Stabilising the flowering time of wheat in response to autumn rainfall decline in southern Australia




Flohr, Bonnie Maree

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Wheat (Triticum aestivum) production is important to global food security and the livelihoods of those who cultivate it. Increases in water-limited potential yield (PYw) and farm yield (FY) are necessary to keep pace with global demand, and in order for Australian growers to remain competitive in a changing climate and with declining terms of trade. In drought prone environments such as south-eastern Australia, alignment of the key developmental stage of flowering to the period that is optimal for the local climate is a critical determinant of yield. The optimal flowering period (OFP) begins when the risk of frost decreases, and ends to avoid increasing temperature, heat and water stress during grain fill. Flowering time is a function of the interaction between the speed of plant development (genetic, G), establishment date (management, M) and prevailing seasonal conditions (environment, E). Autumn rainfall decline, extreme spring weather and increasing farm size challenge traditional G x M combinations which are currently used to achieve the OFP in south-eastern Australia i.e. predominately fast developing spring wheats sown in late-April to early May. The objective of this study was to identify novel G x M combinations that stabilise flowering and maximise yield under changing rainfall patterns and recent changes to farming systems. This study used crop simulation and conducted field experiments in Temora, New South Wales (NSW); Berriwillock, Victoria; Minnipa, South Australia and Cunderdin, Western Australia. Firstly, OFPs were quantified in south-eastern Australia, the area most affected by autumn rainfall decline to align novel G x M strategies accordingly. Simulation demonstrated that the predicted timing and duration of OFPs varied with site and season. The relative importance of seasonal water supply and demand and extremes of temperature in defining the window also varied. To identify the physiological changes associated with breeding, the PYw and other parameters were quantified and compared at common sowing or flowering dates with a historic set of NSW cultivars released between 1901 and 2014. Genetic improvement through this period, increased grain yield at a rate of 26 kg ha-1 pa-1 regardless of sowing or flowering dates. The slow development and stable flowering observed in historic cultivars and superior partitioning to grain of modern cultivars were independent, and could potentially be combined in new cultivars to achieve future yield gains. Yield results for a novel fast-winter genotype (FW, with photoperiod insensitivity and requiring vernalisation) grown in a diverse set of environments, supported this hypothesis. The FW development pattern extended sowing windows while achieving 10-20% higher yields than current spring cultivars. The flowering stability index (1 minus the ratio of range in thermal time for flowering for each cultivar, to the range in thermal time of sowing dates) of the FW genotype was improved for the sowing dates currently used by farmers. Finally, novel agronomic packages to capture the higher yield potential of FW cultivars was investigated using simulation. Reliance on irregular rainfall to establish FW wheat could be reduced, and early establishment opportunities increased by sowing genotypes with long coleoptiles into stored sub-soil moisture accumulated during fallow. Combining the G x M flowering date stabilising factors; winter wheat, long coleoptile, early sowing and fallow reduced the reliance on autumn rainfall for timely crop establishment to provide a further buffer against seasonal climate variability. Consequently, simulated whole farm yield was increased as a greater area of wheat flowered during the optimal period. To achieve the productivity increases demonstrated here requires continued collaboration between agronomists and breeders. This includes the development of winter wheat cultivars with long coleoptiles that are adapted to different growing season lengths and OFPs, such that crops can be established earlier and emerge from a greater depth than current cultivars.



grain yield, optimal flowering period, phenology, time of sowing, wheat




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