Rosa Wichurana Research Articles

Temperature is an important driver for cold acclimation in garden roses

Low non-freezing temperatures and short days are two main environmental factors that can independently or collectively initiate cold acclimation in temperate perennials. Freezing temperatures are required for the full development of mid-winter cold hardiness. In the present study, six rose genotypes with different cold hardiness levels were selected to investigate cold acclimation under both long and short photoperiods to reveal the role of temperature and day length on cold acclimation of roses. A five-week short-day treatment at 20/18 °C did not induce cold acclimation in any of the genotypes. Cold hardiness levels (LT50 values) increased significantly at low non-freezing temperatures (2 °C) and freezing temperatures (-5 °C) irrespective of the photoperiod for all genotypes. The more cold-hardy ‘Dagmar Hastrup’ and ‘John Cabot’ responded strongly, achieving lower LT50 values under low non-freezing temperatures. Low non-freezing temperatures/freezing temperatures but not short days promoted the degradation of starch and the accumulation in sucrose, hexoses, and raffinose. Short days alone induced RhDHN5 in ‘Yesterday’, ‘Abraham Darby’, and Rosa wichurana. However, the expression of RhDHN5 was up-regulated significantly by low non-freezing temperatures in all genotypes. The up-regulation of RhBAM3 by lowering the temperature (low non-freezing temperatures and/or freezing temperatures) is genotype-independent. Freezing temperatures had a prominent role in accelerating the expression of RhGolS2 in all genotypes. The up-regulation of RhRS2 and RhRS6 is mainly induced by low non-freezing temperatures and freezing temperatures, respectively, but transcript levels for both were less pronounced than those for RhGolS2. Stem dehydration during cold acclimation was only found for ‘Chandos Beauty’ under long days and R. wichurana under short day length. R. wichurana was insufficiently acclimated to withstand freezing temperatures under short day length. This study clearly shows that the main factors triggering cold acclimation in roses in 5 rose genotypes are low non-freezing temperatures or freezing temperatures, but a synergistic effect of short photoperiod and low non-freezing temperatures was found for R. wichurana.

Dehydrins and Soluble Sugars Involved in Cold Acclimation of Rosa wichurana and Rose Cultivar ‘Yesterday’

Rose is the most economically important ornamental plant. However, cold stress seriously affects the survival and regrowth of garden roses in northern regions. Cold acclimation was studied using two genotypes (Rosa wichurana and R. hybrida ‘Yesterday’) selected from a rose breeding program. During the winter season (November to April), the cold hardiness of stems, soluble sugar content, and expression of dehydrins and the related key genes in the soluble sugar metabolism were analyzed. ‘Yesterday’ is more cold-hardy and acclimated faster, reaching its maximum cold hardiness in December. R. wichurana is relatively less cold-hardy, only reaching its maximum cold hardiness in January after prolonged exposure to freezing temperatures. Dehydrin transcripts accumulated significantly during November–January in both genotypes. Soluble sugars are highly involved in cold acclimation, with sucrose and oligosaccharides significantly correlated with cold hardiness. Sucrose occupied the highest proportion of total soluble sugars in both genotypes. During November–January, downregulation of RhSUS was found in both genotypes, while upregulation of RhSPS was observed in ‘Yesterday’ and upregulation of RhINV2 was found in R. wichurana. Oligosaccharides accumulated from November to February and decreased to a significantly low level in April. RhRS6 had a significant upregulation in December in R. wichurana. This study provides insight into the cold acclimation mechanism of roses by combining transcription patterns with metabolite quantification.

Characterization of black spot resistance in diploid roses with QTL detection, meta-analysis and candidate-gene identification.

