Mapping quantitative trait loci (QTLs) for resistance to Cercospora leaf spot disease (Cercospora beticola Sacc.) in sugar beet (Beta vulgaris L.)

The breeding of sugar beet varieties that combine resistance to Cercospora and high yield under non-diseased conditions is a major challenge to the breeder. The understanding of the quantitative trait loci (QTLs) contributing to Cercospora resistance offers one route to solving this problem. A QTL analysis of Cercospora resistance in sugar beet was carried out using a linkage map based on AFLP and RFLP markers. Two different screening methods for Cercospora resistance (a field test at Copparo, Italy, under natural infection, and a newly-developed leaf disc test) were used to estimate the level of Cercospora resistance; the correlation between scores from the field (at 162 days after sowing) and the leaf disc test was significant. QTL analysis was based on F₂ and F₃ (half-sib family) generations derived from crosses between diploid single plants of 93164P (resistant to Cercospora leaf spot disease) and 95098P (susceptible). Four QTLs associated with Cercospora resistance (based on Lsmean data of the leaf disc test) on chromosomes III, IV, VII and IX were revealed using Composite interval mapping. To produce populations segregating for leaf spot resistance as a single Mendelian factor, we selected for plants heterozygous for only one of the QTLs (on chromosome IV or IX) but homozygous for the others. Received: 1 September 1999 / Accepted 7 October 1999     

Development and incorporation of microsatellite markers into the linkage map of sugar beet (Beta vulgaris spp.)

A set of informative simple sequence repeat markers has been identified for use in the marker-assisted breeding of Beta vulgaris. Highly enriched small insert genomic libraries were constructed, consisting of 1536 clones (with inserts of between 250–900 bp). Screening the clones with CA, CT, CAA, CATA and GATA nucleotide-repeat probes revealed positive hybridisation to over 50% of the clones. Of these 340 were sequenced. Primer pairs were designed for sequences flanking the repeats and, of these, 57 pairs revealed length polymorphism with 12 Beta accessions. Heterozygosity levels of the SSR loci ranged from 0.069 to 0.809. Heterozygosity levels were found to be similar to those detected employing RFLP probes with the same accessions. Phenetic analysis using the markers, indicated relationships in accordance with known pedigrees. Twenty three of the SSR markers were polymorphic in one or both of two F₂ mapping populations, and were placed relative to a framework of RFLP probes. The markers are distributed over all nine linkage groups of sugar beet. Received: 14 July 1999 / Accepted: 27 October 1999     

The nad4L-orf25 gene cluster is conserved and expressed in sugar beet mitochondria

We have found that a gene coding for NADH dehydrogenase subunit 4L and a presumed gene, orf25, are linked and co-transcribed with each other in sugar beet mitochondria. Ten and twelve C-to-U editing events were observed in the mRNAs of nad4L and orf25, respectively; the amino-acid sequence specified after editing is better-conserved in comparison with the homologues of other organisms. It is interesting to note that the translation initiation codon of nad4L is created by editing. The conservation of the nad4L-orf25 linkage was examined by PCR-amplification of the intergenic region. We obtained successful PCR products from five dicots (spinach, apple, snapdragon, petunia and tobacco) and two monocots (tulip and pineapple), but not in two poaceous plants, rice and maize. The intergenic region, when present, was found to be well-conserved in its sequence, suggesting a monophyletic origin of this linkage. Our result, together with previous reports of Arabidopsis and four poaceous species, favour the argument that the nad4L-orf25 linkage is conserved throughout angiosperms except in the Poaceae. Received: 12 April 1999 / Accepted: 22 June 1999     

Mapping QTLs controlling fruit quality in peach (Prunus persica (L.) Batsch)

 The organoleptic quality of fleshy fruits is in a large part defined by their composition of soluble sugars and organic acids. An F₂ population issuing from a cross between two peach varieties, ‘Ferjalou Jalousia’, a non-acid peach, and ‘Fantasia’, an acid nectarine, was analysed over 2 successive years for agronomic characters and for molecular-marker (isoenzymes, RFLPs, RAPDs, IMAs and AFLPs) segregations. Blooming and maturity dates, as well as productivity, were noted for each tree. Four fruits per tree were analysed at maturity for fresh weight, colour, pH, titratable acidity, soluble-solids content (SSC), acid (malic, citric and quinic acids) and sugar (sucrose, glucose, fructose, sorbitol) contents. QTLs were detected for all fruit components analysed, except for fruit colour. The QTLs for nearly all components were present on two linkage groups. For productivity, fresh weight, pH, quinic acid, sucrose and sorbitol content, all the detected QTLs displayed the same effect as the parental phenotypes. By contrast, for maturity date, titratable acidity, malic and citric acids and fructose, some QTLs displayed the same effect as the parental phenotypes while others displayed the opposite effect. The fraction of the total variation in each trait throughout the population explained by the QTLs was very high and reached more than 90% for some characters. For most of the characters analysed, epistasis was observed between QTLs. Received: 10 October 1997 / Accepted: 18 August 1998     

