The project is suitable for students with a BSc degree (minimum upper second class honours) in biology, chemistry, environmental science or a closely related science.
Phosphorus (P) deficiency is a major constraint to crop production globally due to the limited availability and high cost of P fertilizer resources coupled with low mobility of P in most soils. Certain plant species are well-adapted to growth on low-P soils through a combination of mechanisms internal to the plant allowing more growth for a given amount of P, and external to it, allowing more P uptake for a given concentration in the soil. A promising strategy for more-efficient use of P reserves is to exploit such mechanisms to breed more P-efficient crop varieties. Upland rice – which, unlike lowland, paddy rice, is grown in unflooded conditions – is particularly well adapted to low P soils, and efficient donor genotypes have been identified. Upland rice is a major staple crop, particularly in sub-Saharan Africa where P deficiency is often a principal constraint to yields. In addition, understanding of the mechanisms and genetics of P-efficiency in rice, with its relatively simple genome, could be used to develop P-efficient genotypes of other cereals.
Members of the project team have recently made three advances towards understanding factors that drive P uptake by upland rice. First, we have shown the importance of fine, short, hairy lateral roots, known as S-types, which branch off coarser lateral roots and the main roots (Fig. 1). The S-types massively increase the total root system length, suggesting a particular role in acquisition of P for which a large root surface is important. Second, we have shown with mathematical modelling that S-types play a critical role in P efficiency by increasing the recovery of soil P that has been made more soluble – and hence available for uptake – through root-induced changes in soil chemistry (Fig. 2). Third we have shown that the costs in terms of P invested to construct and maintain S-type laterals are far less than those for other, coarser roots. We estimate that the P costs of constructing S types are paid back by their P uptake within a day of their formation, whereas pay-back times for coarse laterals and main roots are 5 and 25 days, respectively.
The above work focused on the crop establishment and vegetative growth stages. It is possible other processes are involved at later growth stages, for example through symbiosis with mycorrhizal fungi that colonise the roots. As the new mycorrhizal network is established each growing season, mycorrhizal hyphae (the long, branching, thread-like fungal filaments that spread out through the soil) will only provide additional P to the crop once the root system has expanded sufficiently to support them, and their P uptake exceeds the P costs of establishing them.
We have shown genotypic differences in P uptake efficiency exist in rice during this pre-mycorrhizal phase. The aim of this project is to test the hypothesis that genotypic variation in root morphology and root-induced P solubilization are more important for P efficiency than mycorrhizal colonization, particularly during early growth stages. We have the following specific objectives towards this end.
1. To investigate P acquisition processes in contrasting upland rice genotypes over the growing season in controlled-environment experiments in a highly weathered, strongly P-sorbing Oxisol imported to Cranfield from Madagascar in a previous project.
2. To quantify the extent to which mycorrhizas contribute to P uptake in experiments with mutant lines in which the OsPT11 gene, needed to transfer P from mycorrhizal symbionts to the host plant, is knocked out, and using a novel high throughput screening technique for quantifying mycorrhizal colonization of roots based on a biochemical marker in the above-ground shoots.
3. To parameterise our existing mathematical model of the effects of root morphology, solubilization and mycorrhizas on P uptake under our experimental conditions, and to make sensitivity analyses of the model with which to explore genotypic differences in P efficiency mechanisms.
The project builds on the three recent breakthroughs in understanding of P efficiency in rice by members of the project team, described above. It is therefore at the forefront of research into this topic and will feed into continuing efforts to breed more P-efficient genotypes of rice and other cereals that members of the project team are involved in.
This is a great opportunity to work in a project at the cutting edge of bioscience for sustainable food systems and to learn the latest techniques in plant physiology and genetics, soil biogeochemistry, mathematical modelling and marker-aided plant breeding. Training will include interactions and lab visits with Profs Matthias Wissuwa at Bonn and John Hammond at Reading. We are a strongly multi-disciplinary team and our research spans the range of basic plant and soil sciences through to applied plant breeding. The PhD will learn from and contribute to a full breeding programme for crop P-efficiency.
Cranfield PhD students all receive core, generic training, e.g., in project management, data management, statistics, academic writing and presentation skills. A wide range of MSc modules are available at CU, including Evaluating Sustainability and Economic Appraisal. The student will join a group of over 50 PhD students in the Cranfield Environment and Agrifood Theme, including students from other UKRI-funded doctoral training centres, including CENTA (Central England NERC Training Alliance) and DREAM (Data, Risk and Environmental Analytical Methods), as well as the Food Biosystems DTP. They will have access to a full range of associated training modules.
How to Apply
Applications will be by online application form only. Do not send CVs. Please go to the FoodBioSystems website to see guidance for applicants, information on academic and funding eligibility and language proficiency.
Equality Diversity and Inclusion:
The FoodBioSystems DTP is committed to equality, diversity and inclusion. We want to build a doctoral researcher and staff body that reflects the diversity of society, and to encourage applications from under-represented and disadvantaged groups. Our actions to promote diversity and inclusion are detailed on the FoodBioSystemsDTP website.