European Accessions Research Articles

Variability in stem fibre content and its association with other characteristics in 1177 flax ( Linum usitatissimum L.) genebank accessions

The use of short fibres in flax has received increased attention in North America because of the interest in combining seed and stem fibre use in the same cultivar, with fibre being a by-product. In this study, stem fibre contents of 1177 diverse flax accessions representing fibre flax and linseed flax from 55 countries were considered. The relationships of stem fibre content with quantitative (plant height, number of days from emergence to end of flowering, petal width, seed weight, seed oil content and proportion of α-linolenic acid of all fatty acids) and qualitative (stem branching, petal colour, petal overlap, petal margin folding and seed colour) plant characters were investigated. Fibre content (dry matter basis) ranged from 9.0 to 35.0% with a mean value ± standard deviation of 21.4 ± 3.4%. Twenty-eight North American linseed cultivars had an average fibre content of 22.2%, which was 2.1% lower than in 28 European fibre flax accessions. Within the 28 North American linseed cultivars, the highest stem fibre contents (>25%) were found in the cultivars ‘Redwood 65’ (accession no. CN 33388), ‘Flanders’ ( CN 18979), ‘AC Carnduff’ ( CN 18975), ‘CDC Arras’ ( CN 18976) and ‘N.D. Resistant No. 52’ ( CN 97467). In general, fibre flax accessions marked as such either by their passport information, by typical traits such as less branching of the stem, tall growth or by being identified as belonging to the convar. elongatum had a higher fibre content. All associations of stem fibre content with qualitative or quantitative plant characters in flax germplasm were weak and only a few were significant. This indicates that there are no biological restrictions for breeders in combining different performance in qualitative or quantitative characters with high fibre content. The wide variation in fibre content of flax germplasm will be useful for finding germplasm relevant for breeding dual purpose flax.

Putative natural hybrid between Puccinia lagenophorae and an unknown rust fungus on Senecio madagascariensis in KwaZulu-Natal, South Africa

Several specimens of an aecial rust fungus were collected on Senecio madagascariensis during a field survey carried out in KwaZulu-Natal, South Africa. As telia were not present in the specimens collected, DNA sequence analyses were undertaken to determine the identity of the rust species. ITS and β-tub1 sequencing confirmed that one of the isolates recovered is Puccinia lagenophorae sensu lato. On the other hand, sequencing and RFLP analysis revealed the presence of two divergent copies of ITS and β-tub1 in all the other six isolates investigated. In both phylogenetic trees, one copy of the gene region grouped within a well supported clade with sequences of P. lagenophorae accessions from different geographical origins and hosts, and the Australian rusts Puccinia saccardoi and Puccinia stylidii. The other copy of these gene regions grouped within a separate clade comprising European accessions of Puccinia dioicae (ITS) and Uromyces sommerfeltii (β-tub1) that occur on Asteraceae hosts. Multiple copies of these gene regions were not observed in Australian isolates of P. lagenophorae. Our study provides some evidence that an interspecific hybrid rust fungus, with P. lagenophorae as one of its parents, may occur on S. madagascariensis in South Africa. The identity of the other parent remains unknown.

Demographic history of european populations of Arabidopsis thaliana.

The model plant species Arabidopsis thaliana is successful at colonizing land that has recently undergone human-mediated disturbance. To investigate the prehistoric spread of A. thaliana, we applied approximate Bayesian computation and explicit spatial modeling to 76 European accessions sequenced at 876 nuclear loci. We find evidence that a major migration wave occurred from east to west, affecting most of the sampled individuals. The longitudinal gradient appears to result from the plant having spread in Europe from the east ∼10,000 years ago, with a rate of westward spread of ∼0.9 km/year. This wave-of-advance model is consistent with a natural colonization from an eastern glacial refugium that overwhelmed ancient western lineages. However, the speed and time frame of the model also suggest that the migration of A. thaliana into Europe may have accompanied the spread of agriculture during the Neolithic transition.

