Take home messages

• The changing Australian climate is shifting rainfall later in the winter crop season
• The development of a short-season, winter-sown commercial wheat would provide growers with greater flexibility and options
• Winter-sown wheats have the potential to yield well in mild climatic years but are sometimes too phenologically slow
• Further development is required for the release of a commercial variety specifically bred for short-season scenarios.

Background

With a decrease in autumn rainfall attributable to a changing climate (Bureau of Meteorology 2022), and an increase in the spread of herbicide resistant weeds, there is an urgent need for wheat varieties that can be sown late, defined here as being after May and commonly mid-to-late June. Currently, there are limited wheat varieties available to southern and western Australian growers that are phenologically suited to late sowing. A late-sown short-season wheat variety would enable growers to sow mid-winter, into near guaranteed soil moisture and after time-costly double knock strategies have occurred. However, due to the majority of commercial lines possessing a combination of winter alleles of vernalisation and photoperiod genes, these varieties need to be sown in autumn. Often this autumn sowing either results in sowing dry or before appropriate weed control and soil amelioration strategies are finished. If current commercial varieties are sown later in the season, anthesis will occur after the optimum flowering period (OFP) (Flohr et al., 2017). This can lead to significant decreases in grain yield as the risk of heat and drought stress impacting sensitive floral organs greatly increases (Ullah et al., 2022). This paper is a combined analysis of two experiments aimed to (1) determine the ideal combination of flowering genes for late sown southern Australian conditions; and (2) analyse current commercial varieties for their suitability to late sowing.

Methods

Field experiments were conducted at the Wagga Wagga Agricultural Institute in 2022. The aim of the first experiment was to analyse a set of high early vigour pre-breeding wheat genotypes and commercial cereal varieties for their suitability to winter sowing. The 48 wheat genotypes were sown in a randomised complete block design with three replicates of each genotype. Plots were sown to 9m of 6 rows 25cm apart. The second experiment utilised eight near-isogenic wheat lines (NILs) that differed only for their vernalisation and photoperiod alleles (Steinfort et al., 2017). This experiment was sown on June 14 as a split plot design with four replicates of each genotype per heating treatment. The heating treatment was applied using heating cables laid and commenced one week after sowing and removed three weeks later. The heating cables increased soil temperature of the heated plots by approximately 8°C. The specific aim of this experiment was to analyse the effect of temperature and phenology linked genes on the growth and development of short season wheat. Throughout the season, essential metrics including biomass at key stages, phenology, ground cover, light interception, and tiller number were recorded. The inner four rows of plots were hand harvested at maturity to provide final grain yield and other derived harvest metrics. The data were analysed by linear mixed models fitted using ASReml-R (The VSNi Team 2023). Spatial variation was accounted for within the residual component of the model.

Results and discussion

In the first experiment regarding the evaluation of late-sown wheats, none of the commercial varieties flowered within the OFP. A modelled study by Flohr et al., (2017) revealed that the peak mean yield OFP for a mid-fast spring wheat sown at Temora, the closest town to Wagga Wagga in the study, was October 3. It was also modelled in that study that for a wheat to achieve optimum yield on this date it would have been sown on May 14 and would reach an estimated grain yield of 3.04 t/ha. However, as shown in Figure 1, all the wheat genotypes flowered well after October 3, on an average date of October 22, nearly three weeks after the modelled optimum. The single barley genotype, the variety Fathom, flowered on average on October 15, over a week after the optimum date. In terms of yield, the majority of genotypes yielded greater than the model presented in Flohr et al., (2017), with the mean wheat yield of the experiment being 5.5t/ha. However, this was under experimental plot conditions and may be difficult to replicate in full scale paddocks. With sowing occurring on June 14, anthesis would therefore have needed to occur 111 days after sowing to coincide in the OFP.

Figure 1. The relationship between yield (t/ha) and anthesis date for 48 cereal genotypes grown at Wagga Wagga in 2022. Data points represent four groups: barley (red circle), commercial (green triangle), early vigour pre-breeding genotypes (EV) (blue square), and others (purple cross).

All the wheat genotypes in the first experiment possessed at least one winter vernalisation allele, which likely delayed flowering time until after the OFP. The second experiment used NIL wheats that contained combinations of the photoperiod-associated PPD-B1 and PPD-D1 genes and the vernalisation-associated VRN-A1, VRN-B1, and VRN-D1 genes to investigate their individual impacts on growth and development, and their interactions with temperature. A linear mixed model of the effects of genotype and heating treatment revealed no significant effect of treatment (p>0.05) on days to anthesis. Figure 2 summarises the differences in days to anthesis between genotypes. The NILs with a spring (a) allele (represented by an “a”) of the photoperiod associated genes (PPD-B1 and PPD-D1) all took significantly (p<0.05) less days to anthesis than those possessing both winter alleles (represented by a “b”). Amongst NILs with both spring photoperiod alleles (W077, W005, and W007), only W077 had significantly less days to anthesis than W007, likely due to its full complement of spring vernalisation alleles (also represented by “a” in contrast to the winter alleles “v”). W103 had an extra frost tolerance allele at FR-A2 not possessed by any other NIL which slightly delayed its development.

Figure 2. Boxplot illustrating the variation in days to anthesis across NIL genotypes sown in 2022 at the Wagga Agricultural Institute. Each box represents the interquartile range (IQR) of observations for a specific genotype, with the median shown as a horizontal line within the box. Whiskers extend to 1.5 times the IQR, and dots represent outliers. The least significant difference (LSD) in the upper right-hand corner represents statistical significance at a p value of 0.05. Allelic data is displayed in brackets next to each genotypes name for the following order of genes: PPD-B1, PPD-D1, VRN1-A, VRN1-B, VRN-D.

Conclusions

Both experiments (evaluation of genotypes for grain yield in a late sown scenario, and the temperature by NIL genotypes), have aided in the understanding of factors critical in the development of a late-sown, short-season wheat. The first experiment demonstrated that current commercial wheat varieties are phenologically too slow for late sown scenarios. Despite the greater than modelled yields observed in this study, it is likely that in less forgiving years they would suffer larger yield penalties. The second experiment demonstrated that shorter times to anthesis are possible with the right combination of development alleles i.e. a full complement of spring photoperiod and vernalisation alleles. These experiments have demonstrated that profitable grain yields are achievable in late-sown, short-season scenarios but that further development is required for a commercial variety suited to this sowing window.

Acknowledgments

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support. And to Ben Trevaskis for the phenology NILs.

References

Bureau of Meteorology (2022) State of the climate 2022. No. 1486317707.

Flohr BM, Hunt JR, Kirkegaard JA, Evans JR (2017) Water and temperature stress define the optimal flowering period for wheat in south-eastern Australia. Field Crops Research 209, 108-119.

Steinfort U, Trevaskis B, Fukai S, Bell KL, Dreccer MF (2017) Vernalisation and photoperiod sensitivity in wheat: Impact on canopy development and yield components. Field Crops Research 201, 108-121.

The VSNi Team (2023) asreml: Fits Linear Mixed Models using REML.

Ullah A, Nadeem F, Nawaz A, Siddique KMH, Farooq M (2022) Heat stress effects on the reproductive physiology and yield of wheat. Journal of Agronomy and Crop Science 208, 1-17.

Contact details

Timothy Green
Charles Sturt University
Email: tigreen@csu.edu.au

Date published
February 2025

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