Fabrice Foucher

Black spot disease, caused by the fungus Diplocarpon rosae , is a major threat to garden roses, leading to significant defoliation and reduced plant vigour. Several isolates originating from the United States and Europe have been characterised as races with different pathogenicity using a differential set of 10 plant hosts. However, no isolates from France have been tested on this set, and the races present in this country remain unknown. This study investigated the pathogenicity of seven monoconidial D. rosae strains isolated in France on 17 rose genotypes, including the previously published differential host set. Our results revealed that four of these strains have the virulence pattern of race 8, the prevalent race in North America. However, the commercial rose cultivars: Surrey (cultivar: KORlanum), High Voltage (cultivar: BAIage) and Ramblin’ Red (cultivar: RADramblin) showed intermediate reactions to three strains, suggesting additional infection mechanisms. The four resistance genes available in the host set ( Rdr3 , Rdr4 , Rdr5 , Rdr6 ) remained effective against all tested strains. This study provides the first information on the races of D. rosae present in France and will be useful in breeding programmes for black spot‐resistant roses.

BioStudies – one package for all the data supporting a study

Roses hold significant symbolic value in Western cultural heritage, often serving as a symbol of love and romance. Despite their ancient cultivation, the appreciation for the phenotypic diversity of roses emerged relatively recently, notably during the 19th century. This period is characterized by a remarkable expansion in the number of varieties, from around 100 to over 8,000, representing a golden age for roses. To trace the history of rose breeding in Europe and unveil genetic changes during this period, we gathered phenotypic and genetic data from 204 accessions. These included botanical roses and varieties cultivated between 1800 and 1910. Whole-genome sequences from 32 accessions were also included. Our analysis revealed a temporal shift in the genetic makeup, transitioning from a historical European to a near-Asian genetic background within a few generations. This shift was accompanied by a notable reduction in genetic diversity, attributed to the backcrossing with the less diverse Asian genepool, plus some genomic signatures of selection. We have generated the largest GWAS catalog for rose to date, offering a valuable resource for future breeding initiatives. We emphasize the critical importance of preserving ancient rose collections to safeguard diversity and ensure a sustainable breeding for the long-term.

The Biological Resource Center (BRC) ’Pome fruits and roses’ is hosted by INRAE near Angers, France. It includes collections of apple, pear, quince and rose. The apple, pear and quince collections are preserved in orchards on site and as DNA samples. Research accessions of the Rosa genus are preserved both in the field and as DNA samples, whereas traditional accessions are primarily maintained as DNA samples. Traditional roses accessions are preserved in the field by different private and public rose gardens in France. The main BRC’s mission is to preserve these biological resources while improving and optimizing its collections. It also aims to gather and enrich data associated with the conserved genetic accessions, in particular by recording and centralizing phenotypic and genetic characterization data. This ensures the provision of suitable biological material and data for research and selection purposes. Additionally, these data support genetic resources management, especially in the framework of the apple and pear French networks coordinated by BRC. Thanks to these data, pedigrees could be unravelled and association studies implemented.

ISHS XXXI International Horticultural Congress (IHC2022): International Symposium on Innovations in Ornamentals: from Breeding to Market Evolution of scent genes in roses

Nudix hydrolases are conserved enzymes ubiquitously present in all kingdoms of life. Recent research revealed that several Nudix hydrolases are involved in terpenoid metabolism in plants. In modern roses, RhNUDX1 is responsible for formation of geraniol, a major compound of rose scent. Nevertheless, this compound is produced by monoterpene synthases in many geraniol-producing plants. As a consequence, this raised the question about the origin of RhNUDX1 function and the NUDX1 gene evolution in Rosaceae, in wild roses or/and during the domestication process. Here, we showed that three distinct clades of NUDX1 emerged in the Rosoidae subfamily (Nudx1-1 to Nudx1-3 clades), and two subclades evolved in the Rosa genus (Nudx1-1a and Nudx1-1b subclades). We also showed that the Nudx1-1b subclade was more ancient than the Nudx1-1a subclade, and that the NUDX1-1a gene emerged by a trans-duplication of the more ancient NUDX1-1b gene. After the transposition, NUDX1-1a was cis-duplicated, leading to a gene dosage effect on the production of geraniol in different species. Furthermore, the NUDX1-1a appearance was accompanied by the evolution of its promoter, most likely from a Copia retrotransposon origin, leading to its petal-specific expression. Thus, our data strongly suggest that the unique function of NUDX1-1a in geraniol formation was evolved naturally in the genus Rosa before domestication.

