Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/27/2010
Publication Date: 2/1/2011
Citation: Liu, Q., Li, Y., Chen, J. 2011. First report of bacterial wilt caused by Ralstonia solanacearum on Mesona chinensis in China. Plant Disease. 95:222. Interpretive Summary: Jellywort or Xiancao in Chinese, is a herbaceous plant used to make grass jelly, a refreshing drink popular among Asian populations. Currently, jellywort cultivation in South China is a rapidly growing industry with a high profit margin. An estimated 7,000 ha is grown with a value over $50 million USD. In 2009, a wilting disease of jellywort was observed in Guangdong and neighboring provinces in China with incidence up to 50% in severe cases. To investigate what caused the disease, jellywort plants showing typical wilting symptoms were collected from a production field in Guangdong in June 2010. A bacterium was isolated from the symptomatic plants, and caused the same wilting disease when inoculated to healthy jellywort plants. The bacterium also caused similar wilting symptoms in tobacco, potato, tomato, pepper and eggplant. Further analysis identified the bacterium as Ralstonia solanacearum. To our knowledge, this is the first report of a disease caused by R. solanacearum on jellywort. This finding provides new information on the ecology and epidemiology of R. solanacearum, a plant pathogen of national and international importance.
Technical Abstract: Jellywort (Mesona chinensis Benth) is a herbaceous plant in the Lamiaceae Family. The plant is referred to as ‘Xiancao’ (Weed from Angels) in Chinese and is primarily used to make grass jelly, a popular refreshing drink. Currently, Xiancao cultivation is a fast growing industry with a high profit margin in southern China. An estimated 7,000 ha is grown with a value over $50 million USD. In 2009, a wilting disease of Xiancao was observed in Guangdong and the neighboring Guangxi and Fujian Provinces with incidence up to 50%. Affected plants initially show withering symptoms on apical leaves during daytime and recovery at night. As the disease develops, withering leaves spread downward, eventually encompassing the whole plant. Leaves lose vigor but remain green in color. After 3-4 days, wilting becomes irreversible. Roots and basal stem tissues blacken and rot, leading to plant death. Longitudinal sectioning of the basal stem shows browning of vascular tissues with whitish ooze visible when compressed. To investigate the disease etiology, Xiancao plants showing typical wilting symptoms were collected from a production field in Zengcheng City of Guangdong Province in June 2010. A bacterium showing large, elevated, and fluidal colonies with a pale red center was isolated from vascular tissue on TZC medium (2) after incubation at 30 C for two days. Fifteen 45-day old Xiancao plants were inoculated by injection of 20 µL bacterial suspension (1×108 CFU/mL) into the middle stem. Sterile water was used as a negative control. After 4 to 6 days incubation in a greenhouse (28-30'), all (15 / 15) inoculated plants developed wilting symptoms as described above. The same bacterium was re-isolated from inoculated plants. The five negative control plants did not show any wilting symptoms. With the same artificial inoculation procedure, this bacterium also caused similar wilting disease in tobacco, potato, tomato, pepper and eggplant. Based on symptomatology and bacterial culture characteristics, Ralstonia solanacearum (formerly Pseudomonas solanacearum) was suspected as the causal agent. For confirmation, the universal bacterial 16S rDNA primer set E8F(5’-AGAGTTTGAT CCTGGCTCAG-3’) / E1115R(5’-AGGGTTGCGC TCGTTG-3’) (1) was used to amplify DNA from pure culture. A 1,027 bp DNA sequence was obtained and deposited in GenBank with accession number HQ159392. BLAST search against the current version of GenBank database showed 100% similarity with the 16S rDNA sequences of 26 Ralstonia solanacearum strains. Furthermore, primer set PS-IS-F (5’-CGCAACGCTG GATGAACCC-3’) / PS-IS-R (5’-CAGACGATGC GAAGCCTGAC-3’) specific to Ralstonia solanacearum Race 1 (3) was used for PCR and amplified an expected 1,070 bp DNA fragment. To our knowledge, this is the first report of a disease caused by Ralstonia solanacearum on Mesona chinensis.