Efficacy of Bacillus subtilis,Moringa oleifera seeds extract and potassium bicarbonate on Cercospora leaf spot on sugar beet

Cercospora leaf spot caused by Cercospora beticola are among the most dangerous plant diseases on sugar beet plants. It causes heavy economic losses, whether on the yield of roots, the percentage of sugar in them, or the quality of sugar produced. In addition to the economic cost caused by chemical control, these chemical pesticides cause an imbalance in the ecosystem and harm the health of humans and animals. In an attempt to search for a safer method than pesticides and environmentally friendly, an evaluation of using biocontrol agents, Bacillus subtilis as cell suspension (10⁸ cell/ml), was conducted in this study. Seeds extract of Moringa oleifera with two concentrations (25 and 50 g/L) and potassium bicarbonate at (5 and10 g/L (compared to fungicide Montoro 30% EC (Propiconazole 15% + Difenoconazole 15%). The evaluation results for twenty-five sugar beet varieties showed a significant discrepancy between these varieties in the extent of their susceptibility to infection with the disease under investigation. In-Vitro, B. subtilis induced an antagonist to C. beticola, and both M. oleifera seeds extract and potassium bicarbonate significantly reduced the linear growth of this pathogen. Under field conditions, the treatments used have given positive results in controlling Cercospora leaf spots. They significantly decreased the severity of disease and prevented C. beticola from creating conidiophores and conidiospores, along with examining their cell walls with the formation of plasmolysis of the fungus cells and reducing both the number and diameter of the spots on the surface leaves; this was demonstrated using a scanning electron microscope (SEM). It is worth noting that the best results obtained were most often when treated with M. oleifera seeds extract, followed by potassium bicarbonate, then cell suspension of B. subtilis. In addition, the percentage of the content of beet roots from total soluble solids and sucrose has improved significantly due to spraying sugar beet plants with the substances mentioned earlier. These treatments also contributed to a significant improvement in the enzymes polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase.     

Nuclear effect on mitochondrial protein expression of the CMS Owen cytoplasm in sugar beet

In sugar beet, cytoplasmic male sterility (CMS) is conferred by the Owen mitochondrion (Svulg). In order to find polypeptides specific to this cytoplasm and putatively involved in CMS, we assessed the protein expressions of Svulg and a non-sterilizing mitochondrion (Nvulg) by in organello protein synthesis of mitochondria isolated from leaves. Given the hydrophobicity of mitochondrial translation products, we compared the in organello synthesis polypeptides of both cytoplasms with an acid-base two-dimensional electrophoresis adapted to hydrophobic protein separation. To evaluate the possible effect of nuclear background, we assessed the mitochondrial protein expression in three different nuclear backgrounds by using three near-isogenic-line pairs. While three to four variant polypeptides were revealed for each nuclear context, each variant polypeptide was specific to a nuclear-cytoplasmic context. Although this study did not enable us to unambiguously find any variant polypeptide related to CMS, we did observe an effect of the nucleus on mitochondrial gene expression. Received: 25 April 2000 / Accepted: 17 October 2000     

Chromosomal assignment of the nine linkage groups of sugar beet (Beta vulgaris L.) using primary trisomics

 Twenty-four marker loci representing each of the nine linkage groups of sugar beet (Beta vulgaris) have been assigned to the nine primary trisomics of Butterfass (1964). Single-copy RFLP probes were hybridized with filter-bound DNA of the trisomics. The autoradiographs were scanned and analyzed by densitometric methods. Statistics on the integrated optical densities of the RFLP bands revealed a clear relationship of each linkage group to a distinct trisomic type. For the first time each of the linkage groups could unequivocally be assigned to one sugar beet chromosome. A standard nomenclature of the 9 chromosomes of sugar beet is suggested and discussed with respect to previous numbering systems. Received: 27 February 1997/Accepted: 7 March 1997     

