Anthracnose: A New Leaf Disease on Radermachera sinica (China Doll) in China

Radermachera sinica (China doll) is a popular evergreen horticultural crop worldwide. However, little information has been provided to describe the anthracnose disease of R. sinica. In 2018, symptoms suspected of leaf anthracnose were observed on R. sinica in gardens and commercial greenhouses in Guangzhou, China. Lesions on diseased leaves showed thinned and grayish white centers, dark-brown to black borders, and raised black spots. Twenty-seven single-conidia isolates were obtained from symptomatic leaf lesions. Based on morphological characteristics and multilocus phylogenetic analysis, 19 isolates were identified as Colletotrichum siamense and six and two isolates were identified as C. fructicola and C. karstii, respectively. An in vivo pathogenicity test was conducted on leaves of R. sinica plants, and it was discovered that C. siamense was more aggressive under wounded conditions than under unwounded conditions, and caused symptomatic necrotic lesions on the leaf. Afterward, the same pathogen was reisolated from lesions of inoculated leaves to fulfill Koch's postulates. However, neither C. fructicola nor C. karstii caused visible lesions on leaves of R. sinica under wounded or unwounded conditions, indicating that they may be asymptomatic endophytes or opportunistic pathogens on R. sinica. To our knowledge, this study is the first report of Colletotrichum spp. associated with anthracnose disease on R. sinica in China.