There are quite a few newer European roses in the American market which have very good stated disease resistance, particularly to black spot. It would be wondeful to have testing in place where plants of them all could be submitted to determine just how resistant they are, what type of resistance they possess and to which strains. Imagine being able to know where they should be found healthy and which could be efficiently used to create a larger gene pool of horizontal resistance. Wow! Kim
I agree Kim!!! Hopefully we can get that up and running at the U of MN. Stan Hokanson and the Plant Disease Clinic are working on the logistics. Navigating greenhouse space, cost to do the tests, estimating how many people would be interested in it and if enough volume can be had for it to be self supporting, etc. are just some of the details being worked through.
Two thumbs up for U of MN!
I have been told that the technology to test for black spot genes has been developed. I am sure that it must be cost prohibitive at this point in time. But, who knows, as with most new technology, one day the cost may be such that a new rose can be tested for blackspot without the need of field trials.
Hi Joan,
The technology for identifying the genes is developing, but slow and a ways off because so few are characterized enough to have basic markers linked to them. Horizontal resistance is the more practical goal with typically multiple genes each having a small effect compared to the vertical genes.
The technique here to screen roses with multiple races is not too complicated. It just takes a lot of healthy leaves at a common stage of development to harvest and put in humid boxes in the lab where they are innoculated (sprayed) with spores of an array of different races and after 2 weeks document if lesions are present and their relative size after common incubation times. I’m hopeful the logistics will be worked out for greenhouse space, labor for culturing the races, making the innoculations, etc.
I’m glad it only requires foliage to be sent. That would be significantly less time consuming and costly than having to actually grow the varieties! Imagine if we could collect the required foliage of all the “very black spot resistant” varieties and have them indexed in a season! Wow! I’m ready! Kim
Hi Kim!
It is a great technique. As part of it though, a couple plants would need to be sent to the U of MN so they can be grown in a common environment in the greenhouse with the controls. From them all leaves will be harvested that are just fully expanded for the tests. Some challenges with just sending leaves could be different environmental conditions during leaf development relative to the control cultivars (higher light may lead to thicker cuticles, etc.). Also, if it was done by companies to use in their marketing, a less than honest company may choose to send leaves that have at some recent point in history have been treated with a fungicide.
Hi !
Kim,
I would like to know, which newer European varieties are the most prone to black spot there. This year I bought only two Meilland’s roses, but of many Kordes varieties I have, only Rosenstadt Freising gets awfully black spot. I did not collect any hips of it, just because of that. Waisted time to put pollen on it.
Or, better said, is there any common factor within the European roses which do not have very good stated disease resistance ? Europe is quite a large area.
One more thing, I started to think that testing for disease resistance, and it would be quite easy to test it, at least in some scale, also at home. Just take some infected leaves, put them into a zip lock bag, put there also some leaves of a variety you want to test, moist the bag little bit and that’s it. And then, just to wait.
I do not know, if the leaves would rotten before giving any results for disease resistance. 
Most European roses available in the US are from France, Germany, England and the Netherland.“Europe” has really no equivalent climate to The Mid Atlantic and Southern US. All information about disease resistance, and especially Black spot coming from there is to be taken with a grain of salt.
I was reading about several of the Kordes roses and a few Meilland introductions. I realize Europe is a huge area with varying populations of black spot. I hope for us to eventually determine if they are as healthy here as they are stated to be there. I don’t know about anyone else, but my rose budget is much less than in previous years; my space and energy are both significantly reduced from previously available levels; and I have to eliminate something from the garden to make room for anything new. I’d rather not experiment any more than I must. Been there, done that and enjoyed it when I could comfortably do it. I don’t find it as enjoyable now. Kim
Radler and Noak designed home blackspot testing methods. If I remember well mainly under desase inducing conditions spraying with inoculum made from deseased leaves. Results are not so bad.
My growing environment is screening enough for the better at BS resistance vars to be fully tested. Susceptibility varies according to temperature, amount of splashing rain, inoculum abundance and leaf age. I.e. monsoon climates species foliage is more resistant when young than later.
Kordes on commercial site rates his vars resistance on a 0-4 scale. Carefully done but I confirm his 4 stars for BS resistance very nice var Rosenstadt Freising is failing for me also.
Bill Radler sure has done a great job!! The key to be successful is to make sure one has diverse black spot races in ones garden and recognize the race composition that one happens to have can change over time as they outcompete each other or by chance some predominate more or less over time. Having a conducive environment is important, but also enough races that you can strip away the gene for gene resistance and get at the underlying horizontal resistance. That is where the beauty of having characterized races well preserved that can be used to challenge a rose in order to strip away the vertical resistance and get a glimpse at the underlying horizontal resistance. It is essential for breeders to continue to screen as they do. However, now we have a great testing resource to push a rose through, perhaps as a confirmation, before release for its resistance. Breeders may do a great job selecting for a rose with effective vertical resistance in the limited number of test sites they use and excitedly declare it is super resistant and sell it everywhere. Hopefully the resistance will be durable. However, like in the case of ‘Baby Love’ after the single gene effective against many black spot races is broken down, we recognize it goes down fast due to black spot and has relatively low horizontal resistance. It is a nice rose and if you are not spraying and do not have the race that takes it down present, you are in good shape. However, we realize races travel with commerce and the threat is there that just because you don’t have a race in your garden now, doesn’t mean it won’t stay away forever. Strong horizontal resistance is more durable. Combining strong horizontal resistance with some vertical genes over the top is even a better situation, like what is in Knock Out.
