At the Great Rosarians event, information was distributed about black spot research determining eighteen world populations of it and four in the US. It also contained the list of tested cultivars showing which was resistant to which type and that Applejack was the only tested cultivar resistant to all four.
Might anyone know where to find that on line, please? Thanks! Kim
Good Morning Kim:
David Zlezak was doing research at UofM on blackspot so maybe he would be the person to contact for additional information.
The research is quite fascinating regarding the various ‘families’ of blackspot. Not all blackspot has the same causative agent unfortunately. This is why it is so difficult to control what we see in the various gardens.
“The research is quite fascinating regarding the various ‘families’ of blackspot. Not all blackspot has the same causative agent unfortunately. This is why it is so difficult to control what we see in the various gardens.”
Can you elaborate on that, Meg? I’m unaware that there is more than one pathogen that causes Blackspot, but perhaps that’s not what you were suggesting. Thanks!
Not sure if this is what you are looking for but it is interesting…
Link: www.springerlink.com/content/g0528252n7412l68/fulltext.pdf
Hi! I suspect the article is the HortScience article published last December. Oh my! When I did a google search here to get you the link to it, I realize the taped version of the short research presentation I gave on it at the annual ASHS meetings a couple years or so back is edited and online! http://ashs.org/db/horttalks/detail.lasso?id=719 If you have 15 or so minutes to spare you can hear the highlights of the work and see the powerpoint.
Here is the link to the article: Ashspublications.org
Here is some background:
First of all, yes there is just one fungal species causing black spot.
There are different races of black spot and a race can be comprised of different genetically different isolates of the fungus, but what they share are basically the same capacity to infect the same roses due to likely the same virulence genes. Vance worked with Debener (in Germany) and Roberts (England) and his US races (there are 5 unique US ones in the collection and probably a lot more out there) to gather and characterize the international race collection. There are 11 unique races in the collection and a new one to work with here to see if it is the 12th.
We screened the Earth-Kind trial roses to the original 3 Vance described in his Masters. The key I think is the general distinction (holds relatively true) between vertical and horizontal resistance. We need to strip away the vertical resistance to see the underlying horizontal. As breeders and especially rose marketers try to identify resistant ones, roses that have no or super little black spot are highly valued and marketed as very resistant, but then after a single resistance gene in the rose allowing this strong resistance is compromised by the pathogen it looks bad and the reputation of the rose is compromised. A resistance gene in the rose is like a locked door and the virulence gene in the pathogen is like a key- roses may have a series of locked doors and if a race of black spot has all the keys on its key chain it can get in the rose house and cause disease. Baby Love is a great example of a rose with locked doors most races don’t have the right set of keys for and it looked great most all places, but now there are races with the right set of keys. When it gets in, the rose has minimal horizontal resistance and defoliates strongly. Horizontal resistance generally depends on multiple genes each having a small effect and is quantitative in nature. Horizontal resistance limits the pathogen development and reproduction and slows the black spot down. It seems to be generally durable lasting year after year and location after location. Under very unfavorable environments, black spot will make such roses look not so good, but relatively they are still very attractive compared to roses with lower horizontal resistance. Knock Out has both vertical and horizontal resistance as other roses too. THis is the best case senerio. Bill Radler for instance, encouraged lots of races of black spot in his garden and over the years stripped away the vertical resistance genes in his yard to test for and build horizontal resistance over generations. His roses then when out and about with less races around in most people’s gardens can have effective vertical resistance, but where the right sets of keys are, the black spot development is relatively slowed from horizontal resistance.
Having the international race collection allows us to challenge new roses and find races that strip away the vertical resistance and then we can get a glimpse at the underlying horizontal resistance. It will help give us a clue of how the rose will hold up in the landscape after the vertical is stripped away even though under the limited outdoor testing it may not have encountered a race that strips away the vertical resistance yet. So far we haven’t found any rose that has been challenged with the whole race array that has vertical resistance to them all. Races change and move likely through commerce. Vance’s work fingerprinting 50 collections in the US shows there is no real pattern on geography, probably because of mixing around through commerce.
Breeders are encouraged to build and select for horizontal resistance for durable black spot resistance. Vertical resistance looks great and is nice to have, but it is the underlying horizontal resistance that will endure. It takes more work and better understanding of how to accomplish it, but it is something all of us interested in black spot resistance can work towards.
Sincerely,
David
Paul:
Thanks for giving me the opportunity to correct/clarify my previous statements regarding blackspot causative agent.
I was incorrect to give the impression that there were different pathogens when what I meant were what David refers to as ‘races’ of the causative primary pathogen, Diplocarpon rosae Wolf.
From some of David’s research I understand that they are studing at least 11 races of the fungus.
Here are a few more sites to consider.
http://hortsci.ashspublications.org/cgi/content/abstract/45/12/1779?etoc
http://www.rosehybridizers.org/forum/message.php?topid=32630&rc=6&ui=2786993173
The University of Minnesota is serving a key role for the EarthKind
David I watched your presentation today. It was very informative. You are a much better public speaker than I am. So besides Lina and the Fairy what other roses have good horizontal resistance. I am guessing the likes of Carefree Beauty and Hawkeye Belle.
Hi David,
Thank you for posting that link to your fab presentation, it was great to listen to it and learn from it.
David, if it is not too much to ask, are you able to comment from observations of Konck Out and Double Knock out, on their respective black spot resistance profiles (horizontal/vertical)?