The Fungicide Screening,Compound And Synergy Mechanism Of Phytophthora Melonis

Cucumber phytophthora blight, commonly known as plague of cucumber,is one of the main diseases in cucumber production. It is caused by Phytophthora meloins and it happens in cucumber-producing areas all over the nation in varying degrees. It is a destructive soil-borne disease and often causes fruit rot and plant death over large areas, which causes significant yield reduction. Chemical fungicides are still the main control methods of cucumber phytophthora blight. The experiment screened different types of fungicides which have good inhibition effect on cucumber Phytophthora melonis, then we compounded them with different proportions to obtain new synergy mixures.Meanwhile,we explored the functional mechanism of fungicides. The main contents and results were as follows:1.Single dosage:azoxystrobin, trifloxystrobin, kresoxim-methyl and dimethomorph, flumorph which have good inhibition effect on Phytophthora meloins,.The EC50 values of them were respectively 130.4714?g/ml?3.1045?g/ml?0.9042?g/ml?0.0891?g/ml? 0.3291 ?g/ml. Then we mixed azoxystrobin with dimethomorph, as well as kresoxim-methyl and dimethomorph. It showed synergistic action when the ratio of azoxystrobin to dimethomorph was 1:8 and kresoxim-methyl to dimethomorph was 1:6.. Cultured in mediawith homorph(0.2?g/ml) dimetazoxystrobin(5?g/ml) were observed with microscopes and the morphological features were different levels of crimp, rupture, mycelial swelling and plasmarrhexis. Fungicides had lethal effect on Phytophthora meloins in high-concentration medicated medium, however Phytophthora meloins in low-concentration medicated medium can return to normal growth when inoculated to normal medium.2. We tested the impact of dimethomorph and kresoxim-methyl and the mixures of the two fungicides on the formation of sporangia and the release of zoospores of Phytophthora meloins through testing single dosage and compound liquid with different proportions. As for the formation of sporangia of cucumber Phytophthora meloins, the EC50 of dimethomorph was 0.57?g/ml, while the EC50 of kresoxim-methyl was 6.38?g/ml in single dosage experiment. Dimethomorph had a greater suppression effect on the formation of sporangia of cucumber Phytophthora meloins compared with kresoxim-methyl. As for the release of zoospores of cucumber Phytophthora meloins, the effect of dimethomorph was much weaker than kresoxim-methyl. The EC50 of dimethomorph was 22.17?g/ml,while the EC50 of kresoxim-methyl was 0.44?g/ml, which showed strong inhibition effect of kresoxim-methyl on the formation of sporangia of Phytophthora meloins.3. Protein content was determined with Coomassie Brilliant Blue method and dimethomorph single dosage showed slightly stronger inhibition effect than kresoxim-methyl on protein synthesis of Phytophthora meloins. But protein synthesis inhibition rate of Phytophthora meloins increased with the increased proportion of dimethomorph in compound liquid when we mixed kresoxim-methyl with dimethomorph.4. The result of electrical conductivity test showed that the electrical conductivity change values of mycelial cytomembrane in low-concentration dimethomorph and kresoxim-methyl single dosage were similar with control group. But the conductivity value showed varying degrees of increase with the increase of fungicide concentration and the extension of treatment time. High concentration and long time might change the permeability of cytomembrane, lead to cell protoplasm extravasation, which increased electrical conductivity. Electrical conductivity increased as the proportion of dimethomorph in compound liquid increased, which showed both the dimethomorph and kresoxim-methyl can damage the membrane permslectivity of cucumber Phytophthora melonis and dimethomorph played a more significant effect on it. The fungicides lead to cell protoplasm extravasation but the specific mechanism needs further study.5. The effect of kersoxim-methyl and dimethomorph on Phytophthora melonis was positively related with the increasing drug concentration,. Meanwhile, the respiratory metabolism of Phytophthora melonis were also affected and increases. Because Strobilurin can inhibit mitochondrial respiration, kersoxim-methyl's influence on the respiratory metabolism of Phytophthora melonis is obviously stronger than the dimethomorph and effect of dimethomorph is extremely weaked.