Abstract
Frost stress is one of the abiotic stresses that causes a significant reduction in winter faba bean yield in Europe. The main objective of this work is to genetically improve frost tolerance in winter faba bean by identifying and validating QTL associated with frost tolerance to be used in marker-assisted selection (MAS). Two different genetic backgrounds were used: a biparental population (BPP) consisting of 101 inbred lines, and 189 genotypes from single seed descent (SSD) from the Gottingen Winter bean Population (GWBP). All experiments were conducted in a frost growth chamber under controlled conditions. Both populations were genotyped using the same set of 189 SNP markers. Visual scoring for frost stress symptoms was used to define frost tolerance in both populations. In addition, leaf fatty acid composition (FAC) and proline content were analyzed in BPP as physiological traits. QTL mapping (for BPP) and genome wide association studies (for GWBP) were performed to detect QTL associated with frost tolerance. High genetic variation between genotypes, and repeatability estimates, were found for all traits. QTL mapping and GWAS identified new putative QTL associated with promising frost tolerance and related traits. A set of 54 SNP markers common in both genetic backgrounds showed a high genetic diversity with polymorphic information content (PIC) ranging from 0.31 to 0.37 and gene diversity ranging from 0.39 to 0.50. This indicates that these markers may be polymorphic for many faba bean populations. Five SNP markers showed a significant marker-trait association with frost tolerance and related traits in both populations. Moreover, synteny analysis between Medicago truncatula (a model legume) and faba bean genomes was performed to identify candidate genes for these markers. Collinearity was evaluated between the faba bean genetic map constructed in this study and the faba bean consensus map, resulting in identifying possible genomic regions in faba bean which may control frost tolerance genes. The two genetic backgrounds were useful in detecting new variation for improving frost tolerance in winter faba bean. Of the five validated SNP markers, one (VF_Mt3g086600) was found to be associated with frost tolerance and FAC in both populations. This marker was also associated with winter hardiness and high yield in earlier studies. This marker is located in a gene of unknown function.
Highlights
Faba bean is primarily grown as a livestock feed in Europe, while, it is used as a food crop in developing countries due to its highly protein content which ranges from 19 to 39% (Maxted and Bennett, 2001)
The objectives of this study were (1) to construct a genetic map for faba bean using recombinant inbred lines (RILs) population and identify QTL for traits associated with frost stress tolerance, (2) to validate some QTL associated with frost tolerance that were previously reported by Sallam and Martsch (2015) in a different genetic background (RILs population), and (3) to identify candidate genes underlying common QTL controlling frost tolerance in both genetic backgrounds using synteny between the M. truncatula and faba bean genomes
The high genetic variation between genotypes in Biparental population (BPP) and Gottingen Winter Bean population (GWBP) for all traits promises the improvement of frost tolerance in winter faba bean in breeding and genetics programs
Summary
Faba bean is primarily grown as a livestock feed in Europe, while, it is used as a food crop in developing countries due to its highly protein content which ranges from 19 to 39% (Maxted and Bennett, 2001). Frost stress is a major abiotic factor, which affects faba bean growth. Faba bean is considered to be one of the most cold-tolerant major grain legumes. Frost resistance is a limiting factor to faba bean production and productivity in many regions. The faba bean germplasm has different levels of frost tolerance, reaching a maximum in the French cultivar Côte d’Or which can tolerate down to −25◦C without snow coverage (Picard et al, 1985). Faba bean is sown as a spring crop in cool temperate climate countries due to insufficient winter-hardiness and frost tolerance in the current Autumn-sown genotypes (Arbaoui, 2007; Arbaoui et al, 2008a). Breeding for winter faba bean is urgently needed to produce resistant and high yielding cultivars
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