RESUMEN
Blue honeysuckle is emerging as a popular edible fruit and folk medicine. However, from June to August 2021, a serious leaf-spot disease affected the yield and quality of blue honeysuckle in Harbin, Heilongjiang Province, China; the species and characteristics of the pathogens responsible for the disease are unknown. In this study, 30 fungal isolates were obtained from infected blue honeysuckle leaves, identified as Alternaria tenuissima based on morphological and molecular characteristics and phylogenetic analyses. To the best of our knowledge, this is one of the first studies to identify A. tenuissima as the causal agent of blue honeysuckle leaf spots in China. Pathogenicity tests of the isolates revealed that most isolates exhibited moderately pathogenic. All blue honeysuckle cultivars tested were found to be susceptible to 30 A. tenuissima isolates. In addition, elder, Dahurian rose fruit, sea-buckthorn, rowan, hawthorn, bird cherry, and sorb could be infected by A. tenuissima isolates, while European cranberry bush and nanking cherry were not infected. A. tenuissima isolates were highly sensitive to prochloraz (EC50 ≤ 0.50 µg·ml-1) with 86.21% efficacy at 400 µg·ml-1 in the field trials. Therefore, the application of rotation and chemical fungicides are considered to control the disease-causing leaf spots in blue honeysuckle. These results provide a basis for controlling A. tenuissima in blue honeysuckle in China.