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The description page for this rose says it is susceptible to blackspot. There is nothing about that in the references, and the only member comment that mentions blackspot indicates that this rose has good resistance.
The member ratings (which admittedly must frequently be taken with a pinch of salt) claim excellent resistance to disease, but obviously without any indication of which disease this relates to.
There is one photo (Photo Id: 288945) which appears to show some "blackspot", but based on a recent conversation with Michael Garhart (https://www.helpmefind.com/gardening/l.php?l=21.288890&tab=32) it looks to me as though that spotting may be caused by Cercospora instead. The grey centres in the spots are a trait of Cercospora, and don't appear with Diplocarpon.
So the question here is: where did the "Susceptible to blackspot" warning come from?
Edit: Found this over on houzz (in the "Guillot Generosa Roses" thread) - "I used to live in Thailand (20 years ago) and now I live in southern Mississippi. We have very high heat and humidity here too. I have 5 plants of Martine Guillot and they are some of my healthiest roses. They do not have problems with blackspot or mildew and I rarely spray."
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#1 of 5 posted
2 NOV 22 by
Ericchn
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Even the website of Guillot Rose declares that Martine Guillot has excellent resistance to blackspots.
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#2 of 5 posted
3 NOV 22 by
jedmar
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Not clear where this came from. Removed.
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#3 of 5 posted
3 NOV 22 by
Ericchn
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#4 of 5 posted
8 days ago by
Gdisaz10
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This rose in my warm humid climate is healthy and does not have blackspot. The flowers in the sun do not last long and attract many cetonia that ruin them (Oxythyrea funesta)
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#5 of 5 posted
7 days ago by
Ericchn
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Great to hear your confirmation about the disease resistance.
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Double Delight isn't a bad plant, and there are much better actual plants out there, however the coloring of DD just can't be beat in the realm of bi-colors. And, they smell amazing. In Houston it may get a touch of mildew in the spring, or a little blackspot. Nothing tragic.
Double Delight is a garden staple and it's easy to see why it has stuck around so long. Everyone stops to gawk at it, everyone has to put their nose in it, and everyone loves it. It's a bit like having an antique car...sure, there are more reliable and more comfortable newer cars available, but the style and cache of this "oldie but goodie" just can't be beat. IMO, they certainly don't make them like this anymore.
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Cherry Parfait here resembles Double Delight very much. It doesn't have any scent to compare, but it grows without the fungal issues and keep pushing new flowers when Double Delight stops. If you love the Double Delight coloring and don't have to have the scent, but want a stronger grower with healthier foliage, try Cherry Parfait.
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Where does this colour changing ability come from? Would it originally have been inherited form a China rose like 'Archduc Charles'?
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Quite possibly. Some China roses deepen with age, heat and UV. European (and American) types fade.
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#4 of 9 posted
15 FEB 17 by
jedmar
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I believe an important element is 'Rosa foetida bicolor' which is found in the ancestry of many (if not all) red/yellow bicolor roses. This rose has a high concentration of anthocyanin pigments (for red) on the upper side of its petals and an equally high concentration of carotenoid pigments (for yellow) on the lower side. These pigments are then found in varying combinations in its descendants. A good example is 'Rumba', where the red components deepen with time. It is thought that with UV light, biosynthesis of anthocyanins progresses in the direction of higher frequencies of light absorption (darker colours), while biosynthesis of the carotenoids progresses towards lower frequencies of light absorption (orange to light yellow to almost colourless). The resulting effect is that the rose seems to become redder with time. "The Chemistry of Rose Pigments" (1991) by Swiss chemist Conrad Hans Eugster gives a detailed description of these pigments and processes as relating to roses.
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That's very interesting, thank you Kim and Jedmar.
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Thanks for that. Interesting to know, and explains how the 'Charisma' in my garden works.