Two environmentally stable QTLs linked to black spot disease resistance in the Rosa wichurana genetic background were detected, in different connected populations, on linkage groups 3 and 5. Co-localization between R-genes and defense response genes was revealed via meta-analysis. The widespread rose black spot disease (BSD) caused by the hemibiotrophic fungus Diplocarpon rosae Wolf. is efficiently controlled with fungicides. However, in the actual context of reducing agrochemical use, the demand for rose bushes with higher levels of resistance has increased. Qualitative resistance conferred by major genes (Rdr genes) has been widely studied but quantitative resistance to BSD requires further investigation. In this study, segregating populations connected through the BSD resistant Rosa wichurana male parent were phenotyped for disease resistance over several years and locations. A pseudo-testcross approach was used, resulting in six parental maps across three populations. A total of 45 individual QTLs with significant effect on BSD resistance were mapped on the male maps (on linkage groups (LG) B3, B4, B5 and B6), and 12 on the female maps (on LG A1, A2, A3, A4 and A5). Two major regions linked to BSD resistance were identified on LG B3 and B5 of the male maps and were integrated into a consensus map built from all three of the male maps. A meta-analysis was used to narrow down the confidence intervals of individual QTLs from three populations by generating meta-QTLs. Two 'hot spots' or meta-QTLs were found per LG, enabling reduction of the confidence interval to 10.42cM for B3 and 11.47cM for B5. An expert annotation of NBS-LRR encoding genes of the genome assembly of Hibrand et al. was performed and used to explore potential co-localization with R-genes. Co-localization with defense response genes was also investigated.

Improvement of in vitro donor plant competence to increase de novo shoot organogenesis in rose genotypes

A procedure was developed for in vitro propagation of Rosa genotypes along with an efficient de novo shoot organogenesis (DNSO) method. We tested, on one genotype (hybrid of Rosa wichurana), the effects of MS basal medium complemented with two growth regulators to achieve either shoot elongation or shoot multiplication of plants. These media were complemented with carbohydrate concentrations from different sources. Then, the impacts of various carbohydrates (fructose, glucose, maltose, sorbitol, sucrose) on the growth and development of several rose genotypes during donor plant subculturing were studied on SMM. The results showed high variability in growth and development between genotypes. Contrary to other members of the Rosaceae family, no correlation was found between the shoot size and number when the amount of sorbitol was increased.Murashige and Skoog medium supplemented with 3.0 mg L−1 BAP and containing fructose or glucose at 30 g L−1 was chosen to induce leaf explants for the DNSO experiments. MS basal medium complemented with TDZ/IBA at three ratios and the same range of carbohydrate sources were tested for DNSO. Significant genotypic variations with regard to the percentage of regeneration was demonstrated with six genotypes. For two genotypes, a hybrid of Rosa wichurana and Rosa ‘White Pet’, we defined the conditions required to obtain 100% DNSO. For Rosa chinensis ‘Old blush’ and the rootstock genotype Rosa ‘Natal Briar’, we obtained 74 and 87.5% DNSO and only 56.67% and 37.5% for Rosa GUY SAVOY® (‘Delstrimen’) and Rosa ‘Félicité et Perpétue’ respectively. This adventitious shoot regeneration method may be used for large-scale shoot propagation and genetic engineering studies in Rosa.

Development of tools to study rose resistance to black spot

Black spot (caused by the fungal pathogen Diplocarpon rosae) is the most severe disease of roses in the outdoor landscape. Most cultivars are susceptible to this disease and its control requires repeated fungicide treatments. New rules on pesticide use encourage breeders to develop roses with a high resistance level to black spot. Growing genetically resistant rose cultivars is an alternative to chemical control of the disease. Resistance durability depends on the kind of resistance, the plant genetic background, the spatial and temporal deployment of resistances, the integration of resistances in cultural systems, and the dynamic of pathogen adaptation. To date, both dominant resistance genes and partial resistance loci have been described particularly in the genetic background of Rosa multiflora. In this study, a genotype closely related to the wild rose Rosa wichurana was examined to identify new resistance genes. Two progenies, connected by the resistant male parent, were scored for black spot resistance after natural infections in field over three and two years in three and one French locations for HW (Rosa hybrida ‘H190’ × hybrid of Rosa wichurana) and OW (Rosa chinensis ‘Old Blush’ × hybrid of Rosa wichurana) progenies, respectively. Genetic maps based on microsatellite and SNP markers were developed for HW and OW progenies, respectively. One common quantitative trait locus (QTL) was localized on linkage group 3 (LG3) of the male maps; it was revealed in the two progenies for several years and in different locations. Another QTL was identified but only in the HW progeny: it was mapped on LG5. The effectiveness of these QTLs should be confirmed against a wide range of pathogen isolates. To provide tools to study the genetic diversity of D. rosae, we sequenced two strains using Illumina paired-end sequencing technology and developed polymorphic microsatellite markers. The genome size of the two strains was estimated to 31 and 34 Mb. A set of 31 polymorphic markers was obtained. 70 monoconidial strains of D. rosae isolated from leaves of Rosa spp. with black spot symptoms were obtained from various locations in Europe and Asia. The analysis of this Eurasian pathogen collection revealed a strong genetic differentiation between pathogen populations collected from wild roses and those collected from gardens. To screen the resistance level of rose genotypes against pathogen diversity, we inoculated rooted cuttings with monoconidial strains of the pathogen under greenhouse conditions. Disease symptoms were scored 10 and 28 days post inoculation (dpi). This pathological test showed a range of resistance levels in rose against the diverse pathogen isolates collected in France and identified genotypes interesting for breeding.