Prickles are common structures in plants that play a key role in defense against herbivores. In theRosagenus, prickles are widely present with great diversity in terms of form and density. For cut rose production, prickles represent an important issue, as they can damage the flower and injure workers. Our objectives were to precisely describe the types of prickles that exist in roses, their tissues of origin and their development. We performed a detailed histological analysis of prickle initiation and development in a rose F1 population. Based on the prickle investigation of 110 roses, we proposed the first categorization of prickles in theRosagenus. They are mainly divided into two categories, nonglandular prickles (NGPs) and glandular prickles (GPs), and subcategories were defined based on the presence/absence of hairs and branches. We demonstrated that NGPs and GPs both originate from multiple cells of the ground meristem beneath the protoderm. For GPs, the gland cells originate from the protoderm of the GP at the early developmental stage. Our findings clearly demonstrate that prickles are not modified trichomes (which originate from the protoderm). These conclusions are different from the current mainstream hypothesis. These results provide a foundation for further studies on prickle initiation and development in plants.

Key message: Rose has 19 MLO genes. Of these, RhMLO1 and RhMLO2 were shown to be required for powdery mildew infection, which suggests their potential as susceptibility targets towards disease resistance. Powdery mildew, caused byPodosphaera pannosa, is one of the most serious and widespread fungal diseases for roses, especially in greenhouse-grown cut roses. It has been shown that certainMLO genes are involved in powdery mildew susceptibility and that loss of function in these genes in various crops leads to broad-spectrum, long-lasting resistance against this fungal disease. For this reason, theseMLOgenes are called susceptibility genes. We carried out a genome-wide identification of theMLOgene family in theRosa chinensisgenome, and screened for allelic variants among 22 accessions from seven differentRosaspecies using re-sequencing and transcriptome data. We identified 19MLOgenes in rose, of which four are candidate genes for functional homologs in clade V, which is the clade containing all dicotMLOsusceptibility genes. We detected a total of 198 different allelic variants in the set ofRosaspecies and accessions, corresponding to 5–15 different alleles for each of the genes. Some diploidRosaspecies shared alleles with tetraploid rose cultivars, consistent with the notion that diploid species have contributed to the formation of tetraploid roses. Among the fourRhMLOgenes in clade V, we demonstrated using expression study, virus-induced gene silencing as well as transient RNAi silencing that two of them,RhMLO1andRhMLO2, are required for infection byP. pannosaand suggest their potential as susceptibility targets for powdery mildew resistance breeding in rose.

Blooming seasonality is an important trait in ornamental plants and was selected by humans. Wild roses flower only in spring whereas most cultivated modern roses can flower continuously. This trait is explained by a mutation of a floral repressor gene, RoKSN, a TFL1 homologue. In this work, we studied the origin, the diversity and the selection of the RoKSN gene. We analyzed 270 accessions, including wild and old cultivated Asian and European roses as well as modern roses. By sequencing the RoKSN gene, we proposed that the allele responsible for continuous-flowering, RoKSN^copia, originated from Chinese wild roses (Indicae section), with a recent insertion of the copia element. Old cultivated Asian roses with the RoKSN^copia allele were introduced in Europe, and the RoKSN^copia allele was progressively selected during the 19th and 20th centuries, leading to continuous-flowering modern roses. Furthermore, we detected a new allele, RoKSN^A181, leading to a weak reblooming. This allele encodes a functional floral repressor and is responsible for a moderate accumulation of RoKSN transcripts. A transient selection of this RoKSN^A181 allele was observed during the 19th century. Our work highlights the selection of different alleles at the RoKSN locus for recurrent blooming in rose.

Key message 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. Abstract 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 10.42 cM for B3 and 11.47 cM 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.