See: Optimized scarification protocols improve germination of diverse Rubus germplasm - ScienceDirect (if you put the title in Google Scholar, you can get the full paper free by clicking on the PDF link on the right).
The plants studied are similar to roses so scarification, then nitrate may work for roses also. Also, maybe the scarification can be done by enzymes rather than H2SO4. In the past I had tested H2SO4 and it worked. I have not pushed H2SO4 as I feel it is dangerous for home use.
Scarification with sulfuric is a really old method used for hard-seeded legumes that are too small to attack with a file or rolling between layers of sandpaper to abrade (scarify) the surface. Passage though the gut of a bird with gravel in its gullett works pretty well too. But as the authors of the Rubus paper say, you have to know your species.
I seem to recall that Denison Morey tried sulfuric without much success. Some other folks have had OK results with it. But the combination with nitrate is new to me.
I’ve not yet found a rose with achenes so hard that the nitrate itself doesn’t break through in a few months for a majority of the seeds. And I don’t know whether the fraction that fail to germinate might be inviable to begin with. Never got up the ambition to do a large test. Practically speaking with the odd hybrids we are interested in, we can’t afford to do matched comparisons cutting open a couple dozen achenes to get a representative sample for viability studies. It’s easy to do with something that yields seed in abundance, but I already get over 50 % with those, so I’m satisfied. Would be a good project for a student to do the comparison using something like R canina that is notorious.
The last sulfuric acid for roses discussion in this forum was not that long ago.
The link in that thread to the latest paper that I gave no longer works. Here it is again:
If it stops working the following should be enough for the reader to locate on Google Scholar:
“Improved technique for treating seed dormancy to enhance germination in Rosa x hybrida
Muhammad NADEEM1,*, Atif RIAZ1, 2, Adnan YOUNIS1, Masum AKOND3, Amjad FAROOQ1 and Usman TARIQ1
1Institute of Horticultural Sciences, University of Agriculture Faisalabad, Pakistan.
2Amenity Horticulture Unit, Plant Breeding Institute, University of Sydney, Australia.
3Department of Biological Sciences Fayetteville State University 1200 Murchison Road Fayetteville, NC 28301, USA.”
As stated in the H2SO4 paper “So there is need to further investigate the effect of different treatment in combinations to enhance the germination and ultimately for the rescue of hybridization product.” (and I think in other papers that I read), that we are now at the stage that a number of treatments have been discovered that overcome some aspect(s) of dormacy (for example, one not mentioned recently-redlight). The next stage appears to be to find combinations that further increase germination. Especially (in my opinion) for wide crosses.
I have read a published possible explanation as to what nitrate does.
“Action of nitrate on seed germination thus is ascribed to inhibition of catalase either by nitrite or hydroxylamine formed upon reduction, or by nitric oxide. The central question accordingly is, How does inhibition of catalase serve to promote seed germination? A suggested answer is that inhibition of catalase spares some H202 for peroxidase action. We now consider a probable way in which peroxidase action might promote seed germination.” … " Action of nitrate on seed germination thus is ascribed to inhibition of catalase either by nitrite or hydroxylamine formed upon reduction, or by nitric oxide. The central question accordingly is, How does inhibition of catalase serve to promote seed germination? A suggested answer is that inhibition of catalase spares some H202 for peroxidase action. We now consider a probable way in which peroxidase action might promote seed germination." …“We suggest that nitrate and the several other compounds considered here could have a regulatory function in this reoxidation.”
H.Kuska comment: Thus, it appears that adding H2O2 and adding nitrates might be effecting different parts of the same pathway.
So are you suggesting that I try scarification first this fall on my precious modern HT crosses, and just try the chemical methods on the few OP seeds that I am harvesting for experimentation?
The paper quoted above is a classic and the last paper by S.B. Hendricks I think. But in recent year’s we’ve learned a whole lot more about what are called reactive oxygen and nitrogen species. Nitric oxide which is generated from nitrate by the action of nitrate reductase enzyme, is a direct signaling molecule in plants. It is also the ultimate ingredient in nitroglycerin for heart problems and is naturally produced in our bodies from an amino acid called arginine. The details of the pathway(s) in plants are a bit vague. Whether peroxide might work in the same pathway is a really good question that I don’t think is answered yet. But in the model plant arabidopsis at least the very complicated response path is fairly well worked out. If you look at a list of articles that cite the Hendricks 1974 paper, then papers that cite those papers, you can follow the trail. My computer locked up when I tried to access the 2006 paper shown in the right-hand margin on the site Henry provided (slow ATTnet). But I had read it previously. I hope to write a proper research paper on this sometime during the winter. But for now I personally wouldn’t mess with sulfuric acid.
Cathy, regarding your question. I have done very little with hybrid tea X hybrid tea type crosses. Some have reported that they have very satisfactory germination of hybrid teas with no treatments and even no cold stratification. Many years ago the RHA did a survey of germination methods. I do not know if they have done any recently.
I did a lot of crosses with species and near species which sometimes took 2 years (or more) to germinate on their own.
For hard to germinate seeds, It appears we may have to accomplish 1 or more of the 3 tasks listed below before germination occurs.
The first is to remove or weaken the seed coat.
The second is to remove the chemical inhibitors.
The third is to add germination promoting chemicals.