Is there any documented determination/comparison out there regarding the BS disease resistance profile of Double Knock Out? (eg. when compared to its sibling Knock Out, or when compared to unrelated cultivars with great horizontal resistance to BS).
Double Knock Out in our Dec. 2010 article in HortScience evaluating for resistances to races 3, 8, and 9 was very comparable to Knock Out. There was immunity to two of the same races, except DKO had some susceptibility to race 8, but limited the lesion size dramatically. It is a very very black spot resistant rose that appears to have many of the same vertical resistance factors as its sibling Knock Out and like Knock Out, a strong underlying horizontal resistance once those vertical resistance alleles are compromised. The strong underlying horizontal resistance for Knock Out (had vertical resistance to races 3, 8, and 9) was noticed in the work of Vance Whitaker when Knock Out was challenged in his international race array paper and some races could cause infection, but the lesion sizes were limited.
Bill Radler did a great job stripping away vertical resistance in his breeding program with lots of races in his yard and through multiple generations accumulated key genes to build horizontal resistance.
Hi David,
Thank you for the great info! It would seem from what you have said that with regard to vertical resistance, ‘Knock Out’ may be a bit better than ‘Double Knock Out’. Is that correct?
With regard to horizontal resistance, is one better than the other (even by a small bit)?
Jim Sproul
My DKO seedlings are really BS resistant, but mildew has been a problem in some hybrids.
David,
Still wrapping my brain around this subject…
“Bill Radler did a great job stripping away vertical resistance in his breeding program with lots of races in his yard and through multiple generations accumulated key genes to build horizontal resistance.”
I now understand the concept of horizontal resistance. Does the above mean that vertical resistance is something we need to strip away? Not so clear on that part. Isn’t a combination of strong horizontal and vertical resistance a good thing? Thanks!
Rob
Hi Jim,
I’m not sure if Knock Out or Double Knock Out is slightly better in terms of horizontal resistance. We need to challenge them in a common environment to a race they both are susceptible to and then compare the fine differences in lesion growth rate. They both seem to have very strong horizontal resistance.
Hi Rob,
Great question! We need to strip away the vertical resistance to expose and work with the underlying horizontal resistance. After the horizontal resistance is built up, the hope is that there are some vertical resistance genes there too that in other gardens/areas with less races of black spot the vertical will hold up. If it is stripped at that point strong horizontal is left for the plant to still have great utility.
David,
Great answer! Thank you. I’m finding so much on the internet to read about on the subject…fascinating stuff.
Rob
Hi David!
Thanks for posting this great information, it is very much appreciated!!
Thanks David!
This current year, I did a lot of breeding using DKO as the pollen parent. So if there was a difference, I would just want to be using the best that is out there. Powdery mildew susceptibility had been my biggest hesitation in using it (or DK) since I cull severely for powdery mildew. However, since most of the crosses were with the Hulthemias, I will not cull any DKO crosses that produce good blotches, even if they get bad powdery mildew.
Jim Sproul
If it is a tossup for disease resistance, Double Knockout is hardier than Knockout. So I’m glad, Jim, that you are using DKO.
David,
""We need to strip away the vertical resistance to expose and work with the underlying horizontal resistance. After the horizontal resistance is built up, the hope is that there are some vertical resistance genes there too that in other gardens/areas with less races of black spot the vertical will hold up."
Sorry if I seem a bit dense...this is all new to me. I'm a bit confused about the above statement. How do we 'strip away' vertical resistance? After building up horizontal resistance where has the remaining vertical resistance come from? Is it vertical resistance that remained after stripping away previous resistance or is this new vertical resistance that is obtained while building up new horizontal resistance? Thank you!
Rob
For those, like me, that are new to the vertical/horizontal resistance topic I’d like to share a source I stumbled across in my searches. There is a lot of basic information provided including Chapter 3: Resistance: Vertical and Horizontal. The source is:
Return To Resistance
Third Edition, Revised
by Raoul A. Robinson
It looks to be a valuable source of information for the layman.
Link: www.sharebooks.ca/system/files/Return-to-Resistance.pdf
Hi Rob,
Great question. We strip it away by having a race that has the virulence allele that overcomes that single gene. Think of vertical resistance as a locked door in the rose. The rose may have a series of doors and before black spot can effectively enter the rose house, it needs to unlock all those doors. The virulence alleles in the black spot races are keys. We need the right race of black spot with the right set of keys on its keychain in order to unlock all the doors to get in. Black spot can be separated into races depending on what combination of keys they have on their keychain. Those with the same keys are the same race and can enter and cause disease on the same roses.
