Characterization of Alternaria species causing leaf spot on Chinese cabbage in Shanxi province of China

As a devastating disease, leaf spot of Chinese cabbage (Brassica rapa subsp. pekinensis) caused by Alternaria could render the edible leaves unusable and lead to yield loss. Till now, no research related to Alternaria species causing leaf spot on Chinese cabbage was recorded in the Shanxi province of China. In the current study, 246 Alternaria isolates were recovered from diseased leaves of Chinese cabbage with the symptoms of leaf spot and identified based on morphological traits and phylogenetic analysis of the sequences of the internal transcribed spacer regions of ribosomal DNA (rDNA ITS) and the partial coding sequence of the histone 3 gene. These isolates were grouped into four Alternaria species, of which A. tenuissima was predominant (175 isolates, 71.2%), followed by A. alternata (67 isolates, 27.2%), A. brassicicola (three isolates, 1.2%), and A. solani (one isolate, 0.4%). All the tested Alternaria isolates were pathogenic to detached leaves of Chinese cabbage with the disease incidence and disease index ranging from 73.3% to 100.0% and 20.8 to 99.1, respectively. To our knowledge, it is the first comprehensive study of Alternaria species inciting leaf spot on Chinese cabbage in Shanxi province of China; also, this is the first report of A. tenuissima, A. alternata, and A. solani infecting Chinese cabbage in Shanxi province of China. This study provides important information on the Alternaria species associated with leaf spot of Chinese cabbage, which can help design the strategies for managing Alternaria leaf spot disease on Chinese cabbage.