engleski

Progress on the Vicia faba map and applications for breeding

One of the main goals of our group has been to develop a genetic map of faba bean as a necessary complement of tagging of genes of agronomic interest. After successful identification and characterisation of five of the six possible primary trisomics, crosses between an asynaptic line and a normal diploid parent allowed us to generate a composite genetic map of linkage groups localised to their respective chromosomes. Eleven F2 populations with a total of 654 individuals sharing a common female parent were analysed simultaneously. Linkage analysis revealed 15 major linkage groups, 7 of which were located on specific chromosomes. The present map has allowed the detection of QTLs for important agronomic traits as seed weight or broomrape and Ascochyta fabae resistance as well as to tag a gene controlling resistance to Uromyces fabae. A map useful for marker-assisted selection requires saturation especially in the regions harbouring agronomically important traits. Our future aims include: (1) extend the genome coverage to attach all currently unassigned markers and reduce the number of linkage groups to six., (2) continue the mapping of new major genes and QTLs of agronomic interest, and test them in multiple environments and in different genetic backgrounds to identify the QTLs with more stable expression and, (3) establish the extent of synteny between Vicia faba and other legume species. V. faba belongs to what is considered the basal genus in the Viciaceae and thus information about the arrangement of genes on its genome should be very important for examining the evolution of the genome structure in the tribe. However, V. faba possesses one of the largest genomes among legumes (cca. 12.000 Mb), compared with other better-characterized crops as soybean, pea or Medicago (cca. 1.200, 4.000, and 450 Mb, respectively). The large genome size make complete sequencing a cumbersome and costly task and seriously complicate the identification and location of important genes. Syntenic relationships within botanical families make it possible to use plant species with much smaller genomes to facilitate understanding of those with large genomes. At present, molecular studies of faba bean have been limited to morphological traits, isozymes, a few seed-protein genes and microsatellites, and a great amount of RAPD markers. The latter enabled genetic maps to be constructed rapidly, but such maps cannot be aligned with those of other species. To overcome this, we are transforming a set of RAPD markers. The latter enabled genetic maps to be constructed rapidly, but such maps cannot be aligned with those of other species. For breeding purposes, special interest is being focused on RAPD markers tightly linked to genes or QTLs of agronomic interest. In addition to this, 75 Medicago truncatula PCR-based primer pairs and 17 STSs pea markers are being tested on genomic DNA from our faba bean mapping parents. A parallel analysis is being conducted in our chickpea and pea parental lines. There is little information available to predict transferability of STS markers but their ease of assay enables them to be tested empirically. As a large number of STSs are being developed in M. truncatula or pea, even a relatively low level of transferability will provide a valuable marker resource.

Vicia faba; linkage map; trisomics; QTLs; synteny

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