Identification And Biological Control Against Apple Valsa Canker Disease By Bacillus Subtilis LF17

Apple Valsa canker is a destructive disease caused by Valsa spp..There are some limitations in using chemical agents to prevent and control apple Valsa canker in production.Biological control measures are the focus of current research.Bacillus subtilis has shown great potential as a biocontrol bacteria for apple Valsa canker.However,there are few studies on improving the antibacterial and disease prevention stability of B.subtilis against Valsa mali.Inorder to solve this problem,this study identified endophytic bacteria from apple trees,and obtained a B.subtilis strain and named LF17.It has a good inhibitory effect on the apple Valsa canker.The bacteriostatic mechanism,toxin gene,inhibiting pathogenes and controlling disease effect combined with potassium,plant growth promoting,bacteriostatic effect,colonization and microbial community diversity of strain LF17 was studied.As can be seen in the following paragraphs:（1）Based on the morphologic characteristics,16 S r DNA and gyr A sequence analysis,the strain LF17 was defined as Bacillus subtilis.The results of the bacteriostatic mechanism showed that:（1）the inhibition rates of fermentation broth against Valsa mali was 93.80%,its better than chemicals.（2）The effective components in the fermentation broth of B.subtilis have less volatile gas,it may cause less loss in field application.（3）After the fermentation broth of strain LF17 was overwintered,there was no significant difference in the living bacteria number on the surface and underground 20 cm from the control group.It was proved that the temperature had little effect on the living bacteria number when applied on the field surface.（4）The genes of strain LF17 contained srf AB,ynd J,fen D,itu D and bam C.（2）It was shown by the disease prevention test that:（1）The fermentation broth of strain LF17 had a good inhibitory effect on Valsa mali.It can promote the healing of scarred wounds,and the recurrence rate of apple Valsa canker was effectively reduced.The prevention effect of field is higher than that of chemicals.The wound healing area was 9.37-9.79 cm2 after the application of Bacillus subtilis.And the recurrence rate of scab was 3.82%-4.56%.（2）The length of apple Valsa canker scar was reduced by14.38%-10.03% after root irrigation strain LF17.The results showed that strain LF17 was effective in the prevention and treatment of V.mali.The best effect was obtained by 250 m L fermentation broth.The results showed that the resistance to V.mali and the ability of wound healing of apple trees were enhanced by the application of root culture.（3）Combined with potassium,B.subtilis fermentation broth can effectively increase the living bacteria number in the fermentation broth.And to improve the inhibitory rate and stability.The antibacterial effect of fermentation broth combined with KH₂PO₄ was the best,reaching 96.33%,it is higher than that of KCl and K₂SO₄.（4）The strain LF17 fermentation broth was applied to the root of begonia,it can promote the growth of plants.The growth rate of stem length reached 12.35%-15.59%,and the growth rate of root length reached 81.11%-192.21%.Both dry weight and wet weight were significantly higher than the control.It is shown by tem: the B.subtilis has colonization in the intercellular spaces of epidermal cells and sclerenchymatous cells of plant roots and stems,as well as vascular bundles and parenchyma cells.The results showed that the fermentation broth of B.subtilis LF17 could colonization and promote the growth of plants.（5）After applying B.subtilis LF17 fermentation broth,it can increase the beneficial bacterial community and the beneficial fungal community in the soil of apple tree roots.It had a significant effect on the abundance and uniformity of the root flora.The strain LF17 can obviously improve soil microbial community structure,promote nutrient decomposition and improve soil quality.