Suppressive effect of silicon nutrient on Phomopsis stem blight development in asparagus

The effects of silicon nutrition on the resistance to stem blight caused by Phomapsis asparagi was assessed in two asparagus cultivars, UC157 and Gynlim, and the activation of defense responses in inoculated plants was measured in a greenhouse with nutrient solution culture. The supply of silicon (Si) significantly suppressed stem blight development in inoculated plants. The disease index was significantly reduced in Si-supplied plants compared with Si-deprived plants in both cultivars. Supplement with Si enhanced Si accumulation in asparagus root and shoot. Si content was significantly higher in Si-treated plants when compared with control plants, but it was not significantly different between the two cultivars. Interestingly, inoculation with P. asparagi increased Si content in shoots in the cultivar UC157. Root-applied Si significantly enhanced the activities of pathogenesis-related proteins (PRs) such as catalase, peroxidase, polyphenoloxidase, and beta-1, 3-glucanase in inoculated plants. However, Si treatment mostly failed to change significantly the activity of PRs in plants without fungal attack. So continuous feeding of Si to the plant is probably important for enhancing the resistance to infection by P. asparagi in asparagus.