Study On Biocontrol Potential Of Bacillus Subtilis Against Valsa Mali

The cultivated area and yield of apple tree in China plays an important role in the world.Apple is one of the most competitive agricultural and sideline products in our country and abroad.But in the process of planting,all kinds of diseases occur frequently.Among them,apple canker is one of the most widely distributed and harmful diseases,which has become an important factor restricting the rapid development of apple industry in China.So far,the main control methods of apple canker are still agricultural control and chemical control.It is extremely urgent to find green and efficient prevention and cure methods.At present,the combination of Bacillus subtilis and other chemical pesticides is an effective way to control the disease,which is hopeful to solve the problem of colonization of Bacillus subtilis in the field,and at the same time to reduce the risk of drug resistance and environmental hazards.In this paper,we have isolated,screened and identified an antagonistic strain-Bacillus subtilis LF17,which has great effect on Valsa mali.And we have also screened the culture medium of Bacillus subtilis biofilm formation and the environment suitable for the growth and reproduction of Bacillus subtilis was determined,and the indoor and field control effects of the combination of Bacillus subtilis and chemical pesticides.We hope it can provide a reference for the field application of Bacillus subtilis.The findings are summarized as follows:1.Isolation,screening and identification of an antagonistic strain against Valsa mali:Bacillus subtilis,strain number SAASIPPLF17.The inhibitory rate of the strain was 84.16%and the inhibitory rate of fermentation broth was 95.77%2.The correlativity between SAASIPPLF17 absorbance and the spore quantity in the liquid is linear correlation,and the regression equation was:y=3*108x-4*107;R2=0.9142.The lethal temperature of Bacillus subtilis strain SAASIPPLF17 was determined to be 96 ? for 8 min via controlling the temperature and time of the treatment with water bath.The pH of LF17 was determined to be less than 3.0 or more than 10.0 by controlling the pH of Bacillus subtilis medium,and the optimum pH range was 5.0-8.0.3.The optimal culture medium for sporulation of strain SAASIPPLF17:Beef extract 5.0g,Peptone 10.0g,NaCl 5.0g,Glucose 20.0 g,MnCl 5.0 mg.Mn2+ significantly promoted the formation of SAASIPPLF17 biofilm.4.The combination of LF17 and chemical pesticide had a significant effect on the growth of mycelium of the pathogenic bacteria:The combination of three agents(methyl,pyrazole,diphenylethazole)and Bacillus subtilis could significantly increase the inhibition rate of mycelium growth.At the same time,prolong its lasting period.5.The combination of LF17 and chemical pesticide had a significant effect on the conidial germination of the pathogenic bacteria:The combination of three fungicides(methyl,pyrazole,diphenylethazole)and Bacillus subtilis can all inhibited the germination of the conidia of the disease;Compared with the use of biocontrol or chemical agents alone,the combination could effectively increase the inhibition rate of conidia germination of V.mali,but its inhibitory effect on the growth of mycelium was weaker than that on the growth of decomposed fungi.