Application And Mechanism Of Melatonin Synergistic With Fungicide Isoprothiolane In Rice Blast Control

Rice,one of the three major crops of the world,feeding more than half of the population in the world,has been devastated by a variety of diseases,particularly fungal diseases such as rice blast,false smut,and sheath blight.Application of fungicides is one of the common and cost-effective measures in the control of various crop diseases,but overuse of fungicides and relevant fungicide residues leads to environmental degradation,threatening human and animal health as well as biodiversity.Therefore,novel fungicides and methods of fungicide application must be explored to effectively control crop diseases including rice blast,in an environment-friendly manner.In this thesis,we found that melatonin,a low-cost natural small indole molecule with versatile biological functions,inhibits a variety of fungal diseases on rice.The model fungus Magnaporthe oryzae was used to investigate its antifungal mechanism,and then further explore the application potential of melatonin through drug combination.The results are as follows:Melatonin showed a broad‐spectrum inhibitory effect against fungal pathogens of rice.Furthermore,melatonin inhibited the conidial germination and appressorium formation of M.oryzae.Through fluorescence microscopic observation,it was found that melatonin further inhibited the formation of the septin‐ring that is essential for host penetration.The infection assays further verified the effective blast control by melatonin in planta.Then we observed that melatonin delays the transport and metabolism of lipid and glycogen in conidia and interferes with the biosynthesis of β‐1,3‐glucan in the cell wall using staining.By screening for possible synergistic combinations,here,we discovered an ecofriendly combination for rice blast control,melatonin and isoprothiolane.Those compounds together exhibited significant synergistic inhibitory effects on vegetative growth,conidial germination,appressorium formation,penetration,and plant infection in M.oryzae.The combination of melatonin and isoprothiolane reduced the effective concentration of isoprothiolane by over 10-fold as well as residual levels of isoprothiolane which decreased by 81% compared to the control.Meantime,the combination significantly increases the level of melatonin in rice,which is beneficial to the growth and development of rice.Transcriptomics and lipidomics revealed that melatonin and isoprothiolane synergistically interfered with the lipid metabolism of M.oryzae.Furthermore,we found that both melatonin and isoprothiolane may target the isocitrate lyase protein Mo Icl1,and we confirmed melatonin-Mo Icl1 interactions using surface plasmon resonance(SPR)and isoprothiolane-Mo Icl1 interactions using Nano differential scanning fluorimetry(Nano DSF).This study potentially contributes to the environment-friendly and sustainable control of crop diseases and will likely provide valuable information for other possible environment-friendly uses of melatonin in agriculture.