Identification of Pilidium lythri and screening of fungicides in vitro

In recent years, strawberry tan-brown leaf spot disease caused by Pilidium lythri is a serious new disease that has occurred in China. Between 2015 and 2017, a total of 90 symptomatic samples were collected from Changping District, Beijing City; Zhucheng County, Shandong Province; and Loudi City, Hunan Province in China, with 30 samples from each district. Twenty-six fungal isolates were identified as P. lythri based on morphology, molecular biology, and phylogenetic analyses. This is the first report of P. lythri caused strawberry tan-brown spot in Shandong and Hunan Provinces in China. At present, there are no registered fungicides in China for controlling tan-brown spot disease on strawberry caused by P. lythri. In this study, the susceptibility of 26 isolates to eight commonly used fungicides and novel fungicide SYP-14288 were determined in vitro. The result shows that SYP-14288 has the strongest inhibitory activity on the mycelial growth of 26 isolates of P. lythri, with an average EC₅₀ value of (0.33 ± 0.06) μg/mL, can be used as an effective fungicide for the control of strawberry tan-brown leaf spot disease. The average EC₅₀ values were from 3.92 μg/mL to 72.58 μg/mL for epoxiconazole, difenoconazole, prochloraz, tebuconazole, chlorothalonil, and myclobutanil. Among them, azoxystrobin had lower toxicity, and mancozeb had the lowest inhibitory activity. The results of this study can provide an important reference for the rational use of fungicides to control strawberry tan-brown spot disease.