Screening,Identification And Preliminary Mechanism Of Biocontrol Bacteria Against Maize Curvularia Leaf Spot

Curvularia leaf spot is one of the main leaf spot diseases of maize in north China,which seriously threatens the yield of maize and has caused huge economic losses.Using biocontrol bacteria to control plant diseases has become a research hotspot in recent years.To solve this problem,some bacteria have been screened that could induce maize to generate systemic resistance against Curvularia leaf spot in pot and field experiments.At the same time,the effective strain of bacteria was systematically studied in terms of classification and induced systemic resistance mechanism at gene and molecular level.The main results are as follows:1.Screening strains that can induce maize against Curvularia leaf spot.Maize seeds coated by 8 strains were grown on the experimental field of Shenyang Agricultural Uinversity.By the time of July,maize was inoculated with Curvularia lunata spore suspension by artificial spray.One week later,the survey found 3 strains showed the best control effect against Curvularia leaf spot and increased the yield of maize.In addition,3 strains were screened indoors.The results showed that Sneb2249 is an excellent plant growth promoting rhizobacteria that can induce resistance against Curvularia leaf spot and resultantly promote growth of maize.2.Identification of strains that can induce maize against Curvularia leaf spot.The biocontrol bacteria was classified and identified by the methods of classical morphological,physiological,biochemical characteristics and 16 Sr DNA sequence analysis.The result showed that Sneb2249 and Sneb2480 were identified as Pseudomonas putida and Serratia liquefaciens,respectively.3.Analysis of changes about active oxygen content in leaves of maize which was induced resistance against Curvularia leaf spot by Sneb2249.The H2O2 content,O2-content,CAT activity,and clearance rate of O2-in the leaves of maize were detected by kit.The results showed that H2O2 content,O2-content,CAT activity,and clearance rate of O2-in the leaves of maize coated by Sneb2249 were increased at 4-5 days post inoculation(dpi),which indicated that active oxygen metabolism is the mechanism of strain Sneb2249 induced maize against Curvularia leaf spot.4.Analysis of related defense gene in leaves of maize which was induced resistance against Curvularia leaf spot by Sneb2249.The expression of Zm CAT1,Zm APX,Zm POX3,and Zm PAL gene were measured at the transcription level in different time after inoculation point.The results showed that Zm POX3 gene not be up-regulated induced by Sneb2249.The expression of Zm CAT1 and Zm APX genes were up-regulated induced by Sneb2249 at 3-5 dpi.Zm SOD4 gene reached the highest value at 3 dpi induced by Sneb2249.In addition,the expression of Zm PAL gene of group Sneb2249+CX-3 was up-regulated at 1-5 dpi and was significant difference compared with uncoated control at significant difference 0.05 level on day 5 after infection.The above results showed that strain Sneb2249 could induce the expression of Zm CAT1,Zm APX,Zm SOD4,and Zm PAL gene in the interaction between maize and Curvularia,and play an important role in inducing resistance.