瑞香素对烟草青枯病的防治效果及其作用机理

为探究植物次生代谢产物瑞香素对烟草Nicotiana tabacum青枯病的防治效果及其诱导抗性作用，通过室内和田间试验评价瑞香素对烟草青枯病的防治效果，利用高效液相色谱（high performance liquid chromatography，HPLC）和实时荧光定量PCR（real-time quantitative PCR，RT-qPCR）技术分析其对烟草体内酶活性、木质素含量、激素水平和抗性相关基因表达量的影响。结果表明，叶面喷施瑞香素对烟草青枯病有较好的防治效果，其中2.85 mg/L处理的防治效果最佳，其次是5.70 mg/L和11.40 mg/L处理，接种后14 d的相对防效依次为66.93%、42.52%和48.03%。瑞香素处理可显著提高烟草体内过氧化物酶、苯丙氨酸解氨酶和多酚氧化酶的活性，处理后12 h分别较对照显著提高了3.56倍、1.68倍和1.82倍；瑞香素处理后4 d和7 d烟草根部木质素含量分别较对照显著提高了1.33倍和1.54倍；瑞香素处理后6 h烟草体内茉莉酸和脱落酸含量分别较对照显著提高了35.98%和34.55%，而水杨酸含量较对照显著降低了25.56%。同时，叶面喷施2.85 mg/L瑞香素后显著抑制了茉莉酸途径拮抗基因JAZ3的表达，处理后6 h的表达量较对照下调了9.19倍，同时显著促进病程相关基因PR1的表达。提前喷施2.85 mg/L瑞香素能有效控制田间烟草青枯病发生，相对防效达到52.22%~75.54%，显著高于对照药剂苯并噻二唑的相对防效33.50%~53.00%。表明瑞香素能提升烟草体内酶活性和根部木质素含量，促进抗性基因表达，对田间烟草青枯病有稳定的防治效果，具有开发为防治烟草青枯病的植物激活剂的潜力。

Control efficacy of daphnetin against tobacco bacterial wilt and its action mechanism

To investigate the control efficacy of daphnetin on tobacco bacterial wilt and explore the induced systemic resistance of daphnetin on tobacco plants, the pot and field experiments were performed, respectively. Then, plant enzymes, lignin content and plant resistance genes under daphnetin treatment were evaluated by high performance liquid chromatography (HPLC) and real-time quantitative PCR. The results showed that spray application of 2.85 mg/L daphnetin had the optimal control efficacy on tobacco bacterial wilt, with control efficacy of 66.93% at 14 days after inoculation with Ralstonia solanacearum, which was more efficient than 5.70 mg/L and 11.40 mg/L daphnetin treatment, with control efficacy as 42.52% and 48.03%, respectively. Furthermore, daphnetin could significantly induce the activity of plant enzymes, including peroxidase (POD), phenylalanin ammonialyase (PAL) and polyphenol oxidase (PPO), which were improved 3.56-, 1.68-, and 1.82- times compared with control treatment at 12 h after application. Lignin content of tobacco roots was significantly induced 1.33-fold and 1.54-fold at 4 d and 7 d after daphnetin application. Compared with the control at 6 h after daphnetin application, jasmonic acid and abscisic acid contents in tobacco were significantly increased by 35.98% and 34.55%, while salicylic acid content significantly decreased by 25.56%. Meanwhile, daphnetin could significantly down-regulate expression level of jasomonate ZIM-domain 3 (JAZ3) with 9.19-fold, and induce expression level of pathogenesis-related protein gene 1 (PR1). Control efficacy of 2.85 mg/L daphnetin treatment was 52.22%-75.54% in field conditions, significantly higher than benzothiadiazole treatment with 33.50%-53.00%. Therefore, application of daphnetin improved plant enzyme activity and root lignin content, inducing expression levels of plant resistance genes, and displayed stable filed control efficacy on tobacco bacterial wilt. Thus daphnetin could be used as an alternative plant elicitor for controlling tobacco bacterial wilt.