Investigating Cellulose Nanocrystals’ Biocompatibility and Their Effects on Pseudomonas syringae pv. tomato Epiphytic Survival for Sustainable Crop Protection

Abstract

Nanotechnology could play a huge role in ensuring safer and greener agriculture in the years ahead by providing sustainable tools to control plant diseases. In this study, the possibility of using cellulose nanocrystals (CNCs) obtained from tomato waste to control the bacterial speck disease’s causal agent was evaluated for the effects on plant development. Biocompatibility was assessed by studying seeds’ germination, leaf area, biomass and nitrogen balance index of tomato seedlings treated with CNC. Since epiphytic survival represents a relevant phase in early and later infections provoked by Pseudomonas syringae pv. tomato (Pst), the CNC’s ability to lower the level of bacterial cells in the plant canopy was evaluated in treated seedlings at 1, 7 and 14 days after being artificially inoculated. Leaflets were collected and washed to quantify the epiphytic bacterial population and observed through electron microscopy. Obtained results indicate that CNCs are non-toxic, compatible nanomaterials, highlighting at the same time their potential in counteracting bacterial speck disease by decreasing the level of epiphytic population after two weeks from inoculation by up to one log unit (3.08 CFU cm−2) compared to the control (3.94 CFU cm−2). Moreover, we were able to demonstrate that it is possible to cut in half the amount of copper without losing effectiveness in controlling the bacteria by mixing it with CNCs, concluding that CNCs could be used to design innovative sustainable plant protection strategies.

Cellulose Nanocrystal-Based Emulsion of Thyme Essential Oil: Preparation and Characterisation as Sustainable Crop Protection Tool

“…Interestingly, when the NE was used at the same concentration as the EO, a wider inhibition halo around the disc could be appreciated, as can be observed in the plot in Figure 6. Several studies have already pointed out the absence of toxicity for plants treated with CNCs, confirming our results, but when it comes to essential oils, the outcomes can be more unpredictable, since many factors are involved in the biological activity of EOs, such as temperature, humidity, and concentration [71]. However, this experiment highlighted the possibility of using an effective antibacterial amount (0.5% v/v) of Th-EOs without damaging the olive plants' basal growth functions, such as leaf development and nitrogen metabolism.…”

“…As a matter of fact, NBI, which was calculated using the ratio of chlorophyll and flavanol contents in leaves, gives a reliable indication of the health status of the plants: this index considers plants to be in good shape when most of the absorbed nitrogen is used for primary metabolic functions, such as chlorophyll synthesis, while plants could be subjected to abiotic or biotic stress when secondary metabolic products demand more nitrogen, lowering the NBI values [69,70]. Several studies have already pointed out the absence of toxicity for plants treated with CNCs, confirming our results, but when it comes to essential oils, the outcomes can be more unpredictable, since many factors are involved in the biological activity of EOs, such as temperature, humidity, and concentration [71]. However, this experiment highlighted the possibility of using an effective antibacterial amount (0.5% v/v) of Th-EOs without damaging the olive plants' basal growth functions, such as leaf development and nitrogen metabolism.…”

“…The count of developed colonies after it was exposed to increasing concentrations of the NE in a growthpromoting broth revealed the capability of the compound to fully inhibit the bacteria starting from doses higher than 0.05% v/v, while lower doses of 0.1% v/v of NE could inhibit the bacterial growth by 90%, still in a comparable way to the inhibition displayed by copper at the field dose (see Figure 7). As CNCs have been shown to have unique antimicrobial mechanisms on phytopathogenic bacteria, such as inhibition of swimming motility and biofilm production, as well as induction of cell flocculation in liquid media, we hypothesised a synergistic effect of nanocrystals and Th-EO [71]. The presence of CNCs in the formulation could have resulted in the bacterial cell being more exposed to the drug, preventing it from moving freely in the medium and adhering to surfaces, and of course preventing the EO from settling or separating from the liquid phase.…”

“…per at the field dose (see Figure 7). As CNCs have been shown to have unique antimicrobial mechanisms on phytopathogenic bacteria, such as inhibition of swimming motility and biofilm production, as well as induction of cell flocculation in liquid media, we hypothesised a synergistic effect of nanocrystals and Th-EO [71]. The presence of CNCs in the formulation could have resulted in the bacterial cell being more exposed to the drug, preventing it from moving freely in the medium and adhering to surfaces, and of course preventing the EO from settling or separating from the liquid phase.…”