What species roses are best for breeding out blackspot?

Technique Flower Initiation
, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,
21

Larry,
I don’t disagree in principle. But I’d still like to know whether the “new” BS afflicts the old HTs such as ‘La France’, ‘Lady Mary Fitzwilliam’, ‘Mme. Caroline Testiout’. Are the old Tea roses and Noisettes now susceptible to BS?

Another example from the grains is the Southern Corn Blight. In the early 1970s ('71?), there was a panic among American farmers when the Blight abruptly spread far north of its usual range. There was a fear that the Blight had mutated to a more virulent form that put the U.S. corn crop at risk. Fortunately, this was not the case.

Some years earlier, corn breeders located a male sterile line of corn. Popular inbreds were bred into this male sterile line, producing new lines that made it easier and more profitable to raise F1 “hybrids” because it was no longer necessary to hire people to pull out the tassels of the seed parents. No one understood at the time that corn with the “Texas Cytoplasm” were especially susceptible to blight.

Coincidentally, the Summer of the Blight was unusually hot and humid over much of the Corn Belt.

Thus, again, there was both an Internal and an External “cause” of the new epidemic that had nothing to do with any hypothetical changes in the blight itself.

Viruses also offer more puzzlements.

It was learned long ago that peach scions can be grafted onto plum stocks with no limit to species or cultivars. But it was puzzling that certain peach/peach grafts generally failed. The problem turned out to be a virus. Apparently, plums in general are not affected (or infected) by the virus. Peaches, on the other hand, are susceptible to infection, but some cultivars tolerate the virus without expressing adverse symptoms. Grafting a tolerant peach carrying the virus to an intolerant type leads to disease and death of the stock. Reversing the graft (intolerant on tolerant/infected) leads to death of the scion.

22

I believe a good part of the disease issue we now see with previously unaffected types is due to dramatically different climate conditions. What used to be clean started becoming unhealthy rather quickly as heat levels rose; water arrived during heat instead of during cool periods; ground water began running short due to reduced rainfall; light intensities greatly increased in a relatively short period and irrigation water became increasingly “saltier”, combined with the lack of soaking rains to flush the alkalinity through the soil and the salts being drawn to the surface through evaporation and saltier water being “dripped” into the garden. Of course, different parts of the country are dealing with different issues, but I believe similar correlations can be drawn to these from areas which have received too much rain/snow; too little heat; much reduced light, etc. All of these change the environments the fungi exist in and help lead to mutations, adaptations, and stress the plants, making them potentially more susceptible.

23

Rosa rugosa is one source of blackspot resistance. It is worth noting that both ‘Goldilocks’ and ‘Chic’ are descended from Pernetianas. So are ‘Crimson Glory’ and ‘Scarlet Knight’. The “unnamed seedlings” in the ancestry of ‘Radiance’ leave room for doubt.

Andhra Pradesh, Agricultural University
(APAU) was established on June 12, 1964 at Hyderabad.
Breeding for disease resistance (p. 93)
“Black spot is a major foliar disease of roses that causes severe losses to commercial and home gardens. The breeding lines ‘Spotless gold’ (Floribunda, F3 selection: Goldlocks x Rosa rugosa), ‘Spotless Yellow’ (Floribunda, F3 selection; Goldlocks x Rosa rugosa) and ‘Spotless Pink’ (Floribunda, F3 selection: Chic x Rosa rugosa) have been release for use a resistant parents in breeding programmes.”

Americn Rose Annual, 68: 96-97 (1983)
Rose Breeding — Blackspot
Pete Semeniuk
“In the rose breeding program, we are investigating ways and means by which the genes for blackspot resistance can be transferred to our garden roses. Progeny tests are the only feasible means of determining the genetic distribution of a pair of alleles from selfing or crossing resistant and susceptible roses. First generation (F1) seedlings between blackspot resistant breeding lines Spotless Pink, Spotless Gold, and Spotless Yellow crossed with susceptible Pink Radiance, Crimson Glory and Scarlet Knight were inoculated and evaluated to determine the genetic distribution of genes for resistance. The progeny from such crosses gave both resistant and susceptible types with the seedlings segregating into sharply defined groups of unequal numbers. Preliminary results indicate that it should be possible to incorporate blackspot resistance into our everblooming garden roses.”

Reading Eagle, Sunday, September 23, 1979, p. 53
Blackspot-Free Roses on Horizon
“Semeniuk estimates there may be as many as 50 to 100 strains of the blackspot fungus in the United States alone, but he chose seven strains that he had closely studied to test for resistance during his breeding program. The strains, which he maintained in the laboratory, had been cultured from infected leaves from Beltsville, Md.; University Park, Pa.; Ithaca, N.Y.; Tifton, Ga.; Tyler, Texas; Ames, Iowa; and Deleware, Ohio.”
http://news.google.com/newspapers?nid=1955&dat=19790923&id=o_QhAAAAIBAJ&sjid=76AFAAAAIBAJ&pg=5072,1229718

24

Too bad that black spot resistance seems to also contain a rather great susceptibility to rust. Most roses containing (not ALL, but the vast majority I have grown) Rugosa combined with anything have rusted BADLY here.

