Effects Of Psoralea Corylifolia Seed Extract And Methyl Jasmonate On Alternaria Alternata Infection Of Tobacc

Tabacco Brown spot disease caused by Alternaria alternata is widely occurring in tobacco-growing areas in our country,which seriously affects tobacco production.The adoption of green prevention and control technology and the improvement of plant resistance are important means to prevent and control plant diseases.By inducing the expression of disease-resistance related genes,changing endogenous hormone levels,increasing the activity of tobacco defense enzyme system and the content of disease-resistance related substances such as polyphenols,it is beneficial to improve the ability of tobacco plant to resist disease.Therefore,in order to clarify the resistance of tobacco to A.alternata induced by seed extract of Psoralea psoralea and methyl jasmonate,flue-cured tobacco cultivar NC82 was used as experimental materials in vitro leaf method and pot method,respectively.To study the effects of psoralea seed extract and methyl jasmonate treatment on the activity of antioxidant enzymes,the contents of polyphenols and their related enzymes,and the contents of plant endogenous hormones in A.alternata infected tobacco leaves,and analyze the differential expression of disease-resistance related genes and the functional enrichment of differential genes by transcriptome sequencing.To explore the possible physiological mechanism of psoralea seed extract and methyl jasmonate affecting the resistance formation of tobacco to A.alternata,so as to provide theoretical reference for further research on the effects of these two substances in improving tobacco resistance.The results of this experiment are as follows:(1)The inhibitory effects of P.psoralea seed extract and Me JA on the mycelial growth of A.alternata were concentration-dependent.The inhibitory effect of 12.5g/L psoraleae seed extract and 1mmol Me JA on A.alternata mycelia was the best,which were more than 62% and 66.6%,respectively.The effect of 12.5g/L psoraleae seed extract and 0.1mmol/L Me JA on the control of red star disease in the field was the best,and the effect of 1mmol/L Me JA on the control of Tabacco Brown spot disease was bed.(2)0.5g/L psoraleae seed extract could increase the activities of CAT and SOD in tobacco leaves.0.1g/L psoraleae seed extract could increase POD and LOX activity in tobacco leaves.The activities of CAT,POD and LOX in tobacco leaves were increased by 0.1mmol/L Me JA,which maintained a high level after inoculation with A.alternata.However,1mmol/L Me JA inhibited CAT and POD activities in tobacco leaves.After inoculation with A.alternata,the POD and SOD activities of tobacco leaves treated with P.psoralea seed extract were higher.Psoraleae seed extract enhanced LOX activity in tobacco leaves at the late stage of inoculation,and 0.1g/L had the best effect on POD activity.A.alternata infection also increased CAT and SOD activities in potted tobacco leaves.(3)0.5 and 2.5g/L psoralea seed extract could increase PPO activity in tobacco leaves in vitro,and 0.1g/L concentration could increase PAL activity in tobacco leaves.0.1mmol/L had a better inducing effect on PPO activity of tobacco leaves in vitro and pot culture.The PAL activity of tobacco leaves was enhanced by 1mmol/L Me JA.After inoculation with A.alternata,PPO and PAL activities were enhanced in tobacco leaves treated with 12.5g/L psoraleae seed extract and0.1mmol/L Me JA.Chlorogenic acid,neochlorogenic acid and crypt-ochlorogenic acid were the top 3 polyphenols with high content in in vitro tobacco leaves,while chlorogenic acid,rutin and neochlorogenic acid were the top 3 polyphenols with high content in potted tobacco leaves.0.1,0.5 and 2.5g/L psoralea seed extract could induce the synthesis of polyphenols in tobacco leaves in vitro.At the concentration of 0.1g/L,it could induce the synthesis of polyphenols in pott-grown tobacco leaves,but at the concentration of 12.5g/L,it had little effect or even inhibited the synthesis of polyphenols.0.1mmol/L Me JA could effectively induce the synthesis of polyphenols in tobacco leaves and maintain a high content level after inoculation,while 1mmol/L Me JA treatment inhibited the synthesis and accumulation of polyphenols.After inoculation with A.alternata,2.5g/L and 12.5g/L psoraleae seed extracts increased the contents of polyphenols in tobacco leaves in vitro and potted plants,respectively.(4)0.1g/L psoralea seed extract could increase the contents of endogenous hormones SA and Me JA in tobacco.0.1mmol/L Me JA could induce the increase of ACC,JA and Me JA contents in tobacco leaves.The contents of ABA,ACC and JA in tobacco leaves treated with 0.1g/L psoraleae seed extract were increased after inoculation with A.alternata.Psoraleae seed extract inhibited ACC accumulation 4 days after inoculation.0.1mmol/L Me JA increased the contents of ABA,ACC,JA and Me JA in tobacco leaves.A.alternata infection increased ABA and ACC contents in tobacco leaves.(5)After the interaction between P.psoralea seed extract and Me JA with A.alternata,the genes of plant hormone signal transduction pathway,phenylpropane metabolic pathway andα-linolenic acid metabolic pathway in tobacco leaf were differentially expressed.After the seed extract of P.psoralea was inoculated with A.alternata,19 proteases in the plant hormone signaling pathway showed changes(7 up-regulated,8 down-regulated,),32 DEGs involved(TIFY10B,etc.19 DEGs were up-regulated.TIR1,etc.13 DEGs were down-regulated).In the phenylpropane metabolic pathway,6 enzymes related to polyphenol metabolism were changed,involving a total of 17 DEGs(5 DEGs such as TOGT1 were up-regulated,and 12 DEGs such as BGLU14 were down-regulated).Five proteases were changed in the α-linolenic acid metabolic pathway,involving 7 DEGs(AOC,ADH1,0PR1 were up-regulated,LOX6,etc.4 DEGs).After inoculation with A.alternata after Me JA treatment,20 proteases of plant hormone signal transduction pathway were changed,involving 40 DEGs(18 DEGs such as JAZ were up-regulated,and 22 DEGs such as PR1B1 were down-regulated).There were 9 enzyme activity changes in phenylpropane metabolic pathway,involving 25 DEGs(5 DEGs such as 4CLL1 were up-regulated,and 20 DEGs such as BGLU46 were down-regulated).The activity of five proteases(OPR,AOC,OPCL1 up-regulated,TGL4 down-regulated)in α-linolenic acid metabolic pathway of tobacco leaves,and corresponding coding genes of proteases were expressed correspondingly.Psoraleae seed extract and Me JA could improve tobacco resistance by increasing JA-mediated signaling pathway in plant hormone signal transduction,polyphenol synthesis and lignin synthesis in phenylpropane metabolism pathway,and JA and Me JA synthesis in α-linolenic acid metabolism pathway.In summary,treatment of A.alternata and tobacco leaves with or without Me JA and P.psoralea seed extract showed that both agents could inhibit the mycelium growth of A.alternata,induce increased activities of defense enzymes,increased contents of polyphenols and related metabolic enzymes,altered endogenous hormone levels,and regulated the expression of genes related to disease resistance metabolic pathways.And then improve the ability of tobacco plants to resist diseases.