Foliar Spraying Suitable Dosage of Silicon Fertilizer on Wheat Suppressed Inoculated Aphid Reproduction by Activating Plant Induced Defense Response

Abstract Background: Although the ability of silicon to induce plant resistance against some insect is known, it is still unknown that the effect of the different concentrations of silicon on activates the secondary defense system in wheat, and then influence the life cycle table of wheat aphids. In this experiment, different levels of silicon (Si) fertilizer was applied to change the secondary defense system of wheat, to study the impact on the life table parameters of aphid (Sitobion avenae F.) (Hemiptera: Aphididae), and to explore the mechanism of Si application in enhancing wheat resistance to aphids. Wheat seedlings were cultured in a hydroponic experiment with the seven different levels of Si (0, 0.3, 1, 2, 3, 4, 5 and 9 mmol/L). Results: Our findings indicated that the application of Si can suppress the net reproductive rate (R0), intrinsic rate of increase (rm), mean generation time (T), finite rate of increase (λ), and prolong the population doubling time (t) of aphid. Besides, aphid infection elicited immune responses in wheat, which was enhanced by Si: Between the treatments, a foliar application of Si improved the activity of four defense enzymes (PAL, PPO, CAT, LOX), and increased the content of signal transduction substances (JA, SA) and secondary metabolites (tannin, alkaloids, lignin, total phenolics and flavonoids). Moreover, the results of the correlation analysis showed that the concentration of Si in wheat was positively associated with the activities of defense enzymes and the concentrations of secondary metabolites and signal transduction substances. There was a significant positive correlation between the activities of four defense enzymes and the concentrations of secondary metabolites and signal transduction substances in wheat. Furthermore, the activities of defense enzymes, the concentrations of secondary metabolites and signal transduction substances and Si in wheat were negatively associated with the R0, T, rm, ƛ and positively related to the t of the life table parameters from the aphid. Conclusions: In conclusion, the current result suggested that the application of Si can increase the signal transduction pathway of wheat and regulate the secondary metabolism by influencing the concentration of Si in wheat. As a result, the application of Si affected the life table parameters of aphids and enhanced the resistance of wheat. Also that 3 mmol/L Si application was more beneficial to enhance the resistance of wheat than higher or lower concentrations. The application of Si in wheat might provide an important basis for pest management control.