Morphological and molecular characterization of Rhizoctonia solani AG-3 associated with tobacco target leaf spot in China.

ABSTRACT

Tobacco target leaf spot is a leaf disease that seriously affects both the quantity and quality of commercial tobacco crops and has caused huge economic losses in many countries and also pandemics in China since 2006. The anastomosis group-3 (AG-3) pathogen is divided into different subgroups namely AG-3 PT (potato type), AG-3TB (tobacco type), and AG-3 TM (tomato type), based on their host and the combined data from the ribosomal DNA internal transcribed spacer (rDNA-ITS), rDNA intergenic spacer 1 (rDNA-IGS1) regions, and translation elongation factor 1-α (tef-1α) gene. In this study, we collected tobacco leaves showing target spot symptom from four fields in China. We obtained 49 isolates from southwest China (Yunnan Provinces) and six isolates from northeast China (Liaoning Province). Phylogenetic tree based on rDNA-ITS region indicated that 51 isolates (49 isolates from Yunnan and two isolates from Liaoning) and 4 isolates from Liaoning belonged to AG-3 TB and AG-3 TM, respectively.