Studies On The Effect And Mechanism Of Herba Polysaccharides Inducing Resistance Against Powdery Mildew

Wheat powdery mildew is an important fungal disease in wheat production and cultivation,which is caused by Blumeria graminis f.sp.tritici,Bgt.At present,the control of powdery mildew of wheat mainly consists of disease-resistant varieties and chemical agents.The emergence of new physiological small species and drug-resistant strains makes the further development of new agents with high efficiency and low toxicity an urgent need for the control of powdery mildew of wheat.As a new type of inducer of disease resistance,plant polysaccharides have the advantages of high efficiency and low toxicity.In this study,the activity of polysaccharides from 18 kinds of herb was determined,the best concentration of polysaccharide and its induced resistance to powdery mildew were selected.In order to further clarify the induction mechanism,the antioxidant enzyme activity,anaphylactic necrosis,reactive oxygen species accumulation and other indicators of the active polysaccharide on wheat were determined.The main research results are as follows:1.The effects of 18 kinds of polysaccharides of herb on wheat growth were systematically screened.The results showed that most polysaccharides from herb could promote the growth of wheat plants.Among them,that six kinds of polysaccharides of herb,including Rhubarb polysaccharide and Caulis sargentodoxae polysaccharide,could simultaneously promote the growth of wheat plant fresh weight,root length and leaf area.2.Induction effect of 18 kinds of herb polysaccharides on wheat resistance to powdery mildew was conducted by potted experiment.We found the wheat treated with Rhubarb polysaccharide and Caulis sargentodoxae polysaccharide exhibited high induced resistance to powdery mildew,and the control effects were 75.81% and 84.18%,respectively.When wheat was treated with polysaccharides of different concentrations,the two polysaccharides had the best induction effect on wheat resistance to powdery mildew at the concentration of 100mg/L.3.The effects of Rhubarb polysaccharide and Caulis sargentodoxae polysaccharide on the infection structure of wheat powdery mildew and the disease resistance of powdery mildew were determined.The results showed that the activity values of CAT,POD and SOD in wheat were increased by two kinds of polysaccharides.Both polysaccharides could inhibit the infection of powdery mildew fungus: the spore germination rate of powdery mildew fungus on the leaves of wheat treated with polysaccharides was low,The germinal tube continues to elongate,resulting in a deformity that prevents successful invasion.After treatment with Rhubarb polysaccharide and Caulis sargentodoxae polysaccharide,the disease resistance of wheat plants increased,which showed that the accumulation rate of reactive oxygen species in leaves and the rate of cell anaphylactic necrosis increased.4.We analyzed the effects of Caulis sargentodoxae polysaccharide on wheat transcriptome by using RNA-seq.As a result,there were 2578 differently expressed genes,of which 1360 genes were significantly up-regulated and 1218 genes were significantly down-regulated.KEGG annotation results showed that differentially expressed genes were mainly concentrated in Phenylpropanoid biosynthsis,Plant-pathogen interaction,Glyoxylate and dicarboxylate metabolism,etc.