Identification and Characterization of Anthocyanins by High-performance Liquid Chromatography–Electrospray Ionization–Mass Spectrometry in Herbaceous Peony Species

Petal anthocyanins were systematically identified and characterized by high-performance liquid chromatography (HPLC)–electrospray ionization–mass spectrometry (MS) coupled with diode array detection among nine wild herbaceous peony (Paeonia L.) species (15 accessions). Individual anthocyanins were identified according to the HPLC retention time, elution order, MS fragmentation patterns, and by comparison with authentic standards and published data. Six main anthocyanins, including peonidin-3,5-di-O-glucoside, peonidin-3-O-glucoside-5-O-arabinoside (Pn3G5Ara), peonidin-3-O-glucoside, pelargonidin-3,5-di-O-glucoside, cyanidin-3,5-di-O-glucoside, and cyanidin-3-O-glucoside (Cy3G), were detected. In addition to the well-known major anthocyanins, some minor anthocyanins were identified in herbaceous peony species for the first time. Detection of the unique anthocyanins cyanidin-3-O-glucoside-5-O-galactoside and pelargonidin-3-O-glucoside-5-O-galactoside in both Paeonia anomala L. and P. anomala ssp. veitchii (Lynch) D.Y. Hong & K.Y. Pan indicated these two species should belong to the same taxon. Pn3G5Ara was found only in European wild species and subspecies suggesting different metabolic pathways between European and Chinese accessions. Anthocyanins conjugated with galactose and arabinose were observed in the genus Paeonia for the first time. The North American species, Paeonia tenuifolia L., had high Cy3G content in flower petals. This anthocyanin composition is distinct from the anthocyanin composition in Asian and European species and possibly is responsible for the vivid red coloration in flowers.

Geographical variation in the response to nitrogen deposition inArabidopsis lyrata petraea

The adaptive responses to atmospheric nitrogen deposition for different European accessions of Arabidopsis lyrata petraea were analysed using populations along a strong atmospheric N-deposition gradient. Plants were exposed to three N-deposition rates, reflecting the rates at the different locations, in a full factorial design. Differences between accessions in the response to N were found for important phenological and physiological response variables. For example, plants from low-deposition areas had higher nitrogen-use efficiencies (NUE) and C : N ratios than plants from areas high in N deposition when grown at low N-deposition rates. The NUE decreased in all accessions at higher experimental deposition rates. However, plants from high-deposition areas showed a limited capacity to increase their NUE at lower experimental deposition rates. Plants from low-deposition areas had faster growth rates, higher leaf turnover rates and shorter times to flowering, and showed a greater increase in growth rate in response to N deposition than those from high-deposition areas. Indications for adaptation to N deposition were found, and results suggest that adaptation of plants from areas high in N deposition to increased N deposition has resulted in the loss of plasticity.

Variation patterns within 153 flax (Linum usitatissimum L.) genebank accessions based on evaluation for resistance to fusarium wilt, anthracnose and pasmo

Germplasm of 153 flax (Linum usitatissimum) accessions from 24 countries held at Plant Gene Resources of Canada (PGRC) was evaluated for resistance to fusarium wilt (Fusarium oxysporum), anthracnose (Colletotrichum lini) and pasmo (Septoria linicola). The screening was conducted at the All-Russian Flax Research Institute (VNIIL) at Torzhok, Russia, over 3 years for fusarium wilt and anthracnose, and over 2 years for pasmo. A disease severity index ranging from 0% (no infection) to 100% (heavy infection) was calculated based on observations after artificial inoculation with the pathogens in the greenhouse (fusarium wilt) or in field nurseries (anthracnose and pasmo). The average disease severity index for fusarium wilt was 56.6 ± 34.4% (range 0–100.0%), for anthracnose 59.8 ± 8.1% (range 43.8–83.9%) and for pasmo 74.2 ± 11.8% (range 27.3–100.0%). The variation of disease severity indices among the years and within each accession was highest for fusarium wilt. Higher than average resistance for all three diseases was found in accessions from East Asia, while germplasm from the Indian subcontinent showed considerably lower than average resistance. Germplasm from North America and South America (mostly linseed) displayed above average resistance to fusarium wilt, while European accessions (mostly fibre flax) showed lower than average resistance to this disease. The different resistance levels reflected the improvements made by plant breeding and differences in the environments under which the germplasm accessions evolved. Accessions with potential use in linseed and fibre flax breeding were identified.

