Effects And Mechanisms Of Bacillus Subtilis Y14 On Peanut Growth Promotion And Disease Control

Peanut is the important oil crops in China,with the very high nutritional and economic value,however,in recent years the major peanut production areas all under the influence of plant diseases,especially the peanut Sclerotium Blight.The excessive use of pesticides has caused great harm to the ecological environment and the quality of peanut.Using microorganisms to control plant diseases has the advantages of environmental friendliness,less pollution,safety and high efficiency.In this study,bacteria Y14 was identified as Bacillus subtilis which has a significant antagonistic activity against peanut sclerotium blight was screened from rhizosphere soil of peanut,and has strong ability to produce siderophore.Pot experiment was carried out,designed three groups of treatment,treatment A plants were inoculated with the antagonistic bacterium and the pathogen,treatment B plants were inoculated with the carbendazim and the pathogen,treatment C plants were inoculated with the water and the pathogen.From the disease prevention effect,plant-growth promoting,soil enzyme activities and microbial community structure in rhizosphere soil,we showed the effection and mechanism of Bacillus subtilis Y14.Antagonistic inhibition rate was 67.1% by the dural culture method on PDA plates with pathogens,antagonist Y14 and its secondary metabolites can make Sclerotium rolfsii Sacc.mycelium distortion under a microscope.Fungal compartment shortened and increased,generating abnormal,fractured and twisted branches,enlargement of apical mycelium,disintegration of the cell wal,etc.LB fermentation liquid of strain Y14 could inhibit the mycelial growth and sclerotium formation,the sclerotium inhibition rate was 88.91% when the concentration was 15%,inhibiting most of sclerotia.Siderophores of strain Y14 is catechol type siderophores,and the active units up to 86.75,belonging to the super chelating ability siderophore.It will appear orange circle around the colonies at 12 h on CAS plate with stable siderophore production capacity.Peanut plants began to infected in pot experiment at 14 d when alone inoculated Southern Blight pathogen,and it was 21 d when early inoculated antagonistic bacteria Y14 and carbendazim.Y14 reduced disease severity by 47.2% better than carbendazim(11.7%)when inoculated with pathogens for 60 days.The effect of Y14 to disease prevention was significant with well-preserved ground parts and roots when seeding 130 d.The results of agronomic traits and biomass about peanut shown that the antagonistic bacteria Y14 could promote the growth and development of peanut.The height,lateral branch length and pin number of peanut plant has increased significantly especially in 45 d.Peanut biomass,chlorophyll content and root activity of Y14 treatment group in harvest stage were significantly higher than that of control group(p < 0.05),compared with the morbidity of CK group,the peanut yield increased by 32.03%,compared with the carbendazim treatment group,the peanut yield increased by 12.92%.In addition,Y14 treatment can induce peanut leaves associated with system resistance related index significantly increased such as CAT activity,POD activity and SOD activity,results showed that Y14 could affect the physiological and biochemical characteristics of peanut,thus enhance the plant defense system and abiotic stress resistance,which promotes the growth of peanut indirectly.Soil enzyme activity is closely related to soil fertility,it reflect the strength of soil nutrients(especially in C,N,P)transformation,applicable to the evaluation of the effect of the agent.The effect of Y14 on soil enzyme activity was great,which could increase the activity of protease,urease,invertase and phosphatase,and decrease the activity of catalase,the soil enzyme of Y14 group and control group all are significantly different(p<0.05)except urease.The activity of protease,urease and invertase,phosphatase in carbendazim treatment decreased,may sometimes be linked to the harm of soil microbial community structure by chemistry reagent.The effects on soil microbial community structure is an important aspect to assess the evaluation of antagonistic effect and safety,in this study,we analyzed the effect of Y14 on the microbial community structure diversity in the rhizosphere soil of peanut by Illumina Miseq’s sequencing technology.All samples were obtained 48,630 bacterial OTUs and 2,642 fungal OTUs.The Chao index,ACE index and Shannon index were all higher than those in the control group,which indicated that the soil microbial abundance and diversity could be improved after Y14 application.Analysis of microbial community structure on genera level shows that common antagonistic bacteria such as Bacillus,Pseudomonas,Luteimonas and Streptomyces,nitrogen fixing bacteria like Rhizobium,Burkholderia and Azoarcus all improved to different degrees.The richness of beneficial fungi Chaetomium and Clonostachy increased,and produced unique genus such as Acrostalagmus,Mycoleptodiscus and Septoglomus.Plant pathogens Ophiostoma and Athelia disappeared in Y14 group,and the richness of Lophiostoma and Ilyonectria reduced.Results indicated that Bacillus subtilis Y14 could improve rhizosphere ecological environment of peanut,increase the number of beneficial bacteria,and then improved growth and development of peanut.