Characterization and Pathogenicity of Species on cv. Congo in Gansu Province, China.

In recent years in China, leaf spot caused by species has been an emerging disease of cv. Congo. From 2016 to 2019, typical symptoms, appearing as circular or ovoid, sunken, and brown lesions with a yellow halo, were commonly observed on cv. Congo in and around Lanzhou, Gansu Province, China. Conidiomata were often visible on infected leaf surfaces. Leaf disease incidence was approximately 5 to 20%. A total of 126 single-spored isolates were obtained from leaf lesions. Multilocus phylogenetic relationships were analyzed based on seven genomic loci (ITS, , , , , , and ) and the morphological characters of the isolates determined. These isolates were identified as three species in this study. A further 93 isolates, accounting for 74% of all isolates, were described as new species and named as sp. nov. after the host plant genus name, ; another two isolates were named as sp. nov. based on phylogenetic and morphological relativeness to ; the other 31 isolates, belonging to the species complex, were identified as a known species-. Both novel species and belong to the species complex. Pathogenicity tests by both spray and point inoculations confirmed that all three species could infect leaves of cv. Congo. For spray inoculation, the mean infection rate of leaves on the three species was only 4.7% (0 to 12%), and the size on lesions was mostly 1 to 2 mm in length. For point inoculation, 30 days after nonwounding inoculation, the infection rate on leaves was 0 to 35%; in wounding inoculation, the infection rate of leaves was 35 to 65%; wounding in healthy leaves greatly enhanced the pathogenicity of these three species to cv. Congo; however, the sizes of lesions among the three species were not significantly different. To our knowledge, this is the first report of species associated with anthracnose diseases on cv. Congo. Results obtained in this study will assist the disease prevention and appropriate management strategies.