Phenotyping root function in wheat

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In the UK, approximately 30% of the production of wheat is on soils where insufficient soil moisture decreases yields by (on average) 1-2 t/ha. This costs between £112M and £224M each year in lost production (Foulkes et al. 2001). Studies comprising a limited range of wheat cultivars have shown that genotypes with deep root systems have been associated with high yield in water limited environments, while those with shallow root systems have been associated with increased nutrient uptake when soil water is plentiful. However, there is no comprehensive understanding of what configuration of root system architecture leads to improved resilience of yields, water and nutrient use efficiency, or what the trade-offs, if any, there are with yield potential. This is because roots are hidden underground, and important traits are discovered only by laborious, destructive excavation of roots. This project will develop a rapid, non-invasive technique using electromagnetic inductance (EMI) to measure the degree of soil drying at different depths in plots of different wheat varieties. Current EMI technology can be used to profile with changes in conductance with depth, but is not being used to study root activity. A key objective for the project will be to optimise the existing capabilities of EMI, so that they can be used to characterize water extraction profiles beneath different varieties of wheat. We will use electrical resistance tomography (ERT), which is labour intensive, invasive and slow, as a tool to provide high resolution images of soil drying to help with the optimisation of EMI which is rapid, non-contact and efficient. Patterns of soil moisture extraction through the soil profile as the crop develops, which are related to growth and activity of the root system, will be measured with EMI. These data will be validated using conventional techniques such as root sampling via soil coring, buried soil moisture probes, changes in soil strength via penetrometer measurements, and root pulling strength. Initial field tests will comprise 20 UK élite wheat lines, some of which in preliminary data have shown differences in soil water extraction patterns. We will use our new root phenotyping tool kit in field trials with the Avalon x Cadenza mapping population, which has already shown significant genetic variation for nutrient uptake, yield and grain quality. We will determine the correspondence between QTLs identified with our new tool kit and wheat root QTLs already published. We will use soil drying data at various depths to test hypotheses that describe relationships between yield, deep water extraction, soil strength and root placement within drying superficial soil layers. This information is essential for the breeder: for instance, it is not enough to know which varieties can produce deeper roots; confirmation that such a root system translates to greater yield and yield stability across a range of environments is also required before any investment is made in selection for particular root traits. At the start of the project we will establish a project advisory panel comprising breeders and other members of industry to help guide the selection of materials for investigation. This project will provide a completely new measurement possibility that can be applied to large field trials to give a spatial map of soil water at different depths over time. With the help of the project advisory panel we will identify existing field trials that can be used to test our new methods. There are numerous laboratory methods available for phenotyping roots in seedlings that have led to the discovery of QTLs linked to various root traits. However, it is rare that any of these QTLs are validated under field conditions because current methods of examining roots in the field are time-consuming and expensive. The proposed studies will fill this gap, and can possibly complement work on wheat roots in the BBSRC-LINK project based at NIAB.