In rape ( Brassica napus), no resistance to the beet cyst nematode (BCN) Heterodera schachtii is available. This study was carried out to determine the specific chromosome(s) of resistant radish ( Raphanus sativus) carrying the gene(s) for nematode resistance as a prequisite to convert rape from a host into a trap crop for this pest. A Raphanobrassica progeny of 25 plants was analyzed which segregated for all nine chromosomes of the Raphanus genome in a genetic background of synthetic rape. The number of radish chromosomes was determined by fluorescence in situ hybridization, using the Raphanus-specific DNA probe pURsN; and their type was identified by chromosome-specific randomly amplified polymorphic DNA markers. Five different multiple rape-radish chromosome additions (comprising the whole set of nine radish chromosomes, a-i) were selected and crossed to rape. For each cross-progeny, the number of cysts on plant roots was counted 42 days after inoculation with a L2 larvae suspension. Simultaneously, the plants were characterized for the presence or absence of individual radish chromosomes, using sets of chromosome-specific markers. Thus, the effect of each radish chromosome on cyst number was tested. Chromosome d had a major resistance effect, whereas the presence/absence of the other radish chromosomes had nearly no influence on cyst number. Plants with added chromosome d showed a resistance level comparable with that of the radish donor parent. The analysis in the cross to rape of a plant monosomic only for chromosome d confirmed the strong effect of this chromosome on nematode resistance. A further experiment comprising seven crosses using winter rape breeding lines and monosomic addition line d as pollen parent provided the same results on a broader genetic basis. In each case, the added chromosome d in a single dosage caused nearly the full resistance of the radish donor. Resistance was independent of the glucosinolate content in the roots. The possibilities for stabilizing BCN resistance in rape and its use for other crops and nematodes are discussed.

Terpenes are an important group of secondary metabolites in carrots influencing taste and flavor, and some of them might also play a role as bioactive substances with an impact on human physiology and health. Understanding the genetic and molecular basis of terpene synthases (TPS) involved in the biosynthesis of volatile terpenoids will provide insights for improving breeding strategies aimed at quality traits and for developing specific carrot chemotypes possibly useful for pharmaceutical applications. Hence, a combination of terpene metabolite profiling, genotyping-by-sequencing (GBS), and genome-wide association study (GWAS) was used in this work to get insights into the genetic control of terpene biosynthesis in carrots and to identify several TPS candidate genes that might be involved in the production of specific monoterpenes. In a panel of 85 carrot cultivars and accessions, metabolite profiling was used to identify 31 terpenoid volatile organic compounds (VOCs) in carrot leaves and roots, and a GBS approach was used to provide dense genome-wide marker coverage (>168,000 SNPs). Based on this data, a total of 30 quantitative trait loci (QTLs) was identified for 15 terpenoid volatiles. Most QTLs were detected for the monoterpene compounds ocimene, sabinene, β-pinene, borneol and bornyl acetate. We identified four genomic regions on three different carrot chromosomes by GWAS which are both associated with high significance (LOD ≥ 5.91) to distinct monoterpenes and to TPS candidate genes, which have been identified by homology-based gene prediction utilizing RNA-seq data. In total, 65 TPS candidate gene models in carrot were identified and assigned to known plant TPS subfamilies with the exception of TPS-d and TPS-h. TPS-b was identified as largest subfamily with 32 TPS candidate genes.

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After crosses of multiple rape-radish chromosome additions with rape, nine diVerent monosomic additions (2n = 4x = 38 + 1) of individual radish chromosomes, a-i, were isolated, having the genomic background of winter oil seed rape and radish cytoplasm. Extra chromosomes were identiWed with RAPD markers, speciWc for individual radish chromosomes. All radish-plasmic monosomic additions, except that of chromosome f, had low seed production due to pistilloid stamens. Rape cytoplasm was substituted by crossing the monosomic additions as pollinators to rape followed by reselection of the radish chromosome additions. The monosomic additions in rape cytoplasm showed normal male fertility. Average transmission rates of radish chromosomes via egg cells and pollen cells were 37% and 27%, respectively. Lowest male transmission was found for chromosomes e and f with 0.04 and 0.01. Monosomic additions were self-pollinated to produce disomic additions. Monosomic and disomic addition progenies were discriminated by a prescreening with quantitative double primer (dp) RAPDs and cytological conWrmation of preselected candidates by FISH analysis using a Raphanus-speciWc probe. Usability of this complete set of nine disomic rape-radish additions (2n = 4x = 38 + 2) was discussed.

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The beet cyst nematode (Heterodera schachtii Schmidt) can be controlled biologically in highly infected soils of sugar beet rotations using resistant varieties of oil radish (Raphanus sativus L. ssp. oleiferus DC.) as a green crop. Resistant plants stimulate infective juveniles to invade roots, but prevent them after their penetration to complete the life cycle. The resistance trait has been transferred successfully to susceptible rapeseed by the addition of a complete radish chromosome. The aim of the study was to construct a genetic map for radish and to develop resistance-associated markers. The map with 545 RAPD, dpRAPD, AFLP and SSR markers had a length of 1,517 cM, a mean distance of 2.8 cM and consisted of nine linkage groups having sizes between 120 and 232 cM. Chromosome-specific markers for the resistance-bearing chromosome d and the other eight radish chromosomes, developed previously from a series of rapeseed-radish addition lines, were enclosed as anchor markers. Each of the extra chromosomes in the addition lines could be unambiguously assigned to one of the radish linkage groups. The QTL analysis of nematode resistance was realized in the intraspecific F(2) mapping population derived from a cross between varieties 'Pegletta' (nematode resistant) x 'Siletta Nova' (susceptible). A dominant major QTL Hs1( Rph ) explaining 46.4% of the phenotypic variability was detected in a proximal position of chromosome d. Radish chromosome-specific anchor markers with known map positions were made available for future recombination experiments to incorporate segments carrying desired genes as Hs1( Rph ) from radish into rapeseed by means of chromosome addition lines.

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In plants, low molecular weight terpenes produced by terpene synthases (TPS) contribute to multiple ecologically and economically important traits. The present study investigates a carrot terpene synthase gene cluster on chromosome 4 associated with volatile monoterpene production. Two carrot mutants, yellow and cola, which are contrasting in the content of low molecular weight terpenes, were crossed to develop an F2 mapping population. The mapping analysis revealed overlapping QTLs on chromosome 4 for sabinene, α-thujene, α-terpinene, γ-terpinene, terpinen-4-ol and 4-carene. The genomic region of this locus includes a cluster of five terpene synthase genes (DcTPS04, DcTPS26, DcTPS27, DcTPS54 and DcTPS55). DcTPS04 and DcTPS54 displayed genotype- and tissue-specific variation in gene expression. Based on the QTL mapping results and the gene expression patterns, DcTPS04 and DcTPS54 were selected for functional characterization. In vitro enzyme assays showed that DcTPS54 is a single-product enzyme catalysing the formation of sabinene, whereas DcTPS04 is a multiple-product terpene synthase producing α-terpineol as a major product and four additional products including sabinene, β-limonene, β-pinene and myrcene. Furthermore, we developed a functional molecular marker that could discriminate carrot genotypes with different sabinene content in a set of 85 accessions.