AUTOGAMBEAN: Enhancing breeding progress in faba bean through genomics-assisted pure line selection
Faba bean is considered across Europe to be of critical importance as a break crop in environmentally sustainable arable production systems and as a potentially key input into the animal feed chain. There is a valuable and growing human consumption market which can be accessed for high quality produce. Farmers have moved away from faba bean recently because of highly variable yields and an increase in the prevalence of bruchid beetle, which is difficult to control chemically and renders crops unacceptable for human consumption. Yield gain in faba bean has been negligible over the past 20 years and this fact can be attributed to several factors.
Firstly, breeding is slow and costly due to its outcrossing habit and lack of autofertility as all controlled crossing and line development must be carried out in insect-free cages with manual ‘tripping’ of flowers required to induce self-fertilization. No stable CMS system has yet been characterized, which precludes true hybrid breeding, and breeding efforts are thus focused on exploitation of the high natural diversity in domesticated Vicia faba germplasm via the partial heterosis achieved in composite or synthetic varieties. Lastly, the Vicia faba genome, among one of the largest diploid crop genomes known has remained largely unexplored and genetic map coverage is still poor. This final frontier in crop genomics needs to be addressed and put to service to facilitate step changes in bean breeding. These developments are required so that low nitrogen rotations and home-grown protein crops become once again economically feasible options.
The aim of this project is to utilize all that is currently known about auto-fertility and cleistogamy in Vicia faba to set up a thorough, cutting-edge dissection of the genetic architecture of these two traits, and to combine them in an effort to achieve fully autogamous Vicia faba genotypes. In order to facilitate this ambitious goal, new genomic tools which will allow Vicia faba to catch up with other crop species of equivalent economic importance are required, and this is the equal and complementary focus of this project. The genomic sequence of a set of 1,000 genes representing various putative functions of interest from pollen and flower development to biotic and abiotic stress responses and symbiosis will be determined and re-sequenced in a core diversity set of 8 genotypes.
At least 1,000 of the observed SNPs will be integrated into a HTP SNP detection platform which will be put to use in two ways; firstly, to create a new gene-based reference map of Vicia faba, on which the first traits to be mapped will be autofertility and closed flowering, and secondly, to describe patterns of variation in an association mapping exercise designed to reveal the genomic signature of auto-fertilization. A mutant population will be developed and used to isolate further closed flowering types. Autogamy opens up the route to fast and robust selection for complex traits such as yield, drought tolerance, response in low-input conditions and nutritional composition, all major challenges requiring a breeding response. Any move towards pure line selection and control of degree of self-fertilization will increase the prospects for possible use of hybrid breeding methods in the future. The extent to which the autogamous trait needs to be put into or modulated in a range of diverse backgrounds and the feasibility of such a project, in terms of the genetic complexity and environmental sensitivity of autogamy, will become clear by the end of the project.
