A few years back I mentioned I had ‘Rosa Indica Major’ and I was playing around with the idea of using rootstock plants in garden rose crosses to improve own-root traits. I think it was Paul B who said he’d never use it for anything because it suffered badly from mildew for him. My three, mildew-prone, plants set a lot of OP hips last season and I germinated something like 200 of them. 70% of them have been thrown away because they were badly affected by mildew from an early age. The remaining 30% are pretty clean so far. One in particular is shaping up to be my best seedling of the season. It hasn’t flowered, obviously, but the foliage is dark and perfectly clean and the seedling has a nice shape to it already, is tall and strong with an enormous rootsystem. I was wondering whether anyone had noticed any patterns in mildew resistance inheritance? Is it recessive (or somethng similar)? Is it gene mediated or structural (or both)? These were OP seeds so theoretically they could have been pollinated by anything, however, my feeling is they are selfs because the flowers don’t seem to get visited much by insects and they are double enough to conceal the anthers until selfing has occured. I’m going to keep this one on a few years to see how it progresses. I get seedlings all the time that suffer badly from mildew that are from parents that are unaffected but never the other way around, so far. It’s interesting because even roses like Dorothy Perkins has bred roses that have far superior mildew resistance to itself (like Super Dorothy). I’m thinking Indica Major might still be a good proposition if I throw the mildewy ones away very early??? Maybe the Dr might be worth trying too?
“Is it recessive (or somethng similar)”
Congratulations Simon.
There does seem to be a hit or miss quality to mildew resistance.
Crossing two mildew resistant roses together sometimes results in mildew prone offspring.
To my mind it stand to reason the same thing can happen in reverse and in fact I have crossed two mildew prone roses and gotten cleaner offspring on occasion.
Here’s a link to one I dumped because it was prone to mildew infection.
Go figure. It’s quite possible the next generation might prove clean.
I didn’t take a chance. I’m exploring too many tangents as it is.
If you mean powdery mildew than there is a at least one known race-specific resistance gene that is inherited as a dominant. I don’t have the paper which describes the gene but the citation is:
Linde M. & Debener T. 2003.
Isolation and identification of eight races of powdery mildew or roses (Podosphaera pannosa (Wallr.: Fr.) de Bary) and the genetic analysis of the resistance gene
Rpp1. Theor. Appl. Genet. 107: 256-262.
Abstract:
“Powdery mildew, caused by Podosphaera pannosa, is one of the most-severe diseases of roses grown under glass. The differentiation into physiological races and the genetic analysis of resistance in a segregating host population was investigated using single conidial isolates of the pathogen. Using ten rose genotypes, all eight isolates of the pathogen could be ascribed to different races. Five races were isolated from one location, which indicates that populations of P. pannosa exhibit a high racial diversity. Infection experiments in a backcross-population of 114 rose plants resulted in a 1:1 segregation, suggesting control by a single dominant gene. Rpp1 is the first resistance gene against rose powdery mildew to be described.”
Interestingly enough, this gene does not show up on Debener’s recent genetic map although there are quantitative trait loci related to PM resistance that do.
Here’s a related thesis that’s accessible online:
Leus L. 2005.
Resistance breeding for powdery mildew (Podosphaera pannosa) and black spot (Diplocarpon rosae) in roses.
PhD. Thesis, Faculty of Bioscience Engineering, Ghent University
http://biblio.ugent.be/input/download?func=downloadFile&fileOId=489983&recordOId=471624
Here is another paper that may be of interest. It lists specific species (and the particular accessions) that were found to be resistant to the big three diseases.
D. F. Schulz, M. Linde, O. Blechert and T. Debener
Evaluation of Genus Rosa Germplasm for Resistance to Black Spot, Downy Mildew and Powdery Mildew
Europ.J.Hort.Sci., 74 (1). S. 1
I had a thought, Simon (don’t faint! LOL!)… water stress can induce a plant to mildew. Might you have noticed if the susceptible seedlings suffered from inferior root systems to the resistant one? I’m wondering if there is a correlation between propensity to mildew and an insufficient root system? Your good one you describe as having an “enormous root system”. Might you have noticed as you’ve culled the others if they seemed to be “under endowed” in the root department? I have noticed the weaker, more disease prone of the mixed bag crosses I made last year seemed insufficient in the feeder root department. It led me to wonder if they may have been more acceptable budded than own root. No, I’m not intending to bud any of them, except to increase the material and push them along faster, but I’m seriously wondering if the mildew propensity is at least partially due to the lack of root system as it is to inferior foliage?
