First Report of a Bacterial Leaf Spot on Angelica dahurica Caused by Pseudomonas syringae in Gansu, China

Abstract

HomePlant DiseaseVol. 101, No. 7First Report of a Bacterial Leaf Spot on Angelica dahurica Caused by Pseudomonas syringae in Gansu, China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of a Bacterial Leaf Spot on Angelica dahurica Caused by Pseudomonas syringae in Gansu, ChinaY. Wang, L. Jin, Y. E. Yao, C. Y. Zeng, and L. ZhangY. WangSearch for more papers by this author, L. JinSearch for more papers by this author, Y. E. YaoSearch for more papers by this author, C. Y. ZengSearch for more papers by this author, and L. ZhangSearch for more papers by this authorAffiliationsAuthors and Affiliations Y. Wang L. Jin Y. E. Yao C. Y. Zeng L. Zhang , Gansu University of Chinese Medicine, Lanzhou 730000; China. Published Online:27 Apr 2017https://doi.org/10.1094/PDIS-01-17-0078-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Angelica dahurica (Umbelliferae) is a perennial medicinal plant abundant in China, Korea, and Japan (Lee et al. 2011). Its roots are used as traditional medicine in these countries to treat headache, bleeding, menstrual disorders, and neuralgia (Committee of China Pharmacopoeia 2005; Lee et al. 2011). During disease surveys in Gansu, China, on medicinal plants in 2011, a bacterial leaf spot disease was discovered with 32% incidence in cultivation fields in Longxi county. The disease incidence, severity, and area increased quickly in recent years. In 2016, the disease was found in Hezhen county with 70% incidence. The disease symptoms appeared on leaves initially as tiny, yellowish points, then became oil-soiled spots. When the disease was serious, oil-soiled spots densely scattered on leaves, veins became transparent, and the leaf crimped. Then the spot expanded to an irregular yellowish to brown lesion with a grayish inner part, brown oil streaks on leaf veins, and finally the leaves became dry and died. Symptoms were more apparent on new and tender leaves. Diseased leaves with oil-soaked lesions were picked and cut into 4 to 5 mm squares, surface sterilized in 1% sodium hypochlorite for 1 min, and then thoroughly washed three times in sterile distilled water. The tissues were crushed with a sterilized round head glass rod and diffused for 15 min, then loopfuls of the suspensions were streaked on nutrient agar (NA) medium and incubated for 48 h at 28°C. Causal bacterial colonies were circular, convex, milk-white, 0.8 to 1.2 mm in diameter, gram negative, and could induce hypersensitive response on tobacco leaves. The isolate (strain BZ2) can hydrolyze gelatin and starch, produce acid from glucose and mannitol, is positive to catalase, negative to Voges-Prokauer, esterase, and idole production, lack of phenylalanine deaminase, and is fluorescent on KBA. Pathogenicity tests were performed by artificial inoculation on A. dahurica potted plants. The bacterium (strain BZ2) was cultured on NA plate for 24 h, resuspended in sterile water, and adjusted to approximately 107 cfu ml–1. The bacterium suspension was inoculated into 10 leaves of A. dahurica by spraying and 10 leaves through injection method. Control plants were similarly treated with sterilized water. Inoculated plants were kept in a transparent plastic box to maintain >90% humidity at 23 ± 2°C in the lab and disease symptoms were evaluated daily. After 3 days, the typical irregular oil-soaked lesions appeared on the spray- and injection-inoculated leaves. Ten days later, the leaves wilted and the bacteria were reisolated from the diseased leaves, fulfilling Koch’s postulate. The total DNA was extracted from the isolate (strain BZ2) and 16S rRNA gene was amplified using the primer set (27f and 1492r) (Weisburg et al. 1991) and then submitted to GenBank (accession no. KY460679). BLASTn search yielded 100% identity with several strains of P. syringae, including PDD-59b-16 (KR922153), PDD-50b-9 (KR922075), PDD-51b-10 (KR922084), and CC1557 (CP007014). From the colony morphology, biochemical characteristics, and 16S rRNA sequence identity, the pathogen was identified as P. syringae. In 2002, bacterial speck caused by P. syringae on A. dahurica was reported in Jiangsu, Zhejiang, and Anhui provinces in China (Liu et al. 2002). This is the first report of the disease in Gansu Province. Future studies should place an emphasis on researching methods of control.