Authors:W. Dendouga, H. Boureghda, and M. Belhamra
Fourteen strains of Trichoderma spp. were isolated from Algerian desert soils and assessed for their antagonistic activity against Fusarium crown and root rot of wheat. Biocontrol efficiency of Trichoderma spp. was studied by in vitro and in vivo based bioassay against three pathogenic species: F. culmorum, F. graminearum and F. verticillioides. In vitro based bioassay (dual culture) results obtained with all Trichoderma spp. isolates showed significant decrease in colony diameter of Fusarium species compared to the control. The highest percentages of reduction in colony diameter were obtained with T. harzianum Thr.4 causing a growth reduction of 70.68%, 67.05 and 70.57% against F. culmorum, F. graminearum and F. verticillioides, respectively. All Trichoderma spp. isolates were able to overgrow and sporulate above F. culmorum colonies but no overgrowth was observed with F. graminearum and F. verticilliodes. The seed treatment by Trichoderma spp. isolates before sowing in a soil already infested by the pathogens led to a significant decrease of disease severity compared to the untreated control. The highest disease index decrease (>70%) was obtained with two isolates of T. harzianum (Thr.4 and Thr.10) and T. viride Tv.6 against the three fungal pathogens. Lytic enzymes production by Trichoderma spp. isolates was tested in liquid cultures containing fungal cell walls of each pathogen as sole carbon source. Higher levels of protease and chitinase activities were induced by hyphal cell walls of F. graminearum than cell walls of F. verticillioides and F. culmorum. T. harzianum Thr.4 exhibited the highest enzyme activities with hyphal cell walls of F. graminearum and F. culmorum. However, in the medium amended with cell wall of F. verticillioides, maximal lytic activities were recorded for T. viride Tv.6.