Efficacy of Trichoderma longibrachiatum SC5 Fermentation Filtrate in Inhibiting the Sclerotinia sclerotiorum Growth and Development in Sunflower

<i>Sclerotinia sclerotiorum</i> is a destructive pathogen responsible for sunflower sclerotinia rot, resulting in substantial yield and economic losses worldwide. <i>Trichoderma</i> species have demonstrated the capacity to inhibit plant pathogen growth through the production of secondary metabolites. However, there are fewer recent studies focusing on the application of <i>Trichoderma</i> metabolites in inhibiting <i>S. sclerotiorum</i> growth and development and controlling sunflower sclerotinia rot disease. Our results showed that five <i>Trichoderma</i> strains (SC5, T6, TN, P6, and TS3) exhibited mycelial growth inhibition higher than 60% in dual culture assays out of the 11 tested strains. The <i>Trichoderma</i> SC5 fermentation filtrate exhibited superior efficacy compared to other strains, achieving a 94.65% inhibition rate of mycelial growth on <i>S. sclerotiorum</i>, 96% inhibition of myceliogenic germination of sclerotia, and 81.05% reduction in the oxalic acid content of <i>S. sclerotiorum</i>, while significantly increasing the cell membrane permeability. In addition, the <i>Trichoderma</i> SC5 fermentation filtrate significantly decreased the activities of polygalacturonase and pectin methyl-galacturonic enzymes and even caused <i>S. sclerotiorum</i> hyphae to swell, branch, twist, lyse, and inhibited the production and development of sclerotia. Moreover, the <i>Trichoderma</i> SC5 fermentation filtrate downregulated genes expression that associated with the growth and infection of <i>S. sclerotiorum</i>. The control efficacies of the protective and curative activities of the <i>Trichoderma</i> SC5 fermentation filtrate were 95.45% and 75.36%, respectively, on detached sunflower leaves at a concentration of 8 mg/mL. Finally, the <i>Trichoderma</i> SC5 was identified as <i>Trichoderma longibrachiatum</i> through morphological and phylogenetic analysis. Our research indicates that the <i>T. longibrachiatum</i> SC5 can be considered a promising biological control candidate against <i>S. sclerotiorum</i> and controlling the sunflower sclerotinia rot disease, both in vitro and in vivo.