Preparation Of Biocontrol Streptomyces Wettable Powder Against Potato Common Scab

Potato common scab is an important soil-and seed-borne disease that occurs in potato production areas around the world,mainly caused by Streptomyces spp.At this stage of potato scab control measures are mainly based on chemical control,but improper use of chemical pesticides will not only lead to pathogenic bacteria resistance,but also easy to cause soil residues and environmental pollution.Biological control has the advantages of high efficiency,non-toxic,non-harmful,non-pollution,non-resistance and environmental protection,and is an effective way to control plant diseases.In this study,the fermentation medium and fermentation culture conditions of Streptomyces biotrophicus strains PBS9and PBSH9 were optimized at the shake flask level,and a wettable powder of Streptomyces biotrophicus with strains PBS9 and PBSH9 as active ingredients was developed.The results of the study are as follows.1.The best medium formulation of strain PBS9 was obtained:wheat bran 30 g/L,soybean cake flour 5 g/L,K₂HPO₄0.5 g/L,M_gSO₄·7H₂O0.5 g/L,Na Cl 0.5g/L,F_eSO₄·7H₂O0.01g/L.The best fermentation culture conditions were:inoculum amount of 2%of the loading volume,p H 7,28℃Under the optimal fermentation medium and culture conditions,the colony number of fermentation broth of strain PBS9 reached 14.05×10¹²CFU/m L and the inhibition rate reached 76.16%.The best medium formulation of strain PBSH9:wheat bran 10 g/L,soybean meal cake flour 5g/L,K₂HPO₄0.5g/L,M_gSO₄·7H₂O 0.5 g/L,Na Cl 0.5 g/L,F_eSO₄·7H₂O 0.01 g/L.The best fermentation culture conditions were:inoculum amount of 4%of the loading volume,p H 6,temperature28℃,shaking fermentation for 6 d.Under the optimal fermentation medium and culture conditions,the colony number of PBSH9 fermentation broth reached 13.87×10¹¹CFU/m L and the inhibition rate reached 71.9%.2.Through the screening of the carrier and additives of Streptomyces bovis strain PBS9 and PBSH9 wettable powder,the formulation of PBS9 wettable powder（100 g）was determined as follows:187.2 m L of PBS9 fermentation broth,90 g of diatomaceous earth,4.8 g of Tween-60,3.2 g of polyethylene glycol,3.6 g of sodium3.carboxymethylcellulose,0.1 g of dextrin,the PBS9 wettable powder The amount of bacteria is 2.78×1012 CFU/g,wet time is 8 s,suspension rate is 86.77%,fineness is93%,miscellaneous bacteria rate is 0.5%,p H is 7.5,low temperature storage at 4℃for 60d,the survival rate of bacteria is above 84.2%;the formula of PBSH9 wettable powder（100g）is:173.6 m L of PBSH9 fermentation solution,89 g of diatomaceous earth,add 5 g Tween 80,polyethylene glycol 5 g,sodium carboxymethyl cellulose 3.5 g,dextrin 0.1 g.The bacterial amount of PBSH9 wettable powder was 2.68×1012 CFU/g,wet time was 7 s,suspension rate was 87.5%,fineness was 95%,miscellaneous bacteria rate was 0.3%,p H was 6.8,low temperature storage at 4℃for 60 d,and the survival rate of the bacteria was above 83%.4.indoor inhibition test results table PBS9 wettable powder inhibited 78.49%of the pathogenic bacteria of potato scab,PBSH9 wettable powder inhibited 75.55%of the pathogenic bacteria of potato scab.PBS9+PBSH9（7:3）wettable powder mixture with82.33%inhibition,and PBS9+PBSH9（3:7）wettable powder mixture with 81.27%inhibition against the potato scab pathogen PS1.5.The results of the pot test showed that PBS9 WP and PBSH9 WP had good control effect on potato scab,and the control effect was better when mixed than alone.96.31%control effect was achieved when PBS9+PBSH9 WP was mixed in the ratio of 5:5.When PBS9 wettable powder and PBSH9 wettable powder were applied alone,the control effect was 87.54%and 84.3%,respectively.