Main content area

First Report of Pseudomonas syringae pv. syringae Causing Leaf Blight on Hosta ventricosa in China

Liu, Z. X., Dong, A. R., Jia, H. Q., Zhou, Y., Liu, X. F., Zhang, X. Y.
Plant disease 2019 v.103 no.8 pp. 2123
Hosta ventricosa, Pseudomonas syringae pv. syringae, arginine deiminase, bacterial diseases of plants, fatty acids, hypersensitive response, leaf blight, leaf spot, leaves, levan, new geographic records, new host records, nucleotide sequences, pathogen identification, plant pathogenic bacteria, ribosomal DNA, surveys, China
Hosta ventricosa, which is an easily grown herbaceous perennial plant valued for its decorative foliage and dainty, colorful flowers, is massively planted in parks and public gardens for ornamental purposes. In June 2018, bacterial leaf blight was first noticed on this herb in Changchun city, China. At the initial stage of the infection, small soaking spots (0.5 to 2.0 mm) were scattered throughout the leaves, and the mesophyll tissue was transparent. These small transparent spots then gradually formed a sunken and necrotic spot (0.5 to 3.5 cm in diameter). Finally, the whole plant turned yellow to yellowy-brown and died. In the June 2018 survey, the area of leaf blight was about 2.2 ha, and incidence of the disease was approximately 12% in the city. The causal pathogens were isolated from the soaking leaf spots. Five isolates (CC1806, CC1807, CC1808, CC1809, and CC18010) were convex, cream-colored, circular with smooth margins, gram-negative, produced fluorescent pigments on King’s B medium (Braun-Kiewnick and Sands 2001), and produced a hypersensitive response on tobacco. Colonies were levan positive and oxidase negative, arginine dihydrolase negative, and pectolytic negative (Braun-Kiewnick and Sands 2001). In addition, fatty acid analysis (Sasser 1990) and Biolog analysis (Biolog, Hayward, CA) were performed. Fatty acid analysis revealed that the isolates belonged to Pseudomonas syringae, and the Biolog database identified them as P. syringae pv. syringae with 74 to 79% certainty. To further confirm the identity of the bacterial strains, the 16S rDNA, gyrB, and rpoD genes were amplified using primers 27F/1492R, gyrBFor2/gyrBRev2, and rpoDFor2/rpoDRev2 (Murillo et al. 2011), respectively. NCBI-BLASTn searches of the obtained 16S rDNA sequences (accession nos. MK636584, MK788127, MK789722, MK788129, and MK788128) showed 99 to 100% homology with gene sequences of Pseudomonas spp. The housekeeping genes gyrB and rpoD (MK644940 and MK791195 to MK791198; MK644941 and MK791199 to MK791202) shared 99 to 100% identity with P. syringae pv. syringae (FR691733.1 and JX867917.1; FR691732.1 and KC852107.1) in GenBank. Koch’s postulates were completed using healthy plants of H. ventricosa growing in pots in the Northeast Forestry University. Healthy leaves were inoculated by spraying with a bacterial suspension (10⁹ CFU/ml) after growing for 24 h in nutrient agar medium at 29°C. Control treatments were inoculated only with sterile water. They were then incubated at 25°C under 80 to 90% relative humidity. Small soaking spots (5 days after inoculation) and sunken spots (8 days) similar to those observed on naturally infected leaves were observed on all inoculated plants. Finally, the whole plant died after 15 days of inoculation, and control plants showed no symptoms. P. syringae pv. syringae was reisolated and identified from all inoculated plants but not the controls. It has been previously observed to infect many economically important plants including apple (Gašić et al. 2018) and tomato (Garibaldi et al. 2007). To our knowledge, this is the first report of leaf blight on H. ventricosa caused by P. syringae pv. syringae in China.