1. Ecological Sciences Group, The James Hutton Institute, Invergowrie, Dundee DD2 5DA, UK
2. Division of Plant and Crop Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK
3. Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Reading RG6 6AR, UK
4. East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK