| Rice is the most important food crops in the world,more than half of the world’s population living in consumption of rice.The Rice sheath blight caused by Rhizoctonia solani is one of the most important diseases on rice.During the severe year,the yeild of rice will decrease by 50%.It’s difficult to prevent for the characteristic of soilborne.The safe prevention to rice sheath blight makes a great difference to the safe production of rice.In this research we analyze the diversity of rice rhizosphere prokaryotic microorganisms in the rice field,in which rice has been planted for decades of years.At the same time,we isolated and identified good biocontrol strains from the rice rhizosphere soil and root,and encouraged won the following results:(1)During the four growth stages of seedling,tillering,heading and filling stage,we isolated 1592 strains from the rice rhizosphere soil and root.Among them,there are 1126 strains coming from the soil and 466 strains coming from Rhizosphere endophytes.1310 bacteria strains are isolated and we obtained 71 biocontrol bacteria strains by selecting parts of them.The number of isolated actinomycetes strains is 99.What makes us surprised is that 81 strains among them have good antagonistic effect,and the width of antagonistic zone is 3～23 mm,which indicates good antagonistic effect.Besides,some strains are able to produce the volatile substances with antibacterial activity.What’s more,we isolated 183 fungal strains.(2)We identified and evaluated the biocontrol potential strain named of A17,a good biocontrol strain for Rice sheath blight.The 16 S rDNA sequences of it shares 96%similarity with Streptomyces griseoaurantiacus(accession number KT803609).Considering the morphological characteristics(as colonial morphology appear red orange gray,orange,etc.),we identify it as Streptomyces griseoaurantiacus for the time being.By the Antagonistic assessment test to Rice sheath blight,it’s found that A17 can not only secrete the highly active antibiotic substances in the culture medium,but also can produce volatile substances with bacteriostatic activity.These antibiotics have wide antifungal spectrum for the the pathogenic fungi including Magnaporthe oryzae,Ustilaginoidea virens,Botrytis cinerea,Fusarium graminearum,Gaeumamomces graminis,Sclerotinia sclerotiorum,Valsa mali,Pnysalospora pinicola and so on.It has significant inhibitory effect to all of them and can lead to abnormal hyphae form,and it almost stopped the growth of some fungi(Sclerotinia sclerotiorum,Fusarium graminearum,etc.).After shaking 7 days in fluid medium,fermentation broth’s bacteriostasis rate of the 10%concentration is more than 90%.And it is able to bear high temperature and protease.The test of vitro leaf control effect preliminarily indicates that A17 possesses the potential to prevent rice sheath blight.(3)Based on Roche-454 sequencing platform,we carried 16 S rDNA pyrophosphate sequencing,then we analyze the diversity of the rice rhizosphere microbes group in different growth period and management information.In the root endophytes,Proteobacteria is dominant species during the different growth period.Cyanobacteria and Acidobacteria basely are dominant population in the different growth period,but its population level has slightly changed.Nitrospirae has great richness in seedling stage and tillering stage,then rapidly decrease in the late heading stage and filling stage.Nitrospirae,Bacteroidetes,Chloroflexi have significantly increase in heading stage and filling stage.The abundance of Actinobacteria is significant increased,comparing the other periods.Acidobacteria hasn’t significant change and keep the stable number in the four stages.In different management at the same stage,Nitrospira,Proteobacteria,Cyanobacteria are dominant population,and the Microbial community structure has no significant difference.In the rhizosphere soil microbes,Proteobacteria,Chloroflexi,Acidobacteria account for high proportion during different stages and are dominant species.However,at the heading stage,the proportion of Proteobacteria is increased,and the proportion of Chloroflexi,Acidobacteria is decreased.In other periods,their community structure almost has no difference.Actinobacteria is significant rise at the heading stage,then it recover to the primary proportion in the pustulation period.Tenericutes only appear in seeding period,disappear in other periods.Different management makes no difference in the structure of the microbial groups,so Proteobacteria is always the dominant species.Actinobacteria and Nitrospirae significantly increase in Huang Huazhan(a variety of rice)by seeding in paddy field and watering to manage.The different variety and different mangement information make no difference in the structure of the microbial groups;Proteobacteria still is the dominant species. |
