The Study On Gentian Leaf Blight

The leaf blight is a major disease of gentian, occurs generally, and makes huge economic loss. The current study for the gentian leaf blight is still in the blank stage. This paper first definited the Pathogen of the leafblight of gentian, studied on gentian seed infection testing and treatment technology, disease prevalence and forecast. We established an effective technology system controling gentian leaf blight, from seed treatment, seed processing, agricultural measures, such as chemical pesticides. Screening, find out the low toxicity and high performance chemical agents. Also studied the effect of chemical agents on the active ingredient content of gentian, to improve the yield and quality of Gentian, lay the foundation of standard production of Chinese crude drug.First of all we determined the pathogen Alternaria fungi by symptoms, pathogen morphology and inoculation tests.We studied on the incidence and the prediction of the disease, according to the disease index y of different times t using CurveExpert software to build mathematical models. According to disease and environmental factor (temperature, humidity, rainfall) established regressionequation:Y₁=-0.150X₁+1.436X₂-0.855X₃-6.843(R₁=0.8603,R₂=0.4528,R₃=0.2544) Y₂=-0.126X₁+1.325X₂-0.832X₃-15.263 (R₁=0.7689, R₂=0.5163, R₃=0.1956) ,as a forecasting model.(Y₁ for the three-year disease index,Y₂ for thetwo-year disease index, X₁ for temperature,X₂ for humidity,X₃ for rainfall ).Researching on the seed infection testing found that the most convenient way is to carry out germination tests in Petri dishes. Hot water treatment to gentian seed, the condition 50℃15 minutes and 60℃5 minutes is relatively small, and could kill pathogenic bacteria . for chemical agents, Pyrimethanil (diluted 500 times) or 3% Polyoxin (diluted 500 times) orMildothane (diluted 300 times) or Difenoconazole (diluted 1000 times) or Mancozeb (diluted 5000 times) could completely kill pathogens, and didn't have much impact on seed germination rate. The verification test of medicine removal re-affirmed the role of these antimicrobial agents.In this paper we used agricultural control measures to study on the control effect of gentian leaf blight. With different spacing of corn intercropping in the rows on both sides of gentian, we found that 50cm intercropping density was the best control, control effect was 51%.The result of Seed Treatments Control gentian leaf blight show that most pharmaceutical treatment was affect, Pyrimethanil (diluted 400 times)was the best, control effect was79.8%,next was Difenoconazole, control effect was 70.1%,the last was Mildothane, control effect was 44.1%.Indoor pharmacodynamic action experiments of 20 fungicides were carried out, and toxicity regression equation was established to determine the EC50 and the EC100. It was found that all the pharmaceutical products showed significant bacteriostasis on pathogenic bacteria of gentian leaf blight. Of all the drugs, Prochloraz with a concentration of 25% showed best bacteriostasis on the bacteria, of which EC50 was 0.92μg / ml, EC100 was 10μg / ml, followed by Difenoconazole with a concentration of 10%, of which EC50 was 1.78μg / ml, EC100 to 200μg / ml. While Mildothane with a concentration of 70% is the worst, of which the EC50 was 5623.41μg / ml. Field Trial results confirmed that Propiconazole of 1000 times was the best with the prophylactic effect up to 63.7%,followed by the Difenoconazole of 1000 times with the prophylactic effect of 62.2% . According to the Field Trial results, contents of the active components in Chinese Gentian were determined to further evaluate the impact of the screened fungicides on the quality of Chinese Gentian. The quality of gentian used in Field Trial was evaluated with Gentiopicroside and swertiamarin glycosides as an index.