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#8 of 9 posted
17 JUN 19 by
kgs
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I hear that a lot (about Cherry Parfait being similar to Double Delight) but after comparing both roses in their glory at the International Test Rose Garden in Portland, I see why people say that and yet there's something about Double Delight's coloring that is more complex than Cherry Parfait. Maybe it's that there is more yellow in it.
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For me, Cherry Parfait has not personality or charm. The flowers and color change on Double Delight are much more elegant. It's strange how some roses have that indescribable something, while others of very similar coloring lack.
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The section caninae is iregular. In the case of Rosa horrida 4+1 chromosome sets. It is a pentaploid rose. One set has 7 chromosomes thus 7x5 = 35; 2n = 35
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Still as clear as mud. If 2n = 35 then n = 17.5. Where are you getting n from? What is 2n supposed to indicate?
I understand that a pentaploid rose with seven chromosomes would give a total of 35. That part is clear. Are you sure you don't mean 5n = 35?
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#2 of 5 posted
21 MAR 21 by
Plazbo
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It's not algebra, it's not meant to balance like math in this case, more of a science short hand.
2n represents somatic number (effectively the number of chromosomes in a cell)
n (or 1n) represents gametic chromosome number (eg sex cells, sperm, egg, pollen, etc)
x represents genomic chromosome number
Look at rosa canina (just because it's the most studied of these types) it's usually written as 2n = 5x = 35
eg this diagram
www.researchgate.net/figure/Diagram-of-canina-meiosis-Dogroses-with-a-pentaploid-somatic-chromosome-number-2n-5x_fig1_49942591
but happens with other things, eg banana 2n = 3x = 33, like
www.researchgate.net/figure/In-situ-hybridization-to-banana-chromosomes-2n-3x-33-stained-blue-A-D-with-the_fig3_6074746
It's confusing because we also see things like 4n for tetraploid or 6n for hexaploid but those a different system, somatic number is written as 2n regardless of ploidy.
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Sounds completely bonkers. :D But ok. I get it now. Thanks for the explanation.
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#4 of 5 posted
21 MAR 21 by
Plazbo
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I agree. I'm sure it made complete sense when it was thought up within the context it was being used, in hindsight probably would have benefitted from a different symbol or something given the overlap that exists now.
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Uneven meiosis is really nutty. Even nuttier in the caninae clan than for wheat breeding. And to top it off, roughly half of the chromosomes do not distribute when the caninae type is the seed parent. This is why most caninae hybrids look a lot like their parent. When a caninae types is the pollen donor, there is generally greater distribution and intermix. So, the pretend breeding math looks something like x = (2 + [2])+1, where [2] is genetically immobile.
So, lets say you use Peace. It would look like (2 + [2]) x 2, which theoretically would create a 4+2. Inversely, if used as seed, then it would look like 2 x 1, which would theoretically create a 2+1. When a basic modern tetraploid is used as seed, the immobile set of caninae chromosomes essentially drop. So if you were to do [Peace x (Caninae x Peace)], the likely result would be a typical tetraploid arrangement of chromosomes.
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The new comments section of the site is unusable today. Looks like you had another flood of spammers. I know it's not traditional HMF policy, but disabling guest posting would save you having to deal with a lot of crap, and would save legit members having it in their faces until you can deal with it.
Really, if someone does want to post genuine content it's easy to create an account. :)
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Some people understandably do not want to create an account as internet footprints are often abused. We are working on alternate methods to discourage this type of activity but limiting posts to members is still an option under consideration.
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The registrations pending page for the ARS is a tidal wave of spam and made up registrations. Its out of hand.
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American Rose Society? I was curious, so took a quick look. Their site won't even load for me. All I get is a repeating gif of a rose. I still have no idea what their registration page is like (I was going to check through the process).
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Caffeine, go to this: www.modernroses.org/
It's governed by the ARS within their site.
Click 'Pending Roses'. It's uh. Yeah. Loaded with tons of gibberish spam submissions.
I have tried contacting the ARS about this and other things since before Christmas, to no avail :) They don't respond to emails or phone. Will try again next week.... sigh.
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... a valid point, thanks for the input.
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