First report of bacterial leaf spot of cucumber caused by Pseudomonas cichorii in China.
A new cucumber bacterial leaf spot disease was discovered in 2015, during a survey in a cucumber breeding facility in Sanya, Hainan, China. The disease incidence reached 90% in severely infected fields since 2015. Initial symptoms on cucumber leaves were water soaking and light green lesions. Leaves were thinner. Lesion margins gradually turned yellow and the lesion centres turned brown. The range of irregular lesions was 1.5-2.0 cm long and 1-1.5 cm wide. Severely affected leaves showed chlorotic lesions, which coalesced to produce broad necrotic areas. The causal pathogen was isolated and identified as Pseudomonas cichorii based on biochemical, physiological, morphological, molecular and pathogenicity analyses. The obtained sequences were deposited in GenBank (accession nos. MF979525.1 for 16S rRNA and MF979524.1 for rpoB). This is thought to be the first isolation of cucumber leaf spot caused by P. cichorii in China.