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Black spot in roses caused by the hemibiotrophic ascomycete Diplocarpon rosae (Wolf) (anamorph Marssonina rosae) is the most devastating disease of field grown roses and, therefore, affects both consumers of ornamental roses and commercial production. Chemical control of the disease is restricted by regulations, and consumers increasingly demand resistant varieties. As breeding black spot resistant rose varieties is complicated by its polyploid nature and the regular emergence of new pathogenic races of the pathogen, a deeper understanding of the biological characteristics of the interaction between the fungal parasite and its host is urgently needed. This review summarizes some investigations of the parasite and its interactions from early descriptions of the pathogen to recent molecular analyses of the fungus. [ABSTRACT FROM AUTHOR]

Black spot disease caused by the hemibiotrophic ascomycete Diplocarpon rosae is the most devastating disease of field-grown roses. Although resistance to black spot is an important trait for rose breeding, little information on the diversity of the pathogen is currently available. To date, a number of single-spore isolates have been characterized based on a set of test genotypes of the host. In this study, six polymorphic simple sequence repeat ( SSR) markers for D. rosae were developed and their potential application to single-spore isolates collected from a wide range of geographic locations within and outside Europe discussed. Populations of the fungus were then analysed in different German rose collections/populations. Gene diversity was highest in older rose collections managed without fungicide application, and lowest in the two- to three-year-old testing sites of German rose breeders. Additional analyses of a global collection of single samples and populations revealed no unique alleles from any of the locations, indicating that global trading of rose varieties has led to an admixture of the pathogen. [ABSTRACT FROM AUTHOR]

The effect of genotype factors, year and their interaction was assessed on six architectural variables of eight cultivars of rose bush. Plants were grown in pots in a greenhouse in the spring of 2011 and 2012, two highly contrasted years in terms of the quantity of cumulative radiation, with a relative deviation (for 2012 compared to 2011) ranging from −24.6% (April) to +13.7% (March). Their architecture was digitized at two observation scales, the plant and the axis. Highly significant genotype ( G) and year ( Y) effects were revealed for all of the variables measured, as well as a G × Y interaction. Concerning the year effect, it was significantly higher in 2012 and for all of the variables measured. The G × Y interaction was due to (i) different genotype groupings according to year, (ii) difference response amplitudes between years according to genotype. Broad-sense heritability was calculated for each of these variables. It was moderate to high, ranging from 48% for the length of long axes to 98% for the number of metamers on long axes. [ABSTRACT FROM AUTHOR]

Black spot of rose is distributed throughout the world and is the most serious disease of roses ( Rosa spp.) in the outdoor landscape. Resistance breeding has been frustrated by the occurrence of races of the causal pathogen Diplocarpon rosae. Races from Germany, North America and the UK have been characterized and maintained in a pathogenic state. However, these races were characterized using independent sets of host genotypes and are referenced using different nomenclatures. In the present study, a total of 15 D. rosae isolates from these locations, as well as Belgium and Italy, were inoculated to a common set of 15 rose cultivars in replicated, detached leaf trials. Baby LoveTM (cv. Scrivluv) was resistant to all isolates except for one originating from the UK. The rose cultivars Mrs Doreen Pike (Ausdor) and Hansa were resistant to all isolates except for one originating from Minnesota, USA. No rose genotype was universally susceptible. A total of 11 pathogenic races were differentiated based on their unique host ranges and were assigned an international race nomenclature. Nine cultivars are proposed as the first standard set of differential genotypes for characterization of D. rosae races. [ABSTRACT FROM AUTHOR]

A high-density genetic map with a number of anchor markers has been created to be used as a tool to dissect genetic variation in rose. Linkage maps for the diploid 94/1 population consisting of 88 individuals were constructed using a total of 520 molecular markers including AFLP, SSR, PK, RGA, RFLP, SCAR and morphological markers. Seven linkage groups, putatively corresponding to the seven haploid rose chromosomes, were identified for each parent, spanning 487 cM and 490 cM, respectively. The average length of 70 cM may cover more than 90% of the rose genome. An integrated map was constructed by incorporating the homologous parental linkage groups, resulting in seven linkage groups with a total length of 545 cM. The present linkage map is currently the most advanced map in rose with regard to marker density, genome coverage and with robust markers, giving good perspectives for QTL mapping and marker-assisted breeding in rose. The SSR markers, together with RFLP markers, provide good anchor points for future map alignment studies in rose and related species. Codominantly scored AFLP markers were helpful in the integration of the parental maps. [ABSTRACT FROM AUTHOR]

Blackspot, caused byDiplocarpon 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. [ABSTRACT FROM AUTHOR]

Differentiation into physiological races of Diplocarpon rosae, which causes blackspot on wild and cultivated roses, was investigated with single conidial isolates of the pathogen. Infection experiments with a simple excised leaf assay demonstrated differential interactions between single isolates and a set of 10 test rose genotypes. Differential reactions could be observed among rose varieties as well as between and within a wild rose species. Accordingly, five different physiological races can be identified among the 15 isolates tested. A breeding line and one genotype of the wild species Rosa wichuraiana were found to be resistant against all isolates tested. These data will be employed in further investigations on the genetics of blackspot resistance in roses and for resistance breeding programmes. [ABSTRACT FROM AUTHOR]

Abstract A diploid rose genotype previously found to be self incompatible in greenhouse pollination experiments was analyzed in order to investigate the capacity to self fertilize under field conditions. A subset of 36 plants from open pollinations were analyzed by means of AFLP markers. All plants were found to be the result of outcrossing events, thereby demonstrating the utility of these kinds of rose genotypes as effective pollen sinks for future gene flow analyses under field conditions. Furthermore, it was demonstrated that isolation distances of 250 m from large rose plantations are insufficient to prevent gene flow between populations. [ABSTRACT FROM AUTHOR]