[Identification, biological characteristics, and screening of effective fungicides of Phoma rhei causing leaf spot on...

Severe leaf spot on Polygonum cuspidatum was found in the planting base of P. cuspidatum in Fangxian county, Shiyan of Hubei province. To clarify the types of pathogens and their pathogenesis, the present study isolated and purified the pathogen of leaf spot disease of P. cuspidatum according to Koch's postulates, determined the pathogenicity of the pathogen, and investigated its biological characteristics. Meanwhile, the inhibitory effects of 11 types of fungicides on the bacteria were determined according to the mycelium growth rate, and suitable prevention and control drugs were selected. The results showed that the pathogen isolated from the diseased leaves of P. cuspidatum was Phoma rhei by morphological and molecular identification. The colony morphology and microscopic characteristics were the same as those of Ph. rhei. The homology of rDNA-ITS and TEF gene sequences with Ph. rhei reached 99.96% and 99.43%, respectively. The optimal growth temperature of Ph. rhei was 25 ℃, and the optimal pH was 7-10. Furthermore, Ph. rhei grew faster under dark or light conditions. In fungicides, 0.3% eugenol, 250 g·L~(-1) propiconazole, and 33.5% quinoline copper had significant inhibitory effects on the pathogen with EC_(50) values of 57.54, 59.58, 88.69 μg·mL~(-1), respectively. Eugenol is a botanical fungicide, which can be used as a green and environmentally friendly fungicide in the prevention and control of P. cuspidatum. This study reported for the first time that the pathogen of P. cuspidatum leaf spot was Ph. rhei. investigated the biological characteristics of the pathogen, and screened the indoor chemicals, which provided a theoretical basis for the prevention and control of P. cuspidatum leaf spot in production.