Chlorophyll fluorescence imaging for disease-resistance screening of sugar beet

Both biotic and abiotic stresses cause considerable crop yield losses worldwide (Chrispeels, Sadava Plants, genes, and crop biotechnology 2003; Oerke, Dehne Crop Prot 23:275–285 2004). To speed up screening assays in stress resistance breeding, non-contact techniques such as chlorophyll fluorescence imaging can be advantageously used in the quantification of stress-inflicted damage. In comparison with visual spectrum images, chlorophyll fluorescence imaging reveals cell death with higher contrast and at earlier time-points. This technique has the potential to automatically quantify stress-inflicted damage during screening applications. From a physiological viewpoint, screening stress-responses using attached plant leaves is the ideal approach. However, leaf growth and circadian movements interfere with time-lapse monitoring of leaves, making it necessary to fix the leaves to be studied. From this viewpoint, a method to visualise the evolution of chlorophyll fluorescence from excised leaf pieces kept in closed petri dishes offers clear advantages. In this study, the plant–fungus interaction sugar beet–Cercospora beticola was assessed both in attached leaf and excised leaf strip assays. The attached leaf assay proved to be superior in revealing early, pre-visual symptoms and to better discriminate between the lines with different susceptibility to Cercospora.     

Comparative mapping of QTLs for agronomic traits of rice across environments by using a doubled-haploid population

We report here the RFLP mapping of quantitative trait loci (QTLs) which affect some important agronomic traits in cultivated rice. An anther culture-derived doubled-haploid (DH) population was established from a cross between indica and japonica rice varieties. A molecular linkage map comprising 137 markers was constructed based on this population which covered the rice genome at intervals of 14.8 cM on average. The linkage map was used to locate QTLs for such important agronomic traits as heading date, plant height, number of spikelets per panicle, number of grains per panicle, 1 000-grain weight and the percentage of seed set, by interval mapping. Evidence of genotype-by-environment interaction was found by comparing QTL maps of the same population grown in three diverse environments. A total of 22 QTLs for six agronomic traits was detected which were significant in at least one environment, but only seven were significant in all three environments; seven were significant in two environments and eight could only be detected in a single environment. However, QTLs-by-environment interaction was trait dependent. QTLs for spikelets and grains per panicle were common across environments while traits like heading date and plant height were more sensitive to environment. Received: 22 February 1996 / Accepted: 10 May 1996     

RFLP mapping of QTLs conferring salt tolerance during the vegetative stage in tomato

 Quantitative trait loci (QTLs) contributing to salt tolerance during the vegetative stage in tomato were investigated using an interspecific backcross between a salt-sensitive Lycopersicon esculentum breeding line (NC84173, maternal and recurrent parent) and a salt-tolerant Lycopersicon pimpinellifolium accession (LA722). One hundred and nineteen BC₁ individuals were genotyped for 151 RFLP markers and a linkage map was constructed. The parental lines and 119 BC₁S₁ families (self-pollinated progeny of the BC₁ individuals) were evaluated for salt tolerance in aerated saline-solution cultures with the salt concentration gradually raised to 700 mM NaCl+70 mM CaCl₂ (equivalent to an electrical conductivity of approximately 64 dS/m and a water potential of approximately −35.2 bars). The two parental lines were distinctly different in salt tolerance: 80% of the LA722 plants versus 25% of the NC84173 plants survived for at least 2 weeks after the final salt concentration was reached. The BC₁S₁ population exhibited a continuous variation, typical of quantitative traits, with the survival rate of the BC₁S₁ families ranging from 9% to 94% with a mean of 51%. Two QTL mapping techniques, interval mapping (using MAPMAKER/QTL) and single-marker analysis (using QGENE), were used to identify QTLs. The results of both methods were similar and five QTLs were identified on chromosomes 1 (two QTLs), 3, 5 and 9. Each QTL accounted for between 5.7% and 17.7%, with the combined effects (of all five QTLs) exceeding 46%, of the total phenotypic variation. All QTLs had the positive QTL alleles from the salt-tolerant parent. Across QTLs, the effects were mainly additive in nature. Digenic epistatic interactions were evident among several QTL-linked and QTL-unlinked markers. The overall results indicate that tomato salt tolerance during the vegetative stage could be improved by marker-assisted selection using interspecific variation. Received: 4 January 1999 / Accepted: 4 January 1999     

