Characterization of Alternaria Species Associated with Black Spot of Strawberry in Dandong, China

Dandong has become the largest strawberry production and export base in China. Strawberry black spot disease is widespread and causes significant economic losses to strawberry growers in both the growing and harvest seasons. Until now, no study has reported the presence of the Alternaria species, the pathogen of strawberry black spot disease, in Dandong, Liaoning province, China. In 2020–2022, 108 isolates were obtained from strawberry leaves with typical symptoms of strawberry black spot disease from 56 major professional growing operations. Combined with morphological and molecular characteristics, the majority of isolates were identified as A. tenuissima (78 isolates, 72.2%), which had established total supremacy, followed by A. alternata (30 isolates, 27.8%). The pathogenicity results show that A. tenuissima and A. alternata are the two main pathogenic factors of strawberry black spot disease, the disease indexes of which were designated as 49.6–100.0% and 20.4–59.5%. To our knowledge, this paper is the first to identify A. tenuissima and A. alternata as causing black spot disease in strawberries in Dandong, China.