Correlation Study Between Biochemical and Molecular Pathways of Trichoderma harzianum Recombinant Strains on Plant Growth and Health

The genus of Trichoderma are mostly found in soil. Trichoderma species are known as probiotic with biocontrol and biofertilizer activity. They are producers of secondary metabolites like volatile organic compounds (VOCs) with antifungal, antibacterial, and growth promoter properties. Trichoderma VOCs can induce resistance to plant pathogens leading to improved plant growth and health. In this study, we compared the performance of Trichoderma harzianum recombinant strains (T13 and T15), containing chimeric chit42 with Chitin Binding Domain (ChBD) and wild-type (Tw) strain on plant growth promotion. To achieve this goal, the ability of strains in plant growth-promoting (production of IAA and siderophore) and fungal gene expression involved in biocontrol and biofertilizer activity, as well as, VOCs from T. harzianum strains (wild-type and recombinants) by headspace gas chromatography-mass spectrometry (GC-SPME) have been investigated. In addition, bean seeds were exposed to the T. harzianum strains in a shared atmosphere. In addition to growth indices (root fresh and dry weight, root length, and lateral root number), expression of root growth-related genes was measured by qTR-PCR. The results showed that recombinant strains had increased ability to produce IAA and siderophore. In addition, T. harzianum genes expression analysis demonstrated an upregulation in biocontrol and biofertilizer-associated genes in T13 and T15 strains. VOCs profile of strains revealed a total of 11, 57, and 29 metabolites from the Tw, T15, and T13, respectively. Most of the VOCs produced from T13 and T15 had growth enhancement and biocontrol activity, respectively, on the plant. The diversity of VOCs from T. harzianum recombinant strains (T13 and T15) involved in growth-promoting and biocontrol activity, was higher than the Tw strain. These compounds might work synergistically to promote growth, and enhance biocontrol and antifungal activity, and thus, recombinant strains with higher diversity of VOCs might be more effective than Tw. Plant phenotypic characterization and root genes expression showed that the recombinant strains, T13 particularly, were effective in growth-promoting compared to the Tw strain. In this study, we observed a positive correlation among the production of secondary metabolite and molecular pathways of recombinant strains on plant growth activity. This finding can create a link between basic and applied studies in agriculture.