Plant symbiosis assay
Symbiotic assays were performed as previously described . Medicago sativa cv. Marina seedlings were treated with 24 different conditions: only one rhizobial strain (4 treatments), only one Trichodermaspecies (4 treatments) and 4x4 Trichoderma -S. meliloticombinations (16 treatments). For each treatment 3 biological replicates were performed, with 3 to 5 seedlings per pot. Plants were grown in pots containing a 1:3 mixture of sterile vermiculite and sand. After 24 h, they were inoculated with 500 μl of bacterial suspension at OD600 0.1 and/or 500 μl of fresh mycelial suspension (T. gamsii 4.5 mg/ml; T. harzianum 2 mg/ml; T. tomentosum 4.6 mg/ml; T. velutinum 5.16 mg/ml) obtained from 5-days-old fungal cultures grown on PDA plates in a growth chamber at 26±2 °C with a 16h photoperiod. After 5 weeks, the following parameters were measured: nodule number, root, shoot and stem length, number of leaves and plant dry weight.