1. Crop Science Centre University of Cambridge Cambridge CB3 0LE UK
2. Department of Bacteriology University of Wisconsin‐Madison Madison WI 53706 USA
3. Boyce Thompson Institute for Plant Research Cornell University Ithaca NY 14850 USA
4. Department of Biology (Ret.) University of York York YO10 5DD UK
5. Oklahoma State University Ardmore OK 74078 USA
6. Department of Agronomy University of Wisconsin‐Madison Madison WI 53706 USA