Adaptive significance of functional germination traits in crop wild relatives of Brassica

Functional germination traits contribute to both niche competitiveness and crop yield outcomes. However, there is little understanding of the adaptive significance of the germination thermal- and hydro-parameters in crop wild relatives (CWRs), yet these species are anticipated to be the source of adaptive traits for future agriculture. Seeds of 10 seed lots of Brassica species, sub-species and inbred lines from across Europe, North Africa and the Middle East were subjected to a range of temperature and water potential conditions. The germination progress curves recorded were analysed using repeated probit analysis and the functional trait parameters (thermal- and hydro thresholds and times) determined. Relationships between these seed parameters (and the physical trait, seed mass) and the seed source environment were investigated. The Brassica genus was found to have diverse seed germination phenotypes, with thermal (theta(T)) and hydro times (theta(H)) differing by 3 to 7-fold, base temperatures (T-b) by c. 9 degrees C and base water potentials (Psi(b)) by -1.5 MPa. Crop seed lots of Brassica oleracea had shorter theta(H) for germination and higher values of Psi(b), but longer theta(T) for germination than their CWR. For the CWRs, the mean monthly precipitation and the precipitation of the predicted month of germination of the seed collection site, was linearly correlated with T-b, theta(T), and Psi(b). This increases the predictability of identifying valuable brassica germplasm for crop development through regeneration trait screening. In conclusion, the selection of the crop B. oleracea for fastest germination under irrigated conditions likely limits the capacity of the current genepool to cope with erratic periods of drought predicted in future European climates.