Abstract
Ipomoea aquatica is a leafy vegetable widely cultivated in tropical Asia, Africa, and Oceania. Bacterial leaf canker disease has been attacking the planting fields and seriously affecting the quality of I. aquatica in epidemic areas in China. This study examined the microbial composition of I. aquatica leaves with classical symptoms of spot disease. The results showed that Xanthomonas was overwhelmingly dominant in all four diseased leaf samples but rarely present in rhizospheric soil or irrigation water samples. In addition, Pantoea was also detected in two of the diseased leaf samples. Pathogen isolation, identification, and inoculation revealed that both Xanthomonas sp. TC2-1 and P. ananatis were pathogenic to the leaves of I. aquatic, causing crater-shaped ulcerative spots and yellowing with big brown rot lesions on leaves, respectively. We further sequenced the whole genome of strain TC2-1 and showed that it is a member of X. perforans. Overall, this study identified X. perforans as the causal pathogen of I. aquatica bacterial leaf canker, and P. ananatis as a companion pathogen causing yellowing and brown rot on leaves. The correct identification of the pathogens will provide important basis for future efforts to formulate targeted application strategy for bacterial disease control.
Highlights
Ipomoea aquatica Forsk, usually called water spinach, water convolvulus, kangkong, and swamp cabbage, is native to East Asia and has been widely cultivated as a popular green leafy vegetable in tropical and subtropical regions (Ismail and Fun, 2003)
Since 2010, bacterial leaf canker disease has attacked water spinach cultivated in many towns and districts of Dongguan City, Guangdong Province, China
We employed 16S rDNA gene-based metagenomic sequencing to understand the composition of microbiota associated with bacterial leaf canker of water spinach, which provides an important guide for pathogen identification
Summary
Ipomoea aquatica Forsk, usually called water spinach, water convolvulus, kangkong, and swamp cabbage, is native to East Asia and has been widely cultivated as a popular green leafy vegetable in tropical and subtropical regions (Ismail and Fun, 2003). In China, it is the only species of the genus Ipomoea that is grown in paddy fields. It can grow in all provinces of the Yangtze River Basin from April to October, and is suitable to grow in warm and humid climate, as well as fertile and wet soil. In addition to its high nutritive value to humans and animals, I. aquatica possesses medicinal importance (Hu et al, 2010; Lawal et al, 2015, 2017). Genome Sequence of Xanthomonas perforans debility, jaundice (Lawal et al, 2017), nosebleeds, and high blood pressure (Duke and Ayensu, 1985). The extract has been reported to inhibit prostaglandin synthesis (Tseng et al, 1992) and possess antidiabetic (Malalavidhane et al, 2000), antioxidant (Prasad et al, 2005b), antinematodal (Mackeen et al, 1997), and anticancer activities (Prasad et al, 2005a)
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