Causal Pathogen Identification of Gray Mold Rot and Sclerotinia Rot on Oriental Tobacco and Indoor Screening of Fungicides

To control two unknown diseases that seriously affect the yield and quality of oriental tobacco in the Baoshan area of Yunnan province, pathogens were identified based on their morphological, cultural properties and pathogenicity, and confirmed by molecular characterization using ITS regions. The effects of 11 fungicides on pathogen hyphal growth were also tested using the mycelial growth rate method. The results showed that the causal agents of gray mold rot and Sclerotinia rot are Botrytis cinerea Pers.:Fr. and Sclerotinia sclerotiorum (Lib.) de Bary, respectively. Results of the fungicides test showed that the pathogen of gray mold rot is highly sensitive to 50% carbendazim and 70% thiophanate-methyl with the median effective concentration (EC₅₀) to B. cinerea hyphal growth at 0.03 and 0.80 mg/L, respectively. The pathogen is moderately sensitive to 55% dimetachlone-mancozeb with an EC₅₀ value of 6.50 mg/L. Among the tested fungicides, 50% carbendazim, 45% copper oxychloride-dimetachlone, 70% thiophanate-methyl and 55% dimetachlone-mancozeb showed strong toxicities to S. sclerotiorum hyphal growth with the EC₅₀ values of 0.60, 1.05, 1.13 and 1.90 mg/L, respectively. To our knowledge, this is the first report of B. cinerea and S. sclerotiorum causing gray mold rot and Sclerotinia rot on oriental tobacco in China, and pesticides screened in this study will aid local farmers and tobacco technicians in disease control.