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First Report of Anthracnose Caused by Colletotrichum higginsianum on Rumex acetosa in China

Zhang, Y. W., Xue, L. H., Li, C. J.
Plant disease 2018 v.102 no.6 pp. 1174
Colletotrichum higginsianum, DNA primers, Rumex acetosa, Rumex crispus, actin, agar, air drying, anthracnose, bleaching agents, chitin synthase, conidia, culture media, diarrhea, ethanol, fungi, genes, glyceraldehyde-3-phosphate dehydrogenase, growth chambers, histones, internal transcribed spacers, paper, pathogenicity, petioles, photoperiod, planting, plastic film, polymerase chain reaction, relative humidity, ribosomal DNA, sodium hypochlorite, sporulation, temperate zones, tissues, trays, tubulin, China
Rumex acetosa (family Polygonaceae) is a perennial herb widely distributed in temperate climates. The foliage has traditionally been used as a treatment for skin irritations and diarrhea (Sun et al. 2015). In December 2015, lesions on R. acetosa were observed in Xinjin County, Sichuan Province, China (30.47785° N, 103.75878° W), with approximately 88% of the leaves affected in a 500 m² planting of R. acetosa. The symptoms initially appeared as small, scattered, red, circular spots on leaves and petioles. Gradually, the necrotic lesions enlarged, coalesced, and became gray in the center with red or brown margins. Eventually, whole plants yellowed but did not die. Sporulation was not observed on the lesions. Infected tissues from different plants were cut into small pieces (5 × 5 mm²), surface sterilized in 70% ethanol solution for 60 s followed by 5% commercial bleach (∼0.275 NaOCl) for 5 min, rinsed three times with sterile distilled water, air dried, and plated onto potato dextrose agar (PDA). Approximately 40% of the isolates turned out to be the causal organism. An isolate was selected for transfer to PDA, where it did not produce conidia; however, it did produce conidia on synthetic nutrient-poor agar medium after 12 days under near-ultraviolet light with a 12-h photoperiod at 25°C. Conidia were hyaline, aseptate, cylindrical, straight to very slightly curved, with one end rounded and the other truncate, 12.5 to 20.3 × 3.1 to 4.3 µm (average 17.4 × 3.7 µm, n = 50), which was similar to the reported isolate IMI 349063 (Damm et al. 2014). The internal transcribed spacer (ITS) region of rDNA, partial glyceraldehyde-3-phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS-1), actin (ACT), histone 3 (HIS3), and β-tubulin (TUB2) genes were amplified by the primers described previously (Damm et al. 2014) and sequenced. Sequences were deposited in GenBank (MF033888 for ITS, MF033889 for GAPDH, MF033890 for CHS, MF033892 for ACT, MF033891 for HIS3, and MF033895 for TUB2). BLAST analysis showed >99% identity with several reference sequences of C. higginsianum previously deposited in GenBank. On the basis of morphological and molecular characteristics, the isolate was identified as C. higginsianum Sacc. (Damm et al. 2014), belonging to the C. destructivum complex. To verify pathogenicity, 10 healthy, young leaves (3-week-old) from the field were inoculated with a 20-µl conidial suspension (3 × 10⁵ conidia/ml) obtained from isolate C5 and were incubated on moist paper towels in an enamelware tray. An equal number of leaves were inoculated with sterile distilled water as controls. Trays were covered individually with transparent plastic film to maintain high relative humidity and placed in a 25°C growth chamber for observation. After 8 days, red-brown spots appeared on all inoculated leaves, but no symptoms were observed on the control leaves. The same fungus was reisolated from the lesions and confirmed by morphological and molecular identification as described above. Recently, C. destructivum has been reported on Rumex crispus in China (Liu et al. 2017). To our knowledge, this is the first report of R. acetosa as a host for C. higginsianum in China.