Asian foxtail (Uraria crinita (L.) Desv. ex DC.) is an herb cultivated for the use of roots and stems in Taiwanese cuisine. In September 2013, symptoms of leaf blight and basal rot were observed on U. crinita in a commercial field in Longjing District, Taichung, Taiwan, at an incidence of approximately 20%. White mycelia and brown sclerotia formed on the surfaces of the basal stems. The infected plant gradually wilted and eventually died. Diseased lower stem tissues were surface sterilized in 0.6% NaOCl, rinsed with sterile distilled water, and transferred to potato dextrose agar plates. The cultures were incubated at 25°C in the dark. The radial mycelial growth was 9.0 mm/day during the first 4 days, and the diameter of mature sclerotia was 1.76 mm following 3 weeks of incubation. The internal transcribed spacer (ITS) sequence of the isolate was amplified by PCR using the primers ITS5 and ITS4 (2). The amplicon was cloned, sequenced, and deposited in GenBank (Accession No. KJ677121). The sequence similarity was 99% compared with that of Sclerotium rolfsii Sacc. from Spain (GU080230) (1). Based on the characteristics, the fungus was identified as S. rolfsii. The fungal isolate (BCRC FU30230) was deposited in the Bioresource Collection and Research Center, Hsinchu, Taiwan. Pathogenicity tests were conducted on six 2-month-old potted U. crinita plants in a greenhouse. Prior to infesting the plant, fungal inoculum of S. rolfsii BCRC FU30230 was prepared by inoculating the isolate on autoclaved rice (rice/water/dextrose = 50:50:1) in a flask. After 20 days incubation at room temperature, rice colonized by S. rolfsii was placed near the base of the plants (approximately 30 g/plant) in the greenhouse. Sterile rice applied to an equal number of plants served as negative controls. All inoculated plants developed blight symptoms with mycelia and sclerotia produced near the bases of each seedling 1 week after inoculation at an average temperature of 26°C. The control plants remained healthy. The pathogen re-isolated from the inoculated plants was morphologically identical to the original isolate. The pathogenicity test was repeated by inoculated healthy plants with reduced inoculum (five granules/plant). A delay of symptom development was observed and similar results were obtained. To our knowledge, this is the first report of Sclerotium rot on U. crinita in Taiwan, and the first report on U. crinita as a host for S. rolfsii.
References: (1) E. Remesal et al. Plant Dis. 94:280, 2010. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.