Etiology, Biological Characteristics, and Fungicide Sensitivity of Root Rot in Wild Orchardgrass (<em>Dactylis glomerata</em> L.)

Dactylis glomerata L. is a globally important cool-season forage grass with high ecological and economic value. During field surveys conducted in three counties of the Ili region of Xinjiang: Zhaosu County, Tekes County, and Xinyuan County, a previously unreported root rot disease was observed on wild orchardgrass, with disease incidence ranging from 20 % to 72 %. The most severe symptoms were recorded in Zhaosu County. The pathogen was isolated and identified as Bipolaris sorokiniana based on morphological characteristics and multilocus phylogenetic analyses of ITS, GAPDH, and TEF gene sequences. The results of biological characteristics showed that the optimal conditions for mycelial growth were 25℃, pH 7, continuous light for 24 h, potato sucrose agar (PSA) as the culture medium, soluble starch as the optimal carbon source, and peptone as the optimal nitrogen source. In vitro fungicide sensitivity assays indicated that all nine tested fungicides significantly inhibited mycelial growth of B. sorokiniana. Among them, difenoconazole exhibited the highest inhibitory activity, with an EC50 value of 0.0706 mg·L-1, followed by tebuconazole (EC50 = 0.3606 mg·L-1) and tetramycin (EC50 = 0.6815 mg·L-1). These findings provide a scientific basis for further studies on disease epidemiology, pathogenic mechanisms, and integrated management of this disease.