25

Karl, I remember when those papers of Semeniuk first came round. I didn’t have the funds to get those lines and they went extinct because no major breeders picked up on them. Bill Radler no doubt read the works, and those of Griffith Buck. He had the time to pursue it to its logical conclusion. Yes it is possible to select for BS resistance.

If I knew what rose is actually La France I might be able to answer your question. I have grown two purported La France for decades. Both get BS here. One which looks plausible as LF is sterile, so I doubt it is the real thing. It came from the Topeka rose garden as a snippet. The other was purchased from ROY&T. I think it is a later florist’s rose, because it does well in winter under low light in my GH.

I’ve never had the others you mention. My moss roses and Maidens’ Blush are BS free but once-blooming. All the HPs I’ve grown get BS, and are not really perpetual, until you get as new as Frau Karl Druschki and related. Radiance spots badly here, though it survives when not in a rose garden. Crimson Rambler, General Jaq, even the thing called Jacques Cartier get it though not always really bad.

Location is really important. Shockwave, growing along a highway has never shown BS, but all its OP seedlings are dreadful for me.

26

Shockwave may have dreadful OP seedlings (at least in your experience) but I have several offspring of it as the pollen parent that have been outstanding. They all have some degree of BS on occasion and when the weather really encourages it (right now, esp., with low water rationing requirements and a week of post hurricane warm humid air and overcast skies coming up from the gulf)) but several of them are really fast to shed the few BS affected leaves and quick to replace those with new growth. Many of Bayses Legacy seedlings (again pollen parent) also had terrible cases of BS, and like Kim says above, if they did not have BS, many were infected by what looked to me like terminal rust. The difference is that while I discarded all more than lightly infected seedlings in both cases, the Basyes Legacy offspring have not gone on to produce chronically BS’d F1’s, but if crossed with anything that I assume is a carrier of rust, they more than resemble an old Ford in a beach front. It seems that if you are very discriminate about weeding out the BS in BL seedlings, they have a degree of passing along BS resistance.

27

I grew La France, Cl. La France and Legacy of Antoine Esquivel, which was later identified as Striped La France and all three had severe BS and rust issues. I wouldn’t even consider any of them here. This climate would flat out kill them. I am begrudingly about to dump Grace Note. I love the rose, but I can’t keep foliage on it due to the rust. It is as severe here as Wandrin Wind was in the desert.

28

Thanks, Larry. That’s the sort of info I need. Since I haven’t been able (yet) to observe much BS in person.

It’s too bad that the Spotless roses didn’t get on. I have since learned that Semeniuk used a tetraploid Rugosa, induced by colchicine.

I found this today in the Canadian Rose Annual 1985:
“Bill Warriner: We are not using species directly. We are using the spotless thing from Dr. Peter Semeniuk of USDA. We are getting some seedlings from those, but we don’t know if they are any good or not. Most of our mildew and blackspot efforts at the moment are through selections of our hybrids. We have a number of hybrids that are very, very resistant to mildew, and we are starting to outline a very extensive blackspot screening program, that will be introduced into our breeding work.”
http://bulbnrose.x10.mx/Roses/breeding/CRAhybridizers1985.html

29

One factor that helped the Hybrid Teas become popular was their general resistance to rust. Then the Pernetianas came along, blending into the HTs, with their love of blackspot.

It is clear that there are numerous strains of BS, and that rose cultivars vary in their susceptibility to the different races. But I am still inclined to blame the Pernetianas for being incubators to the rapid development of the BS plague.

30

As you mentioned previously, environmental stress has a major influence on susceptibility to infections … in plants as well as in people. Cultural conditions are also a factor. In the Canadian Rose Annual (1985) there was a Hybridizers’ Panel that included this comment:
“Ernie Williams: I am not in a mildew-prone area, but I have observed other areas as well, and the incidence of mildew is in direct ratio to the amount of nitrogen that is available to that plant. If you pour nitrogen on a plant you are more likely to have mildew on it, than if you grow that plant under normal recommended cultural practices.”

Sometimes we push our plants too hard, especially with nitrogen. In the olden days when manure water was the preferred tonic, the problem with infection might not have been so severe.

