Rhizoctonia solani AG-4 HG-I Causing Seedling Damping-off of Schisandra chinensis in Jilin Province, China

Schisandra chinensis(Turcz.) Baill. (family Magnoliaceae) is a perennial herb used in traditional Chinese medicine, mainly for treatments of insomnia and memory decay. In June and July 2014, seedling damping-off symptoms were observed on 2- to 7-leaf-stage of Schisandra chinensis with over 10% incidence in Jingyu County, Jilin Province, China. This disease was also found in Ji'an City, Jilin Province. Infected seedlings showed pale brown lesions on the base of stems or roots, then became girdled, and finally turned into stem or root rot. As a consequence, infected seedlings wilted and died prematurely. Diseased stem and root tissues (5 mm long) were washed with sterilized water, disinfected with 0.5% NaOCl for 2 min, rinsed with sterilized water, then placed on potato dextrose agar (PDA) medium, and incubated at 25[degrees]C in the dark. Twenty four isolates were obtained and designated to LK1 to LK24. Mycelia on PDA medium were initially white, gradually turned light brown with growth rates of 30.5 + or - 3.0 mm in 24h at 25[degrees]C. Hypha were right-angle branching and multinuclear. Sclerotia were brown, 0.75 + or - 0.25 mm in diameter with a feather-like surface on PDA 2 weeks later. Total genomic DNA of all isolates was extracted from the mycelial mat using CTAB method (Murray and Thompson 1980). The internal transcribed spacer (ITS) regions of rDNA were amplified using the universal primer pair ITS1 and ITS4 (de la Cerda et al. 2007). PCR amplicons were purified and sequenced. A BLASTn search revealed that the resulting sequences of strains LK2, LK3, LK1, and LK12 (GenBank Accession Nos. KP411232, KP411233, KP411234, and KP411235, respectively) showed 100% identity with that of Rhizoctonia solani AG-4 HG-I isolate (KM488563). The resulting sequences of other 20 strains showed 99% identity with that of Thanatephorus cucumeis isolate (DQ102447), the teleomorph of R.solani AG-4 HG-I. Thus, the isolates were identified as R. solani AG-4 HG-I based on morphological and molecular characteristics. Pathogenicity tests were done for each of the 24 isolates with healthy 2- to 3-leaf-stage seedlings of Schisandra chinesis. One mycelial plug was placed on the stem or root, and three seedling plants were inoculated with each isolate, and another three seedlings inoculated with PDA medium plugs without fungi were used as controls. All plants were incubated at 25[degrees]C with 14 h light and 10 h dark in a green house for 10 days, and then assessed for disease. S