Effects Of Melatonin Combined With Selenium Treatment On Postharvest Soft Rot And Storage Quality Of Sweet Potato

The soft rot of sweet potato caused by Rhizopus stolonifer is one of the most serious storage diseases of sweet potato in our country.The soft rot caused by the Rhizopus stolonifer is a subphylum fungi.therefore,the main means of effective preservation to maintain the economic value of sweet potato during storage and reduce the loss.In this thesis the sweet potato No.25 was selected in the experiment,and the exogenous Selenium（Se）and Melatonin（MT）were selected as experimental reagent.Damage inoculation and soaking treatments were used to investigate the control of postharvest soft rot of the sweet potato and its effects on quality.The related research was analyzed from in vitro test,postharvest physiology,transcriptome sequencing and other aspects.The main research results are as follows:1.MT was used alone had no inhibitory effect on colony growth of sweet potato pathogen of Postharvest soft rot,the combination treatment of Se and MT could effectively inhibit mycelia growth and spore germination of R.stolonifer,a pathogen of soft rot.At the same time,the membrane system of pathogen was damaged and the activity of R.stolonifer cell wall degrading enzyme was inhibited obviously.Mitochondrial ion(Ca²⁺)and mitochondrial membrane potential（MMP）of R.stolonifer cells were detected.It was found that Se and MT treatment caused Ca²⁺overload and MMP depolarization.2.The combined treatment of Se and MT could significantly inhibit the incidence of soft rot,improve the enzyme activities of soluble protein,superoxide dismutase（SOD）,catalase（CAT）,peroxidase（POD）and phenylalanine ammonlyase（PAL）in sweet potato.At the same time,high free radical scavenging power and total reducing power were maintained,the expression levels of salicylic acid pathway related genes Ib PR1 and Ib PAL were up-regulated.3.Se and MT maintained the decrease rate of pectin content and decreased the cell membrane permeability of sweet potato.At the same time,it can reduce the weight loss rate and maintain the quality of sweet potato in some extent,such as anthocyanin,ascorbic acid,reducing sugar content,etc.4.RNA-seq was performed on the tissue of sweet potato at day 1,2 and 3 after storage by high-throughput RNA-seq technology.The results showed that Se and MT could induce the expression of genes related to plant hormone signal transduction pathway,plant-pathogen interaction,threonine,serine,MAPK signal transduction and other related pathways.Several differentially expressed genes in defense were identified,including WRKY,NAC,MYB,ERF and R genes.These data provide sequence resources for genetic and genomic studies of sweet potato,contribute to deepening the understanding of the disease resistance mechanism of sweet potato and lay a theoretical foundation for the exploration of soft rot resistance mechanism of sweet potato.