Studies On Isolation Of Biocontrol Streptomyces Spp. Strains And Their Control Effects On Wheat Scab

Wheat scab,mainly caused by Fusarium graminearum,could do serious harm to the yield and grain quality.It produces mycotoxins such as deoxynivalenol(DON)and zearalenone(ZON)which can cause livestock poisoning.Currently,chemical control is still the main method to control wheat scab,but it also has negative influences on the environment and food safety,so it’s urgent to develop a new strategy to help chemicals and resistant cultivar to control wheat scab.The purpose of this study is to find biocontrol strains to control wheat scab and study their mechanisms through the dual culture technique,antagonism assays,e GFP labeling,q RT-PCR,Doskochilova 8 solvents system and other experiments.The main results were as follow:1)Isolation and identification of actinomycete strains.24 biocontrol strains were separated using the method of entrapment separation from abnormal tomato leaf mold,including 19 actinomycetes strains and 5 fungi strains.The strain were numbered S1,S2-1,S2-2,S3,S4,S5-1,S5-2 and S6 to S23.The antagonism assay were conducted by Oxford cup method against 15 different plant pathogens,4 actinomycetes strains,S2-1,S2-2,S4,S10 showed broad-spectrum anti-fungi activity and all of them had an excellent inhibition effect on F.graminearum.According to their morphology,culture characteristics,physiological characteristics and 16 S r DNA sequence,4 strains had a close relationship with Streptomyces flavoviridis,S.setonii,S.massasporeus and S.rubiginosohelvolus,respectively.Among them,the result of using S.rubiginosohelvolus to control wheat scab was first reported.2)Inhibition effect on wheat scab.Four strains showed significant control effect on the growth of F.graminearum in both fermentation containing plate and flask exeriments.Strain S10 had the most significant effect,with the increase of S10 fermentation ratio,the F.graminearum mycelium became colorless and got less dry weight.3)Control effect of strain S10 on wheat scab in vitro and pot wheat ear.The control effect in vitro and pot were 92.86% and 68.67%,respectively.The diseases on two wheat varieties in field were also controlled effectively,and the control effect of S10 on Mingxian 169 was95.82%.In different treatments,the DON content in wheat grains were significantly decreased compared with the blank control.The biocontrol strain S10 had a stable and significant control effect on wheat scab.4)Study on the biocontrol mechanism of S10.Previous studies showed that biocontrol agent S10 had a good inhibition effect on wheat scab;it could reduce the severity of disease and the content of DON.Wheat scab in the treated group spread slowly compared with the control group,possibly resulting in the less accumulation? of DON;q RT-PCR results showed that the biocontrol strain S10 could also decreased DON synthesis gene expression in F.graminearum;confocal scanning results show that S10 can colonize in wheat roots.The control mechanism of S10 might be inhibiting the mycelial growth and the related gene expression by active substances in fermentation liquid,root colonization and other aspects to protect wheat from wheat scab.5)Study on S10 active substances.The results showed that the strain S10 had a strong inhibition effect on F.graminearum.The active substances were not sensitive to temperature and proteinase K;it’s activity was stable under acidic and neutral conditions,and the activity was inhibited under alkaline conditions.The active substances mainly existed in ethyl acetate phase of intracellular,the phase could be divided into 5 different Rf value parts after develop by chloroform: methanol =8:2,The 0.74 Rf value part showed the best effect on F.graminearum,the result of Doskochilova eight solvent system showed that the Rf spectrum belonged to the seventh class antibiotic.