Establishment Of Rapid Propagation System And Symbiosis Mechanism With Endophytic Fungi On Houttuynia Cordata Thunb.

Houttuynia cordata Thunb.is a characteristic plant in China,it is also a medicinal and edible plant.A large number of microorganisms were symbiotic in the plant tissue of H.cordata,it faced the challenge of high pollution in establishing a rapid propagation system.In this experiment,different explants were screened,and the relevant conditions for sterilization of explants,seed germination,strong seedlings and seedling transplanting were explored in the process of tissue culture,and a stable rapid propagation system of H.cordata was established.In order to explore the relationship between endophytic fungi and H.cordata,three endophytic fungi were isolated and identified from healthy rhizomes.The growth status,the accumulation of phenolics and volatiles of the seedlings inoculated with the endophytes were monitored to reveal their symbiosis mechanism:1.H.cordata rhizomes and stems contained abundant cultivable endophytic microorganisms,which would cause pollution during tissue culturing.The seeds could be sterilized with 75%ethanol for 30 s+0.2%Hg Cl₂ for 5 min,which could obtain 55.3%germination rate,which was a good explant material;the optimal starting medium was 1/2MS+0.5mg/L GA₃+0.2 g/L activated carbon powder;the optimal seedling medium for seedlings growth was 1/2MS+0.1 mg/L KT+0.3 mg/L NAA+0.2 mg/L GA₃+0.2 g/L activated carbon powder.The tissue cultured seedlings were transferred to natural light and temperature conditions for 1 week,and then open the cover to adapt more 5 days.After planting in soil,the highest survival rate was 86.7%in the nursery soil irrigated with 0.2 g/L thiophanate methyl solution;2.Three endophytic fungi isolated from healthy rhizomes of H.cordata were identified as Ilyonectria liriodendri,Unidentified Fungal sp.and Penicillium citrinum;Endophytic fungi were regulated by the endophytic state,the colonizing microbiome from the rhizosphere,other symbiotic microorganisms,and host metabolism.This mechanism was mutually restricted and balanced;3.I.liriodendri increased the growth of rhizomes and the accumulation of most of the phenolics and volatiles,Unidentified Fungal sp.promoted the accumulation of the medicinal compounds afzelin,decanal,2-undecanone,and borneol without influencing host plant growth,and P.citrinum increased the fresh weight,total leaf area and height of the plants,as well as the growth of the rhizomes,but it had only a small effect on the concentration of major secondary metabolites.In summary:the mature seeds of H.cordata were ideal explants,and the rapid propagation system we established was stable and efficient.There was a competitive relationship among the endophytes.The host plant could regulate the fungal community structure in the tissue through the accumulation of metabolites.The microbiome colonizing the rhizosphere also participated in maintaining the stable symbiosis relationship between endophytes and the host.Inoculating the endophytic fungi could increase the yield and the accumulation of active ingredients of H.cordata.