Biosynthesis of 2-Phenylethanol in Rose Petals Is Linked to the Expression of One Allele of RhPAAS.

Floral scent is one of the most important characters in horticultural plants. Roses (Rosa spp.) have been cultivated for their scent since antiquity. However, probably by selecting for cultivars with long vase life, breeders have lost the fragrant character in many modern roses, especially the ones bred for the cut flower market. The genetic inheritance of scent characters has remained elusive so far. In-depth knowledge of this quantitative trait is thus very much needed to breed more fragrant commercial cultivars. Furthermore, rose hybrids harbor a composite genomic structure, which complexifies quantitative trait studies. To understand rose scent inheritance, we characterized a segregating population from two diploid cultivars, Rosa × hybrida cv H190 and Rosa wichurana, which have contrasting scent profiles. Several quantitative trait loci for the major volatile compounds in this progeny were identified. One among these loci contributing to the production of 2-phenylethanol, responsible for the characteristic odor of rose, was found to be colocalized with a candidate gene belonging to the 2-phenylethanol biosynthesis pathway: the PHENYLACETALDEHYDE SYNTHASE gene RhPAAS An in-depth allele-specific expression analysis in the progeny demonstrated that only one allele was highly expressed and was responsible for the production of 2-phenylethanol. Unexpectedly, its expression was found to start early during flower development, before the production of the volatile 2-phenylethanol, leading to the accumulation of glycosylated compounds in petals.

Cytogenetic approaches enhance advanced breeding in woody ornamental species

Molecular cytogenetic techniques are valuable tools to study chromosome structure and genome constitution and to perform gene mapping and visualization of chromosomal recombination. In woody ornamental species, which are often characterized by small genomes, small-sized chromosomes and low mitotic index in the tiny-to-handle roots, cytogenetic studies are hardly exploited. We developed the “SteamDrop” protocol, which enabled us to prepare high quality chromosome slides for several woody genera e.g. Buxus, Hydrangea, Buddleja, Hibiscus and Rosa. Study of chromosome number and chromosome morphology, together with knowledge of genetic relationships between species, allowed us to create more straightforward breeding programs for these genera. We also successfully implemented genomic in situ hybridisation (GISH) in different woody ornamental species to prove the hybrid nature of offspring from interspecific crosses within Buddleja and Hibiscus. In addition, knowledge of the physical position of specific genes on chromosomes might promote more efficient breeding and selection. We optimised FISH and Tyramide-FISH on mitotic and pachytene chromosomes of roses. Several single-copy genes (1.1-3 kb) involved in abiotic and biotic stress resistance mechanisms were physically mapped on Rosa wichurana Crep. chromosomes 1, 4 and 7 and genetically mapped on the genetic linkage groups. By this, an anchoring of genetic and physical maps was achieved. In the future, these results will facilitate to pyramid stress related genes in specific genotypes.

