Combined Application of Trichoderma harzianum and Paclobutrazol to Control Root Rot Disease Caused by Rhizoctonia solani of Tomato Seedlings

Many root diseases can cause serious damage to tomato (Solanum lycopersicum L.) production during the seedling growth period, particularly Rhizoctonia solani, Pythium spp., and Alternaria spp. Paclobutrazol (PBZ) has proved to reduce the damage of the Alternaria blight disease on tomato seedlings. The present investigation was designated to evaluate the growth of infected tomato seedlings with R. solani under applications of Trichoderma harzianum alone, PBZ alone, both PBZ and T. harzianum, and comparing with applied fungicide. PBZ enhanced the chlorophyll system in tomato seedlings, enzymatic antioxidants, and the total antioxidants, besides the vegetative parameters. The combined application of both PBZ and Trichoderma significantly improved growth parameters, decreased the damping off percent of R. solani, as well as increased the enzymatic antioxidants and the total antioxidants of tomato seedlings. It was found that applying 100 mg L−1 PBZ did not affect the effectiveness of the biocontrol agent of T. harzianum. The images of the scanning electron microscope (SEM) confirm that PBZ showed twisting, shrinking, and collapsing of lysis and hyphae in cultures of R. solani. This is the first report that confirms the biochemical control of R. solani on tomato seedlings using the combined application of PBZ and T. harzianum. Further studies are still needed to test more Trichoderma species and different phytopathogens.