Mycoparasitism of <i>Trichoderma harzianum</i> AF2120E on <i>Fusarium graminearum</i> 4A1F and Their Antagonistic Metabolites During Coculture

Trichoderma harzianum and Fusarium graminearum are canonical biocontrolling and pathogenic fungal species in agriculture, respectively, and they have also been discovered from the marine environment time and again. The antagonistic effect of the marine-alga-derived T. harzianum AF2120E on F. graminearum 4A1F was evaluated by dual culture experiments. The former highly inhibited the colonization of the latter, with excellent mycoparasitism occurring. Chemical examination revealed the production of multifarious metabolites (1-14) during the confrontation, especially the discovery of three new compounds, including a steroid (1), a lipid (2), and a norterpenoid (3). Compared to monocultures, coculture resulted in the yield reduction of 4 and 9-13, but an increment of 14. Bioassay demonstrated that 1 and 5-7 suppressed F. graminearum 4A1F, featuring a minimum inhibitory concentration (MIC) of 128 µg/mL. Compounds 2, 6-8, 10, and 13 showed inhibition of the wheat-phytopathogenic fungi F. graminearum ACCC 39334 and/or Gaeumannomyces graminis ACCC 38864 at the same level, but 1 appeared more active in antagonizing the former. It was unexpected that confrontation increased the production of the Fusarium mycotoxin 14 that inhibited the antagonist T. harzianum AF2120E with an MIC of 32 µg/mL.