Agronomy fellowship: understanding tuber formation to improve tuber quality and reduce greening


Tuber greening is increasingly recognised by packers as a significant contribution to wastage but there had been limited progress in reducing its importance through variety selection or modification to agronomy.  The main aim of this project was to quantify stolon architecture (depth from the soil surface and length) in seven varieties and relate this to the position of tubers in the soil and their susceptibility to being exposed to light, resulting in tuber greening. A further aim was to establish the influence of physiological and environmental factors (seed size, temperature, nitrogen rate) on stolon architecture. The work also contributed to an improved understanding of the effects of differences in stolon architecture on other tuber quality attributes, such as tuber size distribution.


Seven varieties were grown in a replicated experiment in Cambridge for 3 years. Plots were sampled around the time of tuber initiation and the length and depth of every stolon was measured. In the middle of the season, stolon length and depth, and the position of each tuber were measured. Samples were taken after desiccation to assess for tuber greening. One experiment examined the effect of seed tuber size on stolon architecture and tuber greening. Two planting date experiments investigated the extent to which stolon length differed as temperatures varied and also whether the rate of nitrogen affected stolon length. 36 commercial crops were surveyed to quantify stolon architecture and tuber position and relate this to susceptibility to tuber greening.

Key Findings

  • Significant differences in mean stolon length were observed between the varieties each year. 
  • The horizontal position of tubers was closely related to stolon length and tuber length indicating that it is possible to predict the cluster width of a crop for any given stolon length and tuber size.
  • Seed size did not affect stolon length or tuber greening. 
  • Planting date affected stolon length but the effects were inconsistent and difficult to reconcile with variation in temperature. 
  • Nitrogen rate significantly affected stolon length but the extent of the effect was small for a large difference in nitrogen rate.
  • Stolon depth differed between varieties, but the differences were small compared to the differences in stolon length between varieties.
  • Few green tubers were exposed at the soil surface with the majority still covered by soil indicating that cracking of the soil was important in allowing light to reach the tubers.
  • Varieties differed in their sensitivity to light but this did not correspond to their propensity to tuber greening in the field experiments.
  • The survey of commercial crops found a similar range in stolon length as in the experiments and the average stolon depth was c. 75 % of planting depth.
  • Planting depth varied widely, both between and within crops, and influenced the amount of yield close to the soil surface.
  • The planter experiment indicated that hood pressure and ridge shape could influence tuber greening.
Project code:
01 February 2015 - 31 March 2018
Project leader:
David Firman


11140001 Agronomy Fellowship FINAL