Inhibitory Mechanism Of Methyl Gallate Against Ralstorinia Solanacearum And Its Control Efficacy On Tomato Bacterial Wilt

Tomato bacterial wilt caused by Ralstorinia solanacearum is one of the destructive soil-borne diseases. Chemical control is the major means to control the disease at present. However, relatively few bactericides and with intensive and long-term use, pathogens have developed resistance, and the control efficacy was significantly decreased. Therefore, it is a main issue to develop a new bactericide with high efficiency, low toxicity and low-residue to control tomato bacterial wilt.Previous studies indicated that methy gallate (MG) extracted from the leaves of Toxicodendron sylvestre has strong inhibition against R.solanacearum. However, the mechanism of MG for inhibiting the growth of the pathogen and the control efficacy on tomato bacterial wilt remain uncertain. Therefore, a study was conducted to test the physiology and biochemistry changes of R.solanacearum under the MG treatment, to analyze the differential proteome of R.solanacearum under the MG treatment, to value the control efficacy of MG on tomato bacterial wilt and to understand the transmission property of MG in tomato. The major results are as follows.1. MG could break the cell wall, inhibit the ability of secreting pectinase and cellulase, and decrease the activity of POD and CAT in R.solanacearum. The ratio of NADH/NAD+ was raised in the pathogen treated with MG, it implied that MG depressed EMP-TCA cycle of R.solanacearum.2. The total protein expressional differences of Ralstonia solanacearum under the inhibition of methyl gallate (MG) were clarified. The results showed that 29 protein spots in R. Solanacearum treated with MG displayed significantly different expression as compared with solvent control. Twenty two proteins were identified by LC-MS/MS analysis, which included 11 newly increased,5 disappeared,1 up-regulated and 5 down-regulated proteins. These proteins were related to energy metabolism, signal transduction and translocation of solute or DNA repair. The result indicated that the target of MG for inhibiting the growth of R. Solanacearum would be more than one. One of mechanism for inhibiting the growth of R. Solanacearum by MG might be that MG destroyed the energy metabolism of R. Solanacearum.3. F0F1 ATP synthase subunit ε gene RSc3316 deletion mutant of R. Solanacearum and its complementation strain were obtained. The result will provide the basis for us to understand the biological functions of F0F1 ATP synthase subunit ε in R. Solanacearum under the inhibition of MG.4. MG could effectively protect tomato from tomato bacterial wilt. When MG was applied 15d before the pathogen inoculated, the control efficacy could reach 52.15%. However, the control efficacy was only 13.03% when the MG was applied 5 d after the pathogen inoculation. MG could be easily absorbed by tomato roots, and the control efficacy of 96.67% was obtained when tomato roots were dipped into MG 2d before the pathogen inoculation in root. But MG was difficult to transport from root to leaf or from leaf to root. The control efficacy was only 14.44% when roots dipped into MG 1d before the pathogen inoculation on leaves. When leaves treated with MG 1d before the pathogen inoculation in roots, the control efficacy was 9.44%.5. Under the MG treatment, the activities of rooting-related enzymes and induced resistance-related enzymes and secondary metabolism in tomato roots were changed. In tomato roots treated with MG, the activity of indoleacetic acid oxidase (IAAO) was decreased, but the activity of peroxidase (POD) was not changed, and the activity of polyphenol oxidase (PPO) was increased. The activity of phenylalanine ammonia-lyase (PAL) in tomato under the MG treatment after the pathogen inoculation was increased. The concentration of some substances in tomato roots under the MG treatment, such as geraniol, stigmasterol, β-sitosterol and friedelinol, were higher than that in tomato roots treated with 0.1% methanol at the same time.6. MG could promote the seed germination of tomato. The seed germination rate of tomato at 4th day after 20 μg/mL MG treatment、50 μg/mL MG treatment、water treatment and 0.1% methanol treatment were 73.38%、66.69%、53.33% and 48.89%, respectivly. The seed germination rate of 20 μg/mL MG-treatment and 50 μg/mL MG-treatment were all higher obviously than that of water-treatment and 0.1% methanol-treatment at the same time.7. MG could effectively control tomato bacterial wilt in field. The control efficacy of 0.5 g/L MG and 20% Saisentong SC on tomato bacterial wilt in field was 60.22% and 48.86%, respectively. The yield of tomato treated with MG was 2982.4 kg/667 m2, it was 1.54 times more than that of water-treatment. MG could not affect the population and quantity of bacterium in soil.