Effect And Mechanism Of Bacillus Subtilis XZ16-1 On Controlling Wheat Powdery Mildew

Wheat powdery mildew is one of the most serious fungal diseases of wheat caused by Blumeria graminis f.sp.tritici(Bgt).At present,chemical control and resistance breeding are the main methods to control wheat powdery mildew,but chemical control has some disadvantages,such as polluting environment and causing pathogen resistance,however,the resistant varieties gradually became ineffective because of the variation of powdery mildew.In recent years,biological control using biocontrol microorganisms such as Bacillus subtilis has become a hot topic of research,but research on Bacillus subtilis and its mechanism of action against powdery mildew of wheat still needs to be further investigated.In this study,a strain of B.subtilis XZ16-1 with a significant antagonistic effect(p<0.05)on wheat powdery mildew was isolated from soil,and its inhibition activity,control effect and mechanism of inhibition on wheat powdery mildew were investigated,and its promotion effect on wheat was also investigated to analyze its mechanism of biological control of wheat powdery mildew,so as to provide theoretical reference for the application of biological control of wheat powdery mildew.The specific research results are as follows.In this study,a strain of Bacillus subtilis XZ16-1 was isolated from soil,which had significant antagonistic activity against Blumeria graminis f.sp.tritici,at the same time,the growth-promoting effect on wheat was studied,and the mechanism of biocontrol on wheat powdery mildew was analyzed,so as to laid a theoretical foundation for the application of biological control of wheat powdery mildew.(1)A strain XZ16-1 with high antagonistic activity against wheat powdery mildew was isolated from the soil.The culture filtrate of strain XZ16-1 had 96.02%inhibition on spore germination of Bgt.The control effect of strain XZ16-1 on wheat powdery mildew in vitro was 83.82%,and the antagonistic strain was identified as Bacillus subtilis by morphological,physiological and 16S r DNA sequence analysis.(2)The culture filtrate of B.subtilis XZ16-1 and its three crude extracts were highly effective in antagonizing the powdery mildew fungus of wheat.The results of in vitro inhibition tests showed that the culture filtrate of B.subtilis XZ16-1 and three crude extracts,including crude lipopeptides,n-butanol extract,and crude protein,could significantly inhibit Bgt spore germination.Spore germination was inhibited by 96.24%for 50%culture filtrate,98.87%for 10.0 mg/m L n-butanol extract,97.47%for crude lipopeptides and 95.35%for crude protein.(3)B.subtilis XZ16-1 showed a significant pot control effect against powdery mildew of wheat.The results of in vivo biological control tests showed that different concentrations of XZ16-1 culture filtrate had control effects,in which 100%of the culture filtrate significantly reduced the disease index of wheat powdery mildew,with treatment and prevention effects of 81.18%and 83.72%,respectively,and the prevention effects were better than those of the commonly used chemical fungicide triadimefon.(4)B.subtilis XZ16-1 was able to produce antimicrobial substances and cause cellular level damage to wheat powdery mildew.The assay results showed that B.subtilis XZ16-1has the potential to produce inhibitory substances such as hydrolytic enzymes and lipopeptides.B.subtilis XZ16-1 has the potential to cause cellular level damage to Bgt.The results of separate staining observations after treatment of Bgt spores using different concentrations of XZ16-1 culture filtrate showed that B.subtilis XZ16-1 causes damage to the cells through disruption of Bgt cell membranes,elevation of mitochondrial membrane potential(MMP)and inducing reactive oxygen species(ROS).(5)B.subtilis XZ16-1 has growth-promoting properties.The results of the probiotic assay of B.subtilis XZ16-1 showed that B.subtilis XZ16-1 has various growth-promoting properties,such as the production of growth-promoting substances like IAA and ironophilins,and phosphorus solubilizing effects.B.subtilis XZ16-1 had growth-promoting effects on wheat seedlings.The results showed that B.subtilis XZ16-1 suspension showed the most significant growth-promoting effect at 10~6CFU/m L(p<0.05).In addition,B.subtilis XZ16-1could induce systemic resistance in wheat seedlings.The results showed that B.subtilis XZ16-1 could affect the activities of defense enzymes(POD,CAT,SOD,and PAL),improve the health of plants and enhance the resistance to fungal diseases.In conclusion,B.subtilis XZ16-1 is an effective biocontrol strain for wheat powdery mildew control,and this study provides theories and ideas for the development of novel biocontrol agents for wheat powdery mildew by studying its mechanism of action.