Silicon (Si) is recognized for its protective role in decreasing disease damage when absorbed by barley plants and has been proposed as a possible solution against Fusarium head blight, associated with devastating agronomic effects on overall yield and grain quality. However, root treatment of exogenous Si irrigating to enhance host resistance to Fusarium infection is unknown. For this purpose, a series of greenhouse experiments was conducted to examine the effects of Si irrigation at 1.7 mM to roots on pathogen development in barley heads. Two barley cultivars with contrasting FHB resistance (moderately resistant Arabi Aswad, AS, and moderately susceptible Arabi Abiad, AB) and infected with four Fusarium species with diverse pathogenicity were used. The quantification of the disease was through the determination of the disease incidence (DI, Type I resistance), disease severity (DS, Type II) and area under disease progress curve (AUDPC) calculated on the basis of DI and DS. Si absorption in barley enhanced the defense system in head tissues to pathogen invasion; FHB developed more severely on AS and AB plants grown without Si irrigation than on plants supplied with Si. Barley plants treated with exogenous Si irrigating were associated with a reduction of up to 19.3%, 19.8%, 18.7%, and 20.0%, respectively, in DI, DS and AUDPC calculated on the basis of DI and DS. Si contributed to the reduction of FHB in barley, especially for the moderately resistant cultivar; however, Si reduced the intensity of FHB in AB to a level comparable with AS. Importantly, Si treatment at 1.7 mM decreased disease damage FHB in previous bio-trials conducted on AS and AB under in vitro and field environments, showing that Si enhanced the expression of resistance to FHB infection in seedlings and adult barley plants. Taken together, the link of Si and host resistance provided a greater decrease in head blight in which both cultivars had augmented performances upon exogenous Si irrigating to roots; highlighting that Si is a potential safe and efficient policy to defend barley when invaded by Fusarium
