Study On The Mechansim Of Bacillus Amyloliquefaciens Lx-11 Against Xanthomonas Oryzae Pv.oryzicola And Promote The Growth Of Rice

Bacterial leaf streak?BLS?caused by Xanthomonas oryzae pv.oryzicola?Xooc?is one of the four major rice diseases.It is an important quarantine disease in rice production process.It generally leads to the loss of rice 15%to 25%,severe up to 40%to 60%,Bacterial leaf streak as a quarantine disease which has serious threat to the high and stable yield of rice.Controlling rice bacterial leaf streak were based on thiazole fungicides.The control efficiency is only about 50%.Using biocontrol microbes control of plant diseases is prevention approach which has a good promising.Bacillus amyloliquefaciens Lx-11 is a biocontrol microbe which has good control effecton rice bacterial leaf streak.Control efficiencies of strain Lx-11 were 62.5%and 60.2%in pot and field trials,respectively,significantly higher than those of 20%bismerthlazol treatment?51.2%and 45.8%?.For a better understanding of the pathogenesis of Lx-11 control on rice bacterial leaf streak,this paper do the main researches from the following aspects:Strain Lx-11 belonged to Bacillus amyloliquefaciens.In order to more deeply understand the prevention mechanism of the strain Lx-11 and provide theoretical basis for prevention and cure effect,this paper studied its biological characteristics from different temperature,pH,carbon source,nitrogen source,trace elements,inorganic salt and growth curve.So as to understand its growth best laboratory conditions.The experimental results showed that the optimum growth temperature was 28?,optimum pH is 7.0,the best carbon source is sucrose,best nitrogen source is soybean powder,trace element Gly,Glu,VB₂,VB₆ and inositol can promote its growth,which GLY can promote obviously;Inorganic salt KH₂PO₃ and NaCl all can promote its growth.Bio-control bacteria Lx-11 is on the logarithmic growth before 32h.After 32 h,bacteria growth to achieve basically stable.The optimal culture medium composition of the orthogonal experiment is Yeast extract 1 g.L^-1,sucrose 5g.L^-1,tryptone 6 g.L^-1,glycine 0.01g.L^-1 and sodium chloride 0.15 g.L^-1.Bacillus amyloliquefaciens strain Lx-11 is a good biocontrol agent pre-screened in our laboratory and it showed good control effect on rice leaf blight in the field trials.The growth-promoting effect of strain Lx-11 on rice and the growth-promoting substances secreted by it were verified in this study.The different dilutions?10,50,100,200 and 500 factors?of the broth supermatant and the supermatant produced by strain Lx-11's were used to treat the rice seeds and seedings.Then the rice shape index?shoot,root length and height?and the effects of physiological indicators?chlorophyll a,chlorophyll b and total chlorophyll content?were measured.The results showed that stran Lx-11 had good growth-promoting effect on rice.As with the increasing dilution factors of broth supermatant,the growth promoting effect was increasinging apparently.The most obvious effect was the dilution of 100 factors.But abave the 200 factors,the effect was to decrease.The supernatant containing GA₃,ABA,IAA,Sperdimine and Cytokinins were determined by a liquid chromatography-mass spectrometry.The contents were 1200 ng.mL^-1?IAA?,75.5 ng.mL^-1?GA₃?,3130 ng.mL"1?ABA?,811ng.mL^-1?Sperdimine?,1510ng.mL^-1?Cytokinins?separately.This paper also discusses the expression levels of defense genes and the activity of antioxidant enzymes in rice at different times induced by Bacillus amyloliquefaciensLx-11.We test the rice leaves separately with 108 cfu.mL^-1 Lx-11 bacteria liquid and b5^-16 bacteria liquid or test simultaneously with the two bacteria liquid,examined the relative expression of PR4,PRIOa,PAL LOX,POX and the antioxidant enzyme's activity of POD,SOD,CAT,H₂O₂ at the different time of 0 h,12 h,24 h,48 h and 72 h.This experiment showed that the relative expression of the defense genes?PR4?PR10a?PAL?LOX and POX?all have changed in different disposals.When we test simultaneously with the two bacteria liquid,the activity of the antioxidant enzymes?POD,SOD,CAT,H₂O₂?had obvious change trend contrasting with CK.However there was no obvious change trend contrasting with CK when we test separately with the two bacteria.