Priming effect of root-applied silicon on the enhancement of induced resistance to the root-knot nematode Meloidogyne graminicola in rice

BACKGROUND: Silicon (Si) can confer plant resistance to both abiotic and biotic stress. In the present study, the priming effect of Si on rice (Oryza sativa cv Nipponbare) against the root-knot nematode Meloidogyne graminicola and its histochemical and molecular impact on plant defense mechanisms were evaluated. RESULTS: Si amendment significantly reduced nematodes in rice roots and delayed their development, while no obvious negative effect on giant cells was observed. Increased resistance in rice was correlated with higher transcript levels of defense-related genes (OsERF1, OsEIN2 and OsACS1) in the ethylene (ET) pathway. Si amendment significantly reduced nematode numbers in rice plants with enhanced ET signaling but had no effect in plants deficient in ET signaling, indicating that the priming effects of Si were dependent on the ET pathway. A higher deposition of callose and accumulation of phenolic compounds were observed in rice roots after nematode attack in Si-amended plants than in the controls. CONCLUSION: These findings indicate that the priming effect may partially depend on the production of phenolic compounds and hydrogen peroxide. Further research is required to model the ethylene signal transduction pathway that occurs in the Si-plant-nematode interaction system and gain a better understanding of Si-induced defense in rice.