2. The role of nanosilica in crops under biotic stress


Nanosilica has been preliminarily studied in the response to biotic stress. Nanosilica treatment of Arabidopsis leaves in a dose-dependent manner can induce SAR by activating the hormone SA, enhancing Arabidopsis resistance to the bacterial pathogen Pseudomonas syringae at the local and whole-plant levels. This finding clearly shows that nanosilica is an effective, sustainable and economical biostimulant in plants. Nanosilica can reduce the number of bacteria by 8 times within 24 hours. Nanosilica triggers SAR in a dose-dependent manner, and the best antibacterial effect (>90%) is obtained when the concentration of nanosilica is 100 mg/L. This protective effect of nanosilica is not due to a direct inhibitory effect on bacterial growth. When nanosilica and Pseudomonas syringae are cultured simultaneously in vitro, bacterial growth is not inhibited. This shows that nanosilica can make Arabidopsis resistant by activating defense responses rather than by inhibiting or killing pathogens, confirming the effectiveness of nanosilica in activating SAR. However, at a higher concentration of 1600 mg/L, the effect of nano-silica on activating SAR was poor, and it even increased the number of bacterial infections. This may be caused by excessive release of Si(OH)4 by nano-silica, which leads to oxidative stress or excessive nano-silica causing stomatal blockage, which ultimately destroys evaporation. After entering through the stomata, nano-silica disperses in the mesophyll air chamber and slowly releases Si(OH)4. Its protective effect on plants is mainly mediated by the activation of SA-dependent defense responses by nanoparticles. It was found that the application of nano-silica in rice can also activate SAR to resist rice blast, revealing the beneficial role of nano-silica in rice disease resistance. Compared with ordinary silicon fertilizers, nano-silica can be more effectively exerted because it is retained in the spongy extracellular air chamber of the mesophyll cells and will not be washed off the leaf surface. Beneficial nano-silica, as a means of enhancing disease resistance, can bypass the risks associated with plant genetic modification and is a potential new type of safe agricultural input.