Genotypic variation and mechanisms of phosphorus use efficiency in wheat (Triticum aestivum L.)

Author: Van Lam Nguyen

Nguyen, Van Lam, 2017 Genotypic variation and mechanisms of phosphorus use efficiency in wheat (Triticum aestivum L.), Flinders University, School of Biological Sciences

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Wheat (Triticum aestivum L.) is one of the world’s most important food crops and the production of phosphorus (P) efficient wheat could contribute to enhanced crop yield on P-deficient soils. Improving our understanding of the mechanisms of P use efficiency (PUE) is essential for screening and further genetic manipulation, however the mechanisms of PUE are still not fully identified. It is hypothesized that P efficient wheat (low P tolerant) and P inefficient wheat (low P intolerant) differ in their efficiency mechanisms including root architectural and morphological traits and metabolic responses under P deprivation.

Six wheat genotypes including RAC875, Scout, Gladius, Mace, Correll and Wyalkatchem are known to differ in their PUE when analysed in field experiments, and in this thesis, were grown under controlled environment conditions to evaluate their PUE compared to field responses. Results reveal that their responses to P supply in growth room conditions generally correlate with their responses in field experiments. Plants produced greater biomass in the growth room than in greenhouse conditions and their responses to P were consistent between experiments. In the growth room, RAC875 showed greater shoot biomass and grain yield than Wyalkatchem under low P, while the results in the greenhouse were the opposite. To test why differences exist between growth room and greenhouse environments, the effect of light intensity on PUE was evaluated. A greater PUE was observed in RAC875 when compared to Wyalkatchem under both light conditions.

RAC875 possessed a smaller root dry matter but a higher root efficiency (mg shoot P uptake g-1 root dry matter) which appeared to be associated with greater PUE. To test if RAC875 had more favourable root traits contributing to higher PUE, a simple soil-based cultivation was developed to assess root architectural traits related to PUE of RAC875 and Wyalkatchem. Although the majority of root architectural traits were not significantly different between RAC875 and Wyalkatchem, RAC875 showed higher relative ratios between low P and adequate P than in Wyalkatchem. RAC875 had greater root convex hull area (CHA) than Wyalkatchem under low P. Wyalkatchem had longer root hairs than RAC875 at both low and adequate P, while under low P, RAC875 produced more dense root hairs than Wyalkatchem, suggesting that CHA and denser root hairs may contribute to greater yield and shoot biomass in RAC875 during P starvation.

Variation in metabolite profiles between the two wheat genotypes was also investigated to explore metabolic mechanisms of greater PUE in RAC875. Through a metabolomics approach, 79 and 84 metabolites were measured from leaves and roots, respectively. A greater accumulation of raffinose in roots and aspartate, glutamine and β-alanine in leaves were associated with the P efficient phenotype in RAC875. Under P deprivation, the phosphorylated sugars, glucose-6-P and fructose-6-P were maintained in RAC875 and this would allow carbohydrate metabolism to be maintained and lead to greater shoot biomass. The mechanism of RAC875 would therefore be associated with the maintenance of carbon metabolism and transport to sink tissues.

Keywords: Wheat, phosphorus use efficiency (PUE), root architectural and morphological traits, metabolites, phosphorylated sugars, raffinose.

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Biological Sciences
Supervisor: James Stangoulis