First Report of Leaf Spot Caused by Alternaria tenuissima on Coreopsis lanceolata in Anqing, China

Abstract

Coreopsis lanceolata L. (Compositae) is native to North America and was introduced to Jiangxi Province of China as a landscape plant in the 1930s (Wan et al. 2008). This plant is distributed in gardens and green space of Anqing, such as Lotus Lake Park and Ling Lake Park. In May 2015, necrotic leaf lesions were observed on C. lanceolata growing in several land areas in Anqing, located in eastern China (30°50′ to 30°92′N; 117°03′ to 117°40′E). In 1.02 ha, disease incidence was 36%. Symptoms appeared on leaves as small, brown spots. Leaf spots enlarged progressively and developed into a gray-white lesions, surrounded by brown margins, and sometimes had a yellow halo. The size of leaf spot lesions ranged from 1 to 10 mm. Small fragments of tissue from infected leaves were surface disinfested with 70% ethyl alcohol, rinsed with distilled water, and then plated on potato dextrose agar in Petri plates in three repetitions. The plates were incubated at 25°C in darkness for 7 days, and strains were obtained by single-spore isolation. The colony of the fungus was olive-green with 1- to 2-mm white margin and abundant aerial hyphae. Numerous conidia that were melanized and obclavate to obpyriform in long sparsely branched chains on simple short conidiophores. Conidia ranged from 11.3 to 42.7 × 8.2 to 16.7 μm in size, showing one to six transverse septa and zero to two longitudinal septa. The isolates were identified as Alternaria tenuissima based on morphological characteristics as described by Simmons (2007). To confirm the fungus species, molecular identification was carried out by polymerase chain reaction using the internal transcribed spacer (ITS) region primers ITS1/ITS4 (White et al. 1990) and the partial coding sequence (cds) histone gene primers H3-1a/H3-1b (Luan et al. 2007), respectively, and sequenced. ITS sequences (accession nos. MK560081, MK575831, MK575832, MK575833, MK575834, MK575835, MK575836, and MK575837) and histone sequences (accession nos. MK598608, MK598609, MK598610, MK598611, MK598612, MK598613, MK598614, and MK598615) were deposited in GenBank. BLAST analysis of the resulting sequences from eight isolates all showed 100% identity with A. tenuissima strains (MG012286.1 for ITS region and MG012319.1 for partial cds histone gene region). To confirm pathogenicity, a conidial suspension (5 × 10⁵ conidia/ml) and sterile distilled water that served as a control were sprayed on healthy and detached leaves of C. lanceolata, separately. The inoculated leaves were maintained at 25°C with 90% relative humidity under a 12-h light photoperiod. After inoculating for 5 days, the symptoms were similar to those previously observed, and A. tenuissima was consistently reisolated from the artificially infected leaves by both morphology and molecular characterization. Control leaves remained healthy. To the best of our knowledge, this is the first report of A. tenuissima causing leaf spot on C. lanceolata in Anqing, China. Correct identification of this disease is of great importance to develop corresponding management strategies for preventing further spread of the pathogen to other areas.