Screening Of Effective Fungicides Against Tobacco Black Shank And Analysis Of Fungicide Resistance Risk

Tobacco black shank is one of the important diseases caused by Phytophthora nicotianae that harm tobacco production.It causes immeasurable losses to tobacco production every year.However,the current prevention and control methods for tobacco black shank are still based on chemical control.Therefore,screening of fungicides with good control effects on Phytophthora nicotianae is of great significance for controlling the occurrence of tobacco black shank and effectively controlling the losses caused by the disease.This paper mainly focuses on the screening of effective fungicides,the compounding effects of fungicides to the pathogen,and the resistance of the pathogen to fungicides.1.Screening of effective fungicides.Seven effective fungicides were screened out of22 tested fungicides,and they are dipropargyl,bupyridine,dimethomorph,mancozeb,metalaxyl,flumorph and shenqinmycin respectively.The inhibition rate of the seven fungicides on the hyphae of tobacco black shank is more than 70%,and the inhibition rates are 100%,100%,89.45%,88.62%,82.25%,76.82%and 74.46%,respectively.2.Toxicity of effective fungicides to Phytophthora nicotianae.The EC₅₀ values of the mass concentration of seven fungicides on the mycelial growth of tobacco black shank were determined by the mycelial growth rate method,the results showed that the EC₅₀ values of flumorph,shezinomycin,metalaxyl,mancozeb,butypyrmorph,dimethomorph and dipropargyl against the tested tobacco black shank were 2.0230mg/L,1.9230 mg/L,1.8080 mg/L,1.7580 mg/L,1.4000 mg/L,0.7830 mg/L and 0.0180mg/L,respectively.3.Compounding of effective fungicides.After combining dimethomorph,mancozeb,metalaxyl and schicinomycin in the ratios of 1:1,1:2 and 2:1,respectively,the inhibition effect of different compound combinations on the mycelial growth of tobacco black shank was measured,and the co-toxicity coefficient was calculated.The results showed that dimethomorph and metalaxyl at 1:1,2:1,and metalaxyl and mancozeb at2:1 showed synergistic effects.4.Resistance of Phytophthora nicotianae to fungicides.The resistance of tobacco black shank to effective fungicides was studied,and the results showed that tobacco black shank was susceptible to resistance induced by high doses of fluomorph and methomyl.5.After the mixed application of metalaxyl and carbon-based fertilizer,the molecular content of tobacco black shank in the soil was detected.Through real-time fluorescent quantitative PCR detection,it was found that the molecular content of tobacco black shank in the diseased soil after the mixed application of metalaxyl and carbon-based fertilizer was obvious reduced.