The Effect Of Bacillus Amyloliquefaciens L3 On Biological Control And Growth-promoting Of Watermelon

Watermelon is a kind of popular fruit,and it is also a very important economic crop.Watermelon wilt disease is a common soil borne disease which is caused by Fusarium oxyporum f.sp.niveum(FON)and it seriously harms the agricultural production of watermelon.At present,the methods of controlling plant diseases mainly rely on chemical pesticides which not only affect the quality and the safety of watermelon,but also cause resistance of the pathogen and serious environmental pollution.Thus,biological control techniques which the core microbes are plant growth-promoting rhinoacteria(PGPR)increasingly attracted attention and application in agricultural production more widely in plant disease management.Bacillus which have characteristics of strong resistance and ease of cultivation have been studied and applied as the most promising growth-promoting and disease control strain.This study that the purpose is to control watermelon wilt disease,adapts the methods of indoor experiment and pot experiment to screen Bacillus strain that has the effect of growth-promoting on watermelon and wilt disease prevention.Then,carrying out researches on the optimization of culture conditions and the effect of growth-promoting of strain.And we study on the effect of control watermelon wilt disease of biological organic fertilizer which core microbe is this strain.Firstly,Selecting 16 strains from screened antagonistic strains,then screened out the bacteria strains which have antagonism effect both in Fusarium oxysporum f.sp.niveum(FW0),Fusarium oxysporum f.sp.vasinfectun(FP1)and Phytophthora capsici Leonian(PC1)under the condition of plate confrontation.There are 12 strains that have strong antagonistic effect to FW0.Strain L3 has better antagonistic effect to FW0 and FP1,and a little antagonistic effect to PC1.In the pot experiment we studied the effect of bio-control to watermelon wilt disease of strain on watermelon,and in the sand-culture experiment we studied the effect of growth-promoting of strain L3 on watermelon.The results show that under the experimental conditions of greenhouse and artificial climate box,strain L3 shows significant effect of growth-promoting on watermelon,which makes the plant height,leaf number,dry weight and fresh weight of watermelon significantly increase.Among them,in the sand-culture condition strain L3 can make the fresh weight of watermelon and dry weight increased by 37.35%and 36.89%.In pot experiment,strain L3 can make the plant height,fresh weight and dry weight of watermelon increased by 66.8%,37.9%and 88.9%.At the same time,strain L3 can effectively reduce the infection of FON on watermelon.Then,we made the molecular identification for strain L3 and explored the optimum fermentation conditions of strain L3.Through determinating the sequences of the 16SrRNA and constructing the phylogenetic tree of strain L3 we found strain L3 belong to Bacillus amyloliquefaciens.We studied under the most suitable medium,the optimum temperature,the optimum initial pH,the most suitable volume of culture liquid for the fermentation of strain L3,and ultimately determined that the optimum medium was BPY medium,and the optimum fermentation condition are 30? temperature,initial pH was 6.0,liquid volume was 50mL/250mL.Under the optimum fermentation conditions we studied on the growth curve of strain L3.The results showed that lag phase in the growth of strain L3 was very short,the logarithmic growth period was about 10 hours,and the maximum cell concentration was about 1*109CFU/mL.The L3-bio-organic fertilizer(L3-BOF)was made through secondary fermentation by mingling the strain L3 and the make-up organic fertilizer(OF).In pot experiment,we explored the effect of bio-control on watermelon wilt disease and the effect of growth-promoting on watermelon of strain L3 and L3-BOF.The results showed that under the pot experiment conditions strain L3 and L3-BOF can significantly promote the growth of watermelon.The application of L3-BOF on watermelon can make the fresh weight of watermelon increase of 83.3%.Meanwhile,strain L3 can reduce the number of FON of the rhizosphere of watermelon.Under the pot experiment conditions strain L3 can effectively control the watermelon wilt disease,and the relative prevention effect was 87.5%.In conclusion,the strain L3 can reduce the number of FON of the rhizosphere of watermelon,and mitigate the infection of FON on watermelon.Strain L3 can effectively control the occurrence of watermelon wilt disease.Meanwhile strain L3 and L3-BOF have obvious effect of growth-promoting on watermelon,and can significantly increase the biomass of watermelon plants.