This is an excellent discussion with great thoughts being shared - thanks!
Breeding for disease resistance does seem to be a losing battle, but I think that we all would like cleaner roses - even if it is just for a time.
The problem of different races and tendency toward mutation will always be the challenge, even when trying to breed for good horizontal resistance. Unless a particularly clean seedling can be checked for specific resistance to the many available races of PM and BS, the best that we can do is guess that good resistance genes are present.
In my own case, we get hit much harder with PM than with BS, however, the last few years, I have been able to promote BS at least in the springtime. Otherwise, I would not even be able to evaluate for it. The downside of course, is that I probably only have one race of BS that I am testing for.
For PM, I have chosen to be very hard on the seedlings early in the evaluation process. Though I know that some seedlings gain some resistance as they mature, I have seen that those that are resistant even as small seedlings will have the best resistance outdoors (and tend to themselves produce cleaner seedlings). It is also true that I am tossing out lots of seedlings that would probably do “okay” outside. Since I really hate PM (it is very disfiguring and the absolute worse here on the first bloom cycle when the roses should be doing their best) and don’t spray, I want the surviving seedlings to have the best chance for resistance.
For BS, I have sort of taken a “shotgun” approach to breeding. Since I realistically cannot do a comprehensive evaluation for BS susceptibility, I have mixed in either ‘Baby Love’ or ‘Home Run’ into all of my breeding stock. My hope is that there will be at least some BS resistance among some of the seedlings that I am selecting for PM resistance.
I think that Pierre is right that all of these strategies will ultimately fail. But we all keep trying, and whatever success we have is part of the fun!
Jim Sproul
I think we need to take a very long view to judge resistance for as noted above it is an evolutionary process. Consider Dr. Huey, and Peace, two of the most widely grown roses in the U.S. In our town at least there are many bushes of Dr. Huey putting on a splendid show in the yards of rental properties (college town)that have never had a single dose of any fungicide applied. They always get some blackspot, more or less depending on the year. Yet they come back every season; some I have seen for 20 years in the same place. There is a climbing Peace bush along a road that I bicycle by every day that also gets its share of BS but comes back again and again. So the disease is not particularly virulent. Perhaps a survey of these cultivars nationwide would indicate the relative intensity of BS pressure (not the particular races, but the overall virulence). Do you see Dr. Huey and Peace surviving unsprayed in your location? I recall a magnificent climbing Peace in Philly back in the 60s that was never cared for at all but did fine.
As Pierre Rutan says, proximity may be part of it. I’ve seen Austrian copper looking splendid in bloom more or less abandoned in Colorado, but it was far from any other rose.
Resistance does not necessarily break down either.
An example would be Paul’s Scarlet. Does it get any disease anywhere to an extent that matters? My grandmother had Mrs R.M. Finch ( old polyantha/floribunda) in Pittsburgh, completely unsprayed and I don’t recall disease on it either. Likewise Dr. van Fleet/ New Dawn, grown in rural PA or KS has never shown any sign of disease. These roses have had 75-100 yr to get diseases and have not. Carefree Beauty has remained BS free here in KS, and in PA over 20 yr. And only a little PM in one or two seasons.
Various old moss roses, Therese Bugnet, Silver Moon, Shailer’s Provence, assorted rugosas, wild multiflora, common canina, Konigen von Danemark, Maiden’s Blush, Harison’s Yellow stay clean, at least where I’ve grown them. So there is some general or horizontal resistance out there to be incorporated.
But Larry,
Location is the key word. New Dawn is cleaner then others but will get more then 50% leaf loss here by mid summer. It will not weaken the plant, true, but still…
Carfree Beauty, Maiden’s Blush, Harison’s Yellow all will get decent amount of BS, especiall MB and HY can completely defoliarte. They are better then many others but not really resistant here. Old Mosses as well as Gallicas and Albas are a mixed bag. There are some very healthy and some that will 100% defoliate.