Towards a FISH-based karyotype of Rosa L. (Rosaceae)

The genus Rosa Linnaeus, 1753 has important economic value in ornamental sector and many breeding activities are going on supported by molecular studies. However, the cytogenetic studies of rose species are scarce and mainly focused on chromosome counting and chromosome morphology-based karyotyping. Due to the small size of the chromosomes and a high frequency of polyploidy in the genus, karyotyping is very challenging for rose species and requires FISH-based cytogenetic markers to be applied. Therefore, in this work the aim is to establish a FISH-based karyotype for Rosa wichurana (Crépin, 1888), a rose species with several benefits for advanced molecular cytogenetic studies of genus Rosa (Kirov et al. 2015a). It is shown that FISH signals from 5S, 45S and an Arabidopsis-type telomeric repeat are distributed on five (1, 2, 4, 5 and 7) of seven chromosome pairs. In addition, it is demonstrated that the interstitial telomeric repeat sequences (ITR) are located in the centromeric regions of four chromosome pairs. Using low hybridization stringency for ITR visualization, we showed that the number of ITR signals increases four times (1–4 signals). This study is the first to propose a FISH-based Rosa wichurana karyotype for the reliable identification of chromosomes. The possible origin of Rosa wichurana ITR loci is discussed.

Genetic analysis of the flowering date and number of petals in rose

Rose is the ornamental species with the highest financial impact. Floral traits such as the number of petals and the date of flowering are major characteristics of ornamental plants. Our objective is to study the genetic determinism of floral traits: date of flowering and number of petals, which are a major issue for rose breeders. The study was conducted on two interspecific populations interconnected by the male parent: H190 x hybrid of Rosa wichurana (referred to as HW) and “The Fairy” x hybrid of Rosa wichurana (referred to as FW). The number of petals and the date of flowering were scored over 2 and 8 years, respectively. A new HW genetic map covering 468 cM and the already available genetic map of the FW population (Kawamura et al. TAG Theor Appl Genet 122:661–675, 2011) were used for the genetic determinism studies. In each population, half of the hybrids exhibited single flowers (less than 10 petals), whereas the other half revealed double flowers. The number of petals is controlled by the NP gene located on LG3. Additionally, we detected two new major quantitative trait loci (QTLs) on LG2 and LG5, close to RoAP1b and RoRAG, respectively, two genes involved in the control of floral identity. For the date of flowering, three QTLs with a major effect and high stability between years were found on linkage groups 3, 4, and 6, indicating a high stability of QTLs to the changing environment. Candidate genes underlying these QTLs were investigated and key genes were identified. These major QTLs were linked to candidate genes, i.e., the identified QTL on LG4 was linked to RoFT, the one on LG3 to genes involved in gibberellin pathways, and the one on LG6 to RoFD. These QTLs, which are very stable over time, are good candidates to develop markers applicable in marker-assisted selection (MAS).

High resolution physical mapping of single gene fragments on pachytene chromosome 4 and 7 of Rosa.

BackgroundRosaceae is a family containing many economically important fruit and ornamental species. Although fluorescence in situ hybridization (FISH)-based physical mapping of plant genomes is a valuable tool for map-based cloning, comparative genomics and evolutionary studies, no studies using high resolution physical mapping have been performed in this family. Previously we proved that physical mapping of single-copy genes as small as 1.1 kb is possible on mitotic metaphase chromosomes of Rosa wichurana using Tyramide-FISH. In this study we aimed to further improve the physical map of Rosa wichurana by applying high resolution FISH to pachytene chromosomes.ResultsUsing high resolution Tyramide-FISH and multicolor Tyramide-FISH, 7 genes (1.7–3 kb) were successfully mapped on pachytene chromosomes 4 and 7 of Rosa wichurana. Additionally, by using multicolor Tyramide-FISH three closely located genes were simultaneously visualized on chromosome 7. A detailed map of heterochromatine/euchromatine patterns of chromosome 4 and 7 was developed with indication of the physical position of these 7 genes. Comparison of the gene order between Rosa wichurana and Fragaria vesca revealed a poor collinearity for chromosome 7, but a perfect collinearity for chromosome 4.ConclusionsHigh resolution physical mapping of short probes on pachytene chromosomes of Rosa wichurana was successfully performed for the first time. Application of Tyramide-FISH on pachytene chromosomes allowed the mapping resolution to be increased up to 20 times compared to mitotic metaphase chromosomes. High resolution Tyramide-FISH and multicolor Tyramide-FISH might become useful tools for further physical mapping of single-copy genes and for the integration of physical and genetic maps of Rosa wichurana and other members of the Rosaceae.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0233-9) contains supplementary material, which is available to authorized users.

