First Report of Ginseng (Panax ginseng) as a Natural Host of Dodder (Cuscuta japonica) in China

Abstract

Ginseng (Panax ginseng C.A. Meyer) belongs to the Araliaceae family and is a high-value medicinal herb grown mainly in Jilin Province, China. China is the world's oldest and largest producer of ginseng. Annual yield and exports account for more than 78 and 60% for the world, respectively. In July 2009 and August 2010, dodder (Cuscuta sp.), a parasitic seed plant, was observed on 4- and 5-year-old plants that were being cultivated on raised beds under artificial shading in three separate locations approximately 200 kilometers apart in Jilin Province. The infested area was approximately one-third of the field (300 m2 of 10,000 m2), which was previously planted with pine trees and herbaceous plants. Initially, there were no obvious symptoms on ginseng plants, but later, symptoms consisted of poor growth, chlorosis, and wilting, eventually followed by death in large areas throughout the field. One typical representative of 10 samples collected was identified as Cuscuta japonica based on several morphological characteristics, including yellow stems with purplish spots with branches 1.2 to 2.5 mm in diameter. Inflorescences were spicate and measured 3 cm with broadly ovate, scale-like bracts. Flowers were sessile with deeply divided calyxes. The parasite had purplish, ovate sepals with pink or greenish white corollas. The plant had five stamens with yellow, ovate-circular anther. Ovaries were globose and smooth. Capsules contained three to four pale yellow or brown ovate seeds measuring 1.9 to 2.7 mm (3,4). The internal transcribed spacer (ITS) region of rDNA of the representative samples was amplified using primers ITS4/ITS5 (2) and sequenced. BLASTn analysis of the 650-bp amplicon (GenBank Accession No. JF431541) showed 99% sequence identity with C. japonica (Accession Nos. DQ924571 and EU330320). Phylogenetic trees constructed by utilizing the neighbor-joining method with software MEGA 4.0 (1) placed the dodder specimens and C. japonica (DQ924571 and EU330320) into one group. The reported hosts of C. japonica include plants belonging to the Leguminosae, Salicaceae, Polygonaceae, and Compositae. Therefore, to our knowledge, this is the first report of C. japonica naturally infecting P. ginseng in the world. Reference: (1) K. Tamura et al. Mol. Biol. Evol. 24:1596, 2007. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990. (3) Z. Y. Wu. Flora Reipublicae Popularis Sinicae 64:147, 1979. (4) L. P. Yin. Plant Quarantine (in Chinese) 9:292, 1995.