Winter jasmine (Jasminum nudiflorum Lindl.), a trailing, deciduous shrub, is widely used as an ornamental plant. Its flowers and leaves also has great medicinal value for treatment of inflammatory swelling, purulent eruptions, bruises and traumatic bleeding (Takenaka et al. 2002). In October 2022, leaf spot symptoms were observed on J. nudiflorum distributed in Meiling Scenic Spot (28.78°N, 115.83°E) and Jiangxi Agricultural University (28.75°N, 115.83°E), Nanchang, Jiangxi Province, China. In a week-long series of investigations, the incidences of disease could range up to 25%. Initially, the symptoms of the lesions were small yellow circular spots (0.5 to 1.8 mm), and gradually developing irregular spots (2.8 to 4.0 mm) with grayish white central parts, a dark brown inner ring, and outer yellow halo. To identify the pathogen, sixty symptomatic leaves from fifteen different plants were collected, of which twelve were randomly selected, cut into 4-mm2 pieces, and surface sterilized with 75% ethanol for 30s followed by 5% NaClO for 1 min, rinsed four times with sterile water, and then placed on potato dextrose agar (PDA) medium at 25 °C in the dark for 5 to 7 days. Six isolates with similar morphological characteristics were obtained. Aerial mycelium was vigorous, downy and exhibited white to grayish-green coloration. Conidia were solitary or catenate, pale brown, obclavate to cylindrical, apex obtuse, one to 11 pseudosepta, 24.9 to 125.7 × 7.9 to 12.9 μm (n = 50). Morphological characteristics matched Corynespora cassiicola (Ellis 1971). For molecular identification, two representative isolates (HJAUP C001 and HJAUP C002) were selected for genomic DNA extraction, and the ITS, TUB2 and TEF1-α gene were amplified, using the primer ITS4/ITS5 (White et al. 1990), Bt2a/Bt2b (Lousie and Donaldson 1995) and EF1-728F/EF-986R (Carbone and Kohn 1999), respectively. The sequenced loci (GenBank accession nos. ITS: OP957070, OP957065; TUB2: OP981639, OP981640; TEF1-α: OP981637, OP981638) of the isolates were 100, 99 and 98% similar to the corresponding sequences of C. cassiicola strains (GenBank accession nos. OP593304, MW961419, MW961421, respectively). Phylogenetic analyses of combined ITS and TEF1-α sequences was performed using maximum-likelihood method in MEGA 7.0 (Kuma et al. 2016). The result showed that our isolates (HJAUP C001 and HJAUP C002) clustered with four strains of C. cassiicola at 99% bootstrap values in the bootstrap test (1000 replicates). Based on the morpho-molecular approach, the isolates were identified as C. cassiicola. The pathogenicity of one representative strain (HJAUP C001) was tested by inoculating the wounded leaves of six healthy J. nudiflorum plants under natural condition. Three leaves from each of three plants were punctured with flamed needles and sprayed with a conidial suspension (1 × 106 conidia/ml), and three wounded leaves from each of other three plants were inoculated with mycelial plugs (5 × 5 mm3). Mock inoculations were used as controls with sterile water and PDA plugs on three leaves each, respectively. Leaves from all treatments were incubated in a greenhouse at high relative humidity, 25°C, and 12-hour photoperiod. After one week, all wounded inoculated leaves appeared similar symptoms as described above, whereas the mock inoculated leaves were still healthy. Similar isolates with grayish white and vigorous aerial mycelium were reisolated from inoculated and symptomatic leaves and identified as C. cassiicola by DNA sequencing, fulfilling Koch's postulates. It has been reported that C. cassiicola can cause leaf spots on numerous plant species (Tsai et al. 2015; Lu et al. 2019; Farr and Crossman 2023). However, to our knowledge, this is the first report of C. cassiicola causing leaf spots on J. nudiflorum in China. This finding aids in protection of J. nudiflorum, a medicinal and ornamental plant with high economic value.
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Nov 12, 2024
Chen Yu + 7
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