First report of Colletotrichum aenigma causing walnut anthracnose in China.
English/Persian walnut (Juglans regia) is grown as an economically valuable crop in temperate and subtropical regions. In August 2018, serious fruit anthracnose, with brown to black circular or subcircular or irregular sunken lesions, occurred on walnut trees ('Xiangling' and 'Lvling') in 33-, 23- and 20-ha orchards in Lincheng and Neiqiu county, in Xingtai, Hebei, China. Diseased fruits were observed on 41% (about 7,790 trees), 31% (about 4,123 trees), and 34% (about 3,876 trees) of walnut trees. Diseased leaves, with circular or irregular brown to gray sunken lesions, were observed on 2% (about 380 trees), 2% (about 266 trees), and 1% (about 114 trees) of walnut trees. From each orchard, 25 diseased fruits and leaves were collected, respectively. Twenty-one single-spore isolates were obtained from fruits of three orchards and none from leaves. Based on morphological characteristics, multi-gene sequence analysis and pathogenicity tests, the causal agent was identified as Colletotrichum aenigma. This is thought to be the first report of C. aenigma causing walnut anthracnose in China.