Winter hardiness in faba bean: Physiology and breeding

Winter types of faba bean (Vicia faba L.) have existed for at least 200 years. Their superior use of the growing season confers strong yield advantages over spring beans. Nevertheless, yield increases have been slower than in many other crops. There are few sources of winter hardiness and efforts are in progress to combine favourable alleles from accessions such as Cote D’Or and BPL 4628 to increase the crop’s tolerance to frost. Vernalization requirements are quantitative, as vernalization hastens flowering rather than allowing it. Hardening is associated with increases in fatty acid desaturation of membrane lipids and increases in content of soluble osmoprotectants such as proline. Other osmotically active factors such as glycinebetaine, trehalose and antifreeze proteins have not yet been reported for faba bean. Frost tolerance increases after hardening and shows good heritability (h2 = 0.89). Three QTLs (3.6 < LOD < 4.6) have been identified for frost tolerance (explaining 8.6% of the phenotypic variation), and further QTLs for hardening response and cell membrane fatty acid composition. Information on responsive genes and the mode of their action is increasingly available from model plant species but most remains as yet untested in faba bean. There is clear potential for increasing the winter hardiness and yield of winter faba bean so it can be grown in a wider area than at present.