AFLP-based molecular characterization of Brassica rapa and diversity in Canadian spring turnip rape cultivars

Information on genetic diversity and genetic relationships among taxa of Brassica rapa (n = 10, AA genome) is currently limited. Grown for oil, vegetable and fodder use in Europe and Asia, previous studies have indicated western and eastern groups corresponding to independent centres of origin. This study evaluated patterns and levels of genetic diversity in 93 accessions [includes 25 Agriculture and Agri-Food Canada (AAFC) breeding lines (BL)] of B. rapa based on 307 amplified fragment length polymorphisms (AFLP), testing subspecific separateness and the affiliation of four previously unassigned AA genome species (B. perviridis, B. purpuraria, B. ruvo and B. septiceps). AFLP data revealed three main clusters (I, II, III) corresponding to European (I), Indian (III), and a mixed Asian/European/Indian (II) purported origins of the taxa, with several subclusters observed in I and II. Mean AFLP polymorphism levels for Asian, European, Indian and AAFC-BL accessions were 79, 74, 66 and 62%, respectively. Few of the subspecies formed unique clusters and some, particularly subspecies chinensis and pekinensis, were assigned to several clusters. AFLP-based genetic distance information can be used by breeders to select diverse genotypes for cultivar development and fingerprinting of genotypes/cultivars. For example, a single AFLP primer pair was sufficient to uniquely identify all breeding lines in the AAFC B. rapa breeding programme.

Assessment of genetic diversity of yellow-seeded rapeseed (Brassica napus L.) accessions by AFLP markers

The genetic diversity of 35 yellow-seeded <i>Brassica napus</i> L. accessions originating from China, Czech Republic and Poland was assessed by means of Amplified Fragment Length Polymorphism (AFLP) markers based on multiplex PCR using multi-colour fluorescent-labelled primers. Five brown-seeded accessions originating from China and France were selected as outliers. In total, 632 peaks were generated by AFLP reaction using 18 primer combinations. Only distinctly polymorphic markers among them were scored. In total, 242 polymorphic markers were detected with an average of 13.4 markers per primer combination. The AFLP analysis separated forty studied accessions into Chinese and European groups by UPGMA clustering and Principal Coordinates Analysis (PCA). The grouping of accessions based on the cluster analysis and PCA was generally consistent with known pedigree information and geographic origin. Notable geographical divergence was found between Chinese and European yellow-seeded accessions. This information is useful for yellow-seeded hybrid breeding and encouraging breeders to exchange their germplasm as to enlarge the genetic diversity of breeding accessions.

Genetic Diversity and Phylogenetic Relationships among Plum Germplasm Resources in China Assessed with Inter-simple Sequence Repeat Markers

Inter-simple sequence repeat (ISSR) markers were used to evaluate genetic similarity and interrelationship among 104 plum (Prunus L. spp.) and related accessions from the Chinese National Germplasm Repository for Plums and Apricots and the Tianshan Germplasm Repository for Wild Fruit Resources, including six plum species (Prunus salicina Lindl., Prunus simonii Carr., Prunus ussuriensis Kov. et Kost., Prunus domestica L., Prunus cerasifera Ehrh., and Prunus spinosa L.), two related species [apricot (Prunus armeniaca L.) and nanking cherry (Prunus tomentosa Thunb.)], eight putative hybrids between plum and apricot (plumcot), and six accessions of wild European plum (P. domestica). Out of the 42 ISSR primers, 12 were selected, which generated 103 markers in total, 99 of which were polymorphic. Possible accession-specific ISSR bands or patterns were also found. Some possible synonyms or homonyms were clarified or discussed, and closely related accessions such as bud mutants were discriminated. Based on the unweighted pair group method with arithmetic mean (UPGMA) analysis and principal coordinate analysis (PCoA) using the Jaccard coefficient, two different dendrograms were constructed—one including accessions grouped by species and one with all 104 accessions—and a two-dimensional plot was obtained. Three groups were formed in both dendrograms and PCoA plot: Group I including apricot (‘Yinxiangbai’) and plumcot types; Group II containing Asia-originated diploid species [e.g., P. cerasifera, P. ussuriensis, P. tomentosa, and Chinese plum-types (i.e., P. salicina and its hybrids)]; and Group III involving European-origin polyploid species (e.g., P. spinosa and P. domestica) and recently found wild European plum accessions in China. The dendrogram with accessions grouped by species implied that 1) plumcot types had closer relatedness with apricot than with plum; 2) P. simonii should be a variant of P. salicina while P. ussuriensis an independent species; 3) P. domestica was more closely related to P. spinosa than to P. cerasifera. Two accessions of European plum (‘89-7-3’ and ‘Wanhei’) were clustered into outgroups in the dendrogram with all 104 accessions, which could been grouped within Group III in the PCoA plot. The distribution of both European plum and Chinese plum-types across respective groups did not reflect the geographic origins. The present study also further confirmed that the wild plants found in Xinjiang of China were P. domestica.

