Objective 12 - Kim Hammond-Kosack, Malcolm Hawkesford (RRes) and John Foulkes (UoN)

Interconnections between the three soil-based explored traits (UNo and RRes)

The project addresses the genetic improvement of three soil-based traits (N-use efficiency, drought tolerance and take-all resistance/soil build-up) amongst which there will be interconnections. Abiotic stresses rarely occur alone since there are fundamental linkages between them, eg N and water stresses. Therefore breeders must ultimately devise strategies for tolerance to multiple stresses. The interaction between N availability and drought is of particular importance for sustainable wheat production in the UK. In this project we will pay particular attention to the difference in the trade-off of plasticity between NUE and water-use efficiency. The effects of take-all on the crop are similar to those of drought except that it usually causes a progressive limiting of water and N uptake through the season, rather than the relatively sudden and severe effects of drought. Therefore, it is expected there will be some traits conferring tolerance of both drought and take-all root loss, e.g. high stem carbohydrate reserves. In addition, some drought-tolerance traits may influence take-all incidence/severity. For example, economy of tillering (avoiding excessive shoot numbers) is an indicator of efficient water-use and may be linked with restricted crown root production potentially diminishing the rate of secondary infection (infection arising from tissue already infected with the pathogen). The proposed analysis across trait areas will be possible in the following ways:

1. Phenotyping trials dissecting components of NUE and WUE
The phenotyping trials (varieties and exotic lines) in the NUE and WUE topic areas will include at least six common genotypes. For common genotypes key indicators of WUE and NUE at harvest would be assessed in both sets of trials. In the NUE trials, grain samples will be analysed for WUE using the C12/13 technique; and in the WUE trials grain and straw samples analysed for N% using the Dumas method. This data set will allow us to analyse the trade-offs and synergies between the two trait areas with a mechanistic basis.

2. AE Watkins and Gediflux European Collection (drought tolerance and take-all)
Drought-tolerance traits and take-all resistance will be assessed in both topic areas in the AE Watkins and Gediflux Collections allowing cross analysis to test for associations between traits (eg tiller economy) and take-all incidence; as well as impacts of traits on yield components.

3. Avalon x Cadenza DH population (NUE and take-all resistance)
It is proposed that genetic markers for NUE and take-all inoculum build-up will be determined using in the Avalon x Cadenza DH population, allowing QTL locations for N uptake and inoculum build-up to be compared. Co-location of QTLs would indicate common processes involving rooting sub-traits may be involved in N capture and inoculum build-up.

4. Exploring the performance of the best drought tolerance and take-all resistant germplasm in the NUE diversity trial at 4 N rates
In years 4 and 5 of the NUE diversity trial, there will be included four hexaploid genotypes which exhibit a high level of drought tolerance and another four genotypes which exhibit the highest level of resistance to the take-all fungus. If germplasm of this type is abundant, then the selected germplasm will be of diverse parentage Take-all acts to reduce the root system’s ability to supply the plant with adequate water and nitrogen.Once a take-all infection becomes well established its action is in effect to sever the infected root. The main consequence of this is to reduce water and nutrient uptake by the crop (Pillinger et al., 2005). Initially during tillering and stem elongation the main impact is on N uptake. As the stage of development of the crop progresses and nitrogen uptake nears completion, the effect of the disease shifts more towards limitation of water uptake. It is reasonable, therefore, to expect some commonality between varietal traits conferring tolerance of root loss through take-all infection and those conferring tolerance of low N availability and/or drought. Although the disease will not present in the diversity trial, the inclusion of both the drought and take-all resistant genotypes will help to determine whether an underlying common mechanism operates when an abiotic stress, namely N limitation, is imposed. The results of the three-way trait experiment will improve understanding of the multiple stress interactions and help to define ideotypes pyramiding soil-related tolerance traits to maintain yields and quality and reduce the environmental foot-print of non-first wheats.

By taking a range of measurements within the crop as well as at harvest and post-harvest, the inter-relationships between the traits can begin to be explored. Measurements will include soil N uptake and water capture estimated from destructive soil cores taken at the start of stem elongation (GS31) and pre harvest (GS92) split into four horizons: 0-30, 30-60, 60-90 and 90-120 cm. Gravimetric analysis of soil cores will be used to estimate soil water content and chemical analysis used to determine soil N levels. In addition, this data will provide and indirect measure of root activity. Above-ground drought tolerance traits (stem soluble carbohydrate, the stay green trait and WUE) will be assessed using the methods described under activity 9. In addition, the grain yield and quality measurements obtained will be of great interest to agronomists.

Pillinger, C., Paveley, N., Foulkes, M.J., Spink, J. 2005. Explaining variation in the effects of take-all (Gaeumannomyces graminis var. tritici) on nitrogen and water uptake by winter wheat Plant Pathology 2005 54, 491–501.