I can also add, after growing Maytime for years, and here, now, where mildew looks like flocked Christmas trees, it IS clean, totally clean. It seems Dr. Lammerts knew what he was talking about all those years ago when he proclaimed it “immune to powdery mildew”. Kim
Hi Kim!
Wow, that is a great observation about water stress and mildew. I raise seedlings in the house in the basement under lights and come spring some show some signs of mildew. If I have too many to plant out I have culled some because of mildew thinking I was selecting for those with greater resistance. One year I kept track to some degree which had mildew inside the house and then outside and there was not a trend that the mildew they were getting in the basement predicted them being more susceptible to mildew outside. I decided to stop culling so much on a little mildew in the house since then. I just thought that the environment in the house was just that much different. I think your idea of some seedlings just being stressed more can lead to suceptibility makes great sense.
Leen Leus and Johan have a nice review in the issue of FLoriculture and Ornamental Biotechnology devoted to roses.
Leen Leus, Johan Van Huylenbroeck (Belgium) Developing Resistance to Powdery Mildew (Podosphaera pannosa (Wallr.: Fr.) de Bary): A Challenge for Rose Breeders (pp 131-138)
ABSTRACT
Invited Review: Powdery mildew is the major fungal pathogen of roses in greenhouses and also an important disease on field-grown roses. In the past decade different tools have been developed allowing breeders to develop resistant roses in a more efficient way. Different pathotypes of the fungus, important for resistance testing, were detected. Resistance mechanisms in rose leaves were found and characterized. Screening techniques to evaluate powdery mildew resistance are available. These methods allow pathotype specific inoculation on detached leaves or can be used for the selection of resistant genotypes within a population of thousands of seedlings. New information on the genetic background of powdery mildew resistance became available. Genetic maps providing information on resistance markers are currently being developed and integrated. Marker-assisted selection is expected to be ready soon for use in rose breeding programs for powdery mildew resistance among other traits. This review aims to provide an overview on fundamental information and methodology available and necessary to make progress in breeding for powdery mildew resistance in roses.
In animals/us/etc, susceptibility is a 3 pience dance. I use the word dance because it is dynamic. The first part to consider is the hosts genetic relation to a specific disease. The second part to consider is the external environment and how that affects the host. The last part to consider is the hosts internal environment. The interplay between all 3 will play out what will happen between the host and the specific disease.
I realize that some of you know the above. Its basic medicine. But I think it is worth repeating since I cannot really see that a plant as a host would be all that much different in concept.
Interesting, thanks! I frequently noticed at Sequoia roses mildewing under plastic which never mildewed in the open. Finding them infected inside the green houses never prevented me from trying the varieties. If they offended outside, that was something different.
Most probably there are several genes at play when it comes to PM resistance. There is much variation in seedling populations to PM susceptibility. This might also indicate an interplay with PM susceptibility genes, as I think Simon may have suggested. Certainly PM resistance conferred by ‘Baby Love’ appears to be due to a dominant gene. No doubt physical factors also play a part.
Jim Sproul
Kim
That is why I totally disagree advising seedlings early selection for desease resistance.
Just as resistant vars are succeptible at a bad place, desease succeptibility of seedlings moreover in a confined environment is not correlated to adult plant garden succeptibility.
Even open grown young plants are hit by deseases that are no longer bothering them when older.
In this case I think the environment isn’t a variable… well at least not one that I think is particularly relevant IN THIS CASE. All the seedsling were germinated in a greenhouse and moved outside when at first true leaf stage. They were all growing in the same tray in the same soil, receiving the same light, water, ferts, everything. They were only recently sepearted out into their own pots. Kim, I did notice that the ones with fewer roots were more likely to be badly affected by mildew.
If the mildew resistance gene referred to here is dominant then this one either doesn’t have it and must have different structural features that prevent it because both its parents (both Indica Major) are affected by mildew here or there are different genes coming into play here apart from the ones mentioned.
The seedling is about 15-20cm tall now and when I repotted it the root system was easily twice as long with a 10cm spread. I normally take note of how well developed the roots are and was astounded at how large this one’s roots were.
