Storage fellowship - effect of calcium and phosphorus nutrition on potato storage quality

The project was designed to provide a training in crop physiology and biochemical analysis and for the fellow to use these skills to study the influence of crop nutrition on storage quality. The collaboration facilitated the cross-over of experience and techniques used in the top-fruit sector to the potato industry. 

In fruit storage, mineral nutrition (calcium, phosphate, boron, magnesium) are clear determinants in storage potential and are used routinely to characterise the storage potential of consignments alongside starch content and respiration rate. Two aspects were studied in more detail to evaluate their relevance to potato storage.

Phosphorous and low temperature sweetening

The propensity to develop storage disorders such to sensitivity to low-temperature sweetening (LTS) and senescent sweetening (SS) were not well characterised in potato tubers, compared to top fruit. In apple, sensitivity to low temperature breakdown is linked with low phosphate content of fruit at harvest. In potato, low phosphate content during tuber development is associated with low dry matter (DM) content and reduced yield. While work had focussed on improving uptake of phosphate from the rhizophere, less was known about the impact of phosphate on tuber storage quality or sensitivity to low temperature sweetening (LTS).

Calcium and senescent sweetening

In fruit, low calcium increases the propensity for senescent breakdown. In potato, low calcium is associated with russet skin spot. While few soils are considered low in calcium, its movement in the plant is restricted to the xylem, making uptake in the tubers hard to manage. It was proposed that quantifying, calcium, and the ratio of calcium: potassium and calcium: magnesium at harvest may indicate tubers’ propensity to develop senescent sweetening.

The aim of the project was to understand the relationship between calcium and phosphate nutrition in potato tubers and how the nutritional profile of tubers at harvest can influence their storage potential, in particular their propensity to undergo senescent sweetening and low-temperature sweetening during storage.

In addition, the use of real-time respiration rates of tubers was evaluated to monitor tuber health during storage as a way of providing store managers an additional tool for store monitoring.

Field trials investigating the incorporation of calcium and phosphate based fertilisers into the seed bed before planting, and topical application of liquid based calcium and phosphate products during the growing season were studied to assess the capacity for raising calcium and  phosphate in tubers as a way to improve their storage potential.

Results

Application of phosphate fertilisers (triple super phosphate) at field rates of 150-300 kg ha^-1 increased phosphate content of Markies and Pentland Dell at harvest. In the first year (2015), higher tuber phosphate was linked to lower glucose and sucrose content of Markies at harvest. Treatment effects were lost during storage at 3.5^oC or 10^oC and no effect of increased phosphate were observed on sugar profiles in Pentland Dell or Markies during storage. Repeat application of phosphate the following year (2016) led to raised phosphate content inMarkies and Pentland Dell tubers grown under phosphate supplementation of 150-300 kg ha^-1

Raising tuber phosphate content did not alter the sugar profile of Markies or Pentland Dell at harvest, however tubers grown under 300 kg ha-1 P were lower in sugar content during storage at 3.5^oC: Fructose, glucose and sucrose content was lower in Pentland Dell tubers early (2-5 months) in the storage season, while Markies tubers were lower in glucose and sucrose. By the final inspection at 7 months treatment differences were lost. In general, tubers’ propensity to sweeten during storage was not affected by calcium pre-treatments with the exception that Pentland Dell tubers removed from store after 5 months storage at 10^oC subject to calcium treatments (50-200 kg ha^-1) were transiently lower in sucrose. After 7 months storage, sucrose content of tubers had increased to a similar levels across treatments. No treatment differences in fry colour analysis of tubers subject to calcium pre-treatments was observed.