Effects Of Arbuscular Mycorrhiza Fungi On Resistantce To Stalk Rot Of Anoectochilus Roxburghii(Wall.) Lindl

Anoectochilus roxburghii(Wall.)Lindl is a perennial herb of the Orchidaceae,which has high value of food and medicine and strong ornamental.It is a precious medicinal plant in Fujian Province.In recent years,with the continuous expansion of planting area,the occurrence of disease is also increasing,which seriously threatens the healthy production of A.roxburghii.Arbuscular Mycorrhiza(AM)fungi as an important plant biocontrol fungus has always received widespread attention.In this study,the Fujian A.roxburghii were used as test materials,the AM fungi and stem disease pathogens were used as test bacteria.To study the effects and the regulation mechanism of AM fungi on the growth and the stem rot of A.roxburghii.The main research contents and results are as follows:1.Isolation,purification and identification of the pathogen of stem rot in A.roxburghii.A single colony strain was isolated and purified from the diseased plant in A.roxburghii.Based on the analysis of colony morphology and DNA sequence,the pathogen was identified as Fusarium oxysporum,and the disease was stem rot.2.Effects of AM fungi on the growth and active components of A.roxburghii.The results showed that AM fungi could form symbiotic relationship with the root system in A.roxburghii,and the infection rate was as high as 79.66%.The plant height,leaf width,root diameter,dry and fresh weight in A.roxburghii with inoculated of AM fungi were significantly higher than those of the control treatment,the plant height,leaf width and root diameter increased by more than 10%,the dry and fresh weight increased by 23.80% and 18.45%.In addition,the content of polysaccharide and total flavone in the plants with inoculated AM fungi was significantly higher than that in the control treatment,polysaccharide and total flavone increased by 31.90% and 16.30%.3.Under the controlled condition of potted plant in greenhouse,the effect of AM fungi inoculation on the pathogen of stem rot of A.roxburghii was explained from the physiological and biochemical point of view.The results showed that AM fungi could reduce the incidence rate and the disease index,and the relative control effect was 42.07%;The dry weight,fresh weight,root length and root surface area in A.roxburghii with inoculated AM fungi were all higher than those of the single pathogen treatment,the dry weight and fresh weight were increased by 9.09% and 7.46%,and the root length and root surface were increased by 3.02% and 10.00%;In addition,AM fungi could accelerated the improvement of the contents and activities of defensive enzymes in the stem of A.roxburghii,including phenylalanine ammonialyase(PAL),superoxide dismutase(SOD),peroxidase(POD),and decrease the content of malondialdehyde(MDA)in the stem which indicates the degree of membrane lipids peroxidation that plant cells are suffering less.4.The metabolic pathways and differential gene expression in A.roxburghii after treatment with pathogen and AM fungi.The transcriptome sequencing showed that there were 158,316 independent genes,with the total length of 119,033,796 bp,an average length of 751 bp and N50 of 1,429 bp.Through KEGG annotation and enrichment analysis.AM fungi could induce differential gene expression in A.roxburghii,and the number of up-regulated genes is less than the number of down-regulated genes.When inoculation of AM fungi and pathogen,the number of gene differences produced by plantsis the largest.Through KEGG annotation and enrichment analysis,it was found that the disease resistance-related pathways in single inoculated pathogen(CK-vs-FO)and double inoculated AM fungi and pathogens(AMF-vs-AMF+FO),including plant-pathogen interaction,plant hormone signal transduction,MAPK signaling pathway-plant,phenylpropane biosynthesis,peroxisomes,flavonoid biosynthesis and phenylalanine metabolism have obvious differential expression.These pathways play an important role in the process of plant immune response.They may be closely related to the enhancement of resistance in A.roxburghii after AM fungi inoculation.In summary,AM fungi could establish a good symbiotic relationship with A.roxburghii,which was conducived to the growth and promoted the synthesis and accumulation of effective components,and had a certain biocontrol effect on stem rot of A.roxburghii.This study not only provides strategies for ecological control of stem rot of A.roxburghii,but also provides technical support and theoretical reference for the healthy development of A.roxburghii industry in our province.