Nodule sample collection
White clover (Trifolium repens ) root nodules were sampled from
three clover field trials under identical management in Denmark (Store
Heddinge, DK), France (Rennes, F), and the United Kingdom (Didbrook,
UK). At each site, 18 F2 families (1-18) and two commercial varieties (K
and C) were grown in duplicate in a similar block setup (Table
S1 and Figure S1 ). In addition, 50 samples were collected from
Danish clover fields under organic management. The clover varieties
grown at each field can be seen in Table S1. A total of 170 samples was
collected (Figure 1 , Table S1 , UK=40, F=40, DK=40,
DKO1=14, DKO2=8, DKO3=3, DKO4=15, DKO5=5, DKO6=5). Nodules were stored
at -20°C until DNA extraction.