FIRST REPORT OF MYROTHECIUM RORIDUM CAUSING ROUND SPOT ON DENDROBIUM CANDIDUM IN CHINA

X.Q. Chen, M.R. Li, P.X. Lan, L.L. Li, Z.L. Yuan, R. Zhang, Y. Yu, B. Chen, F. Li

Abstract


Dendrobium candidum (family Orchidaceae) is grown as a medicinal plants in China. In July 2013, in some plastic greenhouses of Puer (Southwest Yunnan) round spots were observed on the leaves of D. candidum plants with 20-30% incidence. Initial symptoms included black to brown circular or subcircular lesions 0.5-2.0 cm in diameter, surrounded by water-soaked tissue and later by concentric rings, grey brown and dark green. Infected leaves turned yellow, wilted, and decayed. Symptomatic leaf tissues (4x5 mm fragments) were surface-sterilized and cultured onto potato dextrose agar (PDA) at 25°C in darkness. Developing colonies were white, floccose at the beginning, then produced sporodo- chia in dark greyish-green concentric rings bearing slimy spore masses. Conidia were smooth, hyaline, cylindrical with rounded ends, 4.9-8.9x1.4-2.8 μm in size. DNA was extracted from a fungal isolate denoted YNPE-SH9 using a DNA extraction kit (OMEGA, USA). The internal tran- scribed spacer (ITS) region and 5.8S rDNA gene were am- plified using primer pair of ITS1 and ITS4 (White et al., 1990). BLAST search of the obtained sequence (GenBank accession No. KM986033) revealed a 100% identity with two Myrothecium roridum strains (AJ301995, AJ302001). Leaves of 10 healthy greenhouse-grown D. candidum plants at the seedling stage were inoculated by injecting a conidial sus- pension of M. roridum (1.1×105 conidia per ml) and kept at 28°C, 80% relative humidity and 14-h photoperiod. Seed- lings inoculated with sterile distilled water served as con- trols. Symptoms like those seen in naturally infected plants were observed in all inoculated D. candidum seedlings seven days post inoculation while control plants remained symp- tomless. To our knowledge, this is the first report of natural infection by M. roridum on Dendrobium spp. in China.

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DOI: http://dx.doi.org/10.4454/JPP.V97I4SUP.017

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