<Emphasis Type="Italic">Trichoderma</Emphasis> as a potential biocontrol agent for Cercospora leaf spot of sugar beet

Leaf spot disease caused by Cercospora beticola Sacc. (class Ascomycota, ord. Dothideales, fam. Mycosphaerellaceae) is the most destructive foliar disease of sugar beet. Commercial varieties are partially resistant and require repeated fungicide applications to obtain adequate protection levels; this has a high environmental impact and a risk of selecting resistant pathogen strains. A way of reducing chemical inputs could be to use biocontrol agents to replace or supplement fungicide treatments. A well-known class of biological control agents is represented by the fungi belonging to the Trichoderma genus (class Ascomycota, ord. Hypocreales, fam. Hypocreaceae), but there is a lack of information about its behaviour towards C. beticola. This study reports the evaluation of several Trichoderma isolates as possible biocontrol agents of this pathogen. Preliminary in vitro and in vivo assays led to the selection of two Trichoderma isolates characterised by their ability to reduce pathogen sporulation and antagonism towards the pathogen or competence for sugar beet phyllosphere. Repeated foliar applications of the liquid culture homogenate preceded by a single treatment of difenoconazole in 2 year trials under natural inoculum in field reduced the disease incidence and pathogen sporulation from the necrotic spots. An increase in sugar yield was also obtained by means of isolate Ba12/86-based treatments, perhaps due to induced resistance effects.     

Analysis of complex leaf and flower characters in Rhododendron using a molecular linkage map

 A molecular linkage map of Rhododendron has been constructed by using a segregating population from an interspecific cross. Parent-specific maps based on 239 RAPD, 38 RFLP, and two microsatellite markers were aligned using markers heterozygous in both parents. The map of the male parent ‘Cunningham’s White’ comprised 182 DNA markers in 13 linkage groups corresponding to the basic chromosome number. In the female parent ‘Rh 16’ 168 markers were located on 18 linkage groups. An assignment of putative homologous linkage groups was possible for 11 groups of each parent. QTL analyses based on the non-parametric Kruskal-Wallis rank-sum test were performed for the characters “leaf chlorosis” and “flower colour” scored as quantitative traits. For leaf chlorosis, two genomic regions bearing QTLs with significant effects on the trait were identified on two linkage groups of the chlorosis-tolerant parent. RAPD marker analysis of additional lime-stressed genotypes tested under altered environmental conditions verified the relationship between marker allele frequencies and the expression of chlorosis. Highly significant QTL effects for flower colour were found on two chromosomes indicating major genes located in these genome areas. The prospects for utilization of a linkage map in Rhododendron are discussed. Received: 28 September 1998 / Accepted: 5 November 1998     

Association of dominant loci for resistance to Pseudomonas syringae pv. pisi with linkage groups II, VI and VII of Pisum sativum

Morphological characters, isoenzymes and recombinant inbred lines were employed to assign four loci for resistance to Pseudomonas syringae pv pisi to genetic linkage groups in Pisum sativum. A total of five morphological markers and 11 isoenzyme loci were screened in two independent F₂ P. sativum populations: Vinco × Hurst’s Greenshaft (V×HGS) and Partridge × Early Onward (P×EO). Mapping was also carried out in two recombinant inbred populations, unrelated to the F₂ populations. Previously reported linkage between resistance genes Ppi3 and Ppi4 was confirmed. Linkage was also detected between resistance gene Ppi2 and the isoenzyme locus Aldo (linkage group VII). The linked loci Ppi3 and Ppi4 were associated with a (linkage group II). A further resistance gene Ppi1 was associated with linkage group VI close to the hilum colour gene P1. RAPD markers tested in the cross P×EO were not well targeted; however, one marker, OPA-20_0.71, showed linkage to Ppi3. Received: 3 July 2000 / Accepted: 27 October 2000     

Localization of the rice stripe disease resistance gene, Stv-bi, by graphical genotyping and linkage analyses with molecular markers

