| Tobacco bacterial wilt is an important bacterial disease in tobacco production,which is mainly spread by soil,water and human activities.It has a wide range of harm and has caused extremely serious consequences to tobacco production.Currently,the measures of agricultural,chemical and biological are the main ways to control tobacco bacterial wilt.However,these control measures have their own limitations,resulting in poor control effect.Resistance-induced technology has become a hot spot in the field of tobacco bacterial wilt control because of its safety,non-toxicity,low dosage and broad-spectrum defense.Coumarins are a kind of plant-derived compounds with a variety of biological activities,which are widely used in medicine and agriculture.Among these,Daphnetin(DA)belongs to hydroxycoumarin,which has insecticidal,bacteriostatic and growth-regulating activities,and is a potential plant resistance inducer.Therefore,DA was chosen in the present study as the resistance inducer,focuses on tobacco bacterial wilt as the research objective.Firstly,the resistance-induced activity of DA was evaluated,and the effective concentration and the best method of inducing tobacco against bacterial wilt were screened.Then,the mechanism of tobacco resistance induced by DA was explored.Finally,the prevention and control effect of DA induced tobacco resistance against bacterial wilt was further verified by indoor and field experiments.The main results are presented below.1 DA significantly induced the resistance of tobacco to bacterial wilt and reduced the disease index of bacterial wilt..The control effect of DA induced tobacco resistance was determined by pot experiment.The results showed that the induction treatment with DA concentration of 2.85 mg/L,5.70 mg/L and 11.40mg/L had the best control effect,and the disease index of the three treatments was 2.17,2.61,2.47respectively.The control effects on tobacco bacterial wilt were 44.29%,32.86%and 36.43%,respectively.To study the effect of DA on the infection of tobacco by R.solanacearum,plate counting method was used to determined the effect of DA on the content of R.solanacearum in the root and stem base of tobacco.The results showed that the root bacteria content of the tobacco treated with the concentration of 2.85 mg/L of DA was 7.94×10~5 CFU/g after 10 d of inoculation with R.solanacearum,which was significantly lower than 1.70×10~8 CFU/g of the control,it is reduced by214.11 times.DA treatment could prevent the transmission of R.solanacearum from root to stem base.The stem base bacteria content of the tobacco treated with the concentration of 2.85 mg/L of DA was1.07×10~5 CFU/g,after 10 d of inoculation with R.solanacearum,which was significantly lower than2.34×10~6 CFU/g of the control,it is reduced by 21.87 times.To study the best application method of DA induced tobacco resistance,pot experiment was used to study the effects of induction methods,interval times and treatment times on the occurrence of tobacco bacterial wilt.The results showed that the best induction method of DA was foliar spraying,the best interval time was 3-5 d,and the best treatment time was 2 times.2 DA treatment induced the increase of tobacco defense enzyme activity and the increase of lignin content in tobacco roots..To study the effect of DA treatment on tobacco defense enzymes,the changes of tobacco defense enzyme activities after DA treatment were determined.The results showed that DA treatment could induce the increase of POD,SOD,PAL and PPO activity.The enzyme activity of POD reached the maximum at 12 h,and the enzyme activity treated with DA was about 3.56 times higher than that of the control.The enzyme activity of SOD reached the maximum at 10 min,and the enzyme activity treated with DA was about 1.88 times higher than that of the control.The enzyme activity of PAL reached the maximum at 1 h,and the enzyme activity treated with DA was about 1.51 times higher than that of the control.The enzyme activity of PPO reached the maximum at 12 h,and the enzyme activity treated with DA was about 1.82 times higher than that of the control.To determine the effect of DA on the Lignification of tobacco roots,the changes of lignin content in tobacco roots were determined after DA treatment.The results showed that DA could increase the lignin content in tobacco roots and improve the defense ability of tobacco plants.After 4 d of treatment,the lignin content of DA increased by 1.33 times,after 5 d,the lignin content of DA increased by 1.39times,after 6 d,the lignin content of DA increased by 1.44 times,and after 7 d,the lignin content of DA increased by 1.54 times.3 DA activates tobacco disease resistance mainly through tobacco jasmonic acid pathway..The changes of plant hormone content in tobacco leaves treated with DA were detected by high performance liquid chromatography(HPLC).The results showed that the content of SA in tobacco leaves decreased after DA treatment,which was significantly lower than that of the control at 10 min and 6 h,and decreased by 1.33 times and 1.34 times,respectively.DA treatment could rapidly increase the content of JA in tobacco leaves,which was significantly higher than that of the control at 10 min and 6 h,which was 1.56 times and 1.36 times higher than that of the control,respectively.DA treatment could increase the content of ABA in tobacco leaves,which was significantly higher than that of the control at 6 h,which was 1.34 times higher than that of the control.To further explore the mechanism of DA induced resistance to tobacco,the expression of DA on tobacco resistance genes was detected by real-time quantitative PCR.After treatment with DA for 6 h,12 h and 24 h,the expression of PR1 gene was significantly higher than that of the control,and the expression of NPR1 gene was significantly lower than that of the control at 6 h and 12 h,respectively.The expression of JAZ3 gene was significantly lower than that of the control at 10 min and 6 h,and decreased by 31.59 times and 9.19 times,respectively.The results of plant hormone content determination and resistance gene expression showed that daphnetin-induced resistance was mainly triggered by jasmonic acid pathway,which improved plant disease resistance.4 DA has a good control effect on tobacco bacterial wilt in indoor and field..The control effect of DA on tobacco bacterial wilt was further verified by pot experiment and field experiment.The results showed that DA had a certain control effect on tobacco bacterial wilt under indoor pot conditions.After 16 days of inoculation,the control effects of DA at 2.85 mg/L and11.40 mg/L were 54.20%and 46.56%,respectively,which were significantly higher than those of other treatments.When the concentration of DA was 0.714 mg/L,the control effect was 15.27%,which was lower than 25.95%of BTH treatment.In the field experiment,the relative control effect of DA2.85 mg/L L treatment was 69.93%,which was significantly higher than that of other treatments,while the relative control effects of 0.71 mg/L and 11.40 mg/L treatment were 43.65%and 57.06%,respectively,which were equivalent to 57.63%and 32.77%of the control agents INA and BTH. |
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