Objectives Cyst nematode disease widely happens in China, threatening the food security and environmental health, as well as the sustainable development of agriculture. Silicon, as an inducer, plays a pivotal role in enhancing plant disease resistance. Studying the mechanism underlying wheat defense against cyst nematode diseases induced by silicon fertilizer holds immense significance for both environmental protection and wheat production.

Methods Employing H. filipjevi as the test nematode, a pot experiment was carried out. Five levels of silicon fertilizer were established under the circumstances of no feeding and inoculation: 0, 0.25, 0.5, 1, and 2 g/kg respectively. Two months after inoculation, the amount of sporocyst and plant growth index of wheat were measured, and the optimal silicon fertilizer application concentration was selected. The 2×2 two-factor pot experiment of silicon application and insect-feeding was carried out at the optimal silicon application level, making four treatments in total: no Si application nor nematode infection (CK), Si application without nematode infection (Si), no Si application but with nematode infection (Cyst), and both Si application with nematode infection (Si×Cyst). After 2 months of inoculation, the contents of silicon, nutrients (soluble sugars, soluble proteins and free amino acids), secondary metabolites (lignin and total phenols) and reactive oxygen species (H₂O₂) in wheat were sampled and analyzed. The content activity of the tested indices in wheat without cyst nematode infestation was defined as the constitutive resistance. The difference between the indices before and after cyst nematode infestation was defined as inducible resistance. To explore the constitutive and inducible resistance mechanisms of silicon application to improve wheat's defense against sporocystitis nematodes.

Results The results demonstrated that application of silicon fertilizer at 0.5 g/kg significantly decreased the number of cysts per plant by 67.74%, enhanced above-ground fresh weight, plant height, SPAD value, underground fresh weight, root length, root surface area, number of root tips and root activity in wheat, so was used as the Si application rate on the followed experiment. Compared with no Si application, the Si content significantly increased the above ground and underground fresh weight of the constitutive type by 76.37% and 116.69%, while decreased the underground Si content in the induced type; enhanced the soluble sugar and soluble protein contents, but decreased the free amino acid content by 31.71% in constitutive type. and elevated in inducible soluble sugar and free amino acid levels. Lignin and total phenol contents increased by 37.82% and 35.63%, respectively, while the inducer’s content decreased significantly. Furthermore, after silicon application, there was a reduction of 25.34% in induced hydrogen peroxide content. The results of PCA and correlation analysis showed that above-ground fresh weight and plant height, content of constituent free amino acids, content of silicon and hydrogen peroxide in induced above-ground were the best indexes.

Conclusions In summary, the application of silicon fertilizer can improve the resistance of wheat to cystitis nematodes through the effects of silicon content, nutrients, secondary metabolites and reactive oxygen species on wheat, from the aspects of constitutive resistance and induced resistance.