Effect of high temperature on the production of 2n pollen grains in diploid roses and obtaining tetraploids via unilateral polyploidization

AbstractTo integrate the gene pool of a wild species (primarily diploid) into a cultivated pool (primarily tetraploid), a crossing between a dihaploid cultivated rose and a hybrid of Rosa wichurana allowed to obtain interspecific diploid hybrids that produced 2n pollen grains. A return to a tetraploid level sought by breeders can then be considered using sexual polyploidization, obtained by crossing a tetraploid cultivated rose with these hybrids. Application of a high‐temperature regime led to a small but significant increase in the percentage of 2n pollen grains in these hybrids of up to 4.6%. This result was obtained by applying high temperatures close to 32°C during the day to plants cultivated in a glasshouse during recurrent cycles of bloom. Crosses were made between an unreleased tetraploid hybrid tea rose, as a female, and the diploid hybrid that produces the most 2n pollen grains. Tetraploid (42.1%) and triploid (57.9%) offspring were obtained. The use of these 2n pollen grains of the first division restitution type should facilitate the introgression of complex traits of interest.

Inheritance of garden rose architecture and its association with flowering behaviour

Understanding the genetic basis of plant architecture is limited for woody plants due to the challenges of assessing the inheritance of their complex architecture. We aimed to evaluate the genetic variability of plant form and stature in a garden rose population, analyse the inheritance of plant architecture and its linkage with flowering behaviour and identify the quantitative trait loci (QTLs) controlling garden rose architecture. A total of 98 F 1 hybrids were derived from the cross between two diploid roses, The Fairy (TF) and Rosa × wichurana (RW) that differed in stature and flowering behaviour. The TF exhibits continuous flowering (CF) and has erect stature. The RW is once flowering (OF) and prostrate in stature. Three clones per genotype were multiplied, and a total of 300 plants were cultivated in a field. Flowering behaviour, plant form, plant height, stem diameter and internode length were scored during each of 2 years. All architectural traits had significant genetic variances (29–61 % of their respective phenotypic variances), and their broad-sense heritability estimates were 0.76–0.92. The majority of CF progeny was erect, whereas the OF progeny was prostrate, suggesting a linkage between plant form and flowering behaviour. The QTL analysis identified eight major QTLs controlling architectural traits. Several candidate genes involved in gibberellin biosynthesis and auxin signalling were identified in the vicinity of the QTLs. High heritability estimates obtained for garden rose architecture indicated that architectural characteristics are feasible targets of rose breeding. Linkage of plant form and flowering behaviour, however, prevents independent selection of these traits. The candidate genes identified can be good targets for future physiological studies.

Новий структурний клас 5S рДНКRosa wichuranaCrep.

Новий структурний клас 5S рДНК<i>Rosa wichurana</i>Crep.

Anchoring Linkage Groups of the Rosa Genetic Map to Physical Chromosomes with Tyramide-FISH and EST-SNP Markers

In order to anchor Rosa linkage groups to physical chromosomes, a combination of the Tyramide-FISH technology and the modern molecular marker system based on High Resolution Melting (HRM) is an efficient approach. Although, Tyramide-FISH is a very promising technique for the visualization of short DNA probes, it is very challenging for plant species with small chromosomes such as Rosa. In this study, we successfully applied the Tyramide-FISH technique for Rosa and compared different detection systems. An indirect detection system exploiting biotinylated tyramides was shown to be the most suitable technique for reliable signal detection. Three gene fragments with a size of 1100 pb–1700 bp (Phenylalanine Ammonia Lyase, Pyrroline-5-Carboxylate Synthase and Orcinol O-Methyl Transferase) have been physically mapped on chromosomes 7, 4 and 1, respectively, of Rosa wichurana. The signal frequency was between 25% and 40%. HRM markers of these 3 gene fragments were used to include the gene fragments on the existing genetic linkage map of Rosa wichurana. As a result, three linkage groups could be anchored to their physical chromosomes. The information was used to check for synteny between the Rosa chromosomes and Fragaria.

