Interaction And Pathogenesis Mechanism Study Of Phthalic Acid In Continuous Cropping Salvia Miltiorrhiza Bge.Rhizosphere Soil And Rhizoctonia Solani

Objectives:1.Explore the interaction between phthalic acid and Rhizoctonia solani mycelium growth.2.The harm and mechanism of phthalic acid and Rhizoctonia solani co-culture system on hydroponic Salvia miltiorrhiza Bge.The above two studies have proved that phthalic acid mediates the growth of Rhizoctonia solani,which in turn affects the growth and metabolism of Salvia miltiorrhiza Bge.,resulting in continuous cropping obstacles.This study can clarify the changes and interaction mechanisms of soil microenvironment mediated by phthalic acid.The research results have important theoretical guiding significance to reduce the continuous cropping obstacles of Salvia miltiorrhiza Bge.and improve the yield and quality of medicinal materials.At the same time,the research results also provide an important reference for the reduction of the continuous cropping obstacles of other root medicinal materials.Methods:1.Using GC method,phthalate compounds in Salvia miltiorrhiza Bge.were identified.The effect of phthalic acid on the growth of Rhizoctonia solani and its critical concentration were observed by the indoor hyphae growth inhibition tests.The content changes of phthalic acid were detectedd by HPLC during the tests.2.The SOD and POD activities of the leaves and roots of hydroponic Salvia miltiorrhiza Bge.were determined by NBT reduction method in the co-culture system of exogenous phthalic acid and Rhizoctonia solani.At the same time,the MDA contents were also determined by TBA colorimetry.3.Finally,transcriptome analysis was conducted with the Illumina sequencing platform.Results:1.There are six and five kinds of phthalate lipid components in leaves and roots of Salvia miltiorrhiza Bge.,with the total relative content was 8.264%and 1.069%respectively.The phthalic acid has an obvious effect on the growth of Rhizoctonia solani.The largest number of colonies and the largest diameter were meansured when the concentration of phthalic acid was 0.1 mg·m L^-1.Moreover,the content of phthalic acid did not change in the co-culture system.2.The content of MDA increased by 19.8%when the activities of SOD and POD in the leaves of Salvia miltiorrhiza Bge rasied by 18.64%and 58.35%.While SOD and POD activities in its roots increased by 34.39%and 10.32%respectively,the value of MDA increased by 57.55%in this system.3 The Salvia miltiorrhiza Bge.pathogenic bacteria interaction map of signaling pathway was obtained when transcriptome of hydroponicsand Salvia miltiorrhiza Bge.analysed and its leaves were significantly enriched.In this signaling pathway,the CML gene expression for regulating calcium signaling system was up-regulated,in response to the down-regulated CNGC gene expression transducted by calcium signal.By KEGG enrichment at the root of Salvia miltiorrhiza Bge.,the biosynthesis of phenylalanine,tyrosine and tryptophan was achieved.Meanwhile,the signaling pathway of phenylalanine metabolism and phenylalanine biosynthesis metabolites was formed.The expressions of PAL gene regulating the synthesis of secondary metabolites of Salvia miltiorrhiza Bge.were up-regulated with 4CL gene.The expressions of HCT and C3H genes that regulate the synthesis of lignin were also up-regulated while the expression of F5H gene was down-regulated.Conclusions:1.Phthalic acid is the allelochemical which synthesized in and secreted from Salvia miltiorrhiza Bge.2.The present study revealed that phthalic acid enchanced the growth of Rhizoctonia solani at low concentration treatment and inhibited that while the concentration was high.The tests showed that adding phthalic acid increased the growth and reproduction of Rhizoctonia solani,while its content remained as before under the same culture conditions.As a result,phthalic acid plays the role as the catalyst instead of a C source for Rhizoctonia solani growth.The rapid growth of Rhizoctonia solani is in agreement with the outbreak of Salvia miltiorrhiza Bge.continuous cropping obstacles around August.3.Salvia miltiorrhiza Bge.can resist the stress of pathogens through increasing the activities of antioxidant enzymes,activating the immune system and improving the synthesis of secondary metabolites in the phthalic acid-mediated Rhizoctonia solani co-culture system.But limited by its own defense mechanism,Salvia miltiorrhiza Bge.can not denfend the stress completely without external participation.Furthermore,as the stress time extends,the regulation of gene response in Salvia miltiorrhiza Bge decreases and the plant will become shriveled or die eventually.This study focused on how the catalysis mechanism between and Rhizoctonia solani works and paid attention on further research on the molecular mechanism resulting in continuous cropping obstacles.