Influence of recombinant Trichoderma strains on growth of bean (Phaseolus vulgaris L) by increased root colonization and induction of root growth related genes

Fungi in the genus Trichoderma are frequently found in soils, and many strains have abilities to increase plant growth. The objective of the present study was to evaluate the plant growth- promoting activities of two recombinant Trichoderma harzianum strains (T13 and T15) which were containing chimeric chit 42 (with ChBD) and Trichoderma wild-type (Tw) on bean plants in vivo conditions. In order to achieve this goal, Trichoderma strains comparisons were made of the ability to produce metabolites such as IAA by HPLC technique and siderophore production based on CAS-agar media and the expression of genes associated with plant growth promotion (chit42, Thpg1, qid74, tex10). Additionally, the yield indexes in vivo including root fresh and dry weight, aerial part fresh and dry weight, root and stem length, as well as the growth related genes expression (NAC1, EXP1, DGL1) were measured by using real-time PCR. In vitro assays indicated that T13 strain produced a higher level of auxin and siderophore. Also, gene expression analysis of T. harzianum indicated the chit42, qid74, Thpg1 and tex10 genes up-regulation in recombinant strains. In vivo assays showed that the bean plants treated with T13 had a significantly increased size, root fresh and dry weight, root length compared to the control and those plants treated with Trichoderma wild type. Besides, the plants treated with T13, showed more expression levels of the plant growth-related genes. The results showed that T13 had better performance in terms of increasing nutrient uptake and root growth thereby enhancing the growth rate of the whole plant compared to the plants treated with Trichoderma wild type and control plants. This ability was attributed to its better colonization in the root surface that triggered plant metabolism by changing growth genes expression and increase the production of growth factors such as auxin and siderophore.