Abstract
Trichoderma spp. can be used effectively in both productions of plant growth promoters, (gibberellic acid, GA(3)) and biological control of Rhizoctonia solani to increase plant production. Solid state fermentation of one gram corns stover with 0.22% (NH4)(2)SO4 for 128.42 hrs at 28 degrees C, with the aid of statistical optimization, were the optimal fermentation conditions for the production of GA(3) by T. harzianum, which showed biological activity against R. solani. The resulted GA(3)(F5) and spores (S5) of T. harzianum were evaluated on potato tuber sprouting as compared to the chemical GA(3). Both Trichoderma treatments showed (100%) sprouting as compared to control, F5 exhibited significant effects on sprout weight, root weight and sprout vigor. Under greenhouse conditions, both F5 and S5 gave a significant reduction in each of disease severity and incidence of stem canker and black scurf diseases, as well as, significantly improved growth and yield. Both F5 and S5 were superior in increasing the defense-related compounds (polyphenoloxidase, peroxidase total phenol and chlorophyll content) in potato shoots, even in the presence or absence of the pathogen. This research suggests employing of T. harzianum for the production of GA(3) over a low-cost medium, suppress Rhizoctonia diseases and increase the productivity of potato.