Isolation,Culture And Application Of The Rhizobacteria And Endophytic Bacteria Of Suaeda Salsa

The wetland ecosystem is called the kidney of the earth.It has abundant natural resources and has various ecological functions such as water conservation,local climate regulation,pollutant degradation,and habitat provision for birds.The Liaohe estuary wetland belongs to the coastal wetland.It is a transitional wetland area linking the land and the ocean.It has extremely rich material resources and is the last resort to prevent pollutants from entering the sea from the Liaohe River barrier.The main vegetation of the Liaohe Estuary Wetland is Suaeda salsa,which shows different colors under different environmental conditions.The Suaeda salsa grown in the Liaohe Estuary Wetland is dark purple.The landscape also comes from this.In recent years,the vegetation degradation of Suaeda salsa in Liaohe Estuary Wetland has been extremely serious,and effective and green measures without secondary pollution are urgently needed to restore the damaged Suaeda salsa vegetation.It is ubiquitous that endophytic bacteria colonize within the plant tissues.A remarkable part of these endophytes could promote the growth of host plants.The application of growth-promoting bacteria and plant endophytes in plant growth-promoting and biocontrol has always been a research hotspot.For the time being,reports on the plant growth promoting bacteria of S.salsa remain rare.With an attempt to screen the S.salsa plant growth promoting bacteria,this thesis took S.salsa plants collected from the Panjin Red Beach National Scenic Corridor as the experimental materials and isolated the endophytic bacteria from leaves and roots.The endobacteria were then identified based on the full length sequence of the 16 S r RNA gene.The diversity of culturable endobacteria of S.salsa was analyzed.First,the pathogenicity to the host plant conferred by the culturable endophytes of S.salsa was examined through colonization experiments using hydroponically grown S.salsa seedlings,which was performed in comparing with the culturable rhizobacteria of S.salsa isolated by other members of the group(unpublished).Second,in vitro plating experiments were performed to examine the abilities of dissolving phosphorus,decomposing potassium,fixing nitrogen,producing iron carriers and generating ACC deaminase of the culturable endophytes of S.salsa.Third,not only colonization experiments using hydroponically grown seedlings but also field experiments in Liaohe Estuary were carried out to examine and validate the plant growth promoting abilities of those endophytic bacteria.The results of this paper show that in total 18 strains of culturable endophytic bacteria were isolated from the roots and leaves of S.salsa.Ten strains were isolated from unhealthy leaves,which were identified as being most closely related to Pseudoalteromonas(4 strains),uncultured Pseudoalteromonas(1 strain),Kushneria konosiri(2 strains),Larsenimonas salina(1 strain),Marinomonas profundi(1 strain)and Enterobacter ludwigii(1strain),respectively.Five strains were isolated from healthy leaves,which were identified as being most closely to Chromohalobacter(1 strain),Marinomonas aquimarina(1 strain),Kushneria konosiri(2 strains)and uncultured bacterium(1 strain),respectively.Three strains were isolated from the roots of healthy plants,which were identified as being most closely related to Mesobacillus jeotgali(2strains)and Bacillus(1 strain),respectively.The highest diversity was observed in the culturable endophytic bacteria isolated from the unhealthy leaves.Colonization experiments using the hydroponically grown S.salsa seedlings showed that pathogenicity to the host plant was not observed in all the 18 culturable endophytic bacteria.In contrast,for the culturable rhizobacteria of S.salsa previously isolated,all the 19 strains showed pathogenicity to the host plant,causing withering of the tested seedlings.Four strains labeled as C0RP8 I,C0RP5F,T0RS19 C and T0RS2 A caused the highest severity of pathogenicity,which all belonged to the genus of Enterobacter.Therefore the 19 strains of rhizobacteria were excluded in subsequent plant growth promoting abilities screening.In vitro plating experiments showed that among the 18 strains of culturable endophytic bacteria of S.salsa,4 strains might have the ability of producing iron carriers(labeled as JY21,JY24,BJY23 and BJY323,respectively)and 2 strains might have the ability of generating ACC deaminase(labeled as JY32 and BJY323,respectively).Colonization experiments using the hydroponically grown S.salsa seedlings showed that among the 18 strains of culturable endophytic bacteria,7 strains could significantly promote root elongation as well as stem growth of the hydroponically grown S.salsa seedlings.The results of colonization experiments were partly confirmed by field experiments.Through spraying S.salsa seedlings with single strains,plant density was observed to be increased whereas plant height remained comparable with that of the control group.In this thesis,culturable bacteria were isolated from the leaves and roots of wild Suaeda salsa from Liaohekou Estuary,and the potential growth-promoting bacteria with siderophore and ACC deaminase-producing abilities were obtained.Several strains of endophytic bacteria were screened as being able to significantly promote plant root elongation and plant height growth through colonization experiments using hydroponically grown S.salsa seedlings.The plant growth promoting abilities of these culturable endophytes in field experiments were preliminarily discussed.To sum up,the growth-promoting effect of endophytic bacteria of S.salsa on host plants was systematically studied in this thesis,which will help to enrich the resources of potential S.salsa growth promoting bacteria to be used in Liaohe Estuary.