A Study And Its Use Of A Neotype Synergism Of Bactericide For Controlling Citrus Canker Disease

Citrus canker disease caused by Xanthomonas axonopodispv.citri(Xac)through weaken the plant growth reduce fruit quality.It is one of the most severe bacterial diseases of citrus and threatens the citrus industry worldwide.Long-term use of chemical agents easily causes the pesticides resistance of Xac.Previous studies from our laboratory prove that two kinds of DSF(EDSF and FDSF)signaling molecules are present in Xac.Bactericidal effect of pesticides(streptomycin,zhongshengmycin and oxine-copper)enhance while mixing with DSF signaling molecules.Hence,the DSF signaling molecules have great applicable prospect of its synergistic effect in the control of citrus canker disease.Main finding of the presented study are as follows:1)We found that within the concentration of signal molecules mixing with chemical pesticides(streptomycin,zhongshengmycin and oxine-copper)against Xac have great synergistic effects to the pesticides in compare to 500 times streptomycin.Mixture of EDSF ranging 20μM between 100μM with the 500 times streptomycin treat with Xac,the rate of synergistic effects of EDSF reach 3~300 times,while the rate of the mixture of FDSF ranging 100μM between 500μM reach 2~150 times.2)In compare to 5000 times zhongshengmycin,mixture of EDSF ranging 20μM between 100μM with the 5000 times zhongshengmycin treat with Xac,the rate of synergistic effects of EDSF reach 100~200 times,while the rate of the mixture of FDSF ranging 50μM between 200μM reach 300~800 times.3)In compare to 500 times oxine-copper,mixture of EDSF ranging 20μM between100μM with the 500 times oxine-copper treat with Xac,the rate of synergistic effects of EDSF reach 2~10 times,while the rate of the mixture of FDSF ranging 100μM between500μM reach 2~30 times.4)qRT-PCR detected that the related genes expression of Xag ABC,GumB,ManA,about biofilm formation of Xac treated with the mixture of DSF signal molecules with chemical pesticides(streptomycin and oxine-copper).qRT-PCR results confirmed that Xag ABC genes and GumB about biofilm formation were down-regulated.Also,ManA gene about biofilm dispersion of Xac was significantly down–regulated as well.The outdoors plants inoculation results show as follows:5)Using EDSF ranging 20μM-100μM mixing with streptomycin and oxine-copper while using EDSF ranging 300μM-400μM respectively to treat with outdoor citrus plants which have been inoculated by Xac.Results showed that EDSF and FDSF signaling molecules have similar synergistic effect towards streptomycin or oxine-copper to control citrus canker disease.6)Through the enzyme activity test,the enzymes such as POD,PPO,PAL related to resistance have some changes in citrus plant treated with 50μM and 100μM DSF signal molecule.We found that the activities of POD decreased while,PPO and PAL increased as compared to control.7)DSF and its derivative significantly reduced the stomata opening of citrus plant leaves.In brief,presented study is based on the signaling molecules produced by Xac.We develop a novel biological synergist,which have obvious synergistic effect to chemical pesticides(streptomycin,zhongshengmycin and oxine-copper)against citrus canker disease caused by bacterium Xac.Also,the synergists have good prospect in application.Which play an important role to achieve a development goal of reducing the use of pesticides in controlling the citrus canker disease.