Roses Exhibit Pathotype‐specific Resistance Responses to Powdery Mildew

AbstractDisease resistance is highly desired in roses. Especially in garden rose breeding, efforts are being made to select for plants with raised levels of resistance towards powdery mildew. Despite the description of different pathotypes of powdery mildew and the development of pathotype‐specific QTLs, pathotype‐specific virulence and resistance mechanisms are not well known. To understand resistance in roses, different evaluation methods were used: disease scoring on inoculated detached leaves, evaluation of conidia development and plant responses by cell reactions. In this study, two rose genotypes, Rosa wichurana and Rosa ‘Yesterday’, were found to react differently towards two powdery mildew pathotypes (R‐E and R‐P). Although susceptible to R‐P, ‘Yesterday’ showed immunity to R‐E by arresting fungal development after conidium germination. Rosa wichurana showed partial resistance to pathotype R‐P and was even more resistant to pathotype R‐E by means of increasing amounts of cell reactions. Hybridization of ‘Yesterday’ × R. wichurana resulted in a diploid F1 population (90 genotypes). This population was screened for resistance mechanism–specific segregation to both fungal pathotypes. The results of both pathotypes exhibited a wide variation in resistance among the F1 genotypes. Our results showed that resistance reactions to powdery mildew in roses do not only result in different resistance mechanisms depending on the rose genotype but were also pathotype dependent.

Construction of a genetic linkage map with SSR, AFLP and morphological markers to locate QTLs controlling pathotype-specific powdery mildew resistance in diploid roses

Disease resistance is a sought-after trait in plant breeding programmes. One strategy to make resistance more durable is to increase the number of resistance genes, thereby increasing the number of pathotypes withstood. One of the most important diseases on roses is powdery mildew (PM) (Podosphaera pannosa). Recent studies show that pathotypes of PM and different types of resistances in roses exist. The results of this study aim to contribute to PM resistance in roses by the development of pathotype-specific markers on a genetic map. A diploid rose population (90 genotypes) derived from a cross between Rosa wichurana and Rosa ‘Yesterday’ was used to construct a genetic linkage map encompassing 20 AFLP primer combinations, 43 SSR, and 2 morphological markers. By applying the F1 pseudo test cross population strategy, two parental linkage maps were constructed (parent ‘Yesterday’ 536 cM; parent R. wichurana 526 cM). Both parental maps consisted of seven linkage groups with an average length of 70 cM (Kosambi) corresponding to the seven haploid rose chromosomes. These new maps were used to identify QTLs controlling disease resistance. The offspring population was screened for resistance to two PM pathotypes, R–E and R–P. QTLs for controlling pathotype-specific disease resistance were mapped by applying Kruskal–Wallis rank-sum tests and simple interval mapping. With two pathotypes analysed, nine QTL loci were detected on linkage groups 2, 3, 5 and 6, explaining 15–73% of the phenotypic variance for pathotype-specific disease response. The genetic maps developed here will be useful for future rose breeding, pathotype-specific resistance research and development of a consensus map for roses.

PATHOTYPE-SPECIFIC POWDERY MILDEW RESISTANCE IN ROSES

Differences in resistance to two powdery mildew isolates (R-P and R-E) were evaluated on two rose genotypes, Rosa wichurana and 'Yesterday'. Pathotype-specific resistance reactions to the developing fungus were observed by microscopy. Both rose genotypes expressed a comparable reaction, i.e., cell reactions to mycelium development of R-P. On 'Yesterday', pathotype R-E stopped growing after germination, whereas R. wichurana showed cell reactions upon inoculation with R-E. Crosses between the genotypes 'Yesterday' and R. wichurana resulted in some offspring with transgressive segregation for powdery mildew resistance. Most of the F 1 hybrids showed partial resistance by cell reactions, while others segregated for the arrested development of the germ tube of R-E as seen in 'Yesterday'. These reactions suggest that pathotype-specific resistance, based on different resistance mechanisms, can be used for resistance pyramiding in rose breeding practice.

