Identification of as the new causal agent of leaf blight disease on Thunb., and screenings of effective fungicides for its sustainable management.

Thunb is an evergreen woody ornamental plant with significant economic and ecological values. It also produces aucubin, showing a variety of biological activities. It is widely planted in the southwest region of China, including karst landscape areas in Guizhou Province. In January 2022, a serious leaf blight disease was observed on the leaves of in the outdoor gardens of Guizhou University, Guiyang, Guizhou, China. The causal agent was identified as through amplification and sequencing of the internal transcribed spacer (ITS) region, translation of the chitin synthase () and actin () genes, and morphological characterizations. Koch's postulates were confirmed by its pathogenicity on healthy leaves, including re-isolation and identification. To our knowledge, this is the first report of causing leaf blight on worldwide. To identify pathogen characteristics that could be utilized for future disease management, the effects of temperature and light on mycelial growth, conidia production, and conidial germination, and the effects of humidity on conidial germination were studied. Optimal temperatures for mycelial growth of BY827 were 25-30°C, while 15°C and 35°C were favorable for conidia production. Concurrently, alternating 10-h light and 14-h dark, proved to be beneficial for mycelial growth and conidial germination. Additionally, conidial germination was enhanced at 90% humidity. screenings of ten chemical pesticides to assess their efficacy in suppressing representative strain BY827. Among them, difenoconazole showed the best inhibition rate, with an EC (concentration for 50% of maximal effect) value of 0.0148 μg/ml. Subsequently, field experiment results showed that difenoconazole had the highest control efficiency on leaf blight (the decreasing rate of disease incidence and decreasing rate of disease index were 44.60 and 47.75%, respectively). Interestingly, we discovered that BY827 may develop resistance to mancozeb, which is not reported yet among spp. strains. In conclusion, our study provided new insights into the causal agent of leaf blight, and the effective fungicides evaluated provided an important basis and potential resource for the sustainable control of leaf blight caused by in the field.