LAUSR

Crown daisy (Glebionis coronaria L.), also known as chrysanthemum greens, is a popular vegetable in Asia, especially in China. The leaves have been used in folk medicine as a tonic for the liver, blood, intestines and to control anemia and high blood pressure. In November 2020, severe leaf spot and blight was observed with 80% to 95% incidence on crown daisy growing in greenhouses in Fengxian, Shanghai, China (121°22'E, 30°53'N). Irregular rounded spots appeared with a light gray center and water-soaked margins. Round lesions enlarged and merged with age, followed by the development of a necrotic area resulting in the typical "frog-eye" and causing a continuous deterioration of crown daisy. Diseased leaves were washed in running water for 30 min. Small fragments (5 × 5 mm) taken from the margin of lesions were disinfected with 1% NaClO for 3 min, rinsed three times with sterile water, cultured on potato sucrose agar (PSA) augmented with 50 mg streptomycin/liter at 26 oC,and incubated in the dark. Colonies had identical morphology, and TH11290202 was selected and deposited in the plant pathology lab of Shanghai Academy of Agricultural Sciences. Mycelium was initially cottony and white and became appressed to the medium and dark brown with time. Conidia did not form on any media, including PSA, PDA, V8 agar (V8A), maize leaf carbonate agar (MLPCA), pepper leaf carbonate agar (PLPCA), etc. To confirm the identity of the pathogen, genomic DNA was extracted from TH11290202 with the cetyltrimethylammonium ammonium bromide (CTAB) method from the mycelia. Five loci were PCR amplified, namely, the internal transcribed spacer (ITS), translation elongation factor (TEF), calmodulin (cmdA), histone (H3) and actin (ACT), using primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Jaklitsch et al. 2005), CAL-F/CAL-R (O'Donnell et al. 2000), cylh3f/cylh3r (Glass and Donaldson 1995), and ACT-512F/ACT-783R (Carbone and Kohn 1999), respectively. The resulting sequences were deposited in GenBank (MW819910, MW981277, MW981278, ON798723, and MW981279). Analysis of the ITS, TEF, cmdA, H3 and ACT gene sequences of isolate TH11290202 revealed that it was a member of the genus Cercospora, sharing 99.79%, 99.66%, 98.10% 99.74% and 100% sequence similarity with type strain of Cercospora apii CBS 116455. A multilocus phylogenetic analysis was performed using sequences from other closely related taxa obtained from GenBank. Based on morphological and molecular characteristics, TH11290202 was identified as C. apii (Crous and Braun 2003; Groenewald et al. 2006; Milosavljević et al. 2014). To confirm pathogenicity, Koch's postulates were fulfilled on 30 mature plants, which were maintained in a growth chamber (at 26 °C, relative humidity 90%, 12/12 h light/dark). Surface-sterilized leaves were sprayed with a mycelial suspension. Brown lesions were formed 7 days after inoculation on 15 plants, whereas the noninoculated controls remained asymptomatic on the other 15 plants. To our knowledge, this is the first report of C. apii causing leaf spot and blight on G. coronaria in China and will provide useful information for developing effective control strategies.