First report of dodder (Cuscuta australis) on the invasive weed Xanthium strumarium var. canadense in China.
To determine the distribution and natural enemies of the invasive Xanthium strumarium var. canadense (Canada cocklebur) in Liaoning, China, field surveys were conducted in the summer of 2016. On August 7, dodder was first found on Canada cocklebur at 3 disturbed sites along the Xinkai River in Shenyang (with temperate continental monsoon climate), Liaoning Province, Northeast China. At each site, a nearly circular patch of Canada cocklebur was found (3, 5 and 8 m in diameter, respectively) that was parasitized by dodder. Cocklebur parasitized by the dodder showed wilting and senescent leaves, stunted growth and few or no fruit produced. The dodder wrapped around petioles and stems of the invasive weed and it occasionally spread onto cooccurring native plants, such as Setaria viridis and Humulus scandens. Where the dodder penetrated the cocklebur stem tissues, brownish black lesions developed with small cracks. The dodder species was identified as Cuscuta australis based on morphological and molecular analyses. The obtained sequence was deposited in GenBank (accession no. MH370812). This is thought to be the first report of C. australis parasitizing X. strumarium var. canadense in China.