Diversity Of Endophytic Actinomycetes Isolated From Medicinal Plant Of Thymus In Xinjiang And Their Pathogen Antagonism

Plant diseases such as leaf mildew,Fusarium Wilt and fruit rot seriously affect the quality and high yield of the plants.This situation compels people to find new natural environmental friendly biological active substances,and puts forward higher requirements for the research and development of new drugs.Endophytic actinomycetes commonly exist in the plant tissues,establish mutualism with the host and contribute to plant natural defenses by biocontrol of pathogens due to the ability of produce the same or similar compounds with the host plants.The ability of antimicrobial,anti-inflammatory,growth promoting and etc.plays an important role in biological control of human and plant diseases.Ili and Tacheng is the main distribution area of wild medicinal plants in Xinjiang due to mild climate and abundant rainfall.Thymus had been regarded as the fine sand-fixing pioneer plant for the arid and semi-arid region in China,and the thyme as well as thyme essential oil are widely used in medicine,chemical industry and other fields.There is no published paper on the biodiversity and antimicrobial potential of endophytic actinomycetes from Thymus.In this study,the medicinal plant Thymus roseus Schipcz.from Ili and Tacheng will be used.The main objective of this study was to isolate the endophytic actinomycetes from T.roseus Schipcz.in Ili and Tacheng after using three kind of plant pretreatment methods and 10 kind of isolation medium,compare the effects of each pretreatment methods and media on the releasing rate of endophytic actinomycetes from the plant tissues,compare the diversity of endophytic actinomysetes between Ili and Tacheng by construct the phylogenetic tree based on their 16 S rRNA gene sequences of the strains.In addition,the antimicrobial activities,siderophores and chitinase producing abilitiesas well as the antibiotics biosynthetic genes of isolates were tested.The results showed,A total of 181 endophytic actinomycetes isolated from T.roseus Schipcz.After comparing the effects of each pretreatment methods and media on the releasing rate of endophytic actinomycetes from the plant tissues found,the Freezing treatment method were the more effective method for the isolation of endophytic actinomycetes.Moreover,it is effective to isolate more endophytic actinomycetes to combined humic acid-vitamin(HV)medium with the Freezing treatment method.In the present study,there were 126 endophytic actinomycetes associated with medicinal plants T.roseus Schipcz.from Ili and Tacheng in Xinjiang will be conducted the identifications after removing duplicate strains between pretreatments.A total of 126 isolate belonging to 2 phyla,8 orders,14 families,24 genera,which indicated T.roseus Schipcz.possesses a great diversity in populations of endophytic actinomycetes.The diversity analysis showed that the evaluated parameters from each sample were different,the diversity from Tacheng richer than in Ili,however,genera Streptomyces was the most abundant genus isolated from two samples.The endophytic actinomycete isolates are most dominant in the root parts and most of them belonging to Streptomyces.Besides,several strains have the tissues specificity.The isolated actinomycetes 1-126 were tested in plate confrontation assay for their antibacterial,antifungal properties.Among these tested isolates 54 strains were active against one or more indicates organisms and most of them belong to the genus Streptomyces.Of which,the inhibition ratio of T4SB028(Streptomyces polyantibioticus)reached 67.06 %,64.20 %,70.55 % against Alternaria solani,Valsa malicola,Valsa mali,respectively.This result demonstrates the potential of endophytic actinomycetes from T.roseus Schipcz.in the biocontrol the diseases of Tomato Early Blight,Apple Valsa CankerSalmonella enteritidis and etc.In this study,30.95 %,23.01 % of the endophytic actinomycetes could produce siderophores and chitinase respectively.While,42.86% of the tested strains showed antimicrobial activity against at least one pathogens.This result indicated,some strains were possess of producing chitinase or siderophores and also exhibited obvious antifungal activity,it is expected to be developed as a biocontrol agents.The genes screening results indicated that PKS and NRPS encoding genes were widely spread in the antagonistic strains,and the detection rate of PKS II is higher than that of the other two genes,and most of them belong to the genus Streptomyces.This study is of great significance in the protection of wild medicinal plants of thyme.Meanwhile,it provides a potential biocontrol strains for the high quality and high yield of the plant as well as to provide a theoretical basis for the exploitation of bioactive compounds and new drugs related to the treatment of human diseases.