VIABILITY AND ANTAGONISTIC ABILITY OF THE MOROCCAN STRAIN OF Trichoderma asperellum IN THE PRESENCE OF DIFFERENT HEAVY METALS

The Moroccan strain of Trichoderma asperellum Banklt1902509 SMis 1 KU987252 RAB 95369 isolated from compost and the pathogenic fungus Verticillium dahliae were tested for their tolerance to heavy metals. The growth behavior of these two fungal species and biocontrol ability of T. asperellum against Verticillium dahliae were investigated as a function of both the concentration and type of metals. The growth test indicates that T. asperellum and V. dahliae can tolerate high concentrations of tested heavy metals. At 1000 mg.L-1 of Iron, Zinc, Copper or Sulphur, the colony diameter were respectively 60.8, 22.2, 31.8 and 5 mm relative to 68.1 mm in the control. As regards the germination percentages of T. asperellum conidia recovered from solid PSA medium, with Iron, Zinc, Copper or Sulphur concentration of 1000 mg.L-1 Zinc exhibited the height percentage (90.33%) followed by Iron (60%) whereas Sulphur caused complete inhibition (0%). In liquid medium, the germination percentages decreased to 7.67, 87.67, 0 and 67.67% respectively in presence of Iron, Zinc, Copper or Sulphur compared to 89.67% in control. The fresh biomass of T. asperellum decreased respectively from 7.003, 3.64, 0.364 and 2.342 g at 1000 mg.L-1 of Iron, Zinc, Copper and Sulphur compared to 9.761 g in control. At low concentration, FeSO4 and ZnCl2 have stimulated the sporulation of T. asperellum which produced 10.47×105 and 6.83×105 CFU.mm-2 respectively at 25 mg.L-1 of Iron and 0.25 mg.L-1 of Zinc in comparison to 6.26×105 CFU.mm-2 in control.The viability of T. asperellum in the soil with the heighest metal concentration (1000 mg.L-1) was reflected by maximum colonization percentages varied between 92.77% and 100%. Furthermore, in direct confrontation of T. asperellum, the growth inhibition of V. dahliae reached 71.83, 74.17 and 76.52% respectively in presence of 1000 mg.L-1 of Iron, Zinc, Copper and Sulphur compared to 71.83% in the control. However, those recorded by volatile metabolites were comparable to that of control (76.53%).