Fitness Effects Associated with the Major Flowering Time GeneFRIGIDAinArabidopsis thalianain the Field

To date, the effect of natural selection on candidate genes underlying complex traits has rarely been studied experimentally, especially under ecologically realistic conditions. Here we report that the effect of selection on the flowering time gene FRIGIDA (FRI) reverses depending on the season of germination and allelic variation at the interacting gene FLOWERING LOCUS C (FLC). In field studies of 136 European accessions of Arabidopsis thaliana, accessions with putatively functional FRI alleles had higher winter survival in one FLC background in a fall-germinating cohort, but accessions with deletion null FRI alleles had greater seed production in the other FLC background in a spring-germinating cohort. Consistent with FRI's role in flowering, selection analyses suggest that the difference in winter survival can be attributed to time to bolting. However, in the spring cohort, the fitness difference was associated with rosette size. Our analyses also reveal that controlling for population structure with estimates of inferred ancestry and a geographical restriction was essential for detecting fitness associations. Overall, our results suggest that the combined effects of seasonally varying selection and epistasis could explain the maintenance of variation at FRI and, more generally, may be important in the evolution of genes underlying complex traits.

Genetic diversity of Brassica napus L. Germplasm from China and Europe assessed by some agronomically important characters

The genetic diversity and relationships among 63 rapeseed accessions, including 34 Chinese, 22 Czech, 2 Swedish, 2 German, one French and 2 Canadian accessions, were evaluated by nine agronomically important characters in the field at Yangling, Shaanxi, China. Significant differences between Chinese and European group in plant height, setting position of the first primary branch, number of siliques of the terminal raceme, thousand seed weight and seed yield per plant were detected. There were significant variations in nine agronomic characters among the tested rapeseed accessions. Ward’s minimum variance cluster analysis based on Mahalanobis distances on the raw data of nine agronomic characters clearly separated the European accessions from the Chinese ones. However, the Chinese accessions with erucic acid free and/or low glucosinolates could not be separated from those Chinese accessions with both high erucic acid and glucosinolates. In general, cluster analysis of the 63 accessions based on the selected agronomic characters was consistent with known pedigree information and geographic origin, as well as the previous RAPD results of these accessions. The European rapeseed could be important germplasm resources for enriching the genetic background of Chinese rapeseed, and vice versa.

Variability in leaf and fruit morphology and in fruit composition of chestnuts (Castanea Sativa Mill.) in the Nazilli region of Turkey

The aim of this study is to characterize 10 European chestnut (Castanea sativa Mill.) accessions which were selected among 80 accessions at the end of a selection study in Nazilli in Turkey. During the harvest periods in 2001, 2002 and 2003, European chestnut accessions were examined. Nineteen morphological, pomological and biochemical characters were used. Significant genotype×year interaction were found for all traits but one. Multivariate methods, including cluster and principal component analysis were performed to characterize the accessions. The first five principal components account for 86.44% of the total variance of all traits, indicating a high degree of correlation among the characteristics analyzed. High level of phenotypic proximity was found between the accessions N-20-2 and N-5-1 based on pomological, morphological and biochemical characteristics.

Microsatellites are Used to Examine Apple and Pear Identities and Genetic Relationships

Simple Sequence Repeat (SSR) markers developed in apple and pear were used to determine genetic relationships among heritage apple and pear cultivars from Portugal's Azore Islands, and to develop identity fingerprints for European and Asian pear accessions at the USDA–ARS National Clonal Germplasm Repository (NCGR). We used 11 SSR markers (six from apple and five from pear) to examine 18 heritage apple and 9 heritage pear cultivars from the Azores. Eight additional Portuguese and economically important cultivars of apple and eight of pear were used as standards. Cluster analysis separated the apple and pear accessions into two distinct groups. Among apple genotypes, 12 unique accessions and five groups of synonyms were identified, while, in pear, seven unique genotypes and three pairs of synonyms were found. None of the accessions obtained from the Azores corresponded to widely grown standard Portuguese apple or pear cultivars. To examine 144 NCGR pear accessions, we used nine polymorphic SSR loci that were developed from GenBank sequences. Cluster analysis identified five sets of synonyms (four in P. communis L. and one in P. ussuriensis Maxim.) and four pairs of homonyms (three in P. communis and one in P. pyrifolia Burm. f. Nakai), and confirmed three clonal sets. Morphological evaluations and additional SSR markers will be used to confirm these results, and to genetically document the identities of pear genotypes. SSR markers will greatly assist the management of ex situ pome fruit germplasm collections by helping to eliminate duplicate accessions and expanding the genetic diversity represented.

