First Report of Dodder (Cuscuta australis) Parasitizing the Invasive Jerusalem Artichoke (Helianthus tuberosus) in China

Jerusalem artichoke (Helianthus tuberosus L.; Asteraceae), a tall perennial herb native to North America (Shoemaker 1937), has become a significant invasive weed in Eurasia. The wild neophyte first recorded in Shandong Province in 1918 is now present in 26 provinces in China, except Heilongjiang, Inner Mongolia, Guizhou, Taiwan, Guangxi, Xizang, Hongkong, and Macao (Ma 2013). This invasive weed easily forms dense monospecific stands in disturbed habitats such as farmlands, wastelands, bared slope lands, roadsides, ditches, and river embankments, threatening local biodiversity in China. To determine its distributions and natural enemies in Liaoning Province, field surveys were conducted in summer 2018. Dodder was first found on Jerusalem artichoke along the Xinkai River (N 41°49′, E 123°35′, 62 to 65 m elevation) in Shenyang (temperate continental monsoon climate), Liaoning. Orange leafless dodder was observed mostly wrapped around affected artichoke plants and was also occasionally present on native Humulus scanden, Artemisia lavandulaefolia, and Chenopodium album plants in the swards. Artichoke plants parasitized by dodder were chlorotic on the upper half of the stems, and necrotic on the lower half. Some parasitized plants were also stunted. Haustoria were observed clearly penetrating Jerusalem artichoke stems, and some stem tissues surrounding the haustoria connections developed grayish lesions with short longitudinal cracks. The dodder stems on Jerusalem artichoke were 0.9563 ± 0.146 mm in diameter (mean ± s.d., n = 15). The dodder inflorescences were lateral, compact cymose, and subsessile. Bracts were scale-like. Corolla were creamy white and cupular. Capsules were enclosed by persistent corolla, depressed-globose, not circumscissile, and containing 3 to 4 seeds. Seeds were brownish, ovoid, and scabrous. Based on inflorescence, bract, corolla, capsule, and seed characteristics, the dodder was tentatively identified as Cuscuta australis R. Br (Wu 1979; Zhao et al. 2015). The internal transcribed spacer 2 (ITS2) region of the dodder rDNA was amplified with S2F-S3R primers resulting in a 437-bp product (GenBank accession no. MK070145). This product had 100% similarity with C. australis (MK063811) reference, confirming its identify as C. australis, albeit the ITS2 of C. chinensis (JF421489) was also identical. The dodder, C. australis, is broadly distributed from Central, East, and South Asia southward to Malaysia, Indonesia, and Oceania (Wu 1979). It has been reported parasitizing other noxious invasive weeds such as common ragweed (Ambrosia artemisiifolia) (Zhao et al. 2015) and Canada cocklebur (Xanthium strumarium L. var. canadense) (Wang et al. 2019). To our knowledge, this is the first report of C. australis on the invasive Jerusalem artichoke in China. In addition, few natural enemies have been found on this invasive artichoke, except an introduced insect Ophraella communa, of which only its adults were observed feeding in the laboratory (Hu and Meng 2007). The dodder, as one of a few reported natural enemies on the weed, may alleviate the detrimental impacts of the aggressive Jerusalem artichoke in China, especially in the two Northeast provinces, Jilin and Liaoning.