Vernalisation and photoperiod sensitivity in wheat: Impact on canopy development and yield components

Genetic variation in the VERNALIZATION1 (VRN1) and PHOTOPERIOD1 (PPD1) genes, which control the vernalisation and photoperiod response, underpin wheat adaptation to different environments. Near isogenic lines were used to investigate the role of allelic combinations of VRN1 and PPD-D1, including new alleles for VRN1-A1, on the length of developmental phases, dynamics of leaf and tiller appearance and yield components in complementary irrigated field trials relevant to low latitude wheat growing areas and controlled conditions. Allelic differences in VRN1 had a stronger effect on the duration of the vegetative phase, while photoperiod sensitivity at PPD-D1 lengthened the stem elongation phase (SE) by up to 23%. If a phase was lengthened, flowering was delayed. The level of response to daylength during stem elongation (SE) introduced by photoperiod sensitive alleles was dependent on the VRN1 composition and vernalisation status. A longer SE under short days was achieved by PPD1 sensitive genotypes when one VRN1 spring allele was present and plants were vernalised. The duration of SE was weakly related to spike dry weight m−2 at DC65 in the field but did not translate into higher grain number m−2. In the field, lines with two to three VRN1 spring alleles had shortest development phases, including SE, close flowering dates, sampled similar temperature environments at different stages, and achieved high yields. Yield advantage was explained by higher biomass, harvest index, grain number m−2 and thousand kernel weight. Genotypes with three winter VRN1 alleles were comparatively disadvantaged, with a longer vegetative phase placing SE under higher temperatures. Allelic differences in both genes caused large variation in leaf and tiller number generation but also in tiller mortality and individual leaf size, lessening the impact on leaf area. Changes in plant morphology and yield components that did not seem mediated via the influence of development genes on the duration of different stages and their impact on resource capture deserve further investigation.