Isolation And Function Of Symbiotic Fungi Of Dendrobium Officinale

Dendrobium officinale is an extremely valuable medicinal plant with a large market demand.It is difficult for the seeds to germinate under natural conditions.Although tissue culture techniques increase the reproduction rate of dendrobium officinale,the survival rate of transplanted tissue seedlings is low and the growth rate is slow.In order to solve this problem,this experiment used microbiological methods to isolate symbiotic fungi from the roots of Dendrobium officinale and acted on the culture of their seedlings to find a strain that could promote its growth,carried out taxonomic identification and preliminary study of its functions.Get the following results:1.Selection of beneficial symbiotic fungiFour commensal fungi were isolated from the rhizosphere of Dendrobium officinale,which were used as fungal elicitors and applied to the tissue culture of Dendrobium officinale seedlings.The SDW-2 strain was selected with enhancing the seedling growth and development.The suitable applied concentration of SDW-2 strain inducer to promote the growth and development of Dendrobium officinale was 0.5 g/L medium.The SDW-2strain was inoculated on in vitro peels of oranges,tobacco leaves,pepper leaves,and phalaenopsis leaves for four days without infection,indicating that the strain was not pathogenic to the test plants.2.Identification of beneficial symbiotic fungi SDW-2 strainSDW-2 strain was identified and analyzed by Morphological and fungal ITS sequences.The result indicated that Penicillium chrysogenum and SDW-2 are 99% homologous,belonging to the family Penicillium sp.The character of SDW-2 growing on PDA medium was thatThe colonies are grayish green,granular,with white edges,yellow exudate,and colony color will increase as the culture time longer.Observed under an optical microscope,the hyphae of the strain had a transverse septum,which wasmulticellular fungal;the conidia were spherical or nearly elliptical,the conidial stems were born in the substrate mycelium,and there were three rounds of transverse septum and callus.3.Antibacterial activity of SDW-2 strain and its fermentation supernatant against pathogenic bacteriaThe fermentation supernatant of SDW-2 had inhibitory effects on citrus acid rot,P.avenae peduncle,grape gray mold,and pathogenic bacteria of soft rot of jujube fruit.The diameters of their inhibitory zones are 22 mm,16 mm,23 mm,21 mm,17 mm,and 24 mm,respectively.Among them,the antibacterial effect of pathogenic bacteria screened out from soft rot of jujube fruit was the best,and the diameter of inhibition zone was 24 mm.The strain SDW-2 had antibacterial activity against two strains of pathogenic bacteria,Penicillium citellum pedunculata,and two strains of citrus acid rot.The inhibitory zone diameters were 14 mm,13 mm,15 mm,and 13 mm,respectively.The analysis of the antibacterial components in the fermentation supernatant showed that the ?-lactam antibiotics in the extractive fermentation supernatant also had antibacterial activity.4.Activity of SDW-2 strain supernatant on pathogenic fungiFermentation supernatant of SDW-2 strain against the growth of tomato powdery mildew and Sclerotinia showed significant inhibition.The inhibitory rate of SDW-2 strain fermentation supernatant against inoculated with powdery mildew of tomato was 39.8%,and the inhibitory rate against Sclerotinia was 53.2%.