 We used graphical genotyping and linkage analyses with molecular markers to determine the chromosomal location of the rice stripe disease resistance gene, Stv-b ⁱ . The stripe resistance gene from the indica rice (Oryza sativa) cv ‘Modan’ was introgressed into several Japanese rice varieties. We found 4 RFLP markers in ‘Modan’, five susceptible parental rice varieties (‘Norin No. 8’, ‘Sachihikari’, ‘Kanto No. 98’, ‘Hokuriku No.103’ and ‘Koganebare’) and four resistant progeny varieties (‘St. No. 1’, ‘Aichi No. 6’, ‘Aoisora’ and ‘Asanohikari’). Graphical genotyping of the resistant progeny revealed a chromosomal segment ascribable to ‘Modan’ and associated with stripe resistance. The chromosomal segment from ‘Modan’ was located at 35.85 cM on chromosome 11. Linkage analysis using 120 F₂ individuals from a cross between ‘Koshihikari’ (susceptible) and ‘Asanohikari’ (resistant) revealed another 8 RFLP markers in the same chromosome. We performed a bioassay for rice stripe resistance in F₃ lines of the F₂ individuals using infective small brown planthoppers and identified an 1.8-cM segment harboring the rice stripe disease resistance gene, Stv-b ⁱ , between XNpb220 and XNpb257/ XNpb254. Furthermore, Stv-b ⁱ was linked by 0.0 cM to a RFLP marker, ST10, which was developed on the basis of the results of RAPD analysis. These DNA markers near the Stv-b ⁱ locus may be useful in marker-assisted selection and map-based cloning of the Stv-b ⁱ gene. Received: 26 September 1997 / Accepted: 4 November 1997     

Salt tolerance in Lycopersicon spp. VII. Pleiotropic action of genes controlling earliness on fruit yield

 The change from vegetative to reproductive development (earliness) in Lycopersicon chesmannii line L2 was delayed for 20 weeks when compared to other Lycopersicon species under greenhouse conditions. The interspecific hybrid of L. chesmannii L2 and L. esculentum E9, a cherry tomato cultivar, also showed this delay in reproductive development. The distribution of this character in the F₂-derived population showed a bimodal shape, plants could be scored easily as “early” or “late” in two nutrient conditions (optimum and high salinity). A QTL with major effects on earliness was detected in salinity, which explained 35.6% of the phenotypic variation. The effect of this QTL greatly diminished under control conditions, indicating differences in the genetic control of earliness between treatments. ACC synthase or phytochrome B2 are the products of candidate genes for such a major QTL. Other QTLs with minor effects, and epistatic interactions, are also involved in earliness under both conditions. A “late” F₂ subpopulation yielded twice as much as an “early” F₂; conversely, “early” plants were taller than “late” plants, regardless of the treatment. QTL analysis, carried out in both subpopulations, showed that yield differences may be explained by chesmannii alleles showing negative additive effects at some QTLs only in the “early” subpopulation. The effect of population subdivision on QTL analysis was investigated by computer simulations to show sample-size or random effects; thus, important pleiotropic or regulatory effects of genes controlling earliness on yield that affect QTL analysis, have been reveiled. Therefore alleles controlling earliness in L. chesmannii have to be taken into account for a more efficient utilization of the genetic resources of this species. Received: 30 June 1998 / Accepted: 31 August 1998     

Effects of genetic background and environment on QTLs and epistasis for rice (Oryza sativa L.) panicle number

A double-haploid (DH) population and a recombinant inbred (RI) line population, derived from a cross between a tropical japonica variety, Azucena, as male parent and two indica varieties, IR64 and IR1552, as female parents respectively, were used in both field and pot experiments for detecting QTLs and epistasis for rice panicle number in different genetic backgrounds and different environments. Panicle number (PN) was measured at maturity. A molecular map with 192 RFLP markers for the DH population and a molecular map with 104 AFLP markers and 103 RFLP markers for the RI population were constructed, in which 70 RFLP markers were the same. Six QTLs were identified in the DH population, including two detected from field experiments and four from pot experiments. The two QTLs, mapped on chromosomes 1 and 12, were identical in both field and pot experiments. In the RI population, nine QTLs were detected, five QTLs from field conditions and four from the pot experiments. Three of these QTLs were identical in both experimental conditions. Only one QTL, linked to CDO344 on chromosome 12, was detected across the populations and experiments. Different epistasitic interaction loci on PN were found under different populations and in different experimental conditions. One locus, flanked by RG323 and RZ801 on chromosome 1, had an additive effect in the DH population, but epistatic effects in the RI population. These results indicate that the effect of genetic background on QTLs is greater than that of environments, and epistasis is more sensitive to genetic background and environments than main-effect QTLs. QTL and epistatic loci could be interchangeable depending on the genetic backgrounds and probably on the environments where they are identified. Received: 26 May 2000 / Accepted: 19 October 2000     

RAPD linkage mapping of the shell thickness locus in oil palm (Elaeis guineensis Jacq.)

