First Report of Colletotrichum truncatum Causing Anthracnose of Tomato in China.

Abstract

Colletotrichum truncatum (syn. C. capsici) is an important plant pathogen that has a wide host range including pepper, eggplant, muskmelon, chickpea, grapes, and many other species of plants (1,2). Anthracnose fruit rot incited by C. coccodes is a prevalent disease in some major tomato (Solanum esculentum) producing regions in China. In October 2012, anthracnose symptoms (circular, sunken lesions with spore masses produced in black acervuli) were observed on ripe tomato fruit in Fuzhou City of Fujian Province, China. Three single-spore isolates (FZ-1, FZ-2, and FZ-3) were derived from fungal cultures isolated from different infected fruits from the same farm. A mycelial plug (5 mm in diameter) from the growing edge of an active colony of each isolate was transferred onto potato dextrose agar (PDA) and incubated at 28°C. Colonies grown on PDA changed from grayish to dark grey with an average colony diameter of 71.8 mm after 7 days. Conidia were falcate and 17.6 to 21.6 × 2.57 to 3.31 μm. Growth rate measured by colony diameter was greater at 25 to 30°C than at other temperatures tested (12, 18, 20, and 37°C). Based upon these morphological and cultural characteristics, the causal agent was identified as C. truncatum (3). To test the three isolates for pathogenicity, detached ripe tomato fruits were each inoculated with 1 μl of a conidial suspension (106 conidia/ml) using either injection or applying a droplet of the spore suspension on the surface of each fruit; the control treatment consisted of fruit that was treated with 1 μl of sterilized water using the two methods of inoculation mentioned above. Five replicate ripe fruits were inoculated with each of the three isolates using each method described above, and incubated in a moist chamber at 25°C. Five ripe fruits were used the negative control treatment for each inoculation method. After 7 days, typical anthracnose symptoms had developed on the inoculated fruit but not on control fruit. To confirm identity of the three isolates, the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA), the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, a partial sequence of the actin (ACT) gene, and partial histone 3 (HIS3) gene were amplified with ITS1 and ITS4 universal primers, GDF1 and GDR1 primers, ACT-512F and ACT-783R primers, and CYLH3F and CYLH3R primers, respectively (1). The ITS consensus sequence (Accession No. KC460308) of these isolates shared 99% homology with the ITS sequence of C. truncatum in GenBank (AJ301945), and the three other consensus sequences were all 100% homologous with the corresponding sequences of C. truncatum in Genbank (GU228254, GU227960, and GU228058, respectively). The pathogen was re-isolated from the inoculated fruit but not from the control fruit, and the identity of the re-isolates was confirmed to be C. truncatum by morphological features and based on the ITS, GAPDH, ACT, and HIS3 sequences as described above. To our knowledge, this is the first report of C. truncatum causing anthracnose on tomato in China.