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• Trichoderma stimulates resistance against to Pyricularia oryzae in Lolium multiflorum. • Coated seeds of L. multiflorum with T. atroviride reduces the severity of P. oryzae. • Silicon is accumulated in the leaves and improves the resistance to blast. • Biochemical and physical defenses are related to the protective action against blast. Ryegrass (Lolium multiflorum L.) is a forage species with a high content of protein and good palatability and digestibility. In winter, it is frequently used in southern Brazil as feed for livestock. The high humidity in this region is propitious for gray leaf spot, a disease caused by Pyricularia oryzae , considered to be the region's main biotic problem. In this study, we aimed to evaluate the effect of three types of management, namely seed coating with Trichoderma atroviride (T), application of silicon in the soil (Si), and combination of both treatments (TSi), to reduce the severity of gray leaf spot. In the first phase, the capacity of 10 native isolates of Trichoderma spp. were evaluated in vitro for direct inhibition of P. oryzae based on tests of dual cultures (DC), antibiosis for volatile (Vol), and non-volatile compounds (Nvol). In vivo trials involved the ability to induce resistance responses, such as quantifying severity (SEV) and number of lesions (NL) per cm2 of leaf area. In the second phase, the efficacy of T, Si, and TSi was tested under greenhouse conditions. The lesion expansion rate (LER), relative efficiency of infection (RIE), SEV and NL were measured (after inoculation with P. oryzae), and in parallel the activities of the enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POX) and phenylalanine ammonia-lyase (PAL) were quantified (at 24, 48, 72, and 96 h). The strain TR10 (identified by polyphasic taxonomy as T. atroviride) showed one of the highest inhibition values in Vol (23%) and DC (35%). Plants from seeds treated with the strain TR10 had the lowest levels of SEV (5.5%) and NL (3), in contrast with the other strains according to analysis of variance. Under greenhouse conditions, significant differences (P < 0.0001) were found for LER, RIE, NL and SEV in T, Si, and TSi concerning TE (control treatment). The defense response of T was related to the activities of CAT, POX, and PAL (mainly), while for Si, other mechanisms, which were not evaluated in this study, might have contributed to disease reduction, and TSi did not show an additive effect. The treatment of seeds with T. atroviride and the application of Si in the soil improved the resistance of L. multiforum against infection by P. oryzae. [ABSTRACT FROM AUTHOR]