Identification and ITS sequence analysis of dominant physiological races of powdery mildew pathogen of bitter gourd in Guangxi

【Objective】To identify the species and physiological races of powdery mildew pathogen of bitter gourd in Guangxi, and provide scientific basis for prevention and control of powdery mildew of bitter gourd and breeding for disease resistance. 【Method】From 2016 to 2021, 246 strains of powdery mildew pathogens were collected and isolated from 8 producing areas of bitter gourd in Nanning, Liuzhou, Guilin, Beihai, Yulin, Hezhou, Chongzuo and Guigang of Guangxi, and phylogenetic tree was constructed to identify the species of powdery mildew pathogen of bitter gourd through microscopic observation of conidial morphology and ITS sequence analysis. The host identification and identification standard system of 13 physiological species of muskmelon were used to identify the physiological races of powdery mildew pathogens. By investigating the damage degree and pathogenicity of the dominant physiological races of powdery mildew pathogens in Guinongke 6, Qingcui 277, Cuihua and Haijiashi 183, the species and physiological races differentiation of powdery mildew pathogens in the main producing areas of bitter gourd in Guangxi were determined. 【Result】According to morphology and molecular biology, the bitter gourd powdery mildew disease in Guangxi was caused by Sphaerotheca fuliginea, belonging to the physiological race 1 and 2F. Race 1 was the dominant race of powdery mildew pathogen in Guangxi with 95.72% average isolation frequency during 2016-2021; race 2F was detected only in Guigang with 4.29% average isolation frequency.Through pathogenicity analysis of dominant races of powdery mildew pathogen of bitter gourd, the disease index of the four bitter gourd varieties showed an increasing trend year by year, pathogenicity intensity of physiological race 1 increased, and the disease in the field was serious. 【Conclusion】The pathogen causing powdery mildew of Guangxi bitter gourd is S. fuliginea, and there are two physiological races 1 and 2F, of which physiological race 1 is the dominant race of Guangxi bitter gourd powdery mildew pathogen. The genetic evolution of powdery mildew strains of bitter gourd in Guangxi has certain relationship with the region, but the difference is not obvious.