I’m aware that enclosed, immature plants can be afflicted by diseases the mature, open ground plants will resist. It’s interesting how it appears the extent of the root system relates to mildew resistance, as if the plant is more efficient at scavenging for food, so it is healthier. It impresses me as being related to Iceberg’s black spotting when kept pruned too severely. Malnourishment leading to disease.
I don’t have the luxury of waiting around for years to decide whether something is resistant to disease.
At some point we have to move on. For me that’s in the seedling stage.
To devote any more time space or energy into a plant with no certain future will have fall to someone else.
I was just out with the dogs and noticed a plant of Grey Pearl opening a flower. It reminded me that this rose mildewed under plastic at Sequoia but here, and there, is totally clean. I wonder how much the “bloom” on the foliage is responsible for its health? Not a good plant, and you either love or hate the flowers, but the blamed thing IS healthy!
‘Grey Pearl’ is healthy here too.
‘Magenta’ is as old as it gets for the older mauves in terms of even being a decent rose up here in the land of temperate evergreen rainforest, valleys and decay. The root of the original mauves is definitely a desert one, lol. But that is largely due to blackspot. The irony is that the more modern mauves can be just as mildew prone up here where mildew is usually not an issue. Crystalline and Natasha Monet is nasty, nasty, nasty with both mildew and blackspot here. I do not think mixing in the likes of Color Wonder, Fragrant Cloud, Zorina, Spartan etc. (among other orange-red poly descendants) was very helpful in making mauves more disease resistant, especially to mildew. I LOVE Shocking Blue but I would not want to grow it where mildew is a fact of life. It is oddly one of the best mauves of any type possible for NW Oregon but I am sure it mildews like mad elsewhere.
Mauves still need a lot of work in terms of mildew and blackspot, as well as broadening their color pallette. It seems that that pallette has shrank over time since the addition of red-plum and orange tones, the latter probably being more responsible for mildew than the former – although Crimson Glory is often at the heart of both.
Simon
It is not only a different environment question.
It is also age of the plant with two main consequences:
First is that all foliage is young and close to soil surface. A condition that for me yearly cause a very severe rust autumn case on a few monthes old rugosa derived seedlings. The said plants never more rust in following years. Another occurence: in an environment that rarely allows PM, all species banksiae seedlings I grew were PM white painted in the seed tray. Open grown they were no more succeptible than it is usual for the species.
Second is that there are certitudes that rose health needs cooperating microorganisms. The main one and better studied being mycorhyzae at root level. Here Europe, the organic roses nurseries I know all rely on mycorhyzing. There are other less studied microorganisms that contribute foliage desease protection that as well are promoted by organic sprays.
These symbiotic relations are quite essential, unbypassable. For roses seedlings that all are different establishing them for woody plants takes a few monthes to two years if not actively promoted.I know this as I grow all seedlings for three years without eliminating.
Better studied in our human case, now it is established that we are completely unable to digest our food nor fight deseases by ourself. To be healthy we need as an average for a clean person about one hundred microorganisms for each of our body cells that count a few US billions. And thousands of different ones, by the way there is infinitely more genetical diversity here than among our chromosomes. A unique mostly mother inherited balanced population mix.
I know that most breeders selecting procedure is biased as a fact.
For woody vegetatively propagated plants it is definitely a breeders centered bias.
To conclude I have to say that hability to resist desease as a seedling is not correlated with healthiness as an adult woody plant.
"To conclude I have to say that hability to resist desease as a seedling is not correlated with healthiness as an adult woody plant. "
I’m not sure I agree with this. Using the Indica Major example… there were lots of seedlings… all the same age… some (most) were coated white with mildew. This one was certainly exposed to it yet it didn’t mildew for some reason. I know mildew resistance can develop over time as they mature in ones that show only partial infection while a seedling, but some seedlings seem better right from the start. I will continue to cull out the ones that show mildew as a seedling because I my own personal view is that they may end up ok but why would I bother when I have some that I can see already are ok. 0-47-19 seedlings are another example. I had something like 40-50 seedlings. The majority of these mildewed badly but a handfull didn’t. I tossed the affected ones and planted the clean ones out in the garden where they are still clean and growing along, and in contact with, the ground.
Maybe the fact that there are some roses that seem to have a narrow climatic window within which they will grow cleanly whilst in other areas they are horrible is due to us keeping on too many ‘maybes’ when the ones that are clean from the start may have a wider potential range due to higher than normal resistance abilities.
