While googling for info on black spot, I happened on this comment about mildew:
Right Rose, Right Place (2009) p. 234
Peter Schneider
In the genetics of roses, fragrance and susceptibility to powdery mildew are linked. Many of the hybrid peretuals with enough scent to perfume a room are at the greatest risk of disfiguration from this disease. As hybridizers sought to give us roses that are more resistant to powdery mildew, some of the fragrance has been bred out as a consequence.
Grapes are subject to the same strain of powdery mildew that afflicts roses, and vineyard owners traditionally plant a climbint rose known to be mildew-susceptible at the end or each row of grapes as an early-warning system. (‘Don Juan’ is a favorite for this purpose at American vineyards.)
Sometimes a breeder may concentrate on a few highly desirable but neglect perfume. That happened with Sweet Peas, for a time, until breeders got the message that Sweet Peas should be sweet.
It would be very sad if Schneider is right about the linkage. Any comments or observations?
What comes to mind is the observed genetic link between velvety textured petals; dark crimson coloring (Crimson Glory type); heavy Damask perfume; weak peduncles and mildew. Patrick Dickson, among others, attempted for years to raise a mildew resistant, velvety deep red, Damask scented HT. He produced many fine red roses, but no one has been able to break the link between disease and that color/scent combination. You can raise the healthy Cardinal red scented types and many without scent, but not that combination. And, I remember reading something about fungicides, when applied, inhibited scent expression. Where I read it doesn’t come through, but I do remember reading it very early in my rose experiences.
Wow, maybe I have a few more fragrant seedlings than usual this year! This is true and it might be quite what you are saying. I have been putting more of an effort into fragrant/thornless roses, and even though the parents are not mildew prone, more than a few of the seedlings are. Of course, I have cut back on water (a lot), it has been alternately hot and then overcast and warm, and this combo has probably encouraged a little more mildew also. But the fragrant parents were not notorious for mildew, and I have spotted/sniffed out more than a couple nicely fragrant new seedlings, most of these with little to no mildew so far. I have not always waited for the extremely mildewed seedlings to bloom before culling.
Can’t say as I’ve noticed any such correlation. My most mildew prone roses aren’t roses I find remarkable for their fragrance, and my most fragrant haven’t suffered as much.
But then, perhaps this generalization holds only within one specific class of roses? My chinas aren’t very fragrant, and clove-scented rugosas or fragrant species generally don’t mildew…
I have read of a supposed link between deep crimson and weak necks. ‘Mr Lincoln’ was said to have broken the link, but I don’t know about its offspring. Lammerts’ ‘American Flagship’ (Crimson Glory x self) was described as having strong, straight stems. However, the flowers were smaller than ‘CG’, and the scent was only “mild, spice”.
David Austin also discussed the difficulty of getting a deep red rose on a satisfactory bush, but I don’t have the quote.
Le Grice (1976)
“The remaining, but very popular type, is the bright red, heavily overlaid with blackish maroon with a strong damask perfume: a large, well-built, pointed flower, every attribute except the one quality demanded — a stiff flower neck. This weakness appears to be caused by the over-long flower stem. By breeding a semi-double flower without weight this weakness may not be so marked, but varieties such as Ena Harkness, Etoile de Hollande, and Crimson Glory are cursed by this trouble. Here appears one of the insoluble problems of the hybridist: of obtaining a damask scented, bright red rose overlaid with deeper shading, of good growth and upright flower stem.” http://bulbnrose.x10.mx/Roses/breeding/Legrice/Legrice1.html
Le Grice also commented on the difficulty of breeding a free-flowering white that was not troubled by mildew, but no mention of fragrance in this case.
It seems that the linkage among “Old Rose” fragrance, crimson and weak necks may go all the way back to Rosa gallica, by way of the Hybrid Perpetuals.
This might have been at least partially avoided if the rose show purists had not complained about deeply colored Tea roses. They insisted that Teas should be pastels only. The few red Teas were not as good as they might have become if there had been a broader market.
Cook (1915)
“The magnitude of rose growing as compared to twenty-five or thirty years ago is surprising. All the Tea Roses at that time were lacking in color. Therefore, we used some of the hybrid perpetual roses as pollen bearers (they being richer in color). Through this operation we succeeded in getting deeper colors—reds and deep pinks.”
Large blooms borne singly on stiff stems is a trait found in some Teas; deep crimson coloring is not.
It might be possible to cross a deep red China with a stiff-necked Tea. Careful selection for deepest color and stiffest stem among the progeny could give a new sort of Tea for crossing. It would allow the Tea-side of the ancestry to contribute color, instead of putting the entire burden on the Gallica/HP side.
It is a general rule that crossover frequency declines as ploidy increases. Therefore, it would be desirable to work out the “kinks” at the diploid level when possible. That’s why I suggested crossing a stiff-necked Tea crossed with a crimson China.
Similarly, one might cross a deep orange Dwarf Polyantha (e.g., Orange Mothersday, Gloria Mundi) with a fragrant diploid of similar chromosome structure (e.g., Mevr. Nathalie Nypels, Sweet Chariot) in order to unite color and perfume, in later generations, before bringing these qualities into the tetraploid races of garden roses.
To my nose the dominant notes of Sweet Chariot are terpenoids - and other’s I’ve asked who can detect damascenone don’t smell them in it - do you, Karl? At any rate I’ve been trying to do exactly this for a while although I have not tried Gloria Mundi or Orange MOthersday yet. I’ll take a look at sourcing them.
Years ago (20 something) I raised a pretty Polyantha from Sweet Chariot x Margo Koster. The result was a vivid magenta in cool weather, but faded to a pleasing lilac-pink in warmth. I took some to work, where a colleague commented that it smelled like … a rose. I was pleased that it was fragrant, but wasn’t paying particular attention to details of the scent. That was long before I learned about the carotenoid components of rose perfume.
I ordered ‘Mevr Nathalie Nypels’ this year, but what I got is something quite different; mostly white with a pinkish flush. This one doesn’t take heat as well as the MNN I had in California (purchased from Ralph Moore, as I recall). And I couldn’t find a source for ‘Sweet Chariot’ when I got around to ordering this year.
BTW, while living in southern California I came across a bed of pink sweet peas. I love the scent of sweet peas, but when I stopped to sniff I detected only “rose”. Not damask rose, but rose just the same. This year I’m growing two of the oldest sweet peas, the original Purple and the Painted Lady. They haven’t bloomed yet, but I looking forward (or sniffing forward) to enjoying the REAL scent after so many years.