Screening of compound plant elicitors and the synergistic mechanism for controlling tobacco bacterial wilt

【Objective】The objective of this study was to screen out the best flavonoid compound elicitors, clarify the synergistic mechanism of them on controlling tobacco bacterial wilt, and provide scientific basis for improving the controlling effect against tobacco bacterial wilt and developing new plant compound elicitors.【Method】Flavonoids(flavonoid and hesperidin) were studied. Eight additives(concentrations of 200 mg/L) and 1 mmol/L flavonoid, 1 mmol/L hesperidin were mixed together, to screen the additives that could compound with flavonoid and hesperidin. The effects of them on controlling tobacco bacterial wilt were determined, and the best compound elicitors were screened out by indoor pot experiment. To further evaluate the controlling effect of the best compound elicitors against tobacco bacterial wilt, the mechanism of compound elicitors on controlling tobacco bacterial wilt was clarified by measuring the activities of enzymes such as oxidase(POD), polyphenol oxidase(PPO) and phenylalanine ammonolyase(PAL) in tobacco and the expression levels of some resistance-related genes(NtPR1a, NtPAL, NtNPR1, NtHIN1 and NtEFE26) in tobacco using fluorescence quantitative real-time PCR.【Result】Among 8 additives, silica and lecithin could enhance the effects of flavonoids and hesperidin on controlling tobacco bacterial wilt, and the suitable concentrations were 50 and 100 mg/L respectively. Compared with the single agent of flavonoids, the effect of flavonoid compound elicitors(1 mmol/L flavonoid+50 mg/L silica, 1 mmol/L flavonoid+100 mg/L lecithin, 1 mmol/L hesperidin+50 mg/L silica, 1 mmol/L hesperidin+100 mg/L lecithin) on controlling tobacco bacterial wilt increased by 36.88% to 67.21%. The treatment of flavonoid compound elicitors significantly improved the activities of POD, PPO and PAL in tobacco leaves. Compared with a single agent of flavonoid, the activities of POD, PPO and PAL in tobacco leaves increased by 19.47%-37.95%, 25.89%-66.91%, 22.98%-254.83% in flavonoid+lecithin treatment respectively;compared with a single agent of hesperidin, the activities of POD, PPO and PAL in tobacco leave sincreased by 3.69%-114.37%, 12.27%-58.04%, 28.12%-104.39% in hesperidin+lecithin treatment respectively. Compared with a single agent of flavonoid or hesperidin or the water control group, the application of flavonoid compound elicitors also significantly increased the relative expression levels of resistance-related genes NtNPR1, NtPR1a and NtHIN1(P<0.05).【Conclusion】50 mg/L silica and 100 mg/L lecithin can promote the effects of 1 mmol/L flavonoids and 1 mmol/L hesperidin on controlling tobacco bacterial wilt, and strengthen the activities of defense enzymes and the expression levels of resistance-related genes. This study lays the foundation for the development of new plant elicitors.