Inhibition And Mechanism Of Dissolved Organic Matter Derived From Rape Straw Pretreated With Selenium In Soil On Sclerotinia Sclerotiorum

Sclerotinia sclerotiorum?S.sclerotiorum?is a soil-borne pathogen and theSclerotinia stem rot?SSR?is one of the most serious disease that affecting the oilseed rape production in China.Selenium?Se?is an essential trace nutrient for humans and a beneficial element for plants.About 70%area in China suffered Se deficiency,which contributed to the popularity of Se-enriched agricultural products accompanied with amount of Se-enriched agricultural byproducts such as Se-enriched crop straw.Dissolved organic matter?DOM?is an important nutrition source for microorganism in soil and few researches are available regarding the effect of DOM derived from Se-enriched crop straw on soil-borne pathogens.In order to untilize Se-enriched rape straw,we constructed Se-oilseed rape-S.sclerotiorum experimental system to obtain DOM derived from rape straw?RSDOM?.Based on the fact that RSDOM with Se pretreatment in soil improved the inhibition of S.sclerotiorum growth,we further investigate the biochemical and molecular responses of S.sclerotiorum induced by RSDOM,and explore the reason that caused the improved inhibition.The main results are as follows:1.0.5 mg L^-1Se could inhibit the growth of S.sclerotiorum slightly and induced more protein,lipid,alcohols and alkane.As the Se concentration improved,the inhibition of S.sclerotiorum also increased.High Se concentration(20 mg L^-1)caused severe damage to hyphal morphology,accompanied with tumor-shaped protrusions.Se(?0.5 mg L^-1)increased cell membrane permeability and resulted in electrolyte leakage,which also changed inclusions content in mycelium.Se disturbed energy metabolism to inhibite the growth of S.sclerotiorum and downregulated cell wall degrading enzyme?CWDE?activities to decrease the virulence of S.sclerotiorum.2.RSDOM mainly contained carboxylic acid,amino acid,alcohols and aromatic heterocycle,and elevated Se concentration increased carboxylic acid and aromatic heterocycle contents.Aromatic rings and fulvic acid-like substances existed in RSDOM and Se decreased molecular weight and aromaticity of RSDOM.Se addition in soil improved humification degree of RSDOM and resulted in more complex structure of molecules.3.20 mg mL^-1RSDOM inhibited the growth of S.sclerotiorum significantly while RSDOM with Se pretreatment in soil(RSDOM_Se)showed a better antifungal activity.RSDOM_See accelerated the aging of mycelium and exhibited shriveled hyphae,along with increased electrolytes and inclusions penetration,which resulted in the delaying expansion of S.sclerotiorum.RSDOM_See also decreased CWDE activities and downregulated two pathogenic factor Ggt1 and Bi1 gene expressions,indicating that RSDOM_See reduced the virulence of S.sclerotiorum.4.Compared to the control,29 differential metabolites were identified in RSDOM_N,while 36 differential metabolites in RSDOM_Se,suggesting that RSDOM_See influenced more metabolic processes.Both RSDOM_N and RSDOM_See significant downregulated TCA cycle,alanine,aspartate and glutamate metabolism.RSDOM_See induced S.sclerotiorum to secrete lactic acid,linolenic acid and myristic acid,which are toxicity to pathogens.5.Se addition led to 26 differential metabolites in RSDOM contained 8upregulated metabolites and 18 downregulated metabolites.Among the 8 upregulated metabolites,7 organic acids exhibited inhibitory effect on S.sclerotiorum to various degrees,and phenylacetic acid>maleic acid>malonic acid>fumaric acid>saccharic acid>mucic acid>succinic acid.Meanwhile,the majority of the 18downregulated metabolites are substances that maintain the normal life activities of organism,such as amino acids,sugars and nucleosides.These could be considered that increased content of antifungal substances contributed to the improved inhibition of RSDOM on S.sclerotiorum.dimethachlon combined with RSDOM_See could reduce the dosage of dimethachlon.6.In the preventive trial,neither RSDOM_N?RSDOM with non-Se treatment?nor RSDOM_See exhibited significant inhibition on S.sclerotiorum.In the therapeutic test,RSDOM_See reduced the lesion diameter markedly.The inhibition ratio of RSDOM_See reached 16.9%,while RSDOM_N is only 2.3%.In the pot experiment,all of RSDOM_N,RSDOM_See and phenylacetic acid?PA?significantly decreased the lesion size,and the inhibition ratio is 5.4%,20.1%and 54.2%,respectively.RSDOM_N,RSDOM_See and PA significantly improved contents of chlorophyll and dihydric phenol and enzyme activities of PAL and PPO.