Isolation and identification of root rot pathogens of ancient Camphora officinarum Nees ex Wall and fungicides indoor screening

【Objective】The pathogens that caused root rot of ancient Camphora officinarum Nees ex Wall trees in northern Guangdong were isolated and identified，and appropriate fungicides against Camphora officinarum root rot were screened. This study provided theoretical basis for the identification，diagnosis and prevention of root rot of ancient Camphora officinarum.【Method】The pathogens were isolated from the root tissues of ancient Camphora officinarum collected from northern Guangdong by tissue block separation method. The pathogen was indentified by Koch’s rule. The species of pathogens were identified by morphology and molecular biology，and the indoor inhibitory effect of different fungicides on pathogen was determined by mycelium growth rate method.【Result】Three different strains were isolated from the diseased root tissues of ancient Camphora officinarum，which were marked as SG0122-1，SG0122-2 and SG0122-3 respectively. Strains SG0122-1 and SG0122-3 were the pathogens causing the root rot of ancient Camphora officinarum after Koch’s rule verification. Combined with morphological observation and phylogentic tree analysis，stain SG0122-1 was identified as Phlebia wuliangshanensis and stain SG0122-3 was identified as Ganoderma subamboinense. The results of fungicide screening showed that there were some differences in the mycelium growth inhibition effects of different fungicides on strain SG0122-1 and strain SG0122-3. Among them，chlorofluoroether · pyrazole ester BAS 751 04F had the strongest inhibitory effect on strain SG0122-1，and could completely inhibit the mycelium growth at the lowest test concentration（3.91 μg/mL），followed by 98% bromothalonil and 96.8% difenoconazole，with median effect concentration （EC₅₀）values of 7.48 and 10.63 μg/mL respectively. 98% azoxystrobin and 96.8% difenoconazole had good inhibitory effects on mycelium growth of strain SG0122-3，with EC₅₀ values of 2.13 and 3.11 μg/mL respectively，followed by 97% pyraclostrobin and 98% thiram，with EC₅₀ values of 58.83 and 59.72 μg/mL respectively.【Conclusion】The pathogens causing ancient Camphora officinarum root rot in northern Guangdong are Phlebia wuliangshanensis and Ganoderma subamboinense. Chlorofluoroether · pyrazole ester BAS 751 04F，98% bromothalonil and 96.8% difenoconazole are effective fungicides to control Phlebia wuliangshanensis，while 98% azoxystrobin and 96.8% difenoconazole are effective fungicides to control Ganoderma subamboinense. Among them，96.8% difenoconazole has good inhibitory effect on the 2 pathogens，and the above agents can be used as candidate fungicides to control the root rot of ancient Camphora officinarum in production.