31

Another point about Rugosa that seems to get misplaced. The Japanese race is shallow-rooted and thirsty. The Russian types are more tolerant of heat and drought. It would be useful to distinguish these races when we discuss disease resistance. I’m guessing that a Siberian rose won’t tolerate nearly as much dampness on its leaves as its Japanese cousin. As for rust …

32

And another note from the CRS Hybridizers’ Panel regarding rose breeders and disease:
http://bulbnrose.x10.mx/Roses/breeding/CRAhybridizers1985.html

Q. Why do hybridizers persist in introducing varieties which are very susceptible to mildew?

Sam McGredy: I am going to pass this one to Jack, because who would want to be without ‘Double Delight’?

Jack Christensen: At the risk of sounding brazen, and I don’t really mean to, but perhaps as long as people are willing to buy them, we are willing to market them. And we have varieties which otherwise have excellent qualities, like ‘Double Delight’.

Harm Saville: There is a business decision involved: if you have a good rose that has superb form, beautiful fragrance, excellent bush, good production and yet is somewhat susceptible to mildew, you say: they have fungicides that will take care of it. Maybe they will live with it.

Ralph Moore: One thing that is sometimes overlooked with regard to mildew and other disease resistance is that those may be regional problems. For example, a number of years ago, when Herb Swim was at Armstrong, we had a little, very bright red polyantha rose we wanted to put into the All-America trials. We didn’t have any mildew trouble with it at our place. When he got it down there, he had a lot of mildew on it. At the other end of the spectrum, Dr. Walter Lammerts was at my place, saw some hybrid teas, and wanted to know how we kept them free of mildew. We never had any problem with mildew but in southern California they did. Some places never see mildew on ‘Red Cascade’ and in other places you can’t grow it without getting it white with mildew. We don’t treat our seedlings, because we want to find out if anything is wrong with them. On the other hand, I do test varieties from other breeders and sometimes I can’t keep these free of mildew, because they have been selected under a different situation. If a variety mildews in your own garden, try something else.

Ernie Williams: I am not in a mildew-prone area, but I have observed other areas as well, and the incidence of mildew is in direct ratio to the amount of nitrogen that is available to that plant. If you pour nitrogen on a plant you are more likely to have mildew on it, than if you grow that plant under normal recommended cultural practices.

Bill Warriner: One problem that nobody else has mentioned is that there are many strains of blackspot and there are at least five strains of mildew. This is one reason for regional differences. We have a variety we think is pretty clean, but in another area they have a different strain and it gets hit pretty hard. An example of that: we used a new fungicide in our greenhouse, that was very highly recommended by one of our pathologists, and the whole greenhouse turned white. He forgot to tell me that there was one strain it was not effective on, and we must have had that one strain.

Sam McGredy: I would treat mildew and blackspot very differently because I think blackspot is very much more disfiguring and disasterous than mildew. I don’t spray my seedlings in the field at all against either. By the end of the year, all but 20 or 30% would have had some kind of mildew. All of them, every darn one, will have blackspot of some kind or another. Most of them, without spray, will be defoliated.

33

A note on GardenWeb answered another of my questions.

“After reading comments here for many years, I conclude that the areas with the heaviest blackspot pressure and/or most virulent races are the Mid-Atlantic from NY down to DC and here in Appalachia. Pressure is less in places with very hot summers and less frequent rain. One peculiarity is that in my area we have BS that can defoliate the tea and china roses that are mostly resistant in the deep South.”
http://forums2.gardenweb.com/discussions/1706983/the-black-spot-resistance-hoax

34

Larry,
I just remembered that I photographed ‘Spotless Gold’ at the SJ Heritage garden in 2005. I didn’t know anything about it at the time.

It is not listed in the current catalog of the garden.

35

Imagine how awful it would be here if I had fertilized? I was aware of the excess nitrogen, water stress and mildew connections and have attempted to mitigate as much of all of them as possible. Fun stuff.

36

Pierre,
I thought of you when I found this:

Bull. Mass. Agrl. Exp. Sta. 183: 1-46 pl. 1-3, f. 1-11.
Rose Canker and Its Control by Paul Johnson Anderson

Rose canker is produced by the parasitic growth of a fungus, > Cylindrocladium scoparium > Morg., within the tissues of the host (rose plant). Previous to 1917 this fungus had not been reported as a parasite. It was first found in Ohio by Morgan (1892) growing on an old pod of the honey locust (> Gleditsia triacanthus > L.). Seven years later it was reported again by Ellis and Everhart (1900) as growing on dead leaves of the papaw tree (> Asimina triloba > Dunal), and described as a new species, > Diplocladium cylindrosporum > E. and E.; but a study of the type materials of the two species by Massey showed them to be the same. As far as the literature shows, these are the only times that the organism had been observed up to 1916, and both times as a saprophyte.
Rose Canker and Its Control - Paul Johnson Anderson - Google Books