I sure agree about breeding for horizontal or field resistance (tolerance) versus immunity which is often based on a single gene that can quickly be overcome. Horizontal resistance typically is based on multiple genes and sometimes methods by which the pathogen’s lifecycle can be slowed. It is more consistent usually and typically more durable over time. The all or nothing approach for selecting hybrids that appear disease free due to a single gene and then have it fail is disappointing. What matters for durability seems to be what the underlying horizontal resistance is that is much more difficult to overcome. Knock Out and its offspring Home Run have both very strong horizontal resistance to black spot and also some vertical genes too that are effective depending on the races of the pathogen present. Combining both is the best we can hope for in my opinion.
Prairie Joy has great horizontal resistance to black spot and people have gotten great seedlings out of it, it sounds like. I want to use it more. When I heard someone was steering away from Prairie Joy because of a little black spot that was disappointing. That just demonstrates it does get black spot and has strong horizontal resistance because it doesn’t build fast at all. Prairie Joy doesn’t rebloom very strong unfortunately, but hopefully some of its seedlings can. It is fairly cold hardy which is great as well.
Thank you David. Perhaps I’ve missed it, but is there a list of known varieties which have horizontal resistance; one for vertical and one for both? It would seem if we know which has which, targeting the traits would be a whole lot easier. Thanks. Kim
David,
Thanks for the information regarding horizontal and verticle resistance. I’m not familiar with the concept and see I have some more research to do. 
I will do a search on the subject but if you know of a source that you can point me to to get me stared, that would be greatly appreciated.
I pretty sure that there wasn’t any such thing as full immunity to pathogens and my thoughts were to collect several plants with diverse parentage that are known to show minimal infection, like ‘Knock Out’ for example. A visit to a planting of KO roses this weekend showed <5% BS infection and that’s very acceptable to me.
The thought was that if I cross breed plants from within that collection that I would hopefully be ‘pooling’ genes that control disease resistance into the F1 generation and after.
I was wondering last night if fungal pathogens, like Diplocarpon rosae, can mutate like some viruses can and have the ability to infect plants that were resistant to the premutated pathogen. I’m thinking of Westerland. It’s been ‘disease free’ for me for years and this summer it almost completely defoliated as did its sport, Autumn Sunset. Is it possible that there is a mutation occuring or did the plant’s resistance just break down for some reason?
Thanks again David. Very interesting stuff!
Rob
David,
I found a thread on here, Two important papers for selecting disease resistant breeders, where you go into detail about horizontal and verticle reistance so that is where I’ll start. Thank you
Rob
Link: www.rosehybridizers.org/forum/message.php?topid=33201&rc=4&ui=2806036792
“I’m not familiar with HR’s architecture but saw that it’s described on HMF as rounded tidy habit. What don’t you like about the shrub architecture?”
Rounded, tidy habit? Thats marketing speak for “stubby and congested”! laughs I think it has ugly growth. Hard to point a finger at specifics, I just think it lacks grace.
lol I read here often about good/bad architecture but don’t have a clue as to what makes for great architecture. Thanks Paul.
I well remember the first Knock Out bushes I encountered. “Arthritic” was what came to mind. Stumpy, dumpy, “hard”, lacking grace, not pretty plants at all, but they did have foliage that had nothing on them other than calcium from the sprinklers. They had flowers, but even they were rather “insipid”. Definitely not “red” and too flat and dull to be a pink I’d choose to use. The color was unappealing, no scent and not really anything I wanted to touch, much less smell. They’d been used to line an entry walk here by their landscraper. Their horrid thorniness “impressed” me as I was supposed to make the place look attractive with them and too many white birch trees crammed into too small an area with far too much concrete. That was a challenge! NOTHING grows well in a foot thick mat of birch roots. Kim
“stubby and congested” - that cracks me up Paul!
I think I know what you mean. It really isn’t the epitome of grace! I hadn’t given it a lot of thought but I’ve been having to do a yearly decongestion on mine. When I’ve pruned I’ve tried to take out all but the thickest and best placed “trunks”.
So… have you or anyone else grown seedlings from crosses of ‘Home Run’ with something radically different in growth habit - maybe “rangy and loose” ;0) to see if maybe you could get that healthiness in a whole 'nother architecture.
My Rosa palustris x ‘Home Run’ seedlings so far are looking like they might end up being fairly rangy, but they’re only just starting to get any size to them.
This thread is wandering all over, so let me toss a couple strands. First- Paprika. I got a couple plants and left them in western PA. Bloomed sporadically all summer to Oct, got rather a lot of anthracnose which pretty well defoliated by now, but no B.S. Set OP seed, 1-2/hip on 5 hips I found ripe enough to collect (from July 1-30). FWIW, Carefree Beauty and New Dawn suffered equally as much from the anthracnose planted right next to the Paprika, in fact were the source of inoculum. Strawberry Crush didn’t get as much disease, but didn’t rebloom (as noted by David Z.)
Second the Knock Outs. Rainbow KO is worse stubbiness than the others in our climate and holds those dead petals about 3 weeks. HR under significant shade opens up some, and sets more hips. KO does best with regular heavy irrigation. Plants not watered and fertilized bloomed only 1 flush here, and it wasn’t a drought year. The ones with high maintenance and a fall pruning are what I noticed a couple weeks ago having a tremendous flush of deep maroon foliage. Same in spring. So they are great for marketing, mass production, professional landscapers. A bush seemingly totally sterile but looking good is White Out.