FIELD ASSESSMENT OF BLACK SPOT RESISTANCE IN ROSES IN A HOT HUMID CLIMATE

A replicated rose evaluation trial was planted in the spring of 2006 at the Texas A&M University Horticulture Farm in College Station, Texas (USA). This trial was systematically evaluated for black spot resistance over 3 years. The roses evaluated were composed of a wide range of classes including hybrid teas, polyanthas, shrubs, chinas, teas, and ground covers as well as various experimental breeding lines. Among the roses evaluated, there were those that maintained excellent health and good landscape quality such as 'Belinda's Dream' and 'Knockout.' Others, such as 'New Zealand' and 'Ingrid Bergman' were so susceptible to black spot that they died within 1 or 2 years. Furthermore, some varieties, such as 'Charles Darwin,' showed considerable blackspot infection, but were able to withstand it and continue to bloom. An examination of the parentage of the roses with good to excellent resistance indicated that their resistance came from a wide range of rose species including Rosa wichurana, R. rugosa, R. multiflora, R. carolina, R. virginiana, R. laxa, and R. spinossisima.

New resources for studying the rose flowering process

Knowledge of the flowering process - an important trait in ornamental plants such as roses - is necessary for efficient control of flowering. This study was carried out to develop and characterize new resources to gain further insight into floral control in rose. We studied floral initiation in a nonrecurrent blooming rose (hybrid of Rosa wichurana) and a recurrent blooming rose (Rosa hybrida Black Baccara. In Black Baccara, floral initiation took place rapidly after bud burst, whereas in the greenhouse R. wichurana remained vegetative. During floral initiation, the apex enlarged and domed quickly and concomitantly. This is the first description of this transition between the vegetative and floral bud stages in rose. From these vegetative and pre-floral tissues, two cDNA libraries were constructed and 5,000 ESTs sequenced. By collecting our ESTs and those available in public databases, we developed a comprehensive database representing approximately 5,000 unique sequences after clustering. By screening this database for candidate genes involved in the flowering process, we identified 13 genes potentially involved in gibberellic acid signalling, photoperiod pathways, and floral development. Based on expression data, we put forward different hypotheses on the control of flowering in rose (photoperiod control and involvement of gibberellins) relative to what is already known in Arabidopsis.

Microsatellite Marker Development in Rose and its Application in Tetraploid Mapping

Microsatellite or simple sequence repeat (SSR) markers were developed from Rosa wichurana Crépin to combine two previously constructed tetraploid rose (Rosa hybrida L.) genetic maps. To isolate SSR-containing sequences from rose a small-insert genomic library was constructed from diploid Rosa wichurana and screened with several SSR probes. Specific primers were designed for 43 unique SSR regions, of which 30 primer pairs gave rise to clear PCR products. Seventeen SSR primer pairs (57%) produced polymorphism in the tetraploid rose 90-69 mapping family. These markers were incorporated into existing maps of the parents 86-7 and 82-1134, which were constructed primarily with AFLP markers. The current map of the male parent, amphidiploid 86-7, consists of 286 markers assigned to 14 linkage groups and covering 770 cm. The map of the female tetraploid parent, 82-1134, consists of 256 markers assigned to 20 linkage groups and covering 920 cm. Nineteen rose SSR loci were mapped on the 86-7 map and 11 on the 82-1134 map. Several homeologous linkage groups within maps were identified based on SSR markers. In addition, some of the SSR markers provided anchoring points between the two parental maps. SSR markers were also useful for joining small linkage groups. Based on shared SSR markers, consensus orders for four rose linkage groups between parental maps were generated. Microsatellite markers developed in this study will provide valuable tools for many aspects of rose research including future consolidation of diploid and tetraploid rose genetic linkage maps, genetic, phylogenetic and population analyses, cultivar identification, and marker-assisted selection.