An RFLP linkage map of the potato is presented which comprises 304 loci derived from 230 DNA probes and one morphological marker (tuber skin color). The self-incompatibility locus of potato was mapped to chromosome I, which is homoeologous to tomato chromosome I. By mapping chromosome-specific tomato RFLP markers in potato and, vice versa, potato markers in tomato, the different potato and tomato RFLP maps were aligned to each other and the similarity of the potato and tomato genome was confirmed. The numbers given to the 12 potato chromosomes are now in accordance with the established tomato nomenclature. Comparisons between potato RFLP maps derived from different genetic backgrounds revealed conservation of marker order but differences in chromosome and total map length. In particular, significant reduction of map length was observed in interspecific compared to intraspecific crosses. The distribution of regions with distorted segregation ratios in the genome was analyzed for four potato parents. The most prominent distortion of recombination was found to be caused by the self-incompatibility locus.

Podosphaera pannosa, the causal agent of rose powdery mildew, hampers the production of cut roses throughout the world. A major tool to control this disease is the use of resistant plant material. Single resistance genes, like Rpp1, may be overcome within a few years by high risk pathogens like powdery mildews. Durable resistance could be achieved using quantitative resistances. Here we describe mapping of QTLs for resistance to P. pannosa in six different environments (artificial and natural infections in the greenhouse over 3 years and natural infections in the field over 2 years). AFLPs, RGAs and other marker types were used to construct an integrated linkage map for the diploid population 97/7 containing 233 markers. In a selective genotyping procedure, marker segregation was analysed for 170 of the up to 270 phenotyped individuals. We identified seven linkage groups with an average length of 60 cM, corresponding to seven rose chromosomes in the haploid set. Using an LOD significance threshold of 3.9 we detected a total of 28 QTLs for the nine powdery mildew disease scores under analysis. Using the data from artificial inoculations with powdery mildew race 9, three resistance QTLs explaining about 84% of the variability were mapped. Twelve and 15 QTLs were detected for resistance to naturally occurring infections in the greenhouse and in the field, respectively, over several years.

Allelic complexity is a key feature of self-incompatibility (S) loci in gametophytic plants. We describe in this report the allelic diversity and gene structure of the S locus in Solanum tuberosum revealed by the isolation and characterization of genomic and cDNA clones encoding S-associated major pistil proteins from three alleles (S1, Sr1, S2). Genomic clones encoding the S1 and S2 proteins provide evidence for a simple gene structure: Two exons are separated by a small intron of 113 (S1) and 117 bp (S2). Protein sequences deduced from cDNA clones encoding S1 and Sr1 proteins show 95% homology, 15 of the 25 residues that differ between these S1 and Sr1 alleles are clustered in a short hypervariable protein segment (amino acid positions 44-68), which corresponds in the genomic clones to DNA sequences flanking the single intron. In contrast, these alleles are only 66% homologous to the S2 allele, with the residues that differ between the alleles being scattered throughout the sequence. DNA crosshybridization experiments identify a minimum of three classes of potato S alleles: one class contains the alleles S1, Sr1 and S3, the second class S2 and an allele of the cultivar Roxy, and the third class contains at present only S4. It is proposed that these classes reflect the origin of the S alleles from a few ancestral S sequence types.

Key message Transcriptomic analysis resulted in the upregulation of the genes related to common defense mechanisms for black spot and the downregulation of the genes related to photosynthesis and cell wall modification for powdery mildew. Abstract Plant pathogenic fungi successfully colonize their hosts by manipulating the host defense mechanisms, which is accompanied by major transcriptome changes in the host. To characterize compatible plant pathogen interactions at early stages of infection by the obligate biotrophic fungus Podosphaera pannosa, which causes powdery mildew, and the hemibiotrophic fungus Diplocarpon rosae, which causes black spot, we analyzed changes in the leaf transcriptome after the inoculation of detached rose leaves with each pathogen. In addition, we analyzed differences in the transcriptomic changes inflicted by both pathogens as a first step to characterize specific infection strategies. Transcriptomic changes were analyzed using next-generation sequencing based on the massive analysis of cDNA ends approach, which was validated using high-throughput qPCR. We identified a large number of differentially regulated genes. A common set of the differentially regulated genes comprised of pathogenesis-related (PR) genes, such as of PR10 homologs, chitinases and defense-related transcription factors, such as various WRKY genes, indicating a conserved but insufficient PTI [pathogen associated molecular pattern (PAMP) triggered immunity] reaction. Surprisingly, most of the differentially regulated genes were specific to the interactions with either P. pannosa or D. rosae. Specific regulation in response to D. rosae was detected for genes from the phenylpropanoid and flavonoid pathways and for individual PR genes, such as paralogs of PR1 and PR5, and other factors of the salicylic acid signaling pathway. Differently, inoculation with P. pannosa leads in addition to the general pathogen response to a downregulation of genes related to photosynthesis and cell wall modification.Keywords Black spot · Powdery mildew · MACE analysis · High-throughput qPCR · WRKY genes · PR genes Enzo Neu and Helena Sophia Domes have contributed equally to this work. Electronic supplementary materialThe online version of this article (https ://doi.

The interaction of roses with the leaf spot pathogen Diplocarpon rosae (the cause of black spot on roses) is an interesting pathosystem because it involves a long-lived woody perennial, with life history traits very different from most model plants, and a hemibiotrophic pathogen with moderate levels of gene flow. Here we present data on the molecular structure of the first monogenic dominant resistance gene from roses, Rdr1, directed against one isolate of D. rosae. Complete sequencing of the locus carrying the Rdr1 gene resulted in a sequence of 265,477 bp with a cluster of nine highly related TIR–NBS–LRR (TNL) candidate genes. After sequencing revealed candidate genes for Rdr1, we implemented a gene expression analysis and selected five genes out of the nine TNLs. We then silenced the whole TNL gene family using RNAi (Rdr1–RNAi) constructed from the most conserved sequence region and demonstrated a loss of resistance in the normally resistant genotype. To identify the functional TNL gene, we further screened the five TNL candidate genes with a transient leaf infiltration assay. The transient expression assay indicated a single TNL gene (muRdr1H), partially restoring resistance in the susceptible genotype. Rdr1 was found to localize within the muRdr1 gene family; the genes within this locus contain characteristic motifs of active TNL genes and belong to a young cluster of R genes. The transient leaf assay can be used to further analyze the rose black spot interaction and its evolution, extending the analyses to additional R genes and to additional pathogenic types of the pathogen.