Identification and Pathogenicity of Rhizoctonia solani Isolates Causing Leaf and Stem Rot in Three-Leaf Ladybell

Abstract

In 2020 and 2021, we surveyed diseases of three-leaf ladybell (<i>Adenophora triphylla</i>) plants grown in fields at two locations in Korea. During the disease surveys, severe leaf rot symptoms were observed on the young plants in Hongseong, and stem rot symptoms on the adult plants in Cheolwon. The incidence of leaf rot was 5‒60%, and that of stem rot 1‒10%. We obtained 6 fungal isolates each from the leaf rot lesions and the stem rot lesions. All the isolates were morphologically identified as <i>Rhizoctonia solani</i>. Anastomosis test and investigation of cultural features of the fungal isolates revealed that the isolates from the leaf rot lesions corresponded to <i>R. solani</i> AG-1(IB), and those from the stem rot lesions to <i>R. solani</i> AG-2-2(IIIB). Two isolates each of <i>R. solani</i> AG-1(IB) and AG-2-2(IIIB) were used for DNA sequence analysis and pathogenicity test to three-leaf ladybell plants through artificial inoculation. The anastomosis groups and cultural types of the <i>R. solani</i> isolates were confirmed by the sequence analysis. The pathogenicity tests revealed that the isolates of <i>R. solani</i> AG- 1(IB) caused only leaf rot symptoms on the inoculated plants, and those of <i>R. solani</i> AG-2-2(IIIB) leaf rot and stem rot symptoms. The induced symptoms were similar to those observed in the fields investigated. Leaf and stem rot of three-leaf ladybell caused by the two anastomosis groups and cultural types of <i>R. solani</i> is first reported in this study.