First report of foliar blight in Brassica rapa subsp. chinensis caused by Rhizoctonia solani AG-4
*cxqzb@163.com
1 Phytopathology Lab of Yunnan Province, Yunnan Agricultural University, Kumming 650201, China
2 Faculty of Agriculture, Hokkaido University, Sapporo, Japan
3 Hokkaido Starch Industry Society, Sapporo, Japan
Accepted: 28 Nov 2003
Brassica rapa subsp. chinensis (bok choy) is a vegetable popular in Asia. In July 2003, foliar blight symptoms were first observed on leaves of B. rapa subsp. chinensis at the six-to-eight leaf stage in a field at Jialize Farm, Kunming, Yunnan Province, China. The symptoms appeared as primary lesions consisting of small, circular necrotic spots, 1-3 mm in diameter, accompanied by secondary lesions with large irregular borders (Fig. 1). Under high moisture conditions, white hyphae appeared on the stems, however no lesions were observed. Sections (1 by 2 cm) cut from infected stems were surface-sterilised and plated onto potato dextrose agar. Rhizoctonia solani was recovered consistently from this material. Anastomosis group testing revealed that all 13 isolates belonged to AG4 (Sneh & Ogoshi, 1998).
Pathogenicity tests with a hyphal-tip isolate were carried out using B. rapa subsp. chinensis in two controlled-environment cabinets (one set at 25°C, 16 h day and the other at 16°C, 8 h night cycle), one utilizing seeds and the other, plants at the six-leaf stage. Both were planted in 3-week-old inoculated cornmeal-sand medium. A high level of humidity was maintained by placing a pan of water in the bottom of the incubators. Control plants were planted in uninoculated cornmeal-sand medium. After one week emerging seedlings exhibited both leaf and stem necrosis near the head. On the 6-week old plants, foliar blight of young leaves was more severe than those observed on the older leaves. After 2 weeks, grey-white hyphae appeared on the stem but no lesions were present. Control plants did not develop symptoms. Rhizoctonia solani AG4 was re-isolated from the inoculated plants.
Rhizoctonia foliar blight of cabbage (Brassica oleracea var capitata) has been reported in New York State, USA (Abawi & Martin, 1985). However, this is the first published report of foliar blight of bok choy (Brassica rapa subsp. chinensis) caused by R. solani AG4.
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Acknowledgements
The Yunnan Nature Science Fund supported this study.
References
- Abawi GS, Martin SB, 1985. Rhizoctonia foliar blight of cabbage in New York State. Plant disease 69, 158-161.
- Sneh B, Ogoshi A, 1998. Identification of Rhizoctonia species. Third Edition. St. Paul, Minnesota, USA: The American Phytopathological Society.
This report was formally published in Plant Pathology
©2003 The Authors