Species roses and blackspot

Title: Morphological characterization of the interaction between Diplocarpon rosae and various rose species

Authors: O. Blecherta (a) and T. Debener(b)

Authors affiliation: (a) Federal Centre for Breeding Research on Cultivated Plants, Institute for Ornamental Plant Breeding, Bornkampsweg 31, 22926 Ahrensburg: and (b) University of Hannover Faculty of Horticultural Sciences, Department of Applied Genetics, HerrenhJuser Str 2, D-30419 Hannover, Germany

Published in: Plant Pathology, volumn 54, pages 82-90, (2005).

Abstract: Blackspot, caused by Diplocarpon rosae, is the most severe and ubiquitous disease of garden roses, but information is lacking about genotype-specific forms of resistance and susceptibility of the host. Macro- and microscopic analyses of 34 rose genotypes with a defined monoconidial culture black spot inoculum identified susceptible and resistant rose genotypes and further genotype-specific subdivisions, indicating the presence of partial forms of resistance and different resistance mechanisms. In total, eight interaction types were characterized, five representing compatible (types 1-5) and three representing incompatible interactions (types 6-8). The incompatible interactions were characterized by the lack of any visible fungal structures beneath the cuticle (type 8), single-cell necroses (type 7) or necroses of larger cell clusters (type 6), the latter two types with penetration hyphae and haustoria in epidermal cells.

The following is part of Table 1 from the full paper (the last number in each row is the blackspot rating:

Rosa acicularis CIN 4

R. Arkansana CIN 5

R. Arvensis SYN 3

R. Blanda CIN 3

R. Canina CAN 4

R. Carolina CAR 4

R. Caudata CIN 6

R. Corymbifera CAN 4

R. Foetida PIM 2

R. Foliolosa CAR 3

R. Gallica GAL 6

R. Hugonis PIM 2

R. Jundzillii CAN 6

R. Longicuspis SYN 2

R. Majalis CIN 8

R. Monis CAN 1

R. Moyesii CIN 8

R. Multibracteata CIN 8

R multiflora SYN 7

R. Nitida CAR 8

R. Nutkana CIN 7

R. Obtusifolia CAN 4

R. Omeiensis PIM 8

R. cv. Pariser Charme HT 1

R. Pendulina CIN 5

R. Pisocarpa CIN 5

R. Roxburghii PLA 7

R. Rubiginosa CAN 4

R. Sweginzowii macrocarpa CIN 8

R. Tomentosa CAN 1

R. Villosa CAN 1

R. Virginiana CAR 7

R. Wichurana SYN 7

R. Woodsii CIN 7

All species except R. roxburghii (subgenus Plathyrhodon) belong to the subgenus Rosa. Sections within the subgenus Rosa: CIN, Cinnamomeae; SYN. Synstylae; CAN, Caninae; CAR, Carotinae; PIM, Pimpinellifoliae; HT, cultivar (hybrid tea).

The following is from the results section:


Interactions between 34 different rose genotypes inoculated with black spot conidia and examined macroscopically after 7 days’ either resulted in the formation of acervuli and were classified as compatible (18 rose genotypes), or resulted in no reproductive structures and were considered to be incompatible (16 genotypes) (Table 1). Based on additional information, such as occurrence of necrotic spots and the microscopic investigation of different hyphal structures, the two reaction types were further subdivided.

The compatible interactions were subdivided into a strongly susceptible group designated as interaction types 1 and 2, and a weakly susceptible group (interaction types 3, 4 and 5). Incompatible interactions were designated as interaction types 6, 7 and 8. The classification was based on three independent inoculation experiments in which no qualitative variation could be observed. Only minor differences in the amount of fungal structures developed over the observation period were observed."

“Compatible” means infected (1 and 2) greatest, (3, 4, and 5) lesser extent.

“Incompatible” means very little (6 or 7) or zero infection (8).

That is great Henry! Thank you for sharing.

Thanks Henry, that is very informative.

Unfortunately, as we all now know, the moment you introduce genes of a different species or modern hybrids, most, if not all of the natural species resistance goes away.

Paul, oh? I think what you say may occur if you select only for flower characteristics.

The Kordessi roses are examples where the disease resistance often is still there.

I have many species crosses, and I do not spray. I have very little disease in the crosses that have survived http://home.neo.rr.com/kuska/2004_and_2005_very%20good%20seedlings.htm .

Link: home.neo.rr.com/kuska/2004_and_2005_very%20good%20seedlings.htm

Title: Genetic analysis of resistance to blackspot ( Diplocarpon rosae) in tetraploid roses

Published in: Theor Appl Genet, volumn 96 : pages 228

I agree with Paul. With the exception of Rosa wichuraiana, any blackspot resistant species in a breeding program with modern roses will have no effect in developing blackspot resistant progeny. That is why I have always advocated keeping a breeding program at the species or near species level. I have always said that developing one good Rosa rugosa or Rosa gallica cultivar is better than developing 10 good Floribunda or Hybrid Tea cultivars. A good Rugosa or Gallica cultivar will last forever, but Floribunda and Hybrid Tea cultivars, because they lack disease resistance, are often around for a few years and then never seen again.

The value of using Rosa wichuriana in a breeding program is exemplified by Henry mentioning the disease resistance of Rosa kordesii cultivars. If one is developing a modern rose breeding program, this species or Rosa kordesii (including the L83 Rosa kordesii) should be used to greatly improve chances of developing disease resistant progeny. I think it is also worthwhile to use ‘New Dawn’ hybrids, which of course have Rosa wichuraiana in their pedigrees.

Quite interesting Henri.

I have two questions:

Were there any mention of R. rugosa?

And what are 91/100-5 ancestors and resistance origin?

91/100-5 in Debener et al., 1998 Plant Breeding 117:267-270 has it listed as “breeding line/polyantha”.

Before Debener took over this program diploid lines were raised for inheritance studies and were derrived from open pollinated 3x hybrids from crosses between R. multiflora based germplasm (2x) and modern roses (supposedly 4x). These diploid lines combined traits of R. multiflora type polyanthas and had some influence of modern roses as well. I haven’t found the exact pedigree of 91/100-5 listed anywhere.