| In this study, 206 bacterial strains were obtained by isolating and purificating the bacteria from 77 soil samples of Heilongjiang, Jiangsu, Zhejiang and Hainan province. By using the method of slab confrontation,a strain which had strong antagonistic inhibition effect on Pitaya stem rot disease was screened.According to morphology, physiology,biochemistry and the characteristics of 16S rDNA sequence,it was identified as Paenibacillus polymyxa (Paenibacillus polymyxa Ash, Priest & Collin, numbered as PCY-67). On this basis, the fermentation process of the strain was developed and the biocontrol potential of pitaya was evaluated,which laid the foundation for the application of the strain in the biological control of plant diseases.Main contributions of this work are as follows:The experiment of the antagonistic inhibition of strain PCY-67 on Pestalotiopsis palmarum Cooke,Corynespora cassiicola Berk. & M.A. Curtis,Colletotrichum musae Berk. & M.A.Curtis,Phyllosticta sp.,Colletotrichum sp.,Curvularia lunata R.R. Nelson & Haasis Colleto-trichum sp.,Fusarium sp.,Colletotrichum gloeosporioides Penz,Gloeosporium papaya P.Henn, etc.,revealed that PCY-67 had antagonistic inhibition effect on the tested 10 kinds of plant pathogen.2.Taking aim at the number of viable bacteria in liquid,the method of single-factor test and orthogonal test had been used to study and optimize the fermentation process of PCY-67,which were as follows: the concentration of soluble starch, peptone and sodium chloride were 17.5g/L, 20g/L, 1.25g/L,respectively ; the fermentation temperature was 30 ℃; the initial pH value was7;the rotation speed was 180r/min;the fermentation time was 36h;the inoculation amount was 8% and the medium volume in flask was 80ml/250ml.With this fermentation process, the number of viable bacteria of PCY-67 amounted to 4.3*109CFU/mL.3.The inhibitory effect of PCY-67 fermentation filtrate on Pitaya stem rot disease pathogen was determined.The results showed that when the concentration of fermentation filtrate was 10%, the inhibitory rate was 60%;when it was 30%,the inhibitory rate was 83%and when it was 50%,the inhibitory rate was as much as94%.4.The biological control effect of PCY-67 on Pitaya stem rot disease under different inoculation treatment had been studied.The results showed that if the inoculation of PCY-67 anticipated the inoculation of pathogenic bacteria,the preventive effect was 76.42%;if inoculated them at the same time,the preventive effect was 60.38%;if inoculated pathogenic bacteria first,the preventive effect was 50.06%. When the concentration of PCY-67 fermentation filtrate was 30% the preventive effect of Pitaya stem rot disease was 66.33%;when it was 50%,the preventive effect was 68.45% and when it was 70%,the preventive effect was 70.28%.The preventive effect declined significantly when the concentration was lower than 30%, but there was no significant difference between the concentration of 30% and higher concentrations.Therefore, from the economic point of view, the concentration of 30% PCY-67 fermentation filtrate is supposed to be used.5.The quantitative changes of PCY-67* in the stems of Pitaya plants were detremind.The results showed that,in the time of 1-5d after inoculation,the amount of bacteria decreased from 6.3*105CFU/g to 4.9*104CFU/g;in 5-15d,the amount of bacteria increased gradually,which reached to 5.8*104CFU/g;after 15d,it had a tend of decreasing again,the amount of bacteria had decreased to 6.1*103CFU/g and was relatively stable at 4.4*103CFU/g after 25d even 30d. |
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