Having a wide diversity of characterized and preserved races available to work with really helps breeders. We can characterize parents for their resistance to select ones possessing the types of resistance we are interested in transmitting to seedlings, and then seedlings we would like to more fully characterize resistance for as well.
Bill Radler and other breeders that have made great strides for disease resistance and are providing researchers with the roses important to work with to understand the underlying biology and genetics of resistance in order to more efficiently move this important work forward.
David,
Thank you for the understandable and comprehensive post. I agree that the rose being tested really needs to come in contact with all the bs races known at that time anyway.
I certainly hope that once reliable results start coming out that the cultivars having strong horizontal resistance may be made known to the professional as well as the amateur and hobbyist rose breeders.
I assume that current available varieties that “seem” to have good resistance will be tested as well as the newer varieties just coming or about to come out.
I totally agree that just testing locally or to a few test sites will only give limited and possibly inaccurate results.
Thanks again for all you do and your clarity in your postings,
Jim
Earlier this year a public garden had a group planting of Knock Out and one had substantial black something on the lower leaves. Know doubt Black Spot and now I wonder how fast it will spread and if it is something new. Neil
Hi David, I fully agree when you write: “The key to be successful is to make sure one has diverse black spot races in ones garden and recognize the race composition that one happens to have can change over time as they outcompete each other or by chance some predominate more or less over time. Having a conducive environment is important, but also enough races that you can strip away the gene for gene resistance and get at the underlying horizontal resistance.”
As I have no laboratory or other facilities/equipments and knowledge you are using; my strategy in order to preserve maximal BS races diversity is not eliminating the susceptible plants, be they vars or seedlings. I.e. Baby Love, Knock Out, Pretty Lady are here to maintain the BS races they are susceptible to.
In my species based large population the seed bearers are selected among the best at plant architecture, decorative performance and above all strongest at plant building. All this at high plant density; two rows 40cm apart and 15cm on the row. If debilitated the most susceptible plants have enough horizontal resistance to survive and even the consistently ugly desease ridden are not eliminated.
The climatic conditions are quite difficult here in highlands, in central Spain, thinking of rose hybridizing.
Cold, rainy and very windy spring season starts in March, and continues to the end of June, most of the years.
Then, the summers are very dry and hot, with cool nights.
Nightly automatic watering (for the grass) raises humidity significantly. Daily temperature raises 27 C- 40 C for two months. Sometimes one can not even move a hand outside, because of the heat.
If we are lucky, there are some nice sunny, temper days in the early autumn, like this year.
I have noticed, that if there are not very healthy, strong, vigorous parents used in crosses, no hope that the seedlings would survive here. I do not have a green house at the moment, and the seedlings stay outside in a partly covered terrazza. This year nearly all of them got some (suppose it was downy mildew) attack, and they did not survive. Only tea noisette hybrids grew happily and bloomed wildly without any sign of any disease. Only two of the other crosses survived, despite of being defoliated nearly totally. One was Louise Odier x Rhapsody in blue, the other Ingrid Bergman x Tuscany.
The died seedlings very HT seedlings, floribundas, Austin’s etc. and hybrids of them.
Black spot resistance is very important, but I think some over all resistance with vigor might make it better.
One thing I have noticed this year, when looking some resistant roses for black spot and powdery mildew (for example Perla, Wedding Bells and Claire Austin)that they get some downy mildew, not much, but anyway.
What is my conclusion, that the crosses with some species/ close to the species varieties crossed with the most healthy modern roses are the only way to get overall healthy, disease resistant seedlings and plants.
I’m not sure I’m going to work to hard to “make sure one has diverse black spot races in ones garden.” I mean, swapping cuttings, pollen, and seeds is all good and well, but when someone offers to trade particularly virulent strains of BS, I might be tempted to decline.
Not that I suffer for a want of such…
We know that I have not yet dabbed any pollen, so I beg your indulgence. I have been successfully growing roses in central Florida with a no spray regime (except insecticidal soap when required). My observations mirror your statements Pia. And I think theory might back the hypothesis. How to explain what I mean? I’m thinking recessively linked genetic susceptibility as in royal hemophilia. The quest for something “new” (exempting cross species hybridization) is theoretically often a quest for the recessive. And maintaining the expression of that trait would theoretically perpetuate the linked weakness. I was reading a post here about Ebb Tide and its weaknesses which I’ve observed even on Fort. rootstock. And someone I read here said purples were recessive recessive yellows, I think. So, I thnk you have a very valid point Pia about vigor.
I’m slightly confused Pierre by: “monsoon climates species foliage is more resistant when young than later.” Although not actually in a monsoon climate, Florida simulates it pretty well some seasons and I observe that older plants become increasingly resistant. And that in the older plants it is usually only the foliage about to be shed - there’s got to be a term for that hasn’t there? When the plant decides to cut off the vascular “circulatory” support of a part of itself. Anyway, I observe that when this occurs black spot appears quickly in the day or two prior to leaf drop while the remaining leaves remain quite healthy. Which begs the question in my mind of how accurate a test which removes foliage from the plant will be. I would expect higher infection rates in the test vs. tested on a healthy established plant.