Induced Resistance Of Hesperetin To Tobacco Bacterial Wilt

Tobacco bacterial wilt is the most serious bacterial disease in tobacco production.Breeding disease-resistant varieties and improving the disease resistance of tobacco are the two economical and effective methods.Our previous experiments confirmed that the transcriptome sequencing of resistant and susceptible varieties of tobacco bacterial wilt and field experiments confirmed that the phenylpropane pathway is associated with the resistance of tobacco to bacterial wilt,and field application of rutin has a fair effect on tobacco bacterial wilt.This study selected hesperetin from 12 flavonoids and discussed its mechanism of inducing resistance.The main findings are as follows:1.The minimum inhibitory concentration of 12 flavonoids against R.solanacearum was detected on the BG medium containing TTC.The results showed that the MIC value of 5 flavonoids such as flavonoids and hesperetin was 2m M.Using benzothiadiazole（BTH）as a control,the control efficacy of 12 flavonoids to tobacco bacterial wilt by root irrigation and spraying was evaluated by indoor pot experiments.The results showed that the control efficacy of spray treatment was less effective than root irrigation,among which hesperetin and flavonoid had the best control efficacy on tobacco bacterial wilt,and the control effect of indoor potted plants reached 51.74%and 40.10%,which were significant higher than BTH treatment.The field trail results showed that the control efficacy of 1m M hesperetin and flavonoids on tobacco bacterial wilt were 58.%～63.04%and 29.35%～51.82%,respectively.There were significant differences in the agronomic traits and chemical components of tobacco leaves treated with hesperetin,and the comprehensive traits were better than those treated with flavonoids.The plant height,maximum leaf area and the contents of nicotine,total nitrogen and potassium ions in the middle tobacco leaves were significantly increased,while the sugar-nicotine ratio decreased.The yield per hectar,economic income and unit price of tobacco treated with hesperetin were significantly higher than BTH treatment,the increases were 5.99%-7.69%,12.82%-19.49 and9.48%-12.71%,respectively.2.The induced resistance mechanism of hesperetin to tobacco bacterial wilt was investigate at physiology,biochemistry,transcriptome and metabolome.By measuring the contents of reactive oxygen species,defense enzymes,soluble proteins,phenols and flavonoids in tobacco leaves treated with Hesperetin within 2h～72h,the results showed that the content of soluble protein decreased slowly after hesperetin treatment,and was significantly higher than those only inoculated with R.solanacearum from 2 h to 72 h.The accumulation of H₂O₂ and O₂^-in tobacco leaves started to increase at 24h after inoculation,reaching 2.3 times and 1.47 times than the inoculation control,respectively.The enzyme activities of SOD,POD,PPO,PAL and the contents of total phenols and flavonoids after hesperetin treatment were significantly higher than control treatment.It showed an upward trend first and then declined of the enzyme activities of PAL,POD and SOD,and the maximum values were 3.75,2.01,and 2.23times that inoculated control,respectively.The PPO enzyme activity,total phenolic and flavonoid contents increased slowly after hesperetin treatment,which was significantly higher than inoculated control and BTH treatment,indicating that hesperetin can improve tobacco resistance to bacterial wilt by increasing the activity of defense enzymes,phenolic metabolism,other physiological and biochemical reactions.The transcriptome and metabolome of tobacco roots inoculated with and without R.solanacearum for 24 hours after root irrigation with hesperetin measured.The metabolome analysis showed that hesperetin treatment was significantly increased the contents of metabolites such as p-coumaric acid,caffeic acid,ferulic acid,naringenin,hesperetin,kaempferol,quercetin,and salicylic acid,compared with the treatment only inoculated with R.solanacearum.Transcriptome analysis showed that the genes related to the flavonoid synthesis pathway,such as C4H,4CL,CHI,OMT,and Nt FLS,were significantly up-regulated.Besides,the salicylic acid pathway-related genes PR1,TGA,NPR1 were significantly up-regulated,while the jasmonic acid pathway-related genes JAR1,COI1,JAZ,MYC2 were significantly down-regulated.Combined differential genes and differential metabolites showed that hesperetin-induced expression of salicylic acid pathway-related genes and accumulation of flavonoids increased the resistance to tobacco bacterial wilt.