Chinese skullcap (Scutellaria baicalensis) is a perennial herb in the Lamiaceae, and is grown in Jilin and 10 other provinces in China. Skullcap root extracts are used for treating allergies and respiratory conditions (5), and have inhibitory effects on some plant pathogens (2). In 2012, stem blight on 3-year-old Chinese skullcap plants were observed from mid-June to late-September in a herb garden at Jilin Agricultural University, Jilin Province, China. More than 90% of the 15 ha of skullcap plants were infected, and almost 60% of the infected plants died. A similar situation occurred in other regions of Jilin in 2012 and 2013. Oblong to irregular stem lesions, each 3 to 5 cm long, appeared on the basal stem. Lesions were initially light brown, and turned dark brown because of velvety, thick, gray fungal sporulation that formed over the lesions. The lesions eventually encircled the stems, preventing water and nutrient uptake. The infected plants often turned chlorotic and wilted. Symptomatic stem tissues were collected from three gardens in Jilin Province. Small pieces of diseased stems were surface-disinfested in 3% NaOCl for 2 min, rinsed twice in sterilized distilled water, plated on potato dextrose agar (PDA) medium, and incubated at 22°C for 5 days. Ten isolates were recovered, and all produced gray hyphae and dark sclerotia on PDA. The conidia formed on tree-like, branched conidiophores and were colorless, single, lemon-shaped, smooth-walled, and 9.0 to 16.9 × 5.7 to 9.7 μm. Sclerotia formed when cultures on PDA plates were incubated for 20 days at 22°C. The sclerotia were dark, irregular, and 2.2 to 3.8 × 1.1 to 2.6 mm. To confirm pathogenicity of each of the 10 isolates, five 3-year-old Chinese skullcap plants were each inoculated on the basal stem with an 8-mm-diameter colonized PDA plug of the appropriate isolate. Five plants were inoculated similarly with non-colonized PDA plugs as a control treatment. All plants were maintained at 22°C in a greenhouse. The first lesions appeared on stems 5 days after inoculation, whereas control plants remained healthy. The same fungus was consistently recovered from inoculated lesions as the original isolates, and no fungus was re-isolated from control plants. DNA was extracted from isolate RSL-1 and amplified using the ribosomal DNA (rDNA) internal transcribed spacer (ITS) region primers ITS5/ITS4 (1), glyceraldehyde-3-phosphate dehydrogenase gene (G3PDH) primers G-F/G-R, heat-shock protein 60 gene (HSP 60) primers H-F/H-R, and DNA-dependent RNA polymerase subunit II gene (RPB2) primers R-F/R-R (3). The ITS, G3PDH, HSP 60, and RPB2 sequences (GenBank Accession Nos. JX840480, KJ018760, KJ018758, and KJ018756, respectively) of isolate RSL-1 showed 100% similarity to the ITS sequence of strain WM6 of Botryotinia fuckeliana (anamorph Botrytis cinerea) (JN164269) (1), 100% identity to the G3PDH sequence of isolate Ice-2 of B. fuckeliana (AB546620) (3), 100% identity to the HSP60 sequence of isolate MUCL1152 of B. fuckeliana (AJ716090) (4), and 99.8% identity to the RPB2 sequence of isolate WM6 of B. fuckeliana (JN164272) (1). Based on these characteristics, the fungus was identified as B. cinerea. To the best of our knowledge, this is the first report of B. cinerea causing stem blight on S. baicalensis in Jilin Province, China. This disease may potentially cause great losses under favorable conditions.
References: (1) X. Li. Plant Dis. 95:1592, 2011. (2) J. Y. Liu et al. Hubei Agric. Sci. 50:1809, 2011. (3) K. Maeda et al. J. Gen. Plant Pathol. 76:303, 2010. (4) M. Staats et al. Mol. Biol. Evol. 22:333, 2005. (5) K. Zandi et al. BMC Compl. Alternat. Medicine 13:1472, 2013.
