Mechanistic Study On The Regulation Of Crop Disease Resistance By Typical Nanomaterials

Global pandemic of crop pest and pathogen decreased the crop yield at the range of 20-40%,posing a serious threat to global food security.Unfortunately,the increasing severity of climate changes（e.g.,more frequent temperature extremes）will further worsen this situation.Hence,novel,effective,and sustainable disease management strategies are urgently needing.With the rapid development of nanotechnology,nanomaterials（NMs）exhibited a great potential for managing plant disease due to their excellent physical-chemical properties and high bioavailability.However,the uptake and transport of NMs in crops,and the mechanism of NMs controlling crop diseases are still unclear.In this study,two NMs including lanthanum oxide（La₂O₃）NMs and carbon dots（CDs）,and two plants containing cucumber（Cucumis sativus L.）and tomato（Solanum lycopersicum L.）,were used to explore the optimal system for controlling plant diseases using NMs,the uptake and transport of NMs in planta,the primary mechanisms of regulating crop resistance,and the effect of NMs on crop yield and fruit nutritional quality.The main conclusions are as below:（1）Seed treatment and foliar application of the La₂O₃ NMs at 20-200 mg/kg（mg/L）significantly suppressed cucumber fusarium wilt（decreased by 12.50-52.11%）,and the disease control efficacy of La₂O₃ NMs was concentration-,size-,and surface modification-dependent.The best pathogen control was achieved by foliar application of 200 mg/L PVP-coated La₂O₃ NMs（10 nm）;disease severity was decreased by 67.6%and fresh shoot biomass was increased by 49.9%as compared with pathogen infected control.Importantly,the disease control efficacy of La₂O₃ NMs was 1.97-and 3.61-fold greater than that of La₂O₃bulk particles（BPs）and a commercial fungicide（Hymexazol）,respectively.Additionally,La₂O₃ NMs application enhanced cucumber yield by 350-461%,increased fruit total amino acids by 295-344%,and improved fruit vitamin content by 65-169%as compared with infected controls.Transcriptomic and metabolomic analyses revealed that La₂O₃ NMs:（1）interacted with calmodulin,subsequently activating salicylic acid-dependent systemic acquired resistance（SAR）;（2）increased the activity and expression of antioxidant and related genes,respectively,thereby alleviating pathogen-induced oxidative stress;and（3）directly inhibited in vivo pathogen growth.The findings highlight the significant potential of La₂O₃NMs for suppressing plant disease in sustainable agriculture.（2）Seed treatment（20-150 mg/kg）and foliar application（20-200 mg/L）of La₂O₃ NMs statistically suppressed the tomato bacterial wilt.The best pathogen control was achieved by seed treatment of 100 mg/kg La₂O₃ NMs and foliar application of 200 mg/L La₂O₃ NMs;disease severity was declined by 43.45%and 37.50%,fresh shoot biomass was enhanced by84.93%and 55.56%relative to pathogen infected control,respectively.Moreover,disease control efficiency of La₂O₃ NMs was significantly higher（22.22-39.68%）than that of La₂O₃BPs.Hence,the disease control efficacy of La₂O₃ NMs against tomato bacterial wilt was not only concentration-dependent,but also had a nano-specific effect.Mechanistically,1)La₂O₃NMs increased antioxidative enzyme（superoxide dismutase,catalase,and phenylalanine ammonia lyase）activity and antioxidant（proline）level by 13.0-77.2%in tomatoes,subsequently alleviating pathogen-induced oxidative stress;2)La₂O₃ NMs exhibited direct in vivo antibacterial activity.Metabolomics analysis demonstrated that La₂O₃ NMs not only improved the content of flavonoids（p-coumarin,quercetin-D-glucoside and rutin）,but also enhanced polyphenols（caffeic acid）biosynthesis in tomato shoots.Additionally,La₂O₃ NMs application not only enhanced infected tomato yield,but also alleviated the damage of pathogen to fruit nutritional quality.（3）Foliar application of 10 mg/L nitrogen doped carbon dots（N-CDs）suppressed bacterial wilt in tomatoes,statistically decreased disease severity by 71.19%,and increased the fresh biomass of tomato shoot by 55.86%.The disease control efficacy with N-CDs was1.56-fold greater than the pure CDs（P-CDs）.Mechanistically,1)nitrogen doping enhanced reactive oxygen species（ROS）scavenging ability of P-CDs,and then exhibited higher oxidative stress alleviation ability in tomatoes;2)N-CDs activated the salicylic acid and jasmonic acid dependent plant resistance in tomatoes,with subsequent inhibition in vivo pathogens growth;3)N-CDs activated the antioxidative enzyme activity in tomatoes,and then reduced the pathogen induced oxidative stress.Polyacrylic acid modification eliminated the disease control ability of N-CDs because the modification decreased the direct physiochemical process（e.g.,ROS scavenging）and indirect resistance activation（e.g.,SAR activation）of N-CDs in tomatoes.Based on the above results,we stated that the potential elimination of biological response of NMs by surface modification should be attended during enhancing the bioavailability of NMs.Metabolomics analysis suggested that N-CDs significantly promoted the tricarboxylic acid cycle and fatty acid synthesis in tomatoes.In conclusion,La₂O₃ NMs and N-CDs could increase crop resistance to alleviate crop disease severity.In addition,La₂O₃ NMs could improve the yield and quality of the pathogen infected crop,and exhibited a greater disease control efficacy than La₂O₃ BPs,La ions and the commercial pesticide.The application of La₂O₃ NMs will decrease the La usage,reduce traditional agrochemicals accumulation in the environment,thereby decreasing environmental risks.The application of NMs exhibited a good application in the sustainable agricultural production.