We strip away vertical resistance by having a race that has the right set of keys to cause black spot on our roses. We can do that with trying to encourage black spot and get it from multiple places to increase our diversity of the pathogen. After the rose burglar (black spot) is in the rose house, horizontal resistance is what the rose needs to use to minimize the damage the intruder wants to cause. We need to let the burglar into the rose house by stripping away the vertical resistance so we can see the degree of horizontal resistance present. We want black spot to form on our roses so we can then see which ones have relatively less than others in similar conditions and over similar timeframes in order to pinpoint those with greater horizontal resistance. It is generally a whole continuum of degrees of susceptibility we find. We can then intermate those that have greater resistance, reshuffle the genes, and then hopefully get some seedlings that have even stronger horizontal resistance in the next generations.
Along the generations, those locked doors in the rose get inherited and segregate too. They just are not effective as we have races of black spot with the right keys. After we have our rose with high horizontal resistance, hopefully there are some locked doors in it still. After our rose is planted in a garden where one hasn’t tried to encourage lots of types of black spot, hopefully that gardener doesn’t have a race of black spot with all the right keys to get in. If so, the rose looks great! If all the keys are on some fungi’s keychain, it’ll get in, but then there is strong horizontal resistance to allow the rose to still look pretty good.
I really like this analogy and this idea of vertical and horizontal resistance generally holds up and describes the situation we observe well.
Take Care,
David
David,
Thank you for explaining the answer in a way that was easily understood. It’s much appreiciated!
Can I assume that unless I have access to isolates of various races of black spot that I can never be sure…or can be fairly certain…that whatever horizontal resistance I’m building up will have limited success because I don
I think my answer is in your explaination. Thanks David.
Very interesting thread. As it progressed, I thought of Baby Love. When it first came out, it was considered bullet proof. The American Red Cross in Asheville, NC had a rose garden planted by the local rose society. They had 2 bushes of Baby Love in two separate locations. After a few years, Michael Gillum had reported on Garden Web that one of them had succumbed to black spot. The other still remained “clean as a whistle.” This was about 7 years ago and was the first time I had heard BL wasn’t bullet proof.
I have had 2 plants of BL. The first years I was ecstatic over its health. Then I started to notice it didn’t look so healthy and started to lose vigor. One thing I did notice, the canes developed a “bruised look” as if someone had squeezed longitudinal strips of the outer back and damaged them. I don’t recall whether the leaves had lots of blackspot or not. One plant is now totally dead and the other is reduced to one very thin 6" cane with a fertile hip on top!LOL
Everyone knew over time the BL had excellent vertical resistance to BS until one strain overtook it. But that in general, it lacks good horizontal resistance, since once it succumbs, it succumbs bad. Am I forming the right conclusion concerning BL’s horizontal resistance (though its progeny seem to be healthier with the right outcrossings? Would appreciate your thoughts on this.
Jim
A few random thoughts.
A few roses (like Rose de Rescht) will get Blackspot but will NOT yellow and drop its leaves (but instead will hold onto them quite stubbornly).
I also think that if you start collecting roses from all the various rose nurseries that you will eventually also collect every rose disease known to man (including the various races of BS)…
Home Run… (Knockout with its horizontal resistance & Baby Love with its vertical resistance) 'nuff said.
On the side, I’m really quite impressed with the disease resistance of the alba, Felecite Parmentier, in my garden this year. Contrary to reports, mine is completely spotless as compared to Queen of Denmark which defoliated… so I guess location (and the races of BS that thrive in certain locations) DO make a difference.
This is a fun and thought provoking thread! One challenge or struggle is that after strong horizontal resistance is carefully build up, crossing such material with roses that have low horizontal resistance to bring in other colors, etc. tends do dilute down the general horizontal resistance among the seedlings as a whole. If one is really lucky there may be some seedlings that are more towards the resistance extreme of the horizontally resistant parent, but most are in between. It may take a couple generations in order to build the horizontal resistance up within enough members of the general seedling populations to make some nice selections that also carry along the additional traits of interest.
Rob, that paper that you posted, “Return to Resistance,” is a really helpful, easy-to-read, and thorough explanation of horizontal and vertical resistance.
I really recommend making the click to anyone who wants more knowledge on the subject. The author goes into what he believes is a misguided prejudice by some scientists against breeding for horizontal resistance. He discusses in great detail the evolutionary purposes of the two types of resistance. I’m not real big into technical papers, but I can still understand it.
What biological factors give the ability for roses like DKO to minimise greatly the observable leaf damage that can be caused by a strain of BS that they are susceptible to? … Putting this is in another way, what is it in the biological makeup of roses like DKO which gives them this remarkable degree of horizontal resistance?
I wonder, is horizontal resistance linked to global plant factors such as leaf cell structure, leaf glossiness, leaf thickness…OR perahps is there a set of specific genes that operate to give horizontal resistance??
ALSO… in relation to the “immune systems” of roses:
Are roses able to produce antibodies??
Do roses possess cellular based immune recognition/attack mechanisms?