Evidence for a large‐scale population structure among accessions of Arabidopsis thaliana: possible causes and consequences for the distribution of linkage disequilibrium

The existence of a large-scale population structure was investigated in Arabidopsis thaliana by studying patterns of polymorphism in a set of 71 European accessions. We used sequence polymorphism surveyed in 10 fragments of approximately 600 nucleotides and a set of nine microsatellite markers. Population structure was investigated using a model-based inference framework. Among the accessions studied, the presence of four groups was inferred using genetic data, without using prior information on the geographical origin of the accessions. Significant genetic isolation by geographical distance was detected at the group level, together with a geographical gradient in allelic richness across groups. These results are discussed with respect to the previously proposed scenario of postglacial colonization of Europe from putative glacial refugia. Finally, the contribution of the inferred structure to linkage disequilibrium among 171 pairs of essentially unlinked markers was also investigated. Linkage disequilibrium analysis revealed that significant associations detected in the whole sample were mainly due to genetic differentiation among the inferred groups. We discuss the implication of this finding for future association studies in A. thaliana.

Evidence for a large-scale population structure of Arabidopsis thaliana from genome-wide single nucleotide polymorphism markers

Population-based methods for the genetic mapping of adaptive traits and the analysis of natural selection require that the population structure and demographic history of a species are taken into account. We characterized geographic patterns of genetic variation in the model plant Arabidopsis thaliana by genotyping 115 genome-wide single nucleotide polymorphism (SNP) markers in 351 accessions from the whole species range using a matrix-assisted laser desorption/ionization time-of-flight assay, and by sequencing of nine unlinked short genomic regions in a subset of 64 accessions. The observed frequency distribution of SNPs is not consistent with a constant-size neutral model of sequence polymorphism due to an excess of rare polymorphisms. There is evidence for a significant population structure as indicated by differences in genetic diversity between geographic regions. Accessions from Central Asia have a low level of polymorphism and an increased level of genome-wide linkage disequilibrium (LD) relative to accessions from the Iberian Peninsula and Central Europe. Cluster analysis with the structure program grouped Eurasian accessions into K = 6 clusters. Accessions from the Iberian Peninsula and from Central Asia constitute distinct populations, whereas Central and Eastern European accessions represent admixed populations in which genomes were reshuffled by historical recombination events. These patterns likely result from a rapid postglacial recolonization of Eurasia from glacial refugial populations. Our analyses suggest that mapping populations for association or LD mapping should be chosen from regional rather than a species-wide sample or identified genetically as sets of individuals with similar average genetic distances.

Vernalization sensitivity in Arabidopsis thaliana (Brassicaceae): the effects of latitude and FLC variation

Latitudinal variation in climate is predicted to select for latitudinal differentiation in sensitivity to the environmental cues that signal plants to flower at the appropriate time for a given climate. In Arabidopsis thaliana, flowering is promoted by exposure to cold temperatures (vernalization), and several vernalization pathway loci are known. To test whether natural variation in vernalization sensitivity could account for a previously observed latitudinal cline in flowering time in A. thaliana, we exposed 21 European accessions to 0, 10, 20, or 30 d of vernalization and observed leaf number at flowering under short days in a growth chamber. We observed a significant latitudinal cline in vernalization sensitivity: southern accessions were more sensitive to vernalization than northern accessions. In addition, accessions that were late flowering in the absence of vernalization were more sensitive to vernalization cues. Allelic variation at the flowering time regulatory gene FLC was not associated with mean vernalization sensitivity, but one allele class exhibited greater variance in vernalization sensitivity.

(382) Application of a Molecular Marker for Berry Seed Size to Two Populations of Grapevines (Vitis sp.) Developed in a Breeding Program

