Screening,Characteristics Research And Preliminary Application Of Biocontrol Strain A14 To Phytophthora Capsici

Phytophthora capsici is a kind of soil-borne infection plant diseases which belong to the flagella fungus subphylum fungi.Phytophthora capsici could cause disaster losses in agricultural production.The major way to control Phytophthora capsici disease is pesticide control.Using pesticide probably caused environmental pollution and pesticide resistance.Biological control technology could effectively control the occurrence of Phytophthora capsici.It is non-toxic and has no side effects.In this paper,the isolation,identification,growth characteristics,biocontrol effect and application of biocontrol bacterum have been carried out.More than 60 strains were isolated from fresh soil collected in the woodlands of Zijin mountain and pepper greenhouse of Luhe district in Nanjing,Jiangsu province.Six strains which have different degrees of inhibition to Phytophthora capsici were obtained by early screening,A14 which has better antagonism effect on P.capsici was found in secondary screening.Strain A14 was identified as Streptomyces sp.by morphological observation,physiological characteristics and phylogenetic analysis based on 16S rDNA gene sequence comparisons.The optimum growth temperature of strain A14 was is 28?,the optimal pH is 7.0 and the optimal speed is 160 rpm.Starch is the best carbon source for the growth of strain A14,the best nitrogen source is the beef extract.Strain A14 grows best with the carbon and nitrogen ratio of 5:1.With the biocontrol effect determination of strain A14,the results show that the inhibition rate of strain A14 on P.capsici reached the highest level(63.64%)in 7d.Two kinds of sterile fermented liquid broth of strain A14 had a good inhibitory effect on mycelia growth of P.capsic.The highest inhibition rate of unheated sterile fermented liquid mixed plate was 45.45%for P.capsici mycelium,and the highest inhibition rate for P.capsici mycelium of heated sterile fermented liquid mixed plate was 43.64%.The difference of inhibitory effect is insignificant,which indicat the stabilization of the antagonistic substances in the fermentation filtrate of strain A14.Varying degrees of deformity happened during the growth of the P.capsici mycelium which affected by strain A14 under the microscope.The heredity stability of strain A14 sterile fermented liquid is better,the five generations of sterile fermented liquid has no obvious changes of P.capsici antagonistic effect.Sterile fermented liquid from LB culture medium has the best antagonism effect to P.capsici among different culture medium for P.capsici antagonism test.Strain A14 sterile fermented liquid and P.capsici zoospores mixture has a germination inhibition rate of 84.26%,85.29%and 86%after 4h,7h,12h,which indicates that strain A14 sterile fermented liquid could effectively inhibit the P.capsici zoospore germination.In the experiment of strain A14 fermented liquid in vitro,pepper leaves soaked by strain A14 fermented liquid could effectively resist P.capsici infection.Large black disease spots by P.capsici infection occurred on pepper leaves without soaked by strain A14 fermented liquid.The control efficiency of strain A14 fermented liquid on P.capsici mycelium was 32.23%,and the control effect on P.capsici zoospores was 49.04%.In pot experiment,pepper seedlings with strain A14 fermented liquid filling root in 3d ahead have a remarkable ability to resist P.capsici,the detection control effect is 40%in 10d.