Richard it will be hard to find a non mycorhizal crop since non mycorrhizal plants use to be very specialized (aquatic, pasitic, carnivores, etc.). However in the paper atached there is a full discusion on this an you may find some usefull plant for your experiment.

Thanks for your answer Roberto. The paper indeed also mentions Lupinus as a genera without mycorrhiza. As far as I know they have cluster roots or exudates to mobilise phosphate to compensate for the P uptake lost by lack of mycorrhiza. However when searching for Lupinus species that are also used as a crop I can't find any information whether they have mycorrhiza or not, unfortunately (or should I just assume they are nonmycorrhizal, as the whole genus is nonmycorrhizal?).   

Richard, we lack information on many species. If you really need a negative control for your experiment you may first review roots of the selected plant to be sure it does not form them. I am not aware of the Lupinus species growing on Europe.

my best

Hi Richard,

have you considered using a mutant unable to form mycorrhiza? 

Best regards

Again thanks for your answers

@Roberto:

White, yellow and blue lupine are grown commonly throughout Europe as a crop (and many wild varieties of lupine).

@Guido:

This would be a nice idea, but for my experimental setup I am working with crops and try to replicate a situation that is highly relatable to an agricultural setting. However, I did find some white lupine, which according to Oba et al. (2001) and other sources, should be non-mycorrhizal, and is grown as a crop in Germany. Since I have to start very soon it unfortunately takes too much time to grow this lupine and test it.

Oba, H., Tawaray, K., & Wagatsuma, T. (2001). Arbuscular mycorrhizal colonization in Lupinus and related genera. Soil science and plant nutrition, 47(4), 685-694.