Verticillium Wilt of Redbud in China Caused by Verticillium dahliae.

Abstract

Chinese redbud (Cercis chinensis Bunge), a member of the Fabaceae, is an important ornamental plant native to China with reported desirable medicinal effects, including stimulating blood circulation, detumescence, and detoxification (1). In October 2011, wilt symptoms of gradual leaf yellowing, wilting, scorching (marginal browning), and twig dieback were observed on plants in Yangling, Shaanxi, China. The incidence of diseased plants was about 20% in two main areas (about 20 ha in Zijingshan Park in Zhengzhou, Henan Province; and about 3,000 ha in Taiping National Forest Park in Xi'an, Shaanxi Province). Wilted leaves of diseased plant senesced and died, but defoliation was not observed. Brown discoloration was observed in vascular tissues of petioles, twigs, and stems of diseased plants, sometimes in a ring pattern. The symptoms were often restricted to the lower part of the tree or a few branches. To identify the causal agent, six twigs (each approximately 50 mm in diameter and 10 cm long) sampled from an infected tree in Yangling were rinsed in running water, surface-sterilized with 75% ethanol for 2 min, rinsed in sterilized water three times, dried, cut into 1 cm long segments, and the segments put onto potato dextrose agar (PDA) medium. A fungal isolate was recovered from diseased vascular tissues of each sample when cultured on PDA in the dark at 25°C. After 5 days, colonies changed from white to black as a result of production of microsclerotia. Microscopic observation revealed that conidiophores were hyaline and verticillate, with three to four phialides at each node. Conidia were ellipsoidal, hyaline, single-celled, and 2.5 to 7.5 × 1.25 to 4.5 μm. On the basis of these morphological characteristics, the fungus was identified as Verticillium dahliae (3). To prove Koch's postulates, the roots of 10 healthy, 1-year-old C. chinensis plants were each irrigated in a greenhouse with 50 ml of a conidial suspension (1.0 × 107 spores/ml) of an isolate recovered from an infected plant (2); five control plants were inoculated similarly with sterilized water. Fifteen days after inoculation, the same wilt symptoms observed on the original plants had developed on 9 of the 10 inoculated plants, whereas the control plants remained healthy. The pathogen was recovered 15 days after inoculation by isolating from petiole and stem tissues of symptomatic plants, but was not isolated from the control plants. The internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2) of the nuclear ribosomal DNA was PCR-amplified with primers ITS1 and ITS4 (4), and sequenced. BLAST analysis of the ITS sequence (GenBank Accession No. AB735536) showed 100% homology with that of an isolate of V. dahliae (FJ572050). To our knowledge, this is the first report of Verticillium wilt on C. chinensis in China.