David,
This is a great thread and thank you for your knowledgeable contributions! I’ve had to rethink my whole breeding plan and removed long standing breeders for new roses with good horizontal resistance. Your last bit of information regarding diluting down the general horizontal resistance by introducing roses that have low horizontal resistance to bring in other colors, etc., rounds out my now basic knowledge on the subject. I have ‘Smoke Rings’ which I love for the color and that it is miniature. It was new for me last year and both seasons it’s been spot free until September when it completely defoliated. I’m assuming that vertical resistance was stripped away and since it completely defoliated, there is little horizontal resistance. Based on what I’m learned I believe it should be removed from my breeding stock because to continue to use is with say, Knock Out, would dilute horizontal resistance built up in KO. Thanks again for sharing the knowledge.
Joe,
Yes, I like the paper, Return to Resistance, as well. It’s easy reading and provides a lot of basic knowledge. I’m glad you found it useful as well.
Rob
Hi Rob! I sure wish we had more roses with different colors and traits on hand that possess strong horizontal resistance to work with. Bill Radler sure has some great roses on the market. Thankfully some of his roses not in the Knock Out series have relatively strong horizontal resistance and bring in other colors. I think we are at the beginning here and over time we can build horizontal resistance in hybrid teas, minis, and other classes of roses that traditionally do not seem to have many members with strong horizontal resistance. It’ll just take some time and people willing to put effort in that direction.
That’s a great question George about specific mechanisms!! We sure have much yet to learn in that regard. There is a paper a few years back that looks at wax deposition in Knock Out leaves. It isn’t very convincing that how the wax is deposited is the key, especially as we challenge KO’s with different races we get infection for those races that can unlock the doors. Ethylene sensitivity is sure one major factor in it all. The fungus can emit some ethylene and depending on the plants ability to respond or not to it (other factors may be at play too) we get fast yellowing and defoliation or not. I saw a Blushing Knock Out yesterday with some black spot on it and I had to look up close on it to see it. The leaflets were not yellowing and there was just some small dark lesions on the green leaves. It still looked fantastic as a plant covered with leaves and blooms.
Andy Roberts studied some diploid versus induced tetraploids for their race reactions and in some instances the vertical resistances changed for some races, but not others. Maybe cellular size/structures changed somehow affecting those races, or maybe gene expression and regulation changed that impacted ability to be infected.
It is great to recognize there is hope for the future for breeding for resistance and more for us to better understand and then be able to purposefully work with.
David, very interesting comments on horizontal resistance. I do wonder about one comment, that the fungi produce ethylene. Is there evidence that it is the fungi and not the plants in response to fungal infection? I know that some fungi under some conditions produce ethylene, or consume it, but I don’t know of any reports about B.S.
For sure there are huge differences in ethylene sensitivity of rose leaves. I did an expt 30-some years ago adding exogenous ethylene to cuttings of roses in vermiculite. New Dawn showed essentially no response, while Crimson Glory dropped every leaf at a dose of about 1 ppm as I recall. This was a primitive experiment with just saran wrap (the real kind) covering dishpans to which the ethylene was injected. So it was only a burst of a few min to hours treatment. That was before I found the only published paper on ethylene and blackspot, from a couple decades previous.
At the time I was studying alfalfa infection and found that a fungus elicited ethylene, while a watermold elicited ethane production. So I wonder about rose fungi. Mildew (downy) is one of the watermolds. Powdery mildew deforms long before it defoliates. And I wonder if anthracnose elicits any ethylene production, as the leaf loss is very slow. Not like B.S.for sure. Any info on that one?
Someone ought to methyl cyclopropene to block the ethylene response and see if B.S. sensitivity can be delayed.
Do you think the small black spots on Blushing K.O., are perhaps a hypersensitive response, which is a form of resistance.
Reading the paper, “Return to Resistance” one cannot ignore how much it is a charge at mendelian breeding.
And how much advocating population breeding.
As for me the backcross strategy is an obvious failure at building durable desease resistance I began turning my work to population breeding some ten years ago.
I started from species and allways do some reverse backcrosses to the best modern roses at (failing) desease resistance. Reverse backcrosses are crosses where the recurrent parent is a population.
Getting away from species non horticultural features while holding desirable qualities was difficult and not efficient at first. Necessitating incorporation of other species at cost of the drawback that allows future progress.
Great points and questions Larry. I looked through Vance Whitakers disease resistance review in Plant Breeding Reviews and how he wrote one sentence seems to suggest ethylene is produced at least in part by the fungus, and he sites
McClellan, W.D. 1953. Survey of rose diseases. Am. Rose Annu. pp. 70
Thanks David, I think you are recalling the same articles that I referred to. But back then, evidence for which partner produced the actual ethylene was small to non-existent. The tools were not there and the pathway to ethylene in plants was not known. I’ll do some lit searching. The qn still interests me.
Lesions over 1 mm probably are not HR. The way KOs hang onto foliage in winter suggests they may be as insensitive as ND to ethylene.
I ended up testing it as a way to promote rooting too. Marvelous stimulator of callus production. That’s reasonable since the abscission layer is kind of like callus. And rooting hormones interact with ethylene pathways.
Wounded roses produce ethylene as it is known for florist roses. I remember anti ethylene chemicals have a positive effect on cut flowers duration.
David,
“I sure wish we had more roses with different colors and traits on hand that possess strong horizontal resistance to work with.”
I removed ‘Smoke Rings’ and replaced her with ‘Trumpeter’ and ‘Livin Easy’. From my reading both have good disease resistance and the color range that I wanted to include in my breeding stock.
I’m guessing, but not sure, that species roses add to horizontal resistance. ‘Trumpeter’ has R. multiflora, R. Kordesii, R. macrophylla and R. roxburghii in her background.
‘Livin Easy’ has R. roxburghii, R. setigera, R. multibracteata and R. kordesii way back in her ancestry. Hopefully both have retained some horizontal reistance from those species.
…any input regarding ‘Trumpeter’ and/or ‘Livin Easy’ as parents/health would be appreciated.
Livin Easy and Remembrance have been great for me as plants and as breeders.
Is there some sort of trial roses can be submitted for horizontal resistance testing? Black spot is an issue here, but nothing resembling what it is elsewhere. Finding out if some of our creations possess the desired resistance would be a real benefit. Kim
Great question Kim!!
Stan Hokanson is working things out with the director of the Plant Disease Clinic at the U of MN to hopefully someday in not the too distant future allow breeders and other interested parties to be able to submit plants for screening with the international races.
Hi David,
That would be wonderful and would help save the rose breeders and commercial rose growing companies a ton of time in rose evaluations!
Jim Sproul
Wonderful David! Thank you! I have five or six I’d love to test. Kim
WOW!!
I wonder if we will ever get that type of resource going here, Downunder!!!
That is great news David! Maybe there would end up being a collaborative effort with U of MN and other organizations. That would be cool.
Michael,
Does Livin Easy pass on disease resistance from your experience?
Rob
Yeah, its been a decent parent for general health.