Phosphorus Use Efficiency in Potatoes
A parallel activity in SP4 was to identify physiological and genetic factors affecting Phosphorus Use Efficiency (PUE) in potatoes. A disproportionately large amount of P-fertilizer is applied to potatoes, compared to other field crops, and this can result in high P-losses and associated environmental pollution. This work, which was largely conducted at The James Hutton Institute (JHI), aimed to:
- quantify genetic and environmental variation in PUE
- identify chromosomal loci (QTL) affecting PUE
- identify physiological mechanisms underpinning PUE, and
- determine the effects of N-fertiliser management on PUE in potatoes.
An existing tetraploid genetic mapping population (12601ab1 x Stirling) was grown in the field in 2009 and 2010 both with and without the application of P-fertiliser. Tuber yields and tuber mineral concentrations were determined at commercial maturity and mineral concentrations in diagnostic leaves were determined at canopy closure. These data, together with data obtained in previous studies of this population, were used to identify QTL for (a) tuber yield, (b) P concentrations in diagnostic leaves ([P]leaf), and (c) tuber yield / [P]leaf (PUtE), and their responses to P-fertilisation. It was observed that consistent QTL affecting yield, [P]leaf and PUtE could be identified in experiments performed in different years and with contrasting P-fertiliser applications, and that major QTL for all these traits co-located with a QTL explaining about half the phenotypic variation in crop maturity. These data could be used to develop molecular markers for breeding for PUE in potato.
A NUE_Crops Core Collection, comprising 32 Solanum tuberosum genotypes, was grown in the field in 2009 and 2010 both with and without the application of P fertiliser. Tuber yields and tuber mineral concentrations were determined at commercial maturity and mineral concentrations in diagnostic leaves were determined at canopy closure. These data were combined with previous studies of the SCRI Commercial Core Collection (e.g. White et al. 2009, HortScience 44: 6 -11) to estimate the effects of genotype, P-fertilisation, and location/year on (a) tuber yield, (b) [P]leaf, and (c) PUtE. Eight genotypes with contrasting yields at low P input, yield responses to P-fertiliser addition, PUtE and leaf P concentration were identified for subsequent physiological and genetic studies.
Fig. 1. "Shovelomics" - excavation of a juvenile potato root system (Dundee, 2011)
The eight genotypes selected for contrasting PUE traits were grown in the field in 2011 both with and without the application of P fertiliser. Significant positive relationships between the size of the juvenile root system and early plant vigour, canopy development, P accumulation and final yield were observed.
Fig. 2. Field trial of eight genotypes selected for contrasting PUE traits (Dundee, 2011)
The same eight genotypes were grown in the glasshouse in pots in 2012 and detailed assessments of root system architectures were made on juvenile plants. The nomenclature developed by Wishart et al. (2013, Plant & Soil 368: 231–249) was adopted. Relationships were observed between various aspects of root system architecture and phosphorus uptake, shoot growth and PUE in the field.
Fig. 3. Potatoes grown in pots for studies of root system architecture (Dundee, 2012)
To obtain further insights to the physiology of PUE in potato, gene expression was investigated in roots of four genotypes with contrasting PUE traits (12601ab1, Pentland Dell, Maris Piper, Stirling) grown in flowing nutrient solutions containing either low (25 µM) or sufficient (250 µM) phosphorus concentrations. Gene expression in roots differed between potato genotypes, and changed with P supply. Seventy three genes differed in their expression between roots of P-replete and P-starved plants of all genotypes. These genes represent a common transcriptional response to P-starvation, and might be used to diagnose P-starvation in potato (c.f. Hammond et al. 2011, PLoS ONE 6(9): e24606). A specific transcriptional response associated only with roots of genotypes with high yields in the absence of P-fertiliser application in the field was also identified. Sixty seven genes differed in their expression between roots of P-replete and P-starved plants of the high-yielding genotypes Maris Piper and Stirling, but not between roots of P-replete and P-starved plants of the low-yielding genotypes 12601ab1 and Pentland Dell. Since the expression of these genes is correlated with high yields at low P inputs, they might provide candidates for understanding the differences in yield responses of potato genotypes to P-supply.
A theoretical study was undertaken to explore the relationships between the use efficiencies of nitrogen (NUE) and phosphorus (PUE) by the potato crop. It was concluded that, for a given combination of P and N availability to a crop, the rankings of genotypes for their agronomic NUE and PUE will be identical. However, selecting simultaneously for greater N and P uptake efficiencies, or greater N and P utilization efficiencies, is not so simple because these traits vary independently among potato genotypes. Nevertheless, many plant traits can benefit both NUE and PUE because they serve to increase tuber yield. Such traits include, for example, accelerated root growth, production of an extensive root system with low tissue density and long root hairs, greater root penetration of strong subsoils, accelerated canopy development, greater photosynthetic efficiency and greater harvest index.
Fig. 4. Potatoes growing hydroponically for studies of gene expression (Dundee, 2012)
Activities in WP4.2 resulted in two peer-reviewed publications which are listed here:
Dietrich RC, Bengough AG, Jones HG, White PJ (2012) A new physical interpretation of plant capacitance. J Exp Bot 63 (17):6149-6159
Dietrich RC, Bengough AG, Jones HG, White PJ (2013) Can root electrical capacitance be used to predict root mass in soil? Annals of Botany:1-8. doi:doi:10.1093/aob/mct044