Disease severity (% infected roots) MS1MS2MC1MC2Vouvry Suppressive soils Tobacco Cotton Peanut Cherry tree Conducive soils T. basicola density (log10 endoconidia g -1 soil) 2 = ■, 3= ■, 4= ■ b bc c c c b d de ef d e d de b bc b ab b bc c d e c d e c d de b bc b b c de e c e c aa bc aa b c d b c d b c cd Fig. S1. Impact of Thielaviopsis basicola inoculation on black root rot severity of tobacco, cotton, peanut and cherry plants grown in Morens suppressive soils MS1 and MS2, Morens conducive soils MC1 and MC2, and Vouvry conducive soil (modified from Stutz, 1985). Inoculation was carried out using 102 (yellow bars), 103 (orange bars) or 104 (red bars) endoconidia of T. basicola D127 per g of soil and disease level was recorded at 21 days, with 5 replicates of 20 plants each for tobacco, cotton and peanut (growth chamber tests), or 2 replicates of 5 plants each for cherry trees (open-air pot tests). No disease symptoms were observed in non-inoculated plants. Disease severity is expressed as the percentage of root surface covered by T. basicola chlamydospores. For each plant species, different letters above bars indicate a significant difference between treatments (P < 0.05).

Disease severity (% infected roots) Suppressive soil MS1Conducive soil MC1 Fig. S2. Influence of soil sampling season on black root rot severity of tobacco (growth chamber tests) grown in Morens suppressive soil MS1 and conducive soil MC1 (modified from Stutz, 1985). Inoculation was carried out using 104 endoconidia of Thielaviopsis basicola D127 per g of soil and disease level was recorded at 21 days, with 5 replicates of 20 plants. No disease symptoms were observed in non-inoculated plants. Disease severity is expressed as the percentage of root surface covered by T. basicola chlamydospores. Results indicate that disease severity did not depend on the season during which soil was collected for the growth chamber experiment.

Fig. S3. Farmers’ fields from Morens with the lower parts of the fields corresponding to soils developed from the molasse sandstone (conducive) and the upper parts to soils developed from the sandstone-overlying morainic deposits brought by the Rhône glacier (suppressive). Soil developed from morainic material (disease suppressive) Soil developed from molasse sandstone (disease conducive) Soil developed from morainic material (disease suppressive) Soil developed from molasse sandstone (disease conducive) Photo M. Kyselková