Model plants are facilitating the genetic characterization and comparative mapping of a number of traditional crops. Medicago truncatula has been widely accepted as a model plant to this end as it provides the essential tools for multiple aspects of legume genetics and genomics. A large set of markers from highly conserved M. truncatula gene regions is being created and used to establish a worldwide framework for comparative genomic studies in legumes. We have investigated the potential for cross-species amplification of 209 expressed sequence tag (EST)-based and 33 bacterial artificial chromosome (BAC)-based microsatellites from M. truncatula in the three most important European legume pulses-pea, faba bean and chickpea-that might facilitate future comparative mapping. Our results revealed significant transferability of M. truncatula microsatellites to the three pulses (40% in faba bean, 36.3% in chickpea and 37.6% in pea). The percentage of M. truncatula EST-SSRs (simple sequence repeats) amplified in the three crops (39-43%) was twofold higher than that of the genomic SSRs (21-24%). Sequence analysis determined that the level of conservation in the microsatellite motif was very low, while the flanking regions were generally well conserved. The variations in the sequences were mainly due to changes in the number of repeat motifs in the microsatellite region combined with indel and base substitutions. None of the functional microsatellites showed direct polymorphism among the parental genotypes tested, consequently preventing their immediate use for mapping purposes.

BackgroundFaba bean (Vicia faba L.) is among the earliest domesticated crops from the Near East. Today this legume is a key protein feed and food worldwide and continues to serve an important role in culinary traditions throughout Middle East, Mediterranean region, China and Ethiopia. Adapted to a wide range of soil types, the main faba bean breeding objectives are to improve yield, resistance to biotic and abiotic stresses, seed quality and other agronomic traits. Genomic approaches aimed at enhancing faba bean breeding programs require high-quality genetic linkage maps to facilitate quantitative trait locus analysis and gene tagging for use in a marker-assisted selection. The objective of this study was to construct a reference consensus map in faba bean by joining the information from the most relevant maps reported so far in this crop.ResultsA combination of two approaches, increasing the number of anchor loci in diverse mapping populations and joining the corresponding genetic maps, was used to develop a reference consensus map in faba bean. The map was constructed from three main recombinant inbreed populations derived from four parental lines, incorporates 729 markers and is based on 69 common loci. It spans 4,602 cM with a range from 323 to 1041 loci in six main linkage groups or chromosomes, and an average marker density of one locus every 6 cM. Locus order is generally well maintained between the consensus map and the individual maps.ConclusionWe have constructed a reliable and fairly dense consensus genetic linkage map that will serve as a basis for genomic approaches in faba bean research and breeding. The core map contains a larger number of markers than any previous individual map, covers existing gaps and achieves a wider coverage of the large faba bean genome as a whole. This tool can be used as a reference resource for studies in different genetic backgrounds, and provides a framework for transferring genetic information when using different marker technologies. Combined with syntenic approaches, the consensus map will increase marker density in selected genomic regions and will be useful for future faba bean molecular breeding applications.

Broomrape (Orobanche crenata Forsk.) is a major root-parasite of faba bean (Vicia faba L.), that seriously limits crop cultivation in the whole Mediterranean area. This parasitic weed is difficult to control, difficult to evaluate and the resistance identified so far is of polygenic nature. This study was conducted to identify genetic regions associated with broomrape resistance in recombinant inbred lines (RILs) and to validate their previous location in the original F(2) population derived from the cross between lines Vf6 and Vf136. A progeny consisting of 165 F(6) RILs was evaluated in three environments across two locations in 2003 and 2004. Two hundred seventy seven molecular markers were assigned to 21 linkage groups (9 of them assigned to specific chromosomes) that covered 2,856.7 cM of the V. faba genome. The composite interval mapping on the F(6) map detected more quantitative trait loci (QTL) than in the F(2) analysis. In this sense, four QTLs controlling O. crenata resistance (Oc2-Oc5) were identified in the RI segregant population in three different environments. Only Oc1, previously reported in the F(2) population, was not significant in the advanced lines. Oc2 and Oc3 were found to be associated with O. crenata resistance in at least two of the three environments, while the remaining two, Oc4 and Oc5, were only detected in Córdoba-04 and Mengíbar-04 and seemed to be environment dependent.

Ascochyta blight, caused by Ascochyta fabae Speg., is a disease of faba bean (Vicia faba L.) of worldwide distribution. In this study we have conducted an experiment on Ascochyta fabae resistance in 165 recombinant inbred lines (RILs) developed by single-seed descent from the cross between resistant and susceptible lines (Vf6 × Vf136) in which A. fabae resistance QTLs (quantitative trait loci) have been previously reported in the original F2 population. Recombinant inbred lines were inoculated under controlled growth chamber conditions and evaluated for disease severity and infection type index. The linkage map was constructed by MAPMAKER V2.0 and the QTL analysis was carried out using QTL Cartographer. Two hundred and seventy-seven markers (238 RAPDs, 4 isozymes, 5 ESTs, 1 SCAR, 6 SSRs, 2 STSs, and 21 intron-spanning markers) mapped into 21 linkage groups covering 2.856.7 cM, with a mean inter-marker distance of 12.72 cM. Composite interval mapping identified two zones of putative QTL action in the RIL population for DSL (disease severity on leaves) and DSS (disease severity on stems) traits. Putative QTLs (Af1 and Af2) were identified on chromosome 3 and chromosome 2, respectively, and jointly explained 24% of the phenotypic variance of DSL and 16% of DSS. With this study we have (1) confirmed the QTLs for ascochyta blight resistance found in F3 families in the derived RILs (F6), (2) re-estimated their position and genetic effects, and (3) assessed the stability of these QTLs in different genetic backgrounds by comparison of the mapping data with a previous QTL study.

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