Introgression of an intermediate VRNH1 allele leads to reduced vernalization requirement without affecting freezing tolerance

The process of vernalization is mainly controlled by two genes in winter barley (Hordeum vulgare L.), VRNH1 and VRNH2. A recessive allele at VRNH1 and a dominant allele at VRNH2 must be present to induce a vernalization requirement. In addition, this process is usually associated with greater low-temperature tolerance. Spanish barleys originated in areas with mild winters and display a reduced vernalization requirement compared with standard winter cultivars. The objective of this study was to investigate the genetic origin of this reduced vernalization requirement and its effect on frost tolerance. We introgressed the regions that carry VRNH1 and VRNH2 of a typical Spanish barley line into a winter cultivar, Plaisant, using marker-assisted backcrossing. We present the results of a set of 12 lines introgressed with all four possible combinations of VRNH1 and VRNH2, which were evaluated for vernalization requirement and frost tolerance. The reduced vernalization requirement of the Spanish parent was confirmed, and was found to be completely due to the effect of the VRNH1 region. The backcross lines showed no decline in frost tolerance compared with that of the recurrent parent unless they carried an extra segment of chromosome 5H. This extra segment, a carryover of the backcross process, apparently contained the well-known frost tolerance QTL Fr-H2. We demonstrate that it is possible to manipulate the vernalization requirement with just minor effects on frost tolerance. This finding opens the path to create new types of barley cultivars that are better suited to specific environments, especially in a climate-change scenario.