| Fusarium wilt of watermelon is one of the main diseases of watermelon.In recent years,with the continuous expansion of watermelon planting area,the occurrence of the disease has become increasingly serious,seriously affecting the yield and quality of watermelon.The biological activity of three plant extracts,Syzygium aromaticum,Stellera chamaejasme and Glycyrrhiza uralensis,against Fusarium oxysporum of watermelon Fusarium wilt was determined to verify whether the plant extracts had inhibitory effect on the pathogen of watermelon wilt.Molecular biological techniques and biology were used to verify the inhibitory effect of plant extracts on the pathogen of watermelon wilt.Physiological and biochemical indicators preliminarily validated the mechanism of three plant extracts on pathogenic bacteria of plant Fusarium wilt.In addition,through pot experiments,the invasion mode of fungi in the stem base of watermelon plants and the changes of defense enzymes after drug action were analyzed by paraffin section technique and physiological indexes of defense enzymes.The effects of extracts of clove,licorice and Stellera chamaejasme on the appearance and microscopic morphology of healthy and diseased watermelon plants were further studied.The experimental results are as follows:The pathogen of Watermelon Fusarium wilt produces pigments and dense hyphae on PDA medium.Microscopic examination showed that the conidia were meniscus-shaped and the hyphae were septate,belonging to Fusarium.Molecular identification showed that Fusarium oxysporum was the infective fungus of Watermelon Fusarium wilt.The extracts of clove,licorice and Stellera chamaejasme have good bacteriostatic effects on Fusarium oxysporum and watermelon wilt plants.The extraction rate of clove by mixed solvent was 39.01%.The best antimicrobial effect of clove was 100% and 94.14% at the concentration of 1 mg/ml.Microscopic observation showed that when clove with 0.5 mg/m L concentration acted on the mycelium of Fusarium oxysporum,the change of mycelium was mainly due to the decrease of surface attachment and theshrinkage and rupture of mycelium.The results showed that clove mainly acted on the cell membrane,mainly destroying the cell membrane and destroying the integrity of mycelium.In paraffin section,it was observed that the mycelium was blocked by clove treatment on the outside of epidermal cells,making it difficult to invade.It is the main mechanism of action of clove.The extraction rate of Stellera chamaejasme by mixed solvent was 36.44%.The bacteriostasis of Stellera chamaejasme 2mg/m L was 100%.When the extract of Stellera chamaejasme(2mg/m L)acted on the mycelium of Fusarium oxysporum,the main change of mycelium was abnormal protuberance and bifurcation growth in the mycelium.The results showed that Stellera chamaejasme mainly acted on the inner mycelium,causing malformation of mycelium growth.After combination,the protein content of Stellera chamaejasme was the highest.The growth of mycelium mainly depends on the expression of internal proteins,so Stellera chamaejasme can cause mycelial growth deformity and protuberance.Stellera chamaejasme can tighten the vascular bundle sheath and increase the number of threaded vessels,which is the main manifestation of Stellera chamaejasme.The extraction rate of Glycyrrhiza uralensis with mixed solvent was 40.01%,and the bacteriostatic effect of Glycyrrhiza uralensis with 2mg/m L was 45.63%.However,the extraction rate of Glycyrrhiza uralensis with mixed solvent was 40.01%.The combination of the two showed that the practical value of extracting effective components of Glycyrrhiza uralensis uralensis with mixed solvent was the greatest.When 2 mg/m L Glycyrrhiza extract acted on the mycelium of Fusarium oxysporum,the main change of mycelium was mycelial deformity and multi-branched bifurcation.The main function of Glycyrrhiza uralensis is to change the growth of hyphae,which indicates that Glycyrrhiza uralensis is an abnormal growth and development of hyphae.In paraffin section,it was observed that the vascular bundles became dense,which was the main expression of plant resistance.The effect of plant extract on fungal cell membrane was that the bacterial suspension treated by plant extract increased to different extent compared with the control.The results were as follows: liquorice >Stellera chamaejasme > clove.The effect of plant extracts on soluble sugar and protein in mycelial fermentation broth was as follows on the fourth day of fungal liquid culture.When absolute ethanol accounted for 80% of the total volume,the content of soluble sugar in mycelial fermentation broth was clove > blank control > licorice > Stellera chamaejasme.The effects of three plant extracts on soluble protein content in mycelial fermentation broth were mainly Glycyrrhiza > Stellera chamaejasme > clove > blank control.The results showed that Glycyrrhiza extract had the highest protein content in Mycelial Fermentation broth.The effects of three plant extracts on soluble sugar content in mycelium were clove > licorice > blank control > Stellera chamaejasme.After spraying on the 8th day,the content of MDA began to decrease.On the 9th day,the activities of MDA were Glycyrrhiza uralensis,healthy plants,cloves and Stellera chamaejasme.POD began to rise,followed by Stellera chamaejasme,licorice and clove from top to bottom.Clove had the fastest rate of increase,indicating that clove had the fastest recovery of POD activity in watermelon plants and had a better effect.SOD activity fluctuated greatly in plants.Compared with healthy plants,the enzymatic activity of inoculated plants began to increase after medication.Glycyrrhiza had the greatest effect on SOD activity,followed by Stellera chamaejasme and clove.The results of paraffin sections of watermelon plants and watermelon wilt plants showed that Fusarium oxysporum ruptured the epidermal cells of watermelon plants when they invaded,invaded from the cortex along the cell gap between cambium and parenchyma cells,and began to propagate and spread at the catheter.After clove treatment,fungi mainly concentrate on the epidermis and cortex and are difficult to enter.Compared with the inoculated plants,there were innumerable dots in parenchyma cells,tight vascular bundles,less vessel space after licorice treatment,and mycelia were still confined to epidermis after 13 days of invasion.After treatment with Stellera chamaejasme,compared with the inoculated plants,the rupture of epidermal cells was lighter and the rupture of parenchyma cells was serious,but the invasion of fungi was reduced.The differential proteins of plant extracts acting on bacteria and control bacteria mainly act on small molecular proteins of 45-60 Kb,which need further analysis.The results showed that the extracts of clove,licorice and Stellera chamaejasme had good control effect on the Fusarium wilt plants of watermelon cultured in laboratory.Therefore,clove,licorice and Stellera chamaejasme could be used as one of the sources of plant-derived pesticides to control Fusariumwilt.After improved processing,the next field control effect test can be carried out,and the development test of medicaments can also be carried out.It provided scientific basis for further development and utilization of clove,licorice and Stellera chamaejasme. |
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