CSL-gel promotes plant growth and enhances the resistance against plant virus
The chitosan present on the surface of CSL-gel can form a robust electrostatic force with sodium alginate, resulting in the accelerated release of calcium ions from the gel. To test our hypothesis, we soaked the SL-gel or CSL-gel in water and measured the concentration of Ca2+ in the water solution at 2-day intervals. As shown in Figure 3a , the amount of Ca2+released from the CSL-gel was significantly higher than that of SL-gel. To assess whether the released Ca2+ can promote plant growth and development, we measured the plant height, leaf width, dry weight, and fresh weight of N. benthamiana at 14 days after SL-gel or CSL-gel treatment. Figure 3b-g showed CSL-gel-treated plants displayed a significant increase in plant growth, including height, plant width, leaf width, dry weight compared to that of the water-treated plant. In addition, the growth indexes of plants treated with CSL-gel were higher than those of the S-gel-treated and control plants (Figure 3b-g ). Moreover, After 30 days of treatment, the growth trend of CSL-gel-treated plants was significantly higher than that of the water-treated and SL-gel-treated group (Figure S2 ). These results demonstrated that CSL-gel promotes plant development.
To examine the anti-virus activity of the CSL-gel with the sustained release of LNT and calcium ion, we applied the CSL-gel into the soil surrounding the plant root. SL-gel serves as a control. We inoculated the TMV-GFP by rubbing on the leaves of the plant at 7 day after CSL-gel application. As shown in Figure 3h , at 2 dpi the number of green fluorescent spots in CSL-gel-treated N. benthamiana was the same as that on the SL-gel-treated plants. At 7 dpi, the green fluorescent signals present in the young leaves of the CSL-gel-treated plant were significantly weaker than that of the water and SL-gel treatment groups (Figure 3h ). qPCR analysis showed that the number of TMV-CP transcripts between the two treatment groups was no significant differences, but at 7 dpi the expression level of TMV-CP in the CSL-gel-treated plant was significantly lower than that in the SL-gel-treated and control plants (Figure 3i-j ). Taken together, we can conclude that the CSL-gel with the sustainable release of LNT and calcium ion significantly enhances the tobacco resistance against TMV as well as promoting the plant development.