Shell thickness is an important trait in oil palm breeding programs and is the basis for the classification of the varieties of oil palm into the types dura, tenera and pisifera. This trait seems to be controlled by a single locus, with two alleles (sh ⁺ and sh ⁻) showing codominant expression. Two single-tree linkage maps were constructed for a maternal tenera (sh ⁺ sh ⁻) palm and for a paternal pisifera (sh ⁻ sh ⁻) palm using the pseudo-testcross mapping strategy in combination with RAPD markers through the analysis of an F₁ tenera×pisifera progeny. A total of 308 arbitrary primers were screened in a sample of eight F₁ plants and 121 markers were detected in a testcross configuration. An average of 1.66 polymorphic marker per selected primer were identified in this cross. At LOD 5.0 (with some few exceptions) and θ=0.25 the maternal tenera map included a total of 48 markers distributed in 12 linkage groups or pairs of markers (449.3 cM) while the paternal pisifera map included 42 markers distributed in 15 linkage groups or pairs of markers (399.7 cM). We used RAPD and bulked segregant analysis (BSA) to identify markers more tightly linked to the sh ⁺ locus. A total of 174 new primers not previously used in the linkage analysis were screened using bulks of DNA extracted from plants selected for the contrasting shell-thickness phenotypes. Two RAPD markers (R11–1282 and T19–1046) were identified to be linked on both sides of the sh ⁺ locus on linkage group 4. The estimated map distances from sh ⁺ to R11–1282 and to T19–1046 were 17.5 cM and 23.9 cM, respectively. The results demonstrate the usefulness of RAPD markers and the pseudo-testcross mapping strategy for developing genetic linkage information, and constitute an important step towards early marker-assisted selection for shell thickness in oil palm. Received: 21 February 1999 / Accepted: 29 April 1999     

Construction of an RFLP linkage map for cultivated sunflower

 An RFLP linkage map was constructed for cultivated sunflower Helianthus annuus L., based on 271 loci detected by 232 cDNA probes. Ninety-three F₂ plants of a cross between inbred lines RHA 271 and HA 234 were used as the mapping population. These genetic markers plus a fertility restoration gene, Rf ₁, defined 20 linkage groups, covering 1164 cM of the sunflower genome. Of the 71 loci 202 had codominant genotypic segregation, with the rest showing dominant segregation. Thirty-two of the 232 probes gave multiple locus segregation. There were 39 clusters of tightly linked markers with 0 cM distance among loci. This map has an average marker-to-marker distance of 4.6 cM, with 11 markerless regions exceeding 20 cM. Received: 17 June 1997 / Accepted: 19 June 1997     

AFLP based alternatives for the assessment of Distinctness, Uniformity and Stability of sugar beet varieties

Three approaches for addressing criteria for Distinctness, Uniformity and Stability (DUS) assessment by means of AFLP data are presented. AFLP data were obtained for three consecutive seed deliveries of 15 sugar beet varieties that were under investigation for the official Belgian list (’93, ’94 and ’95). In total, 696 AFLP markers were scored on 1350 plants. As a first approach, a cluster analysis based on Nei’s standard genetic distances between varieties and/or seed deliveries was made. Three major groups put together varieties belonging to corresponding breeding programmes. Statistical procedures, involving bootstrapping and random sampling of subsets of markers, were applied to test the reproducibility of the ordinations and the redundancy present in the data set. In a second approach, the genetic structure inferred by varieties and seed deliveries was submitted to an Analysis of Molecular Variance (AMOVA). Major genetic variation was attributed to individual plant differences within seed deliveries. Differences among seed deliveries seemed to be as important as differences among varieties or breeding programmes. Individual plant data were used for assignment tests. The computation of the assignment was based on the ranking of individual genotypes to one other (based on Jaccard similarity coefficients). The distribution over the accessions for each variety or seed delivery was used to check what group of plants each individual is genetically most similar to. Varieties were classified according to the degree to which the distribution over the different accessions was mainly allocated to their appropriate seed deliveries (from the same variety) or cross- allocated to other varieties. Criteria for DUS-evaluation could be set by each of the approaches; it is discussed in what way the result obtained differs and agrees. Received: 26 June 2000 / Accepted: 13 March 2001