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Australian wheat (Triticum aestivum) producers have been sowing crops earlier to adapt to reduced autumn rainfall, extreme spring weather and increasing farm size. Analysis of sowing date records indicate a shift of around 1.5 days/year over a 10 year period. The most suitable development patterns to maintain or increase yield at earlier sowing times have not been identified. Field experiments were conducted over two years at a range of sites and times of sowing (TOS), comparing a novel cultivar with fast-winter (FW) development to current elite spring and winter cultivars, and near-isogenic lines that differed only in major development genes. In cooler environments, the FW exhibited a more stable flowering time across a broader range of TOS compared to spring or slower developing winter cultivars. The optimal sowing window was shorter in warmer environments for the FW. Early-sown FW wheat yielded 8% more than fast-developing spring wheat sown later but flowering concurrently. FW wheat yielded 17% more than the elite mid-winter cultivar, and 18% more than elite slower developing spring cultivars when averaged across all TOS. The FW development pattern has potential to extend sowing periods while achieving 10–20% higher yields and flowering time stability. Wheat cultivars with altered development patterns must be developed to ensure crops flower during optimal periods from earlier sowing times.

The impact of different allelic combinations of VERNALIZATION1 (VRN1) and PHOTOPERIOD1 (PPD1) on the development of reproductive structures, spike dry weight (SDW) and its links to the duration of stem elongation (SE) and yield components was assessed using Near Isogenic Lines (NILs) of the cultivar Sunstate for both genes. Emphasis was on observations on the main shoot and tillers, linking to plant and canopy level in Steinfort at al. (2016). Experiments under controlled and irrigated field conditions relevant to the northern wheat growing region of Australia were designed. In vernalised plants, the number of fertile florets in the main shoot spike was positively related to the number of fertile spikelets, the duration of SE, the SDW at anthesis and the sum of the radiation intercepted during SE, while no associations were found under non vernalised and slow vernalising field conditions. Vernalised plants also produced more grains in the average tiller spike, compared to non vernalised plants, particularly under short days. Both main shoot and tiller grain number per spike contributed to the higher grain number per plant observed in vernalised plants in Steinfort et al. (2016), as spike number was similar. In the field, higher yield of lines with spring alleles of VRN1 was underpinned by longer spikes, with fewer spikelets but more fertile florets per spikelet in the main shoot spike, and more grains per tiller. When non vernalised, winter lines had an apex that grew slower, shorter spikes and higher spikelet density compared to the other genotypes. The utilisation of sensitivity to VRN1 or PPD1 to increase the duration of the SE and the number of fertile florets and grains is a more complex process than originally proposed.

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.

We developed a photoperiod-corrected thermal model that can predict wheat phenology based solely on the combination of photoperiod (Ppd) and vernalisation (Vrn) alleles to identify the phenological suitability of germplasm across the cropping region in southern Australia. More than 200 wheat genotypes that vary in combinations of Ppd and Vrn alleles were grown at 17 locations spanning 11° Latitude, thus providing a wide range in temperature and daylength gradients. The phenological sensitivities of a genotype to varying basic temperature, photoperiod and vernalisation requirement was adjusted via optimisation to minimise the least square difference between the measured and predicted dates of both terminal spike (TS) and flowering (AN). The model predicted dates of TS and AN to within 5 days of the field values. Information was used to identify the alleles required to achieve a wheat ideotype defined in a previous study. The optimum allelic combinations required to target the optimum flowering period for different locations when sown on different dates were also identified. The use of allelic based phenological models has the potential to reduce the costs to breeding programs and accelerate the release of better adapted germplasm to new and changing environments.

MADS-box transcription factors specify plant meristem identity. In doing so, they determine when floral organs are produced at the shoot apex and control the timing of flowering. The transcriptional activity of key MADS-box genes is controlled by temperature in many plants, and this synchronises flowering with changing seasons. Here we review how seasonal temperature variation influences the developmental programme of plants via transcriptional regulation of MADS-box genes. In particular we examine the role of MADS-box genes in regulating the acceleration of flowering by vernalization (prolonged periods of cold), using FLOWERING LOCUS C of Arabidopsis and VERNALIZATION1 of cereals as examples. A potential role for SHORT VEGETATIVE PHASE-like genes in controlling winter bud dormancy is also examined, as are potential roles for MADS-box genes in regulating developmental responses to elevated growth temperatures. We conclude that understanding how temperature regulates the transcription of MADS-box genes provides insight into how seasonal fluctuations in temperature influence plant development. Plant breeders may be able to use natural variation in temperature-responsive MADS-box genes to breed future crop varieties.

Genetic analyses have identified three genes that control the vernalization requirement in wheat and barley; VRN1, VRN2 and FT (VRN3). These genes have now been isolated and shown to regulate not only the vernalization response but also the promotion of flowering by long days. VRN1 is induced by vernalization and accelerates the transition to reproductive development at the shoot apex. FT is induced by long days and further accelerates reproductive apex development. VRN2, a floral repressor, integrates vernalization and day-length responses by repressing FT until plants are vernalized. A comparison of flowering time pathways in cereals and Arabidopsis shows that the vernalization response is controlled by different MADS box genes, but integration of vernalization and long-day responses occurs through similar mechanisms.