Evaluation of potential antifungal activity of secondary metabolites produced by Trichoderma harzianum against Alternaria blight disease of Cumin

This study was aimed to identify secondary metabolites produced by native Trichoderma harzianum isolates and investigate the effect of ethyl acetate (EtOAc) extract of constituents extracted on seed germination and control of Alternaria blight disease. The phytochemical constituents of EtOAc extract of T. harzianum were identified by gas chromatography-mass spectrometry techniques. Also, the effects of foliar application, seed and soil treatments of EtOAc extract and its constituents: benzoic acid, palmitic acid and diisooctyl phthalate, on Alternaria blight disease index was investigated. All T. harzianum isolates were able to significantly reduce the mycelial growth of A. alternata by producing volatile and non-volatile metabolites. The major constituents of the EtOAc extract were 2-phenylethanol (14.36%), palmitic acid (12.07%), diisooctyl phthalate (11.23%), which have antifungal effects against A. alternata. The lowest values of minimum inhibitory concentration (MIC) of the EtOAc extract and its main constituents were in the range of 1,044-3,970 μg. mL-1. The MIC value of the benzoic acid (1,044 μg. mL-1) against A. alternata was lower than iprodione-carbendazim (1,391 μg. mL-1) and mancozeb (1,600 μg. mL-1). Combining benzoic acid with diisooctyl phthalate induced a synergistic activity against A. alternata and in combination with palmitic acid caused an additive effect. Seed treatment with EtOAc extract and/or benzoic acid significantly reduced the development of Alternaria blight disease of Cumin compared to foliar and soil applications. The seed treatment with EtOAc extract and palmitic acid significantly improves the seed germination by 11.34% and 9.57%, respectively. The findings provide new perspectives on the effect of the secondary metabolites produced by native T. harzianum isolates on the quality characteristics of seeds and the rate of soil-borne and seed-borne diseases progression caused by A. alternata.