shortened internodes.
Thanks again for sharing this article, it will spare me a lot of time and false hopes!

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