First Report of Rhizoctonia solani AG-2-2 IIIB Causing Foliar Blight on Bletilla striata in China

Bletilla striata (Thunb.) Rchb. f. (Orchidaceae), a perennial plant, is traditional Chinese herb (known as baiji) used to treat hemorrhage, scalding injuries, gastric ulcers, pulmonary diseases, and inflammation (Zu et al. 2019). In May 2019, foliar blight symptoms were observed on approximately 25% of B. (cv. Guiji No.1) plants in three plantations (∼4.5 hectares total) Ziyuan County, Guangxi Province, China. Initial light brown, irregular, water-soaked spots the plant leaves. Several often merged, forming large, lesions that extended onto stem after week led leaf abscission, even death. To determine causal agent, 5-mm squares cut from margin 6 infected leaves surface disinfected 1% sodium hypochlorite solution for 2 min, rinsed times with sterile distilled water, plated potato dextrose agar (PDA), incubated at 28°C (12-h light-dark cycle) 3 days. The emerging hyphal tip single mycelium was transferred PDA obtain pure cultures isolates. Twenty isolates obtained, 10 (50%) initially white before turning brown (∼4 days). Septate hyphae 4.29 10.75 μm (average 6.42 μm) diameter branched right angles constriction origin branch point. Staining safranin O 3% KOH (Bandoni 1979) revealed multinucleated cells (3 9 nuclei per cell, n = 142). This morphology typical Rhizoctonia solani Kühn (Meyer 1990). For species confirmation by molecular identification, (BJ101.6, BJ101.11, BJ102.2) cultured 4 days, then DNA extracted using CTAB method (Guo 2000), ribosomal ITS1-5.8S-ITS2 region amplified PCR universal fungal primers ITS1 ITS4 (White Internal transcribed spacer (ITS) sequences strains BJ101.6, BJ102 (deposited GenBank under accession nos MT406271, MT892815, MT892814, respectively) had over 99% similarity those R. AG-2-2 IIIB (accession JX913810 AB054858) (Carling 2002; Hong 2012). Phylogenetic analysis ITS showed clustered monophyletically IIIB. AG confirmed their ability grow well 35°C, which separates IV (Inokuti Based morphological characteristics nucleotide sequence analysis, identified Pathogenicity tested 1.5-year-old grown perlite peat moss mixture (1:3) 7-cm pots. Healthy inoculated an aqueous suspension (approximately 1 × 5 fragments/mL, 100 μL) prepared BJ102.2, each isolate plants; other water served controls. All enclosed transparent plastic bags greenhouse 14 days photoperiod). Three post-inoculation, exposed mycelial fragments similar originally field. No detected control plants. Experiments replicated results. fulfill Koch’s postulates, re-isolated symptomatic sequencing, whereas no fungus isolated our knowledge, this first report causing China, these findings will be useful further strategies research.