| More than 700 strains of bacteria and fungi were isolated from the soil in Hainan,Henan,Hebei,etc,and the soil bacteria was tested by inhibition zone method that had antagonistic effects against the bacterium Pectobacterium carotovorum subsp.carotovorum(Jones)Bergey by the inhibition zone method.Among them,the strain numbered B3 has the best antagonistic effect.The antagonistic bacteria were identified by morphological observation,physiological and biochemical characterization,16 S r DNA homology sequence analysis.B3 strain was positive in gram staining reaction,capable of hydrolyzing starch and liquefied gelatin,negative in methyl red test and negative in acetylmethyl methanol test.Malonate could not be used,but fructose,raffinose,galactose and mannitol could be used for fermentation to produce acid.Glucose,lactose,galactose,sucrose,raffinose and fructose can be used as carbon sources.Sorbitan,sorbitol,rhamnose and sweet alcohol cannot be used as carbon sources.Combining 16 S r DNA homology sequence analysis,the strain B3 was identified as Bacillus amyloliquefaciens(Wang et al.2008).The optimum liquid culture conditions of antagonistic bacteria under laboratory conditions were determined by single factor variable method.The results showed that the optimum p H of B3 was 7,the optimum culture temperature was 30 ℃,the optimum carbon source was glucose,the optimum nitrogen source was urea,the optimum rotating speed of the shaking table was 180 r/min,and the optimum culture time was 36-48 h.Rifampicin was used to label antagonistic bacteria to explore the colonization rule of antagonistic bacteria on cucumber leaves.The test results showed that the antagonistic bacteria could colonize on cucumber leaves,at the beginning of inoculation,the amount of bacteria was the highest,and gradually decreased over the time.Under different light treatment conditions,we found that there was no significant difference in the colonization amount of the induced strain under 12 h light and 12 h darkness compared with that under24 h light,but the colonization amount of the labeled strain was significantly reduced under 24 h darkness.The results showed that the bacteria could colonize cucumber plants under natural light.Three methods were used to study the effect of B3 controls cucumber leaf spot disease.That is cucumber leaves first sprayed with antagonistic strain suspension and 24 hours later sprayed Pathogen suspension;The antagonistic strain suspension and the Pathogen suspension suspension were sprayed at the same time;First sprayed the Pathogensuspension and 24 hours later sprayed antagonistic strain suspension;Cucumber leaves with only the pathogen bacterial suspension as a control.The results showed that the control effects of of B3 controls cucumber leaf spot disease in the three treatment methods were 70.3%,67.01% and 50.6%,respectively.It is indicating that most effective control is observed when B3 strain is applied before pathogen application,while applying B3 strain after pathogen application is least effective.After the antagonistic strain B3 treated the cucumber plants,the activity of five defense enzymes in the cucumber body was significantly increased compared with that before,among which POD activity was 2.22 times as active as that in the control group,PPO activity was 2.80 times as active as that in the control group,CAT activity was 2.48 times as active as that in the control group,SOD activity was 3.03 times as active as that in the control group,and double PAL activity was 7.25 times as active as that in the control group.Therefore,it can be inferred from the change of defense enzyme activity that the antagonistic bacteria B3 can induce the cucumber plants to produce disease resistance after the cucumber plants are treated,so as to resist the infection of pathogenic bacteria.(significant difference analysis)... |
PDF Full Text Request