Inhibitory Effect And Mechanism Of 34 Plant-Derived Terpenoids On Rice Sheath Blight Pathogen

Using the mycelium growth rate method,a total of 34 compounds of terpenoids,terpenic carboxylic acids,oxime compounds,hydrogenated norbyl tertiary amines and their quaternary ammonium salts from plant-derived terpenoids were analyzed and determined against Rhizoctonia solani.The results showed that except for ketotonic acid,the other 33 compounds showed a certain inhibitory effect on the growth of Rhizoctonia solani and the inhibition rate changed with the concentration of the compounds.Three compounds were screened from 34 compounds with good bacteriostatic effect against Rhizoctonia solani,which were in the order of pinenoic acid,hydronobate and hydronobitol,with EC₅₀of 7.2432,17.12482,and34.9826mg/L.Three compounds（pinenoic acid,hydronobolic acid,and hydronobitol）with good inhibitory effect on Rhizoctonia solani were identified and their bacteriostatic mechanism was preliminary studied.The growth stages of Rhizoctonia solani were determined according to the growth curve and provide the basis for experimental design.The effects of three compounds on the dry weight of rice sheath blight mycelia were measured.Compared with the control group,the dry weight of the mycelium in the treatment groups was all reduced and the effect of pinenoic acid inhibition was the best one with its weight reduced by 46.42%.In addition,the permeability of the cell membrane was measured and analyzed.The changes in the relative conductivity of the three compounds after the treatment of rice sheath blight mycelia and the effects on the MDA content were determined.The measurement results showed that compared with the control group,the mycelial conductivity and MDA content of the treated group increased,which indicated that the compound caused the cell membrane destruction and leakage of internal electrolytes of Rhizoctonia solani.And the increased MDA may be due to the stress of the compound,which increased the level of reactive oxygen species in the rice sheath blight fungus.The activity of four protective enzymes（SOD,POD,CAT,and PPO）,five cell wall degrading enzymes of Fusarium oxysporum（PG,PMG,Cx,PGTE,and PMTE）and the content of protein in the fungal cells after the treatment of rice sheath blight mycelium with three compounds were measured.The results showed that the four protective enzymes decreased to varying degrees after camphenic acid treatment,the cell resistance weakened,the CAT content increased slightly after the treatment with hydronobic acid and hydronobyl alcohol,and the activities of the other three enzymes were reduced.The mycelial protection enzyme system has a corresponding resistance to the treatment of the compound,and the CAT enzyme activity was not fully inhibited.The results of the five cell wall degrading enzymes measured showed that only the mycelial PMG activity after myronic acid treatment was slightly higher than that of the control group.The analysis showed that pinenoic acid had no inhibitory effect on PMG activity or did not proceed.Other cell wall degrading enzyme activities were reduced to varying degrees.After the mycelium was treated with the compound,the protein content of the mycelium was reduced to varying degrees.Finally,the ultrastructure of the mycelium treated with the three compounds was observed by scanning electron microscope.The results showed that the surface of the control group had fine wrinkles and the mycelium was cylindrical with the surface was smooth and the thickness was uniform.After treatment with the three compounds,the mycelium was dry and rough.In addition,there were a lot of wrinkles on the surface of the mycelium,and the shape of the cylinder was partially lost.On the local mycelium surface,obvious ridge-like protrusions on the surface of the mycelium,and even breakage.The results showed that the cell structure of the mycelium changed after the three compounds treatment.