First Report of Sieversian Wormwood (Artemisia sieversiana) as a New Host of Dodder (Cuscuta australis) in China

Abstract

Sieversian wormwood (Artemisia sieversiana Ehrhart ex Willd; Compositae), annual or biennial herb, is a widely used medicinal plant in both traditional Chinese medicine and Tibetan medicine (Jiangsu New Medical College 1977). Sieversian wormwood has a broad spectrum of pharmacological activities such as antiphlogosis, detumescence, and hemostatic. This wormwood is widely distributed in many provinces of China, including the three northeastern provinces of Liaoning, Jilin, and Heilongjiang, and has been planted and grows in Shandong and Jiangsu. On 22 July 2018, dodder was first found on Sieversian wormwood on the north embankment of the Xinkai River (N 41°48′36.51″, E 123°33′21.32″, 53 m elevation) in Shenyang (temperate continental monsoon climate), Liaoning. About 15 Sieversian wormwood plants in approximately 10 m² were parasitized by the dodder. The dodder was mostly located in the middle-third to upper canopy, where the Sieversian wormwood stalks and petioles were firmly entwined by the dodder. The branched dodder stems spread among neighboring Sieversian wormwood plants and were also found parasitizing surrounding Chenopodium album L., Kochia scoparia (L.) Schrad., Setaria viridis (L.) Beauv., and Artemisia annua L. The Sieversian wormwood plants parasitized by the dodder showed chlorotic and wilting leaves, droopy branches, and stunted growth. All wilt symptoms were most evident on warm, sunny days. However, the affected host had no clear lesions around the plant tissues where the dodder haustoria were clearly observed penetrating. The orange, leafless dodder was 0.6044 ± 0.093 mm in diameter (mean ± SD, n = 15), reproduced synchronically with its new host. The dodder inflorescences were compact cymose and subsessile. Corolla were creamy white and cupulate, abutted by oblong, not overlapping calyces, corolla lobes were obtuse, upright to spreading. Capsules were depressed-globose, not circumscissile, and only its lower half was typically enclosed by the withered corolla. There were four seeds per capsule. Seeds were brownish, ovoid, scabrous, and with a short line hilum. The dodder was tentatively identified as Cuscuta australis R. Brown, Prodr. according to its inflorescence, petal, calyx, pedicle, capsule, ovary, and seed characteristics (other specific features see Wu 1979; Yuncker 1932). The 436-bp internal transcribed spacer 2 region (ITS2) of our dodder rDNA (deposited in GenBank, accession no. MK106064) had the highest similarity with C. australis references (GenBank nos. KF454371 [99.03%], MG548813 [99.31%], and MH370812 [99.54%]). The 209-bp chloroplast trnL intron of our dodder (GenBank no. MK879383) had 100% similarity with C. australis reference (GenBank no. MK879385), as well as 99.62% with another reference (AY558828). The two gene sequences together confirmed its identity as C. australis, albeit the dodder ITS2 was also with high similarity (99%) with C. campestris. The dodder, C. australis, has been reported on many plants of the families Compositae, Leguminosae, and Polygonaceae, mainly on widely cultivated crops and local-specialty medicinal herbs in agricultural fields, such as chickpea (Cicer arietinum L.) and niuxi (Achyranthes bidentate Blume) (Chen et al. 2014, 2016). To our knowledge, this is the first time that C. australis has been observed on Sieversian wormwood in China. The dodder, as a pest plant, may inevitably limit the availability of the wild Sieversian wormwood resource.