Designing resource-efficient ideotypes for new cropping conditions: Wheat ( Triticum aestivum L.) in the High Rainfall Zone of southern Australia

Abstract

With the ultimate aim of developing a Crop Design Tool that will specify resource-efficient ideotypes for any environment, modelling procedures are proposed and tested here whereby wheat phenology can be optimised according to risks of abiotic damage (frost, heat and drought) to seedling establishment and grain set. Then crop growth can be estimated from availability of water and solar radiation, and optimum DM partitioning to grain can be specified by allocating a minimum of support dry matter (DM) to stems (to resist lodging), leaves (to optimise photosynthesis), and flowers (to bear grains). Ideotypes for reference regions (with mature wheat breeding programmes) of the Mallee and Wimmera in Victoria, the Canturbury plains in New Zealand and Norfolk in the UK gave estimated grain yields of 1.9, 3.0, 7.2 and 6.2 t ha −1 DM respectively, similar to those shown by current cultivars, but with earlier flowering and harvest dates, with heavier stems, and high redistribution of stem DM to grain. Ideotypes for five sites in the Australian High Rainfall Zone showed high grain yield potentials, ranging from 4.5 t ha −1 DM at Kojonup to 7.8 t ha −1 DM at Hamilton, allowing for yield loss due to abiotic stress. These were characterised by early stem extension and flowering dates but also by long crop construction periods (from the start of stem extension to anthesis) of 800–1100 °Cd and increased harvest indices compared to cultivars currently adopted from other regions. The challenges in testing these ideotypes will be in finding germplasm that demonstrates unusual phenology with short stature, and growing these to maximise light interception in spring. The main uncertainties in the estimation procedures arose from poor quality wind data, a poorly quantified association between stem material density and stem strength, and lack of data on maximum capacity to store redistributable stem DM. Sensitivity analysis showed grain yields of ideotypes to depend on maximum wind gusts during grain production as well as on plant-available water. The most effective single means of increasing potential grain yields was predicted clearly to be through increasing the conversion of radiation to DM.