Konigin von Danemark for example is very healthy here.
Olga
Olga, I realize that there’s a huge variation with location. That’s why I posed the question. You don’t say what part of the world you are in. I only know western PA and central KS which is a very small area. Yes, I had read that HY defoliates which surprised me bcs it got hauled all the way to TX before fungicides were invented. So the question is whether we could make a general map based on some common cultivars and their disease resistance across the U.S. and northern Europe perhaps?
Are you sure it is BS on ND and not anthracnose. Mine gets black flecks with a red edge by autumn but leaves don’t come off.
Here Peace gets a lot of BS, but overall it manages in many areas with minimal maintenace, somehow surviving in neglected yards. Likewise Paul’s Scarlet and Dr. Huey.
This ability to survive and come back with flowers year after year is the essence of horizontal resistance, or perhaps tolerance would be better way to think of it. One big factor is sensitivity to ethylene induced defoliation. ND is very resistant, while Crimson Glory is very susceptible. So the same load of BS will defoliate CrGl easily, bcs BS induces ethylene production. My impression is that some yellow CV are even more sensitive. That result was published a long time ago in an obscure journal and I didn’t find it until after I had done the expt myself testing different levels of ethylene on different CV of rose ( abt 30 yr ago). Mildew doesn’t do the ethylene production trick so it just makes a mess.
In crops, many old cultivars get disease, such as rust on wheat, but not to an extent that it destroys the whole crop. Griffith Buck used the same breeding principle with his early selections. I’m not sure about all of them, but survival in a field in Iowa was the basis for CB and others.
If you ever saw late season mildew on phlox or zinnia you’d say on one should not bother to grow them. But they do what they are asked to do, producing a good show for a reasonable time before failing. And spider mites can destroy impatiens and several other kinds of flowering plant under some conditions. But most people are not demanding perfection, just good enough.
We should not forgive that generations of breeders tried to hybridize the ideal rose. They tried many many things. If there were something like a dominant gene for any desease resistance somewhere among roses species it would have been incorporated in actual HT long ago.
In a less than adequate climate or location there is no resistance. Except in isolation and unspraied as Larry points. Or in desertic no rain no dew climate where you can grow unspraied florist roses in a well irrigated airy and not too much sun exposed garden.
Apparently only wichuraiana and a few close to this species hybrids can be qualified of definitely desease resistant. Experience (mine as well…) shows its resistance is readily diluted and lost in a very few generations.
Rugosa when in a bad location is PM and/or rust laden as are the usually so clean laevigata or banksiae.
Horizontal resistance is neither unfailible nor strong if supposed not to be evercome. It is enough resistance in not too bad conditions. A fondamental ingredient of horizontal resistance is genetical diversity.
Here is something our predecessor breeders did wrong.
That is the problem.
As it is another question I will continue opening a new topic.
Austrian copper has an easy time in most of colorado. Most of this state is semi arid. Before irrigation this state was ounce known as the great american desert. I have never seen this plant in wetter areas like loveland, sterling or similar. It is always growing where it is more suitable for the climate. Like the dryer mountains or the dry praries. It makes an impressive specimen in these areas.
Pierre I do agree that we need to breed more genetic variation. It seems like we only add a dose here and their through the hystory of roses. If we have any hope at horizontal resistance a large dose from many source needs to be added then worked through.
Larry, I am in MD not that far away from you.
I do distinguish between BS, cercospora and anthracnose. ND is very succeptable to sercospora (not anthracnose) here in the fall. But in summer it gets plain old BS with fringed edges, yellow color, etc. The same for it sport Awakening. They still keep most of their leaves and doesn’t loose vigor but looks kind of bare. This is not an observation from just my garden. I know several people here in MD including couple of my coworkers and my sister who grow ND and also get BS on it.
HY gets BS not every year but most of the years and Dr Huey is always completely bald after the flush.
Olga