The influence of photoperiod on the Vrn-H2 locus (4H) which is a major determinant of plant development and reproductive fitness traits in a facultative X winter barley (Hordeum vulgare L.) mapping population

To determine the effect of Vrn-H2 locus on plant developmental and agronomic traits, detailed controlled environment tests involving a factorial set of vernalization and photoperiod treatments were carried out using doubled haploid lines developed from a facultative (Vrn-H2(-)) x winter (Vrn-H2(+)) barley cross. The allele phase at the Vrn-H2 locus influenced heading date as well as the developmental and agronomic traits. The performance of Vrn-H2(+) lines was significantly influenced by vernalization: reproductive fitness traits showed significant decreases without vernalization. However, the effects of alleles at the Vrn-H2 locus extended beyond simple satisfaction of the vernalization requirement. Vrn-H2(+) lines showed increased reproductive fitness compared with Vrn-H2(-) lines when vernalization was followed by a long photoperiod. The responses of the two Vrn-H2 allele classes to photoperiod duration were quite different in terms of heading date, developmental and agronomic traits. These results suggest that alleles at the Vrn-H2 locus - and/or tightly linked gene(s) - respond primarily to the exogenous signal of vernalization (temperature), but when the vernalization requirement has been fulfilled, they also respond to photoperiod duration.