Phylogenetic Diversity of Trichoderma Strains and Their Antagonistic Potential against Soil-Borne Pathogens under Stress Conditions

Trichodermaspecies are known as excellent biocontrol agents against soil-borne pathogens that cause considerable crop losses. Eight strains ofTrichodermawere isolated from five Egyptian regions. They identified based on translation elongation factor-1 alpha (TEF1) sequencing as four differentTrichodermaspecies:Trichoderma asperellum,Trichoderma harzianum,Trichoderma viride, andTrichoderma longibrachiatum. Optimal growth conditions (temperature and media), and the phosphate solubilization capability ofTrichodermastrains were evaluated in vitro. Further, the ability of these strains to antagonizeFusarium solani,Macrophomina phaseolina, andFusarium graminearumwas also evaluated. The results revealed thatTrichoderma harzianum(Th6) exhibited the highest antagonistic ability againstF. solani,M. phaseolinaandF. graminearumwith inhibition rates of 71.42%, 72.97%, and 84.61%, respectively.Trichoderma viride(Tv8) exhibited the lowest antagonism against the same pathogens with inhibition rates of 50%, 64% and 69.23%, respectively. Simple-sequence repeats (SSRs) and random amplified polymorphic DNA (RAPD) markers were used to evaluate the genetic variability of theTrichodermastrains. The results revealed that of 45 RAPD amplified bands, 36 bands (80%) were polymorphic and of SSRs amplified 36 bands, 31 bands (86.11%) were polymorphic. The amplification of calmodulin and beta-1,3-endoglucanasewas noted at 500 bp and 230 bp, respectively. Data indicated thatT. viride(Tv8) had the highest phosphate solubilization index (10.0 mm), whileT. harzianum(Th6) had the lowest phosphate solubilization index (4.0 mm). In conclusion,T. harzianum(Th6) had the highest antagonistic activity in dual culture assay along with the growth rate; whileT. viride(Tv8) had the highest phosphate solubilization activity. There are still gaps in obtaining new formulations, selecting potentTrichodermastrains to confirm disease control in planta. For improvingTrichodermarecommendation in the organic agricultural system and sustaining the fertility of the soil, the field application of highly antagonistic biocontrol agents in different types of soil and plant species will be the first approach toward bio-pesticide treatments along with bio-fertilizer inoculation. Furthermore, secondary metabolites will be investigated for the most promising strains with the combination of different pathogens and application timing.