Utilización de variedades primitivas en la ampliación de la base genética de Vicia faba L

Abstract

Nowadays, the main crops are characterized by their limited genetic diversity. The narrowing of the genetic diversity caused dramatic consequences in the past, and, thus, it supposes a serious threat to the future. As a consequence, the widening of the genetic bases is a crucial goal to deal with this problem. In faba bean (Vicia faba L.), the best option to cope with this problem is the use of old cultivars. However, the use of this material also implies difficulties. Indeed, old cultivars contain beneficial alleles for most of the traits of interest in breeding. However, these alleles are usually linked with other undesirable alleles. The existence of „blocks of genes‟ have been usually referred by breeders as „co-adapted genes‟ to highlight the that the transfer of a single gene from old cultivars to new ones is far from easy. In this context, it is crucial to investigate the genetic basis for the traits of interest and, similarly, the development of new plant materials which allow these studies is a worthy objective in itself. Thus, we proposed the specific objectives of this PhD thesis. This thesis has allowed the development of several Recombinant Inbred Line (RIL) populations derived from crosses between genotypes belonging to the four botanic types described in this species: major, equina, minor and paucijuga. These populations constitute an idoneous plant material to investigate the genetic basis of yield-related traits throughout genetic mapping. Similarly, the characterization of early generations of these populations (F2 and F2:3) has provided valuable information on the genetic basis of the traits of interest in breeding. Furthermore, the extensive phenotyping of the individuals forming these RILs may allow the identification of new individuals with high potential for the faba bean breeding program. The development of new biotechnological resources, such as sequencing of model species, constitutes an important source of information for faba bean. Indeed, the existence of synteny among legumes makes possible the transference of knowledge from one species to another. However, the synteny relations between faba bean and the model species Medicago truncatula L. were incomplete since all previous efforts had failed to assign chromosome IV from V. faba to M. truncatula. However, the results obtained in this thesis have allowed overcoming this situation which has benefited the development of consensus maps in the species. Similarly, molecular tools also facilitate the transference of traits (genes) from old plant materials to elite cultivars. Indeed, the identification of molecular markers tightly linked to genes/QTL would allow their quick selection in breeding programs. However, the association between markers and traits has to be validated in different environmental conditions and/or genetic backgrounds prior to their effective use in breeding programs. In this thesis we have validated several QTLs for plant architecture and yield-related traits in the RIL population derived from the cross Vf6 × Vf27. In some cases, these QTL have been identified in a previous work but their validation was still pending. Our work has allowed both the validation of some important QTLs and the identification of new regions related to the traits under study. Furthermore, some QTLs have been validated using four different F2 populations and/or through comparison with previous works based on common markers around the regions of interest. All this information will be very useful to breeding programs. Finally, although molecular markers linked to traits of interest are very useful their selection efficiency diminish with the distance to the gene/QTL responsible of the trait. Thus, the identification of candidate genes directly responsible of the variation is very interesting since they allow the development of diagnostic markers, i.e., markers with selection 100% selection efficiency. The existence of synteny among legumes, along with comparative mapping efforts, has proven the existence of a high degree of collinearity between faba bean and M. truncatula. Thus, the public release of the M. truncatula genome sequence constitutes a valuable source of information for faba bean. These resources have allowed us the identification of candidate genes for plant height in the chromosome III. In summary, this thesis has produced the following advances: (i) increased knowledge of the genetic basis of agronomic and yield-related traits in faba bean; (ii) identification of chromosome IV of faba bean for synteny-related projects; (iii) validation of QTLs and identification of candidate genes to increase the opportunities for markerassisted selection; (iv) establishment of the bases for more detailed studies such as genotype x environment variation throughout the development of suitable plant materials.