The development of grapevines with berries with small seed traces, so-called seedless grapes, is a costly process. Marker assisted selection would save time and money. Adam-Blondin et al. (Vitis 40:147. 2001) demonstrated that a sequence characterized amplified region, SCC8, could identify seedless grapevine cultivars in European accessions of Vitisvinifera L. We have applied this marker to two populations of grapevines in a breeding program in California. One population consisted of 100 individuals while the second had 109. The two crosses had a common female parent, derived from `Flame Seedless'. Fruit were evaluated over several seasons for parameters including total weight of seeds or traces. DNA was isolated from leaves during the spring. Amplification was carried out with SCC8 primers, followed by digestion with Bgl II, and agarose gel electrophoresis. Individuals were scored as homozygous SCC8+ (small seeded), heterozygous SCC8+/scc8-(intermediate sized seeds), or homozygous scc8-(large seeded) and mean total seed weight per berry was calculated for each genetic class. In the first population, the number of individuals in the inferred genotypes fit an expected 1:2:1 distribution (χ2 = 0.480, P> 0.787) and seed weights for each genetic class were reasonable. For the second population, it was necessary to postulate a null allele in one parent, with a 1:1:1:1 expected distribution for genotypes SCC8+/SCC8+, SCC8+/null, SCC8+/scc8-, and scc8-/null. The actual distribution was in agreement with this model (χ2 = 4.379, P> 0.223). The genotype SCC8+/null had the SCC8+ marker and total seed weight >10 mg per berry. Large seeded individuals and heterozygotes could be reliably identified with this marker.

Chloroplast Microsatellites to Investigate the Origin of Grapevine

The origin of the grapevine, Vitis vinifera ssp . sativa L., has been investigated with archaeobotanical–archaeological, cultural and historical data indicating a unique domestication centre located in the Caucasian and Middel-East regions about 6–7000 years ago, but, events leading to the domestication of this species are still an open issue. In this work, eight universal chloroplast microsatellites are used to assess genetic relationships among varieties selected as representatives of four distinct geographical groups from Middle-East to Western European regions. Results show that two out of the eight analysed chloroplast loci are polymorphic within the 142 individuals. Allele variants of the cpSSR loci combine in a total of six different haplotypes. The analysis of haplotypes distribution and haplotype diversity (HD) suggest that only three out of the six haplotypes are represented in the Caucasian and Middle-East samples, with 90% of individuals sharing the same haplotype. Moreover, the presence of all six haplotypes in the European accessions, with a high level of haplotype diversity, suggests varietal influx in these areas. Concerning the Western European varieties, especially in Spanish accessions, half of the individuals share haplotype VI which is completely absent in the Caucasian and Middle-East cultivars. This result opens the discussion about the existence of a unique and common domestication centre, located in the Caucasian and Middle-East area, for all the European cultivars.

SSR allelic diversity changes in 480 European bread wheat varieties released from 1840 to 2000

A sample of 480 bread wheat varieties originating from 15 European geographical areas and released from 1840 to 2000 were analysed with a set of 39 microsatellite markers. The total number of alleles ranged from 4 to 40, with an average of 16.4 alleles per locus. When seven successive periods of release were considered, the total number of alleles was quite stable until the 1960s, from which time it regularly decreased. Clustering analysis on Nei's distance matrix between these seven temporal groups showed a clear separation between groups of varieties registered before and after 1970. Analysis of qualitative variation over time in allelic composition of the accessions indicated that, on average, the more recent the European varieties, the more similar they were to each other. However, European accessions appear to be more differentiated as a function of their geographical origin than of their registration period. On average, western European countries (France, The Netherlands, Great Britain, Belgium) displayed a lower number of alleles than southeastern European countries (former Yugoslavia, Greece, Bulgaria, Romania, Hungary) and than the Mediterranean area (Italy, Spain and Portugal), which had a higher number. A hierarchical tree on Nei's distance matrix between the 15 geographical groups of accessions exhibited clear opposition between the geographical areas north and south of the arc formed by the Alps and the Carpathian mountains. These results suggest that diversity in European wheat accessions is not randomly distributed but can be explained both by temporal and geographical variation trends linked to breeding practices and agriculture policies in different countries.

Different Resistance Mechanisms of Medicago truncatula Ecotypes Against the Rust Fungus Uromyces striatus

ABSTRACT A pathosystem consisting of the model plant Medicago truncatula and the rust fungus Uromyces striatus was characterized. From a collection of 113 mostly European accessions of M. truncatula, the vast majority were found to be susceptible to U. striatus, whereas 5 accessions showed strong resistance reactions. Stomatal surface characteristics, even if partly occluded, did not interfere with the ability of U. striatus germ tubes to infect. After penetration, the resistant ecotypes reacted with various degrees of cell death during different stages of haustorial establishment. Whereas four ecotypes showed a typical hypersensitive reaction by developing necrotic lesions, one ecotype (F11.008) exhibited a prehaustorial type of defense without hypersensitive response. This ecotype may be used as a source of nonhost-type of resistance against U. striatus.