Assessment of the antifungal activity of selected biocontrol agents and their secondary metabolites against Fusarium graminearum

Fusarium graminearum (teleomorph: Gibberella zeae) is the causal agent of several destructive diseases in cereal crops worldwide. In the present study we have evaluated the potential of two strains of Trichoderma sp. (T23, and T16), a strain of Paecilomyces sp. (PS1), and their secondary metabolites (SMs) in suppressing F. graminearum. Results from dual culture experiments show that in the presence of either Trichoderma sp., or Paecilomyces sp. mycelial growth of F. graminearum is considerably inhibited. Strain T23 causes the greatest inhibition (83.8%), followed by strain T16 (72.2%), and strain PS1 (61.9%). Likewise, mycelial growth of the pathogen is completely inhibited (≥ 98%) when grown under exposure to volatile metabolites excreted from Trichoderma cultures. Bioautographic analyses using culture filtrates revealed that several antifungal SMs are excreted. Among five metabolites tested, 6-pentyl-alpha-pyrone (6PAP) from strain T23, and PF3 from strain PS1 exhibit pronounced antifungal activity against F. graminearum. A new method for mass production of perithecia of F. graminearum which is simple and more effective than traditional methods was developed, which allows an increase in perithecial formation of more than 5-fold. Using this method, we found, that in the presence of SMs perithecial formation was negatively affected. Perithecial production was suppressed by 81.4% and 76.6% using 200 μg ml−1 of either 6PAP or PF3, respectively. Moreover, ascospore discharge was significantly suppressed (67.0%) when perithecia were exposed to the metabolite F116 produced by T16. Including 6PAP or PF3 in conidial suspensions impeded germination of conidia completely. Similarly, both metabolites strongly inhibited ascospore germination (˃ 90%).