Strains and growth conditions
Four S. meliloti strains were used for this study: 1021
(indicated also as Rm1021) a spontaneous streptomycin-resistant
derivative of the isolate SU47 recovered from Medicago sativaroot nodules ; AK83, isolated from the root nodules of Medicago falcata
in the North Aral Sea Region of Kazakhstan by the Russia Institute of
Agricultural Microbiology (RIAM, St. Petersburg, Russia) ; BL225C,
isolated from Medicago sativa plants grown on soil of Lodi,
Italy, during previous experiments ; a cis-hybrid strain between 1021
and BL225C . This cis-hybrid strain harbours the symbiotic megaplasmid
pSymA from BL225C strain and the chromosome and pSymB chromid of 1021
strain, resulting in a ca. 30% of 1021 genome substituted by BL225C
genome. The strains are cultured from isolates derived from glycerol
stocks (25%) stored at -80°C.
Trichoderma strains (T. gamsii MIAE00029, T.tomentosum MIAE01053, T. harzianum MIAE00047,T. velutinum MIAE00033) belong to the collection
“Microorganisms of Interest for Agriculture and Environment” (MIAE,
UMR Agroécologie AgroSup/INRAE/uB Plant-Microorganism Interactions
Department, Dijon, France). Fungi were stored on Potato Dextrose Agar
plates at 4°C. Trichoderma spp. liquid cultures were grown on
minimal medium containing (mg/ml): glucose 20;
(NH4)SO4 5;
KH2PO4 15; MgSO4 0.6;
CaCl2 0.6; FeSO4 * 7H2O
0.005; MnSO4 *H2O 0.0016;
ZnSO4 * 7H2O 0.0014, and
CoCl2 0.002. All liquid cultures of Trichodermawere grown in 100 ml medium, at 25°C, 100 rpm agitation. Inoculation was
done with conidial suspensions adjusted to deliver a final concentration
of 107 spores/ml.