I’m not sure there is any correlation between the size of the root system and the immunity now that I think about it as either. The seedlings came from Indica Major, which was/is the favoured rootstock for Teas here in Australia because of its tremendously strong root system (which is why I was playing around with it) and its strike-a-bility, yet it mildews quite badly here.
I’m really just wondering what others have observed in relation to HOW it seems to be passed on because it looks like some kind of recessive interaction or maybe it’s structural or maybe it’s all of these… how is that a mildew-free seedling can come from badly affected parents if it is a dominant gene etc.
Both certain internal plant chemicals, especially in growth shoots and as seedlings, and nitrogen can cause an expedient elongation of cells, sometimes doubled length in 6 hours. I am unsure as to how this affects cell position vertical, horizontal, etc) but I imagine that it would likely make them cells to amass vertically, paralell with the direction of growth. This could, in turn, create a scenario where the plant walls are now more permeable (just as they are more susceptible to UV), as well as create a scenario where excesss biomass is created. Both aspects could be prime targets for mildew.
Personally, I think resistance should be thought of in a more holistic way-- Genetics. Culture. Mechanics, etc. I cannot imagine that resistance is simple.
1-72-1 can mildew but frequently creates healthy babies. Torch of Liberty was always clean in the Santa Clarita Valley yet it black spots here in Encino. It’s the seed parent for Lynnie, who isn’t perfect, but extremely healthy and very cold hardy in many different climates here and in Europe.
I am inclined to believe in Jadae’s holistic thought. If resistance were simple, why is it so easy to force a resistant rose to mildew by allowing it to dry too far? Why should it be easy to induce Iceberg, which usually doesn’t black spot here, to spot badly by continually over pruning? I also feel this is tied in to the root system issue. I have noticed those seedlings in each cross which are more sickly, also suffer from inferior root systems compared to their healthier siblings. Many had strong roots but with few to virtually no “feeder” types. Yes, I know it’s the chicken or the egg scenario, but with a seedling, it needs roots first and if they aren’t there, the rest doesn’t follow.
Agreed, Indica is used as a stock because of not only ease of rooting but for its roots. But, your seedlings aren’t Indica, they are a massaged version of it and show varying expressions of its traits. For one to have a more massive root system in conjunction with increased health, I feel, does say something for the idea that a reduced “digestive tract” yields increased disease proclivity.
The fact that it has a proclivity towards increased disease resistance throws up a conundrum for me though. Lots of people on here say they will not use such and such a rose because it is mildew-prone for fear of passing on this predisposition to its descendants. ‘Indica Major’ has indeed passed it onto many of its progeny (many of which also had poor root systems), however, I have a handfull that show none of these mildewing tendencies, not all of which have such extensive root systems; I think this one is a freak of nature and it is probably adding a lot more to its ability to resist everything than the others but it is not unique among its siblings in its mildew resistance (though none that show this amount of resistance with smaller root systems could be accused of having poor root systems… they just aren’t as big as this particular seedlings root system). This one seedling is bomb-proof so far here. I’m discounting environment and cultural practices as being variables here because it hasn’t received any special treatment compared to the others. Internal environment is different issue. Do I bother keeping it on to breed with on the assumption that the genetic factors predisposing it to mildew and black spot have been ‘bred out’ or do you think that it has these traits carried somewhere in it. I believe in a wholistic approach too, but in this case when everything has had the same opportunities the only part of the wholistic equation that has changed is the internal environment which is genetically controlled.
The feeder roots concept is an interesting one. The seedling in question has an enormous amount of the finer feeder roots whilst the others, that also show this mildew resistance, but are less vigorous do not. They have good roots but nothing like the network of roots this one seedling has. I only noticed this because it made transplanting it difficult. I had to use a finer soil than I would normally use, try to spread the roots out as best I could, and shake it into the roots thoroughly and it was hard to get worked in. Sans-soil, it had a tendency to want to flop all the roots together in a mass and would have just laid them altogether, like a wet mop lifted out of the water, in the new potting medium rather than in a spread out dentricular fashion as it was pre-transplant. I can see this one is going to be a pain in the future as it will become pot bound in a very short time but will make transplanting into the garden equally painful in the future. The plan was to leave it in its pot for just a short time to fill out a bit and then put the whole thing in the garden early so it can spread out as it wants.