Effect of nitrogen fertilizers and Trichoderma harzianum on Sclerotium rolfsii

The effect of urea, sulfate ammonium, nitrate potassium and horse manure on S. rolfsii was tested in vitro, alone and in combination with T harzianum. Tests on liquid culture media showed that Sclerotium rolfsii did not utilize urea as a source of nitrogen while sulfate ammonium and nitrate potassium allowed the growth of the fungus. On a solid medium, the fertilizers at rates of 12 g N.m(-2) and 18 g N.m(-2) had an inhibitory effect on the growth of Sclerotium rolfsii mycelium. The highest effect was observed for urea. In contrast, Trichoderma harzianum assimilated all fertilizers but had a preference for sulfate ammonium. The antagonistic activity of Trichoderma harzianum on Sclerotium rolfsii on solid culture media was stimulated in the presence of the three nitrogen sources. The horse manure at high rates inhibited the growth of S. rofsii, favored the development of T harzianum and enhanced its antagonistic effect on S. rolfsii. The confrontation of Trichoderma harzianum with sclerotia of Sclerotium rolfsii in soil fertilized separately with urea, sulfate ammonium, nitrate potassium or manure showed an increase in the antagonistic activity. Particularly, the manure in combination with T. harzianum induced high mortality of sclerotia of the fungus. In the agronomic context of the region of Doukkala, it seems adequate to add these nitrogen sources to contribute to the biological control of Sclerotium rolfsii.